oxytocin and Dehydration

A thorough presentation of the influence of thyroliberin (TRH) on vasopressin and oxytocin release from the hypothalamo-neurohypophysial system is presented. Thyroliberin affects in different ways both neurohormone secretion in females during lactation according to the water-electrolyte metabolism in the course of the circadian rhythm of vasopressin and oxytocin release as well as during in vitro incubation of isolated neurointermediate lobe or hypothalamo-neurohypohysial explants. The results showed that: TRH acts as a stimulator of oxytocin release into the blood by equilibrated water-electrolyte metabolism, TRH acts in the central nervous system as an inhibitory neuromodulator of vasopressin and oxytocin release from the hypothalamo-neurohypophysial system under in vitro conditions, by osmotic stimulation, as well as in females during lactation, TRH inhibits AVP release in acute bleeding-provoked hypovolemia and alters the circadian rhythm of vasopressin and oxytocin release. It is assumed that this neuropeptide can interact with the mechanisms engaged in vasopressin and oxytocin release and can disturb these mechanisms, especially under conditions of augmented demand of the organism for these neurohormones.

Topics: Animals; Dehydration; Disease Models, Animal; Dogs; Female; Humans; Hypothalamo-Hypophyseal System; Lactation; Male; Oxytocin; Pituitary-Adrenal System; Pregnancy; Rats; Thyrotropin-Releasing Hormone; Thyroxine; Vasopressins; Water; Water Deprivation

Magnocellular oxytocinergic neurons in the hypothalamus offer a striking example of a mammalian neuronal system whose basic architecture and synaptic circuitry can be reversibly modified in adulthood. During parturition, lactation and prolonged osmotic stimulation, glial coverage of oxytocinergic neurons markedly diminishes and their surfaces are left in extensive juxtaposition; concurrently, there is formation of new synapses, which are predominantly GABAergic and which couple two or more oxytocinergic neurons simultaneously. These structural changes do not permanently modify the anatomy of the system since upon cessation of stimulation, neuronal juxtapositions and shared synapses disappear, to reappear upon new stimulation. At present, we can only speculate about the cellular mechanisms and factors responsible for these reversible neuroanatomical changes. However, oxytocin itself appears to be of primary importance since it can induce similar anatomical changes when chronically infused into the third ventricle.

Topics: Animals; Dehydration; Female; Lactation; Neuroglia; Neuronal Plasticity; Oxytocin; Pregnancy; Rats; Supraoptic Nucleus; Synapses

Topics: Animals; Dehydration; Glomerular Filtration Rate; Homozygote; Humans; Kidney Concentrating Ability; Osmolar Concentration; Oxytocin; Rats; Rats, Brattleboro; Vasopressins

Topics: Blood Volume; Child; Craniocerebral Trauma; Deamino Arginine Vasopressin; Dehydration; Diabetes Mellitus, Type 1; Diuresis; Female; Humans; Kinetics; Male; Models, Biological; Neurophysins; Osmolar Concentration; Oxytocin; Pituitary Gland, Posterior; Postoperative Complications; Pregnancy; Pregnancy in Diabetics; Thirst; Urine; Vasopressins

Topics: Animals; Dehydration; Guinea Pigs; Oxytocin; Paraventricular Hypothalamic Nucleus; Pituitary Gland, Posterior; Rats; Receptors, Adrenergic; Receptors, Cholinergic; Supraoptic Nucleus; Synaptic Transmission; Vasopressins; Water-Electrolyte Balance

Topics: Adenylyl Cyclases; Adrenal Glands; Adult; Animals; Body Water; Chlorpropamide; Dehydration; Diabetes Insipidus; Genes; Growth Hormone; Heterozygote; Humans; Hyponatremia; Hypothalamus; Oxytocin; Pituitary Gland; Pituitary Gland, Posterior; Rats; Sodium; Vasopressins

Topics: Dehydration; Glucose; Humans; Hypertonic Solutions; Nicotine; Osmotic Pressure; Oxytocin; Pituitary Function Tests; Sodium; Vasopressins

Vasopressin (AVP) and oxytocin (OXT) are neuropeptides produced by magnocellular neurons (MCNs) of the hypothalamus and secreted through neurohypophysis to defend mammals against dehydration. It was recently demonstrated that MCNs also project to limbic structures, modulating several behavioral responses.. We found that 24 h of water deprivation (WD) or salt loading (SL) did not change exploration or anxiety-like behaviors in the elevated plus maze (EPM) test. However, rats deprived of water for 48 h showed reduced exploration of open field and the closed arms of EPM, indicating hypoactivity during night time. We evaluated mRNA expression of glutamate decarboxylase 1 (Gad1), vesicular glutamate transporter 2 (Slc17a6), AVP (Avpr1a) and OXT (Oxtr) receptors in the lateral habenula (LHb), basolateral (BLA) and central (CeA) amygdala after 48 h of WD or SL. WD, but not SL, increased Oxtr mRNA expression in the CeA. Bilateral pharmacological inhibition of OXTR function in the CeA with the OXTR antagonist L-371,257 was performed to evaluate its possible role in regulating the EPM exploration or water intake induced by WD. The blockade of OXTR in the CeA did not reverse the hypoactivity response in the EPM, nor did it change water intake induced in 48-h water-deprived rats.. We found that WD modulates exploratory activity in rats, but this response is not mediated by oxytocin receptor signaling to the CeA, despite the upregulated Oxtr mRNA expression in that structure after WD for 48 h.

Topics: Animals; Central Amygdaloid Nucleus; Dehydration; Mammals; Oxytocin; Rats; Receptors, Oxytocin; RNA, Messenger; Water; Water Deprivation

Water homoeostasis is achieved by secretion of the peptide hormones arginine vasopressin (AVP) and oxytocin (OXT) that are synthesized by separate populations of magnocellular neurones (MCNs) in the supraoptic and paraventricular (PVN) nuclei of the hypothalamus. To further understand the molecular mechanisms that facilitate biosynthesis of AVP and OXT by MCNs, we have explored the spatiotemporal dynamic, both mRNA and protein expression, of two genes identified by our group as being important components of the osmotic defence response: Caprin2 and Creb3l1.. By RNA in situ hybridization and immunohistochemistry, we have characterized the expression of Caprin2 and Creb3l1 in MCNs in the basal state, in response to dehydration, and during rehydration in the rat.. We found that Caprin2 and Creb3l1 are expressed in AVP and OXT MCNs and in response to dehydration expression increases in both MCN populations. Protein levels mirror the increase in transcript levels for both CREB3L1 and CAPRIN2. In view of increased CREB3L1 and CAPRIN2 expression in OXT neurones by dehydration, we explored OXT-specific functions for these genes. By luciferase assays, we demonstrate that CREB3L1 may be a transcription factor regulating Oxt gene expression. By RNA immunoprecipitation assays and Northern blot analysis of Oxt mRNA poly(A) tails, we have found that CAPRIN2 binds to Oxt mRNA and regulates its poly(A) tail length. Moreover, in response to dehydration, Caprin2 mRNA is subjected to nuclear retention, possibly to regulate Caprin2 mRNA availability in the cytoplasm.. The exploration of the spatiotemporal dynamics of Creb3l1- and Caprin2-encoded mRNAs and proteins has provided novel insights beyond the AVP-ergic system, revealing novel OXT-ergic system roles of these genes in the osmotic defence response.

Topics: Animals; Arginine Vasopressin; Cyclic AMP Response Element-Binding Protein; Dehydration; Gene Expression; Gene Expression Regulation; Oxytocin; Paraventricular Hypothalamic Nucleus; Rats; RNA-Binding Proteins; RNA, Messenger; Supraoptic Nucleus; Water

What is the central question of this study? What is the effect of an obesogenic diet on the control of hydromineral balance in rats? What is the main finding and its importance? The results showed that, when dehydrated, rats fed a high-fat diet drink less water than their control-diet-fed counterparts. Changes in aquaporin-7 and peroxisome proliferator-activated receptor α expression in the white adipose tissue might be involved.. High-fat diet (HFD) increases fat accumulation, glycaemia and blood triglycerides and is used as a model to study obesity. Besides the metabolic changes, obesity likely affects water intake. We assessed the effects of HFD on behavioural and hormonal responses to water deprivation. Additionally, we measured if the adipose tissue is differentially affected by water deprivation in control and HFD-fed rats. HFD rats showed a decreased basal water intake when compared to control-fed rats. When subjected to 48 h of water deprivation, as expected, both control and HFD rats drank more water than the hydrated rats. However, the increase in water intake was lessened in HFD dehydrated rats. Similarly, the increase in haematocrit in dehydrated rats was less pronounced in HFD dehydrated rats. These results suggest that HFD diminishes drinking behaviour. White adipose tissue weight, glycaemia and plasma glycerol concentration were increased in HFD rats; however, after 48 h of water deprivation, these parameters were significantly decreased in dehydrated HFD rats, when compared to controls. The increase in adipose tissue caused by HFD may mitigate the effects of dehydration, possibly through the increased production of metabolic water caused by lipolysis in the adipocytes. Oxytocin possibly mediates the lipolytic response, since both its secretion and receptor expression are affected by dehydration in both control and HFD rats, which suggests that oxytocin signalling is maintained in these conditions. Changes in mediators of lipolysis, such as aquaporin-7 and peroxisome proliferator-activated receptor α, might contribute to the different effects observed in control and HFD rats.

Topics: Animals; Dehydration; Diet, High-Fat; Male; Obesity; Oxytocin; PPAR alpha; Rats; Rats, Wistar; Water; Water Deprivation

The neurohormones arginine-vasopressin (AVP) and oxytocin (OT) synthesised in supraoptic and paraventricular nuclei of neurohypophysis regulate lactation, systemic water homeostasis and nociception. Using transgenic rats expressing AVP and OT tagged with fluorescent proteins we demonstrate that both neurohormones are expressed in sensory neurones both in vitro, in primary cultures, and in situ, in the intact ganglia; this expression was further confirmed with immunocytochemistry. Both neurohormones were expressed in nociceptive neurones immunopositive to transient receptor potential vannilloid 1 (TRPV1) channel antibodies. The AVP and OT-expressing DRG neurones responded to AVP, OT, 50 mM K

Topics: Animals; Dehydration; Exocytosis; Female; Fluorescence; Ganglia, Spinal; Lactation; Male; Nociception; Oxytocin; Pituitary Gland, Posterior; Rats, Transgenic; Receptors, Oxytocin; Receptors, Vasopressin; Sensory Receptor Cells; Vasopressins

The oxytocin (OT) and vasopressin (VP) neurons of the supraoptic nucleus (SON) demonstrate characteristics of "metabolic sensors". They express insulin receptors and glucokinase (GK). They respond to an increase in glucose and insulin with an increase in intracellular [Ca(2+)] and increased OT and VP release that is GK dependent. Although this is consistent with the established role of OT as an anorectic agent, how these molecules function relative to the important role of OT during lactation and whether deficits in this metabolic sensor function contribute to obesity remain to be examined. Thus, we evaluated whether insulin and glucose-induced OT and VP secretion from perifused explants of the hypothalamo-neurohypophyseal system are altered during lactation and by diet-induced obesity (DIO). In explants from female day 8 lactating rats, increasing glucose (Glu, 5 mM) did not alter OT or VP release. However, insulin (Ins; 3 ng/ml) increased OT release, and increasing the glucose concentration in the presence of insulin (Ins+Glu) resulted in a sustained elevation in both OT and VP release that was not prevented by alloxan, a GK inhibitor. Explants from male DIO rats also responded to Ins+Glu with an increase in OT and VP regardless of whether obesity had been induced by feeding a high-fat diet (HFD). The HFD-DIO rats had elevated body weight, plasma Ins, Glu, leptin, and triglycerides. These findings suggest that the role of SON neurons as metabolic sensors is diminished during lactation, but not in this animal model of obesity.

Topics: Alloxan; Animals; Dehydration; Diet, High-Fat; Dietary Fats; Enzyme Inhibitors; Female; Glucokinase; Glucose; In Vitro Techniques; Insulin; Lactation; Neurons; Obesity; Oxytocin; Rats; Rats, Sprague-Dawley; Receptor, Insulin; Supraoptic Nucleus; Vasopressins

The magnocellular vasopressin (AVP) and oxytocin (OT) neurones exhibit specific electrophysiological behaviour, synthesise AVP and OT peptides and secrete them into the neurohypophysial system in response to various physiological stimulations. The activity of these neurones is regulated by the very same peptides released either somato-dendritically or when applied to supraoptic nucleus (SON) preparations in vitro. The AVP and OT, secreted somato-dendritically (i.e. in the SON proper) act through specific autoreceptors, induce distinct Ca(2+) signals and regulate cellular events. Here, we demonstrate that about 70% of freshly isolated individual SON neurones from the adult non-transgenic or transgenic rats bearing AVP (AVP-eGFP) or OT (OT-mRFP1) markers, produce distinct spontaneous [Ca(2+)]i oscillations. In the neurones identified (through specific fluorescence), about 80% of AVP neurones and about 60% of OT neurones exhibited these oscillations. Exposure to AVP triggered [Ca(2+)]i oscillations in silent AVP neurones, or modified the oscillatory pattern in spontaneously active cells. Hyper- and hypo-osmotic stimuli (325 or 275 mOsmol/l) respectively intensified or inhibited spontaneous [Ca(2+)]i dynamics. In rats dehydrated for 3 or 5days almost 90% of neurones displayed spontaneous [Ca(2+)]i oscillations. More than 80% of OT-mRFP1 neurones from 3 to 6-day-lactating rats were oscillatory vs. about 44% (OT-mRFP1 neurones) in virgins. Together, these results unveil for the first time that both AVP and OT neurones maintain, via Ca(2+) signals, their remarkable intrinsic in vivo physiological properties in an isolated condition.

Topics: Animals; Calcium; Calcium Signaling; Dehydration; Green Fluorescent Proteins; Male; Neurons; Osmolar Concentration; Oxytocin; Rats, Wistar; Supraoptic Nucleus; Vasopressins

Previous studies from our laboratory have shown that methysergide, a serotonergic antagonist, injected into the lateral parabrachial nucleus (LPBN) combined with a pre-load of 2 M NaCl, given by gavage, induces 0.3 M NaCl intake. The mechanisms involved in this paradoxical behavior are still unknown. In the present work, we investigated the effect of serotonergic blockade into the LPBN on hindbrain and hypothalamic activity, gastric emptying and arterial blood pressure in cell-dehydrated rats. Methysergide plus 2 M NaCl infused intragastrically or intravenously promoted 0.3 M NaCl intake in two-bottle tests. In cell-dehydrated rats with no access to fluids, methysergide compared to vehicle increased Fos immunoreactivity in the medial nucleus of the solitary tract, area postrema and non-oxytocinergic cells of the ventral portion of the hypothalamic paraventricular nucleus (PVN). There was no alteration in the number of neurons double-labeled for Fos-ir and oxytocin in the PVN and supraoptic nuclei. There was also no alteration in plasma oxytocin and vasopressin, or arterial pressure. In rats cell-dehydrated by i.v. 2 M NaCl, methysergide also did not change the amount of an intragastric load of 0.3 M NaCl retained in the stomach or intestine. The results suggest that methysergide injected into the LPBN of cell-dehydrated rat does not alter primary inhibitory signals that control sodium intake. The inhibitory signals blocked by methysergide in the LPBN possibly originated from activation of brain osmoreceptors, second order visceral/hormonal signals or a combination of both.

Topics: Animals; Area Postrema; Arterial Pressure; Dehydration; Disease Models, Animal; Gastric Emptying; Male; Methysergide; Neurons; Oxytocin; Parabrachial Nucleus; Proto-Oncogene Proteins c-fos; Rats, Sprague-Dawley; Saline Solution, Hypertonic; Serotonin Antagonists; Sodium Chloride, Dietary; Solitary Nucleus; Supraoptic Nucleus; Vasopressins

We present the novel urine collection method used during in-home interviews of a large population representative of older adults in the United States (aged 62-91, the National Social Life, Health and Aging Project). We also present a novel assay method for accurately measuring urinary peptides oxytocin (OT) and vasopressin (AVP), hormones that regulate social behaviors, stress, and kidney function.. Respondents in a randomized substudy (N = 1,882) used airtight containers to provide urine specimens that were aliquoted, stored under frozen refrigerant packs and mailed overnight for frozen storage (-80 °C). Assays for OT, AVP, and creatinine, including freeze-thaw cycles, were refined and validated. Weighted values estimated levels in the older U.S. population.. Older adults had lower OT, but higher AVP, without the marked gender differences seen in young adults. Mild dehydration, indicated by creatinine, specific gravity, acidity, and AVP, produced concentrated urine that interfered with the OT assay, yielding falsely high values (18% of OT). Creatinine levels (≥ 1.4 mg/ml) identified such specimens that were diluted to solve the problem. In contrast, the standard AVP assay was unaffected (97% interpretable) and urine acidity predicted specimens with low OT concentrations. OT and AVP assays tolerated 2 freeze-thaw cycles, making this protocol useful in a variety of field conditions.. These novel protocols yielded interpretable urinary OT and AVP values, with sufficient variation for analyzing their social and physiological associations. The problem of mild dehydration is also likely common in animal field studies, which may also benefit from these collection and assay protocols.

Topics: Age Factors; Aged; Aged, 80 and over; Aging; Creatinine; Dehydration; Female; Humans; Kidney; Longitudinal Studies; Male; Middle Aged; Oxytocin; Risk Factors; Sex Factors; Social Behavior; Stress, Psychological; United States; Urine Specimen Collection; Vasopressins

The immunoglobulin heavy chain binding protein (BiP) is an endoplasmic reticulum (ER) chaperone that facilitates the proper folding of newly synthesized secretory and transmembrane proteins. Here we report that BiP mRNA was expressed in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in wild-type mice under basal conditions. Dual in situ hybridization in the SON and PVN demonstrated that BiP mRNA was expressed in almost all the neurons of arginine vasopressin (AVP), an antidiuretic hormone. BiP mRNA expression levels were increased in proportion to AVP mRNA expression in the SON and PVN under dehydration. These data suggest that BiP is involved in the homeostasis of ER function in the AVP neurons in the SON and PVN.

Topics: Animals; Corticotropin-Releasing Hormone; Dehydration; Endoplasmic Reticulum Chaperone BiP; Heat-Shock Proteins; Male; Mice; Mice, Inbred C57BL; Neurons; Oxytocin; Paraventricular Hypothalamic Nucleus; Supraoptic Nucleus; Up-Regulation; Vasopressins

The deactivation of the inhibitory mechanisms with injections of moxonidine (α2-adrenoceptor/imidazoline receptor agonist) into the lateral parabrachial nucleus (LPBN) increases hypertonic NaCl intake by intra- or extracellular dehydrated rats. In the present study, we investigated the changes in the urinary sodium and volume, sodium balance, and plasma vasopressin and oxytocin in rats treated with intragastric (i.g.) 2 M NaCl load (2 ml/rat) combined with injections of moxonidine into the LPBN. Male Holtzman rats (n=5-12/group) with stainless steel cannulas implanted bilaterally into LPBN were used. Bilateral injections of moxonidine (0.5 nmol/0.2 μl) into the LPBN decreased i.g. 2 M NaCl-induced diuresis (4.6±0.7 vs. vehicle: 7.4±0.6 ml/120 min) and natriuresis (1.65±0.29 vs. vehicle: 2.53±0.17 mEq/120 min), whereas the previous injection of the α2-adrenoceptor antagonist RX 821002 (10 nmol/0.2 μl) into the LPBN abolished the effects of moxonidine. Moxonidine injected into the LPBN reduced i.g. 2 M NaCl-induced increase in plasma oxytocin and vasopressin (14.6±2.8 and 2.2±0.3 vs. vehicle: 25.7±7 and 4.3±0.7 pg/ml, respectively). Moxonidine injected into the LPBN combined with i.g. 2 M NaCl also increased 0.3 M NaCl intake (7.5±1.7 vs. vehicle: 0.5±0.2 mEq/2 h) and produced positive sodium balance (2.3±1.4 vs. vehicle: -1.2±0.4 mEq/2 h) in rats that had access to water and NaCl. The present results show that LPBN α2-adrenoceptor activation reduces renal and hormonal responses to intracellular dehydration and increases sodium and water intake, which facilitates sodium retention and body fluid volume expansion.

Topics: Adrenergic alpha-2 Receptor Agonists; Adrenergic alpha-Antagonists; Animals; Arginine Vasopressin; Atrial Natriuretic Factor; Blood Volume; Brachial Plexus; Dehydration; Diuresis; Hormones; Idazoxan; Imidazoles; Imidazoline Receptors; Kidney; Male; Natriuresis; Osmolar Concentration; Oxytocin; Potassium; Rats; Rats, Sprague-Dawley; Renin; Sodium; Sodium Chloride; Water-Electrolyte Balance

The supraoptic nucleus (SON) of the hypothalamus is an important integrative brain structure that coordinates responses to perturbations in water balance and regulates maternal physiology through the release of the neuropeptide hormones vasopressin and oxytocin into the circulation. Both dehydration and lactation evoke a dramatic morphological remodeling of the SON, a process known as function-related plasticity. We hypothesize that some of the changes seen in SON remodeling are mediated by differential gene expression, and have thus used microarrays to document global changes in transcript abundance that accompany chronic dehydration in female rats, and in lactation. In situ hybridization analysis has confirmed the differential expression of three of these genes, namely TNF-induced protein 6, gonadotropin-inducible transcription factor 1, and ornithine decarboxylase antizyme inhibitor 1. Comparison of differential gene expression patterns in male and female rats subjected to dehydration and in lactating rats has enabled the identification of common elements that are significantly enriched in gene classes with particular functions. Two of these are related to the requirement for increased protein synthesis and hormone delivery in the physiologically stimulated SON (translation initiation factor activity and endoplasmic reticulum-Golgi intermediate compartment, respectively), whereas others are consistent with the concept of SON morphological plasticity (collagen fibril organization, extracellular matrix organization and biogenesis, extracellular structure organization and biogenesis, and homophilic cell adhesion). We suggest that the genes coordinately regulated in the SON as a consequence of dehydration and lactation form a network that mediates the plastic processes operational in the physiologically activated SON.

Topics: Animals; Dehydration; Female; Gene Expression Regulation; Lactation; Male; Neurons; Oxytocin; Rats; Rats, Sprague-Dawley; Reproduction; Supraoptic Nucleus

Secretory-type Na-K-2Cl cotransporter (NKCC1) is known to play roles in both acid and sodium excretion, and is more abundant in dehydration. To determine the mechanisms by which dehydration stimulates NKCC1 expression, the effects of vasopressin, oxytocin and hyperosmolality on NKCC1 mRNA and protein expressions in the outer medullary collecting duct (OMCD) of rats were investigated using RT-competitive PCR and western blot analysis. Microdissected OMCD was incubated in isotonic or hypertonic solution, or with AVP or oxytocin for 60 min at 37 degrees C. Hyperosmolality induced by NaCl, mannitol or raffinose increased NKCC1 mRNA expression in OMCD by 130-240% in vitro. The stimulation of NKCC1 mRNA expression by NaCl was highest at 690 mosmol kg(-1) H(2)O and gradually decreased at higher osmolalities. The incubation of OMCD with AVP (10(-7) M) for 60 min increased NKCC1 mRNA expression by 100%. The administration of AVP to rats for 4 days using an osmotic mini-pump also increased NKCC1 mRNA and protein expressions in OMCD by 130%. In contrast, oxytocin (10(-7) M) did not stimulate the NKCC1 mRNA expression in OMCD in vitro. Chronic injection of oxytocin increased the NKCC1 mRNA expression by 36%. These data showed that hyperosmolality and vasopressin stimulate NKCC1 mRNA and protein expressions in rat OMCD. It is concluded that NKCC1 expression is regulated directly and indirectly by vasopressin.

Topics: Animals; Blotting, Western; Dehydration; DNA Primers; Dose-Response Relationship, Drug; Kidney Tubules, Collecting; Male; Microdissection; Oxytocin; Rats; Rats, Sprague-Dawley; Renal Agents; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sodium-Potassium-Chloride Symporters; Solute Carrier Family 12, Member 2; Vasopressins; Water-Electrolyte Imbalance

Dehydration increases vasopressin (antidiuretic hormone) secretion from the posterior pituitary gland to reduce water loss in the urine. Vasopressin secretion is determined by action potential firing in vasopressin neurones, which can exhibit continuous, phasic (alternating periods of activity and silence), or irregular activity. Autocrine kappa-opioid inhibition contributes to the generation of activity patterning of vasopressin neurones under basal conditions and so we used in vivo extracellular single unit recording to test the hypothesis that changes in autocrine kappa-opioid inhibition drive changes in activity patterning of vasopressin neurones during dehydration. Dehydration increased the firing rate of rat vasopressin neurones displaying continuous activity (from 7.1 +/- 0.5 to 9.0 +/- 0.6 spikes s(1)) and phasic activity (from 4.2 +/- 0.7 to 7.8 +/- 0.9 spikes s(1)), but not those displaying irregular activity. The dehydration-induced increase in phasic activity was via an increase in intraburst firing rate. The selective -opioid receptor antagonist nor-binaltorphimine increased the firing rate of phasic neurones in non-dehydrated rats (from 3.4 +/- 0.8 to 5.3 +/- 0.6 spikes s(1)) and dehydrated rats (from 6.4 +/- 0.5 to 9.1 +/- 1.2 spikes s(1)), indicating that kappa-opioid feedback inhibition of phasic bursts is maintained during dehydration. In a separate series of experiments, prodynorphin mRNA expression was increased in vasopressin neurones of hyperosmotic rats, compared to hypo-osmotic rats. Hence, it appears that dynorphin expression in vasopressin neurones undergoes dynamic changes in proportion to the required secretion of vasopressin so that, even under stimulated conditions, autocrine feedback inhibition of vasopressin neurones prevents over-excitation.

Topics: Action Potentials; Animals; Cholecystokinin; Dehydration; Electrophysiology; Enkephalins; Female; Hypernatremia; Hyponatremia; Immunohistochemistry; In Situ Hybridization; Naltrexone; Narcotic Antagonists; Neurons; Oxytocin; Protein Precursors; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; RNA, Messenger; Vasopressins

The bHLH-PAS transcription SIM1 is required for the development of all neurons of the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. Mice with a loss of Sim1 die within a few days of birth, presumably because of the lack of a PVN and SON. In contrast, mice with a decrease of Sim1 survive, are hyperphagic and become obese. The mechanism by which Sim1 controls food intake remains unclear. Here we show that the development of specific PVN and SON cell types is sensitive to Sim1 gene dosage. Sim1 haploinsufficiency reduces the number of vasopressin (AVP)- and oxytocin-producing cells in the PVN by about 50 and 80%, respectively, but does not affect the development of Crh, Trh and Ss neurons. A decrease of AVP-producing cells increases the sensitivity of Sim1 heterozygous mice to chronic dehydration. Moreover, retrograde labelling showed a 70% reduction of PVN neurons projecting to the dorsal vagal complex, raising the possibility that a decrease of these axons contributes to the hyperphagia of Sim1(+/-) mice. Sim1 haploinsufficiency is thus associated with a decrease of several PVN/SON cell types, which has the potential of affecting distinct homeostatic processes.

Topics: Animals; Basic Helix-Loop-Helix Transcription Factors; Brain Stem; Dehydration; Eating; Hypothalamus, Anterior; Male; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Mice, Transgenic; Neural Pathways; Neurons; Osmolar Concentration; Oxytocin; Paraventricular Hypothalamic Nucleus; Repressor Proteins; Sodium; Vasopressins

In a search for novel genes involved in the hypothalamic control of body energy homeostasis bioinformatic tools were applied. Analysis of the presence of structural features characteristic for secretory peptides was used as a first step in the identification of novel neuropeptides, and was followed by analysis of expression patterns. The gene product previously named TAFA5 was identified during this process. The overall mRNA expression pattern of TAFA5 was assessed using quantitative PCR on rat cDNA libraries. Furthermore, the brain mRNA and polypeptide expression patterns were examined in rats using in situ hybridization and immunohistochemistry. Our results substantiate previous findings that TAFA5 is mainly expressed in the central nervous system. Furthermore, we found TAFA5 mRNA to be highly expressed in the hypothalamic paraventricular nucleus (PVN) where it co-localized with vasopressin and oxytocin in magno- and parvocellular neurons. Immunohistochemical analysis revealed TAFA5 immunoreactivity in the PVN in accordance with the in situ hybridization data. Given the high levels of expression in the PVN, it was investigated whether TAFA5 mRNA levels were affected by fasting or dehydration. Interestingly, it was observed that TAFA5 mRNA was specifically down-regulated in the PVN following water deprivation. Based on our findings we suggest that TAFA5 may be involved in the regulation of fluid homeostasis.

Topics: Analysis of Variance; Animals; Computational Biology; Cytokines; Dehydration; Down-Regulation; Gene Expression; Male; Neuropeptides; Oxytocin; Paraventricular Hypothalamic Nucleus; Peptides; Rabbits; Rats; Rats, Sprague-Dawley; Time Factors; Vasopressins

1. This study presents a time course analysis of the messenger RNA (mRNA) levels of c-fos, vasopressin (VP), and oxytocin (OT) in the paraventricular (PVN) and supraoptic nucleus (SON), following acute and chronic dehydration by water deprivation. 2. Male Wistar rats were separated into five groups: nondehydrated (control group) and dehydrated for 6, 24, 48 and 72 h. Following water deprivation, animals were decapitated, their blood was collected for hematocrit, osmolality, and plasma sodium measurements, and brains were removed for dissection of both PVN and SON. 3. As expected, the hematocrit, osmolality, plasma sodium, and weight loss were increased after water deprivation. In SON, a significant increase in both VP and OT mRNA expression was observed 6 h after dehydration reaching a peak at 24 h and returning to basal levels of expression at 72 h. In the PVN, an increase in both VP and OTmRNA expression occurred 24 h after dehydration. At 72 h the VP and OT mRNA expression levels had decreased but they were still at higher levels than those detected in control animals. 4. These results suggest that SON is the first nucleus to respond to the dehydration stimulus. Additionally, we also observed an increase in c-fos mRNA expression in both PVN and SON 6 h after water deprivation, which progressively decreased 24, 48, and 72 h after the onset of water deprivation. Therefore, it is possible that c-fos may be involved in the modulation of VP and OT genes, regulating the mRNA expression levels on a temporally distinct basis within the PVN and SON.

Topics: Animals; Dehydration; Gene Expression; Hematocrit; Hypothalamus, Anterior; Male; Osmolar Concentration; Oxytocin; Paraventricular Hypothalamic Nucleus; Proto-Oncogene Proteins c-fos; Rats; Rats, Wistar; RNA, Messenger; Sodium; Vasopressins; Water Deprivation; Weight Loss

The hypothalamic-neurohypophyseal system (HNS) mediates neuroendocrine responses to dehydration through the actions of the antidiuretic hormone vasopressin (VP) and the natriuetic peptide oxytocin (OT). VP and OT are synthesised as separate prepropeptide precursors in the cell bodies of magnocellular neurones in the hypothalamic supraoptic nucleus (SON) and paraventricular nucleus, the axons of which innervate the posterior pituitary gland (PP). Dehydration evokes a massive release of both peptides into the circulation, and this is accompanied by a function-related remodelling of the HNS. Microarray studies on mRNAs differentially expressed in the SON revealed that transcripts encoding the Ywhag and Ywhaz isoforms of the 14-3-3 family of regulatory proteins, are increased in the rat SON by 3 days of water deprivation; findings that we have confirmed by the real-time polymerase chain reaction. Because there is no necessary proportionality between transcript and protein abundance, we next examined Ywhag and Ywhaz translation products throughout the HNS in parallel with 14-3-3 post-translational modification, which is known to be an important determinant of functional activity. Both proteins are robustly expressed in the SON in VP- and OT-containing neurones, but the abundance of neither changes with dehydration. However, the total level of Ywhaz protein is increased in the neurointermediate lobe of the pituitary (NIL, which includes the PP), in parallel with a basic post-translationally modified isoform, suggesting transport from the cell bodies of the SON of newly-synthesised protein and changes in its activity. The level of an acidic, probably phosphorylated, Ywhag isoform is down-regulated in the SON by dehydration, although total levels are unchanged. Finally, based on the presence of a phosphorylated 14-3-3 binding motif, we have identified a 14-3-3 binding partner, proteasome subunit, beta type 7, in the NIL. Thus, we suggest that, through complex transcriptional, and post-translational processes, 14-3-3 proteins are involved in the regulation or mediation of HNS plasticity following dehydration.

Topics: 14-3-3 Proteins; Animals; Cysteine Endopeptidases; Dehydration; Gene Expression Profiling; Gene Expression Regulation; Hypothalamo-Hypophyseal System; Male; Oligonucleotide Array Sequence Analysis; Oxytocin; Protein Isoforms; Proteome; Rats; Rats, Sprague-Dawley; Supraoptic Nucleus; Vasopressins; Water Deprivation

Regulation of vasopressin (VP) and oxytocin (OT) secretion involves integration of neural signals from hypothalamic osmoreceptors, ascending catecholaminergic and peptidergic cell groups in the brain stem, and local and autoregulatory afferents. Neuropeptide Y (NPY) is one factor that stimulates the release of VP and OT from the supraoptic (SON) and paraventricular nuclei of the hypothalamus via activation of Y1 receptors (Y1R). The current studies were designed to assess the regulation and distribution of NPY Y1R expression in the SON of male rats that were either given 2% NaCl drinking water (24-72 h) or water deprived (48 h). Subjecting male rats to these conditions resulted in significant increases in both the number of cells expressing Y1R immunoreactivity (ir) and the amount of Y1R protein per cell within the SON. Y1R immunoreactivity was increased in the magnocellular but not medial parvocellular paraventricular nuclei, and Y1R mRNA levels were increased in the SON of salt-loaded rats. Subpopulations of both VP and OT cells in the hypothalamus express Y1R immunoreactivity and a greater percentage of VP-ir cells express Y1R after salt loading. To control for potential effects of dehydration-induced anorexia, a group of euhydrate animals was pair fed with animals consuming 2% NaCl. No detectable change in Y1R expression was observed in the SON of pair-fed animals, even though body weights were significantly lower than controls. These data demonstrate that NPY Y1R gene and protein expression are increased in the SON of salt-loaded and water-deprived animals and provide a mechanism whereby NPY can support VP/OT release during prolonged challenges to fluid homeostasis.

Topics: Animals; Blood; Body Weight; Dehydration; Gene Expression; Hypothalamus; Immunohistochemistry; Male; Neurons; Osmolar Concentration; Oxytocin; Paraventricular Hypothalamic Nucleus; Rats; Rats, Sprague-Dawley; Receptors, G-Protein-Coupled; Receptors, Neuropeptide; Sodium Chloride; Supraoptic Nucleus; Vasopressins; Water Deprivation

Nitric oxide (NO) is a gas molecule to signal neurotransmission in the hypothalamo-neurohypophysial system during osmotic regulation. We previously reported that osmotic stimulation increased nitric oxide synthase (NOS) activity in the supraoptic nuclei (SON) and neural lobe. The aim of this study is to define the role of NO in the regulation of Ca(2+)-activated K(+) channels (BK channels) expression in the magnocellular system following dehydration. We used Western blot analysis and quantitative immunocytochemistry to conduct the experiment in rats. In the immunoblot study, we found that water deprivation significantly increased the expression of BK channels in the SON and neural lobes. Dehydration also enhanced the profiles of neurons expressing vasopressin and oxytocin significantly. In about 70% of these neurons, BK channels were co-localized in the same neuron, and their expression increased significantly during dehydration. We further examined the effects of intracerebroventricular administration of sodium nitroprusside (a donor of NO) and L-NAME (an inhibitor of NO synthase) on expression of BK channels in the SON. We found that compared to animals treated with the donor of NO, there were significant decreases in the expression of BK proteins in animals receiving L-NAME. These results suggest that NO may enhance the expression of BK channels in the supraoptic nuclei and neural lobe of rats following dehydration.

Topics: Animals; Dehydration; Frontal Lobe; Gene Expression Regulation; Immunohistochemistry; Large-Conductance Calcium-Activated Potassium Channels; Nitric Oxide; Oxytocin; Rats; Supraoptic Nucleus; Water Deprivation

A second vesicular glutamate transporter (VGLUT2) is detected in magnocellular neurons in the rat hypothalamus. The present study revealed what phenotype of neurons express VGLUT2 mRNA by the histological method. We found that most vasopressin (VP) neurons and several oxytocin (OT) neurons express VGLUT2 mRNA. VGLUT2 gene expression in VP and OT neurons is enhanced with osmotic challenges. In the neurohypophysis, VGLUT2-staining in OT terminals was reduced with osmotic stimulation. These results indicate that VGLUT2 is principally expressed in VP neurons and also in some OT neurons and that VGLUT2 in VP and OT neurons is involved in osmotic regulation.

Topics: Animals; Cell Shape; Dehydration; Male; Neurons; Osmolar Concentration; Oxytocin; Paraventricular Hypothalamic Nucleus; Rats; Rats, Sprague-Dawley; Salts; Supraoptic Nucleus; Up-Regulation; Vasopressins; Vesicular Glutamate Transport Protein 2; Water Deprivation

Drinking 2% NaCl decreases interleukin (IL)-1beta in the neural lobe and enhances IL-1 Type 1 receptor expression in magnocellular neurones and pituicytes. To quantify cytokine depletion from the neural lobe during progressive salt loading and determine whether the changes are reversible and correspond with stores of vasopressin (VP) or oxytocin (OT), rats were given water on day 0 and then 2% NaCl to drink for 2, 5, 8 or 5 days followed by 5 days of water (rehydration). Control rats drinking only water were pair-fed amounts eaten by 5-day salt-loaded animals. Animals were decapitated on day 8, the neural lobe frozen and plasma hormones analysed by radioimmunoassay (OT, VP) or enzyme-linked immunosorbent assay (IL-1beta). IL-1beta, VP and OT in homogenates of the neural lobe were quantified by immunocapillary electrophoresis with laser-induced fluorescence detection. Differences were determined by ANOVA, Tukey's t-test, Dunnett's procedure, Fisher's least significant difference and linear regression analysis. In response to salt-loading, rats lost body weight similar to pair-fed controls, drank progressively more 2% NaCl and excreted greater urine volumes. Plasma VP increased at days 2 and 8 of salt-loading, whereas osmolality, OT and cytokine were enhanced after 8 days with IL-1beta remaining elevated after rehydration. In the neural lobe, all three peptides decreased progressively with increasing duration of salt-loading (IL-1beta, r2 = 0.98; OT, r2 = 0.94; VP, r2 = 0.93), beginning on day 2 (IL-1beta; VP) or 5 (OT), with only VP replenished by rehydration. IL-1beta declined more closely (P < 0.0001; ANOVA interaction analysis) with OT (r2 = 0.96) than VP (r2 = 0.86), indicative of corelease from the neural lobe during chronic dehydration. Local effects of IL-1beta on magnocellular terminals, pituicytes and microglia in the neural lobe with activation of forebrain osmoregulatory structures by circulating cytokine may sustain neurosecretion of OT and VP during prolonged salt-loading.

Topics: Analysis of Variance; Animals; Dehydration; Interleukin-1beta; Male; Osmolar Concentration; Oxytocin; Pituitary Gland, Posterior; Pituitary Hormones, Posterior; Rats; Rats, Sprague-Dawley; Sodium Chloride, Dietary; Statistics, Nonparametric; Vasopressins; Water-Electrolyte Balance

We have generated transgenic rats expressing an arginine vasopressin (AVP)-enhanced green fluorescent protein (eGFP) fusion gene. The expression of the eGFP gene and strong fluorescence were observed in the supraoptic nucleus (SON), the paraventricular nucleus (PVN), and the suprachiasmatic nucleus (SCN) in transgenic rats. The hypothalamo-neurohypophyseal tract, isolated SON neurons, and isolated axon terminals in the neurohypophysis also showed robust eGFP fluorescence. Water deprivation for 2 d increased the fluorescence of the eGFP in the SON and the PVN but not the SCN. The whole-cell patch-clamp technique was then used to record the electrical activities specifically identifying eGFP-expressing SON, PVN, and SCN AVP neurons in in vitro brain slice preparations. The AVP-eGFP transgenic rats are a unique new tool with which to study the physiological role of AVP-secreting neurons in the central nervous system and the dynamics of the regulation of AVP secretion in the living neurons and their axon terminals.

Topics: Animals; Animals, Genetically Modified; Arginine Vasopressin; Brain; Dehydration; Gene Expression; Green Fluorescent Proteins; Immunohistochemistry; In Situ Hybridization; In Vitro Techniques; Nerve Endings; Neurons; Oxytocin; Patch-Clamp Techniques; Rats; Rats, Wistar; Recombinant Fusion Proteins; RNA, Messenger; Tissue Distribution; Water Deprivation

Evidence in rats suggests that central oxytocin (OT) signaling pathways contribute to suppression of food intake during dehydration (i.e., dehydration anorexia). The present study examined water deprivation-induced dehydration anorexia in wild-type and OT -/- mice. Mice were deprived of food alone (fasted, euhydrated) or were deprived of both food and water (fasted, dehydrated) for 18 h overnight. Fasted wild-type mice consumed significantly less chow during a 60-min refeeding period when dehydrated compared with their intake when euhydrated. Conversely, fasting-induced food intake was slightly but not significantly suppressed by dehydration in OT -/- mice, evidence for attenuated dehydration anorexia. In a separate experiment, mice were deprived of water (but not food) overnight for 18 h; then they were anesthetized and perfused with fixative for immunocytochemical analysis of central Fos expression. Fos was elevated similarly in osmo- and volume-sensitive regions of the basal forebrain and hypothalamus in wild-type and OT -/- mice after water deprivation. OT-positive neurons expressed Fos in dehydrated wild-type mice, and vasopressin-positive neurons were activated to a similar extent in wild-type and OT -/- mice. Conversely, significantly fewer neurons within the hindbrain dorsal vagal complex were activated in OT -/- mice after water deprivation compared with activation in wild-type mice. These findings support the view that OT-containing projections from the hypothalamus to the hindbrain are necessary for the full expression of compensatory behavioral and physiological responses to dehydration.

Topics: Animals; Anorexia; Blood Volume; Dehydration; DNA; Eating; Food Deprivation; Genotype; Hindlimb; Immunohistochemistry; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Oxytocin; Proto-Oncogene Proteins c-fos; Rhombencephalon; Vasopressins

This study compared the renal metabolism of arachidonic acid in Brattleboro (BB) (vasopressin deficient) and Long-Evans (LE) control rats and the effects of a cytochrome P-450 (CYP) inhibitor 1-aminobenzotriazole (ABT) on renal function in these animals. The production of 20-hydroxyeicosatetraenoic acid (20-HETE) by renal cortical and outer medullary microsomes was significantly greater in BB than in LE rats (155 +/- 16 vs. 92 +/- 13 and 59 +/- 7 vs. 33 +/- 3 pmol.min(-1).mg protein(-1)). Renal cortical epoxygenase activity was not different in these strains. The expression of CYP4A proteins was 58 and 78% higher in the renal cortex and outer medulla of BB than in LE rats. Chronic treatment of BB rats with a vasopressin type 2 receptor agonist for 1 wk normalized the renal production of 20-HETE. Chronic blockade of the formation of 20-HETE and EETs with ABT had little effect on renal function in LE rats. However, urine flow increased by 54% and urine osmolarity decreased by 33% in BB rats treated with ABT. Plasma levels of oxytocin fell significantly from 7.2 +/- 1.3 to 3.9 +/- 1.0 pg/ml. The effects of ABT in BB rats were attenuated by chronic infusion of oxytocin (0.7 ng.min(-1).100 g(-1)) to maintain fixed high plasma levels of this hormone. These results indicate that the expression of CYP4A protein and the renal formation of 20-HETE are elevated in the kidney of BB rats due to a lack of vasopressin and that chronic blockade of the formation of 20-HETE and EETs with ABT promotes water excretion in vasopressin-deficient BB rats by reducing the circulating levels of oxytocin, which is a weak vasopressin agonist.

Topics: 8,11,14-Eicosatrienoic Acid; Animals; Arachidonic Acid; Cytochrome P-450 CYP4A; Dehydration; Diabetes Insipidus; Hydroxyeicosatetraenoic Acids; Kidney; Male; Oxytocin; Rats; Rats, Inbred BB; Rats, Long-Evans; Triazoles

The anteroventral region of the third ventricle (AV3V) is critical in mediating osmotic sensitivity. AV3V lesions increase plasma osmolality and block osmotic-induced vasopressin (VP) and oxytocin (OT) secretion. The aim was to evaluate the effects of AV3V lesions on neurosecretion under control/water replete conditions and after 48 h dehydration. The focus was on central peptidergic changes with measurement of OT and VP content in the hypothalamic paraventricular (PVN) and supraoptic (OT) regions and the posterior pituitary. AV3V-lesioned rats exhibited an elevated plasma osmolality and higher OT content in SON and PVN. There was an increase in VP content in PVN, but no change in SON. As predicted, the plasma peptide response to dehydration was absent in lesioned animals. However, dehydration produced depletion in posterior pituitary VP in lesioned animals with no change in OT. No changes in nuclear VP and OT levels were seen after dehydration. These results demonstrate that AV3V lesions alter the VP and OT neurosecretory system, seen as a blockade of osmotic-induced release and an increase in basal nuclear peptide content. The data indicate that interruption of the osmotic sensory system affects the central neurosecretory axis, resulting in a backup in content and likely changes in synthesis and processing.

Topics: Animals; Brain Diseases; Dehydration; Hypothalamo-Hypophyseal System; Male; Microdissection; Osmolar Concentration; Osmotic Pressure; Oxytocin; Paraventricular Hypothalamic Nucleus; Pituitary-Adrenal System; Radioimmunoassay; Rats; Rats, Wistar; Supraoptic Nucleus; Third Ventricle; Vasopressins; Water; Water-Electrolyte Balance

Galanin (Gal) as a neuropeptide with widespread distribution in the central nervous system may be involved in the mechanisms of vasopressin (AVP) and oxytocin (OT) release from the hypothalamo-neurohypophysial system. Vasopressin and oxytocin content in the hypothalamus and neurohypophysis as well as plasma level of both neurohormones were studied after galanin treatment in euhydrated and dehydrated rats. In not dehydrated rats intracerebroventricular (i.c.v.) injections of Gal did not affect the hypothalamic and neurohypophysial OT content, however, distinctly increased plasma OT concentration. In the same animals Gal diminished the hypothalamic AVP content but was without the effect on neurohypophysial AVP storage; plasma AVP level then raised. Galanin, administered i.c.v. to rats deprived of water, distinctly inhibited AVP and OT release from the hypothalamo-neurohypophysial system. Simultaneously, plasma AVP and OT level was significantly diminished after Gal treatment in dehydrated rats. These results suggest that modulatory effect of galanin on vasopressin and oxytocin release depends on the actual state of water metabolism. Gal acts as an inhibitory neuromodulator of AVP and OT secretion under conditions of the dehydration but stimulates this process in the state of equilibrated water metabolism.

Topics: Animals; Body Water; Dehydration; Drug Administration Schedule; Galanin; Hypothalamo-Hypophyseal System; Hypothalamus; Injections, Intraventricular; Male; Oxytocin; Pituitary Gland, Posterior; Radioimmunoassay; Rats; Rats, Wistar; Vasopressins

Our objective was to test the hypothesis that the cGMP signal-transduction mechanism mediates nitric oxide's (NO) modulation of oxytocin (OT) and vasopressin (VP) secretion from the hypothalamo-neurohypophysial system. Three studies were conducted in adult male Sprague-Dawley rats: (1a) Euhydrated rats received an intracerebroventricular (icv) infusion (1 microl/min for 30 min) of artificial cerebrospinal fluid (aCSF), vehicle (2.6% dimethyl sulfoxide [DMSO]) or 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) (0.05 microg/microl), an inhibitor of soluble guanylyl cyclase (sGC). ODQ did not affect basal levels of plasma VP or OT; (1b) Rats dehydrated for 24 h received aCSF or 8-Br-cGMP (icv), a membrane-permeable analog of cGMP, and plasma hormones were measured 2 min later. 8-Br-cGMP did not significantly change VP or OT levels; (2) Rats ingested water or 2% NaCl for 4 days, and NO synthase (NOS) and sGC activities were measured in posterior pituitaries, the anatomical site of hormone secretion. Salt loading enhanced (P < 0.001) production of [(14)C]citrulline, the coproduct of NO synthesis, without altering cGMP; (3) One SON was microdialyzed with [(14)C]arginine and NOS and sGC activities were quantified in microdialysates during intravenous (iv) infusion of isotonic or hypertonic saline in awake and anesthetized rats. In awake rats, [(14)C]citrulline recovery, but not cGMP, increased (P < 0.05) during intravenous infusion of both isotonic and hypertonic solutions, and after insertion of microdialysis probe itself. In anesthetized rats, however, where basal NOS activity is low, intravenous infusion of hypertonic, but not isotonic solution, increased [(14)C]citrulline recovery without affecting cGMP. Thus, in the forebrain, neither NO produced basally nor during osmotic stimulation depends on cGMP to modulate plasma vasopressin and oxytocin secretion.

Topics: Animals; Citrulline; Consciousness; Cyclic GMP; Dehydration; Enzyme Inhibitors; Guanylate Cyclase; Hypothalamo-Hypophyseal System; Injections, Intraventricular; Isotonic Solutions; Male; Microdialysis; Nitric Oxide; Nitric Oxide Synthase; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Sprague-Dawley; Saline Solution, Hypertonic; Signal Transduction; Sodium Chloride; Supraoptic Nucleus; Vasopressins; Water-Electrolyte Balance

Since the thyrotropin-releasing hormone (TRH) can modulate the processes of vasopressin (AVP) and oxytocin (OT) biosynthesis and release mainly at the hypothalamo-neurohypophysial level, the present experiments were undertaken to estimate whether TRH, administered intravenously in different doses, modifies these mechanisms under conditions of osmotic stimulation, brought about by dehydration. AVP and OT contents in the hypothalamus and neurohypophysis as well as plasma levels of AVP, OT, free thyroxine (FT4) and free triiodothyronine (FT3) were studied after intravenously TRH treatment in euhydrated and dehydrated for two days male rats. Under conditions of equilibrated water metabolism TRH diminished significantly the hypothalamic and neurohypophysial AVP and OT content but was without the effect on plasma oxytocin level; however, TRH in a dose of 100 ng/100 g b.w. raised plasma AVP level. TRH, injected i.v. to dehydrated animals, resulted in a diminution of AVP content in the hypothalamus but did not affect the hypothalamic OT stores. After osmotic stimulation, neurohypophysial AVP and OT release was significantly restricted in TRH-treated rats. Under the same conditions, injections of TRH were followed by a significant decrease of plasma OT level. I.v. injected TRH enhanced somewhat FT3 concentration in blood plasma of euhydrated animals but diminished FT4 plasma level during dehydration. Data from the present study suggest that TRH displays different character of action on vasopressin and oxytocin secretion in relation to the actual state of water metabolism.

Topics: Animals; Arginine Vasopressin; Body Water; Dehydration; Hypothalamus; Male; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Wistar; Reference Values; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine

To investigate the involvement of serotonin (5-hydroxytryptamine - 5-HT) receptors in mediation of stress-induced arginine vasopressin (AVP) and oxytocin (OT) secretion in male rats.. Experiments on laboratory rats with control groups.. Different stress paradigms were applied after pretreatment with intracerebroventricular infusion of saline or different 5-HT antagonists.. Restraint stress (5 min), hypotensive hemorrhage or dehydration for 24 h increased AVP secretion fivefold and OT secretion threefold. Swim stress for 3 min had no effect on AVP secretion, but increased OT secretion threefold. Ether vapor or hypoglycemia had no effect on AVP or OT secretion. The restraint stress-induced AVP response was inhibited by pretreatment with the 5-HT(2A+2C) antagonists ketanserin (KET) and LY-53857 (LY) and the 5-HT(3+4) antagonist ICS-205930 (ICS), whereas the 5-HT(1A) antagonist WAY-100635 (WAY) had no effect. The OT response to restraint stress was inhibited by WAY, KET and LY but not by ICS. KET and LY inhibited OT response to dehydration, and LY inhibited OT response to hemorrhage. Neither of the antagonists affected AVP responses to dehydration or hemorrhage, nor the swim stress-induced OT response.. 5-HT(2A), 5-HT(2C) and possibly 5-HT(3) and 5-HT(4) receptors, but not 5-HT(1A) receptors, are involved in the restraint stress-induced AVP secretion. 5-HT does not seem to be involved in the dehydration- or hemorrhage-induced AVP response. The restraint stress-induced OT response seems to be mediated via 5-HT(1A), 5-HT(2A) and 5-HT(2C) receptors. The dehydration and hemorrhage-induced OT responses are at least mediated by the 5-HT(2A) and 5-HT(2C) receptors. The 5-HT(3) and 5-HT(4) receptors are not involved in stress-induced OT secretion.

Topics: Animals; Arginine Vasopressin; Cold Temperature; Dehydration; Hemorrhage; Jugular Veins; Male; Oxytocin; Rats; Rats, Wistar; Restraint, Physical; Serotonin; Serotonin Antagonists; Stress, Physiological; Swimming

Brain-derived angiotensin II (ANG II) and prostaglandins have important roles in the regulation of body fluid and blood pressure homeostasis. In the present studies we investigated the central interactions between these two neurochemical products in regulating the hypothalamo-neurohypophysial system during dehydration. Intracerebroventricular (icv) administration of prostaglandin D(2) (PGD(2); 20 microg/5 microl) to conscious adult male Sprague-Dawley rats deprived of water for 24 h did not alter significantly the already elevated plasma levels of vasopressin or oxytocin. When PGD(2) was administered in combination with losartan, an antagonist of ANG II AT(1)-receptor subtype, however, concentrations of both hormones in plasma became further elevated. Icv administration of ANG II (50 ng/5 microl) increased further the enhanced plasma levels of vasopressin and oxytocin, as expected. Pretreatment with indomethacin (200 microg/5 microl; icv), an inhibitor of cyclo-oxygenase, significantly attenuated the ANG II-induced increase in oxytocin secretion only. Independent of the presence of ANG II, however, indomethacin decreased plasma levels of vasopressin, but not oxytocin. These results indicate that a prostaglandin is required for the stimulated release of vasopressin during dehydration and that the elevation of oxytocin secretion in response to ANG II depends largely on activation of cyclo-oxygenase and production of prostaglandins. The oxytocin response to exogenously administered PGD(2), however, can be negatively modulated by a mechanism dependent upon ANG II AT(1) receptors.

Topics: Angiotensin II; Animals; Antihypertensive Agents; Brain Chemistry; Central Nervous System; Cyclooxygenase Inhibitors; Dehydration; Indomethacin; Injections, Intraventricular; Losartan; Male; Oxytocin; Prostaglandin D2; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Vasoconstrictor Agents; Vasopressins

Arginine vasopressin- (AVP) and oxytocin- (OXT) secreting magnocellular neurons undergo gross structural changes with chronic physiological stimulation. Here, we investigated subcellular aspects of plasticity in rat neurohypophysial terminals during dehydration. Ultrastructural analyses demonstrated that chronic dehydration by 2% NaCl drinking for 7 days significantly decreased the numbers of neurosecretory granules and microvesicles but not the numbers of mitochondria. Moreover, in dehydrated rats, terminals making neurovascular contacts enlarged, whereas terminals in apposition to astrocytes, i.e., neuroglial contacts, became smaller. Western blot analyses demonstrated significant decreases in the levels of F3 and Thy-1 together with those of AVP- and OXT-neurophysin, but the levels of synaptophysin, SNAP-25, and GAP-43 were unchanged. Both F3 and Thy-1 were recovered in the buffer-insoluble pellet, and phosphatidyl inositol-specific phospholipase C treatment released both molecules from the crude membrane fraction, indicating that they are attached to terminal membranes by glycosylphosphatidyl inositol anchors. Confocal microscopic observations demonstrated that F3 colocalized with Thy-1 in the same terminals of magnocellular neurons. In contrast, the level of calretinin, a Ca(2+) binding protein was significantly increased with chronic dehydration. Thus, the present results suggest that enhancement of neurovascular contacts results from rearrangement of terminal-astrocyte and terminal-vessel contacts rather than enlargement or sprouting of magnocellular terminals themselves. The down-regulation of F3 and Thy-1 may contribute to enhancement of neurovascular contacts that accompany increased peptide release during dehydration.

Topics: Animals; Arginine Vasopressin; Calbindin 2; Cell Adhesion Molecules, Neuronal; Contactins; Dehydration; GAP-43 Protein; Male; Membrane Proteins; Microscopy, Electron; Nerve Tissue Proteins; Neuronal Plasticity; Neurons; Oxytocin; Rats; Rats, Wistar; S100 Calcium Binding Protein G; Synaptophysin; Synaptosomal-Associated Protein 25; Thy-1 Antigens

The mammalian pineal gland is known to receive a noradrenergic innervation originating from the superior cervical ganglion which corresponds to the primary regulatory input for melatonin synthesis. However, many peptidergic fibers containing peptides such as vasopressin and oxytocin have also been found in the rat pineal gland. The present study was performed to investigate the possible role of vasopressin and oxytocin on melatonin secretion in vivo. Therefore, both neuropeptides were delivered for 2 h through a trans-pineal microdialysis probe directly into the gland at different times during the nocturnal phase of the light:dark cycle. At the same time pineal dialysates were collected continuously. Melatonin concentrations were measured by radioimmunoassay. Melatonin synthesis potentiation was achieved when vasopressin was infused locally in the pineal, during the onset of nocturnal melatonin secretion. In order to assess the possible role of a physiological increase of endogenous circulating vasopressin on pineal metabolism, melatonin synthesis was recorded in the same animals before and after a prolonged dehydration period. Night time melatonin concentration was increased after the water deprivation vs control conditions. Contrary to that, oxytocin seems not to affect pineal metabolism in the rat since no significant change was observed on melatonin secretion in response to a local oxytocin infusion. These results show that vasopressin can modulate melatonin synthesis in the rat pineal whereas no effect was obtained with oxytocin, at least under the present experimental conditions.

Topics: Animals; Circadian Rhythm; Dehydration; Drug Synergism; Infusions, Parenteral; Kinetics; Male; Melatonin; Microdialysis; Oxytocin; Pineal Gland; Rats; Rats, Wistar; Vasopressins; Water Deprivation

Inhibiting NO synthase (NOS) with N(G)-nitro-L-arginine methyl ester (L-NAME, 250 microg/5 microl of artificial cerebrospinal fluid (aCSF)) injected intracerebroventricularly (i.c.v.) increased already enhanced levels of oxytocin, but not vasopressin, in conscious adult male Sprague-Dawley rats dehydrated for 24 h. Intracerebroventricular pretreatment with indomethacin (200 microg/5 microl aCSF), an inhibitor of cyclo-oxygenase, but not with losartan (25 microg/5 microl aCSF), an antagonist of angiotensin II (ANG II) AT(1)-receptor subtype, nearly prevented the elevation in oxytocin levels after L-NAME. Thus, NO inhibits prostaglandin (but not ANG II) mediated the modulatory actions of NO on oxytocin secretion from the hypothalamo-neurohypophysial system (HNS) during water deprivation.

Topics: Angiotensin II; Animals; Dehydration; Hypothalamo-Hypophyseal System; Indomethacin; Injections, Intraventricular; Losartan; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Oxytocin; Prostaglandins; Rats; Rats, Sprague-Dawley; Vasopressins; Water Deprivation; Water-Electrolyte Balance

The water-seeking behavior (WR) of toads (Bufo viridis) was investigated. Fully hydrated toads that are allowed free choice of wet or dry filter paper voluntarily and spontaneously select to sit on water-soaked paper at a regular frequency during trials. Dehydration of bladder-emptied toads by 14% elicits WR in all animals. Injection of aldosterone or angiotensin-I reduced the dehydration threshold to 7% weight loss. WR frequency increased when plasma osmolality was elevated by injection of NaCl or other solutes (both ionic and non-ionic). Only urea, to which cell membranes are highly permeable, was the exception that did not produce this response. The increase in WR frequency induced by elevated plasma osmolality was augmented by injection of aldosterone or angiotensin-I. In vivo water uptake, measured in a water bath, was increased by an NaCl or oxytocin injection, but not by aldosterone. It is concluded that elevated plasma osmolality induces an increase in WR frequency that is separate and prior to the water uptake process. Different hormones are involved in each step.

Topics: Aldosterone; Angiotensin I; Animals; Behavior, Animal; Body Weight; Bufonidae; Dehydration; Female; Male; Osmolar Concentration; Osmosis; Oxytocin; Skin Absorption; Sodium Chloride; Urea; Urinary Bladder; Water

Ultrastructural studies of the supraoptic nucleus (SON) of the hypothalamus suggest that an active retraction and extension of astrocytic processes (structural plasticity) from between magnocellular neuroendocrine neurons plays a role in the release of oxytocin, vasopressin, or both peptides that accompanies parturition, lactation, and dehydration. In support of this, Salm et al. (1985) previously demonstrated a lactation-associated reduction in immunoreactive glial fibrillary acidic protein (GFAP), an astrocyte-specific cytoskeletal constituent. To determine if similar changes occur in response to dehydration, and if they are reversible, the present study examined GFAP-immunoreactivity (IR) in the SON under various hydration states. Rats were dehydrated for 7 days by substitution of drinking water with 2% saline (n = 3), or dehydrated for 7 days followed by 7 days of rehydration (n = 3). A control group (n = 3) with free access to tap water was used for comparisons. The optical density of GFAP-IR was obtained from the SON, globus pallidus, and lateral hypothalamic regions. The areas of the ventral glial limitans subjacent to the SON (SON-VGL) and of linearly equivalent segments of glial limitans more distant from the SON were also determined. Dehydration resulted in a significant reduction in GFAP-IR in the SON compared to control and rehydrated levels. We also found that the area of the SON-VGL was significantly larger than that of linearly equivalent segments of glial limitans elsewhere and that it was significantly reduced in dehydrated rats, returning to control levels with rehydration. GFAP-IR and glial limitans thickness in regions unrelated to body fluid homeostasis lateral to the SON, overlying to dorsal cortex, and subjacent to the optic chiasm were not significantly changed by hydration state. These results are similar to the changes of GFAP-IR reported for lactating rats and provide further evidence for a role of structural plasticity of astrocytes in events surrounding the selective functional activation of local neurons.

Topics: Animals; Antibodies; Astrocytes; Dehydration; Fluid Therapy; Glial Fibrillary Acidic Protein; Male; Neuronal Plasticity; Oxytocin; Rats; Rats, Inbred Strains; Supraoptic Nucleus; Vasopressins

Intracerebroventricular (i.c.v.) injection of the inhibitor of NO synthase (NOS), N(G)-nitro-L-arginine methyl ester (L-NAME) (250 microg/5 microL) attenuated the drinking response in rats deprived of water for 24 h. Moreover, oxytocin (OT) levels in plasma increased after 2 min, whereas both oxytocin and vasopressin levels were elevated at 120 min after intracerebroventricular injection. The delayed effect of L-NAME on both hormones was not observed in dehydrated animals allowed to drink water. Blood pressure remained stable after injection of artificial cerebrospinal fluid (aCSF) in dehydrated rats not allowed to drink. In rats having access to water, however, there was an immediate but transient pressor response (0-5 min) with a delayed hypotension from 45 to 120 min. L-NAME consistently increased blood pressure in a biphasic mode, whether the animals drank or not, with an early peak at 5 min that decayed after 15-30 min and a second pressor response beginning at 30-45 min and remaining elevated at 120 min when the experiment ended. These pressor responses were independent of the adrenal glands. Thus, centrally produced nitric oxide facilitates drinking, inhibits release of vasopressin and oxytocin from the magnocellular system, and maintains resting arterial blood pressure in normally hydrated and dehydrated rats.

Topics: Animals; Blood Pressure; Brain; Dehydration; Drinking; Enzyme Inhibitors; Injections, Intraventricular; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Oxytocin; Rats; Rats, Sprague-Dawley; Vasopressins; Water Deprivation; Water-Electrolyte Balance

N-Methyl-D-aspartate receptors are thought to be involved in synaptic signaling within the hypothalamo-neurohypophysial system, but the extent and nature of their involvement has not been determined. In this study, in the rat, we evaluated the effect of hyperosmotic stimulation on the N-methyl-D-aspartate receptor subunit, NR1, which confers function to N-methyl-D-aspartate receptor heteromers. Co-localization of immunoreactivity for NR1 and vasopressin- or oxytocin-associated neurophysin in magnocellular neurons of the supraoptic and paraventricular hypothalamic nuclei was accomplished using double-label immunohistochemistry. Our results show that vasopressin- and oxytocin-neurophysin-positive populations contained detectable levels of NR1 labeling. Using NR1 labeling as a measure of N-methyl-D-aspartate receptor density, we examined the effect of dehydration in these nuclei. Using computer-assisted densitometry, we found significantly greater NR1 labeling densities in the magnocellular regions of both the supraoptic and paraventricular nuclei of saline-treated rats than of control rats. This increase was not due to methodological factors, since no changes in NR1 labeling density were found in a nearby nucleus, the nucleus reuniens. Western blot analysis showed similar selective increases in NR1 labeling in homogenates from the supraoptic nucleus, paraventricular nucleus and in some cases from the anterior hypothalamic area. In both immunohistochemical and western blotting experiments we did not observe a dehydration-induced increase in NR1 in other brain areas examined. Our results showing an up-regulation of NR1-containing N-methyl-D-aspartate receptors during dehydration suggest that these receptors are involved in the regulation of body water and may represent an adaptive physiological response following activation of the hypothalamo-neurohypophysial axis. In addition, these results suggest that the functional expression of N-methyl-D-aspartate receptors is dynamic and may be modified according to the physiological state of the animal.

Topics: Animals; Blotting, Western; Dehydration; Immunohistochemistry; In Vitro Techniques; Male; Neuronal Plasticity; Neurophysins; Oxytocin; Paraventricular Hypothalamic Nucleus; Rats; Receptors, N-Methyl-D-Aspartate; Supraoptic Nucleus; Up-Regulation; Vasopressins; Water-Electrolyte Balance

This study describes a competitive reverse transcriptase polymerase chain reaction (RT-PCR) method for assaying the amounts of vasopressin (AVP) and ocytocin (OT) mRNAs in the rat hypothalamus and uterus. Despite the low concentrations of these mRNAs, the RT-PCR method readily measured both AVP and OT mRNAs in the same sample. A common internal standard for both reactions was designed to quantify the reaction. Both AVP and OT mRNAs were readily quantified in a 75 ng sample of total RNA from the hypothalamus. Water deprivation stimulated AVP mRNA production 3-fold and OT mRNA production 1.7-fold in the hypothalamus. Gestation only influenced the amount of OT mRNA in the hypothalamus (3-fold increase) and uterus (38-fold increase). The amount of AVP mRNA in the hypothalamus remained unchanged and no AVP mRNA was detected in the uteri of either non-pregnant or pregnant rats. This competitive RT-PCR is a powerful tool that provides rapid and precise assays of AVP and OT mRNAs.

Topics: Animals; Arginine Vasopressin; Base Sequence; Dehydration; DNA; DNA Primers; Female; Hypothalamus; Male; Molecular Sequence Data; Oxytocin; Polymerase Chain Reaction; Pregnancy; Pregnancy, Animal; Rats; Rats, Sprague-Dawley; RNA, Complementary; RNA, Messenger; Sensitivity and Specificity; Sequence Alignment; Transcription, Genetic; Uterus

Topics: Animals; Biological Transport; Dehydration; Hypothalamus; Immunohistochemistry; Male; Oxytocin; Peptides; Pituitary Gland; Rats; Rats, Wistar; Vasopressins

In a previous study in rats we demonstrated the existence of osmoregulatory natriuretic mechanisms distinct from the natriuretic mechanisms that are dependent on volume stimulation. At the same time, we found that oxytocin (OT) receptors were important mediators of natriuresis induced by hypernatremia but not of that induced by isotonic volume expansion. In the present study, the role of OT in dehydration natriuresis was examined in conscious rats. Dehydration for 24 h caused hypernatremia (from 142.1 +/- 0.4 to 147.7 +/- 0.7 mmol/l) and natriuresis accompanied by an approximately 30% spontaneous reduction of food intake. In conjunction with renal retention of water caused by an increase in circulating vasopressin, the natriuresis and probably the reduction of food intake can help to counteract the rise in body fluid osmolality. This natriuresis could not be fully explained by the reduction in plasma aldosterone. Plasma OT concentration had increased from 15.5 +/- 1.2 to 23.8 +/- 2.0 pg/ml at the end of 24 h of dehydration. Intravenous infusion of a selective OT-receptor antagonist [Mpa1,D-Tyr(Et)2, Thr4, Orn8]-OT using osmotic minipumps prevented dehydration natriuresis. It is concluded that in a dehydration-induced hypernatremic state OT is released, inducing natriuresis and facilitating sodium homeostasis. This mechanism is activated by Na osmoreceptors, but is not primarily dependent on the volume status.

Topics: Aldosterone; Animals; Dehydration; Diuresis; Hybridization, Genetic; Injections, Intravenous; Male; Natriuresis; Oxytocin; Rats; Rats, Inbred Strains; Receptors, Oxytocin; Sex Characteristics

The effects of osmotic stimulation on Fos expression and cell size increase in the supraoptic nucleus were evaluated in intact, sham-operated, and AV3V-lesioned rats. Fos-positive neurons were found mainly in the AV3V regions and the hypothalamic magnocellular neurons in the forebrain in dehydrated intact rats. Intraperitoneal injection of hypertonic saline and chronic dehydration induced a significant increase in number of Fos-positive neurons in the supraoptic nucleus of intact and sham-operated rats. AV3V lesions completely abolished the expression of Fos in SON neurons of rats that were intraperitoneally injected with hypertonic saline and were chronically dehydrated. Chronic dehydration increased significantly cell size of the OXT and AVP magnocelluar neurons in intact and sham-operated rats. However, there was no increase in cell size of those in the AV3V-lesioned rats. These results demonstrate that neural input derived from AV3V regions plays a significant role in causing Fos expression and structural changes such as cell size increase in the hypothalamic magnocellular neurons with osmotic stimulation.

Topics: Animals; Cell Size; Cerebral Ventricles; Dehydration; Gene Expression; Hypothalamus; Immunohistochemistry; Male; Neurons; Oncogene Proteins v-fos; Oxytocin; Rats; Rats, Wistar; Vasopressins

Dehydration associated with hyperosmolality and decreased extracellular volume stimulates arginine vasopressin (AVP) and oxytocin (OT) secretion from magnocellular neurons of the hypothalamus. The effects of hyperosmolality and decreased extracellular volume on the magnocellular neurons are mainly indirect and seem to be mediated centrally via several neurotransmitters and neuropeptides. Because histamine (HA), which serves as a central neurotransmitter, releases AVP and OT from the neurohypophysis when administered centrally, we investigated the possible role of HA in dehydration-induced AVP and OT secretion. To do this, we studied 1) the effect of dehydration on messenger RNA (mRNA) expression of the HA synthesis enzyme, histidine decarboxylase (HDC), in the tuberomammillary nucleus of the hypothalamus; and 2) the effect of HA synthesis inhibition during dehydration on AVP and OT mRNA expression in the supraoptic nucleus of the hypothalamus as well as on plasma AVP and OT levels. Forty-eight hours of dehydration increased the mRNA level of HDC in the tuberomammillary nuclei, whereas 24 h of dehydration had no effect. Pretreatment with the HA synthesis inhibitor alpha-fluoromethylhistidine (alpha FMH) increased the expression of HDC mRNA in 24-h dehydrated rats, but had no effect in euhydrated rats. In rats dehydrated for 48 h, the already increased level of HDC mRNA was not increased further by alpha FMH. Twenty-four and 48 h of dehydration increased AVP and OT mRNA levels in the supraoptic nucleus. This effect was inhibited by alpha FMH pretreatment. Dehydration increased the plasma levels of AVP and OT to an extent which depended on the duration of dehydration. Pretreatment with alpha FMH inhibited the hormone responses to 24 h of dehydration, but did not affect the responses to 48 h of dehydration. Twenty-four and 48 h of dehydration had no significant effect on the contents of AVP and OT in the neurohypophysis, whereas pretreatment with alpha FMH combined with 48 h of dehydration led to depletion of AVP stores in the neurohypophysis. Based on the present findings, we conclude that hypothalamic histaminergic neurons are involved in the regulation of dehydration-induced stimulation of magnocellular AVP and OT neurons.

Topics: Animals; Arginine Vasopressin; Dehydration; Gene Expression; Histamine; Histidine Decarboxylase; Hypothalamus; In Situ Hybridization; Male; Methylhistidines; Oxytocin; Pituitary Gland, Posterior; Radioimmunoassay; Rats; Rats, Wistar; RNA, Messenger; Supraoptic Nucleus; Time Factors

Sheep which were predominantly urinary excretors (U) or faecal excretors (F) of sodium were exposed to a 75% reduction of water intake for 72 h. The experiment was performed on moderate, low or high sodium intakes (0.4, 0.05 or 1.2 mmol kg-1 day-1) to test the hypothesis that dehydration natriuresis was not a cause of sodium depletion but a defence against hypernatraemia. Dehydration caused elevation of plasma sodium concentration, osmolality, antidiuretic hormone (ADH) and oxytocin but, as in other experiments, a fall in haematocrit. The two higher levels of sodium intake were associated with dehydration natriuresis but also a smaller increase in faecal sodium excretion in both U and F sheep. On low sodium intake, however, neither urinary nor faecal sodium excretion increased in either group of sheep although the rise in plasma sodium concentration caused by dehydration was similar. Thus, when there is a risk of sodium depletion, due to low sodium intake, dehydration natriuresis does not occur, consistent with the hypothesis. Active sodium transport inhibitor (ASTI) and atrial natriuretic peptide (ANP) fell rather than rose during dehydration. Since aldosterone is suppressed by the higher levels of sodium intake, none of these hormones is likely to mediate dehydration natriuresis in sheep. F sheep showed more effective renal and faecal water conservation when dehydrated. During water restriction, the urinary potassium excretion of U sheep was significantly reduced, unlike that of F sheep; moreover, the latter maintained an identical plasma potassium concentration between baseline and restriction period, whereas in U sheep it was 0.3 mmol l-1 higher during water restriction. Increased drinking rather than reduced urine output was the basis of rehydration when ad lib. water intake was restored.

Topics: Animals; Atrial Natriuretic Factor; Dehydration; Feces; Female; Natriuresis; Oxytocin; Sheep; Sodium; Sodium Chloride, Dietary; Vasopressins; Water; Water Deprivation

Topics: Animals; Dehydration; Homeostasis; Infusions, Intravenous; Isotonic Solutions; Kidney; Natriuresis; Oxytocin; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Oxytocin; Saline Solution, Hypertonic; Sodium; Sodium Chloride; Vasotocin

I.c.v. administration of a nitric oxide (NO) synthase inhibitor (NG-monomethyl-L-arginine, NMMA, 500 micrograms/5 microliters) to conscious rats deprived of water for 24 h attenuated drinking and decreased glucose utilization in the subfornical organ and median preoptic nucleus. NMMA did not alter the enhanced glucose utilization in the hypothalamo-neurohypophysial system (HNS) of dehydrated rats, although it has been shown to increase, selectively, oxytocin (OT) secretion [18]. This suggests that NO may act in the neural lobe to inhibit OT secretion and promote the preferential release of vasopressin during dehydration. This effect is similar to the blockade of endogenous opiate receptors by naloxone.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Dehydration; Deoxyglucose; Drinking; Glucose; Hypothalamo-Hypophyseal System; Injections, Intraventricular; Male; Nitric Oxide Synthase; omega-N-Methylarginine; Oxytocin; Preoptic Area; Rats; Rats, Sprague-Dawley; Subfornical Organ; Vasopressins

1. In many mammals, severe dehydration is known to cause exhaustion of the vasopressin content of the neural lobe. Here, we have examined the physiological state of the neurohypophysis of the jerboa Jaculus orientalis, a rodent inhabitant of a semi-desert climate. 2. Isolated neurohypophyses and neurosecretory nerve endings were perfused in vitro and vasopressin and oxytocin release were determined by radioimmunoassay. 3. Electrical stimulation of the neurohypophysis with bursts of pulses mimicking the activity of hypersecreting neuroendocrine neurones induced similar increases of secretion in both control animals and animals dehydrated for up to 2 months. Neurohormone release was greatly potentiated when the bursts of pulses were separated by silent intervals. 4. Prolonged stimulation of neurohypophyses from both control and dehydrated animals induced a sustained increase of vasopressin release; in contrast, oxytocin release under similar conditions showed a biphasic secretory pattern consisting of a transient increase that subsequently decreased to a steady level whose amplitude was similar to that for vasopressin. 5. K(+)-induced secretion was largely inhibited by the Ca2+ channel blockers nicardipine and omega-conotoxin, suggesting that in this neurosecretory system both L- and N-type calcium channels play a major role in stimulus-secretion coupling. Depolarization of isolated nerve endings using a fast-flow perifusion system showed that there was no difference in the amplitude and the time course of the secretory response in dehydrated and hydrated animals. 6. The results demonstrate that, despite the climatic conditions in which the jerboas live, their neural lobes retain the capacity to release, upon depolarization of the plasma membrane of the nerve endings, large amounts of neurohormone. It is concluded that the neurohypophyseal peptidergic release system in the dehydrated jerboa functions adequately even under extreme environmental stress.

Topics: Animals; Calcium Channel Blockers; Calcium Channels; Cell Membrane; Dehydration; Electric Stimulation; Nerve Endings; Oxytocin; Perfusion; Pituitary Gland, Posterior; Potassium; Radioimmunoassay; Rodentia; Vasopressins

Intracerebroventricular (i.c.v.) administration of NG-monomethyl-L-arginine monoacetate (NMMA; 500 micrograms; 402 mM) and NG-nitro-L-arginine methyl ester (NAME; 270 micrograms; 200 mM), inhibitors of nitric oxide synthase, enhanced the rise in oxytocin but not vasopressin levels in plasma of conscious rats following 24 h of water deprivation. This effect of NMMA occurred by 10 min after administration, reached its peak at 15 min and decreased by 20 min. Daily administration of lower doses (50 micrograms and 0.5 microgram/5 microliter, i.c.v.) of another inhibitor of nitric oxide synthase, NG-nitro-L-arginine, just before and after 24 h of water deprivation and in control animals treated similarly were without effect on either vasopressin or oxytocin levels. Nitric oxide, therefore, attenuates preferentially the release of oxytocin during dehydration.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Dehydration; Male; Nerve Tissue Proteins; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; omega-N-Methylarginine; Oxytocin; Paraventricular Hypothalamic Nucleus; Pituitary Gland, Posterior; Rats; Rats, Sprague-Dawley; Supraoptic Nucleus; Vasopressins

1. The neurohypophysial osmoregulatory hormones of the African toad Bufo regularis, a species adapted to estivate under dry and hot conditions, have been investigated. Vasotocin and hydrin 2 (vasotocinyl-Gly) have been identified by their retention times in high-pressure reverse-phase liquid chromatography and coelution with synthetic peptides, their pharmacological properties (vasotocin) and microsequencing. 2. Vasotocin-associated neurophysin (MSEL-neurophysin type) has been characterized by its N-terminal amino acid sequence. 3. In toads subjected to dehydration by evaporation (20% weight loss) or to osmotic stress by immersion in 2% NaCl for 3 hr (6% weight loss), the molar ratio hydrin 2/vasotocin (about 2:1) remained similar to the one observed in control animals. 4. In toads exposed to saline solution, there was a large decrease (roughly 30%) in the amounts of both hormones in the neuro-hypophysis. Environmental conditions for distinct secretions of vasotocin and hydrin 2 remain to be found.

Topics: Amino Acid Sequence; Animals; Arginine Vasopressin; Biological Assay; Bufonidae; Chromatography, High Pressure Liquid; Dehydration; Environment; Female; In Vitro Techniques; Molecular Sequence Data; Neurophysins; Osmolar Concentration; Oxytocin; Pituitary Gland, Posterior; Pregnancy; Protein Precursors; Rats; Spectrophotometry, Ultraviolet; Vasotocin

Rats euhydrated and dehydrated during two or four days were given intracerebroventricularly (i.c.v.) thyrotropin-releasing hormone (TRH) in a daily dose of 200 ng dissolved in 10 microliters of 0.9% sodium chloride. A single dose of TRH injected to euhydrated animals increased the hypothalamic vasopressin content but did not affect significantly the content of vasopressin in the neurohypophysis as well as that of oxytocin both in the hypothalamus and neurohypophysis. In rats deprived of water for two days TRH completely prevented the decrease of neurohypophysial oxytocin due to stimulation of osmoreceptor origin. Similarly, TRH restrained both the hypothalamic and the neurohypophysial vasopressin and oxytocin depletion in rats dehydrated for four days.

Topics: Animals; Dehydration; Hypothalamo-Hypophyseal System; Hypothalamus; Male; Oxytocin; Pituitary Gland, Posterior; Radioimmunoassay; Rats; Rats, Wistar; Thyrotropin-Releasing Hormone; Vasopressins

Ethanol ingestion affects the hypothalamo-neurohypophysial system resulting in increased diuresis, dehydration and hyperosmolality. We studied the supraoptic nucleus, of the hypothalamus, in ethanol-treated rats, to determine if ethanol alone and/or the associated disturbances of water metabolism lead to structural alterations in a nucleus known to play a central role in fluid homeostasis. Groups of male and female rats were ethanol-treated until 12 and 18 months of age and compared with age-matched pair-fed controls. Twelve and 18-month-old control groups and 12-month-old water control groups (rats submitted to chronic dehydration) were also included in this study in an attempt to differentiate between the effects of undernutrition and dehydration/hyperosmolality, and the specific neurotoxic effects of ethanol. We estimated the volume of the supraoptic nucleus and the numerical density of its neurons and calculated the total number of supraoptic neurons. The volume of both supraoptic neurons and neuropil were also estimated. In immunostained material the ratio of vasopressin to oxytocin neurons and the cross-sectional areas of the two neuronal types were evaluated. There was marked neuronal loss in alcohol-treated rats, but the volume of the supraoptic nucleus was increased. The increase in the volume of the supraoptic nucleus correlated with and was due to increases in the volume was particularly marked for vasopressin neurons. No significant differences were found between controls and pair-fed controls in any of the parameters investigated. In water control rats, the volume of the supraoptic nucleus and of the supraoptic neurons and neuropil was also greater than in pair-fed controls. However, the variations found were not as marked as in ethanol-treated rats and there was no cell loss. These findings reveal, for the first time, that chronic ethanol consumption affects the morphology of supraoptic neurons and neuropil and, consequently, the structure of the entire supraoptic nucleus. Moreover, this study supports the view that ethanol has direct neurotoxic effects on supraoptic neurons because the alterations that occur are not mimicked in animals in which water metabolism alone is disturbed.

Topics: Animals; Brain; Dehydration; Ethanol; Female; Immunohistochemistry; Male; Neurons; Organ Size; Oxytocin; Rats; Rats, Wistar; Sex Characteristics; Supraoptic Nucleus; Vasopressins; Water-Electrolyte Balance; Weight Gain

A study was performed investigating the daily patterns of hormone release accompanying changes in fluid balance in the male rat during 48 h of dehydration. The blood volume decreased by 18%, the largest change occurring during the initial period when the rats showed an effective loss of body sodium. During the second day of dehydration, sodium retention was again seen. Plasma sodium concentrations showed a progressive increase, the total rise being 5-6%; the greatest changes were seen during the dark phases of the cycle which may be due to the nocturnal food intake. Plasma vasopressin and oxytocin concentrations were significantly elevated throughout dehydration to levels which could be reproduced by acutely increasing plasma sodium and decreasing blood volume to the same extent. The observed increases were influenced by the phase of the day-night cycle, being greatest over the dark phases of the cycle. The overall increases were greatest when dehydration commenced at the start of the dark phase. Dehydration initially led to a rise in plasma corticosterone concentrations, whilst plasma concentrations of atrial natriuretic peptide were decreased. Plasma angiotensin II concentrations rose significantly during the later period of sodium retention.

Topics: Angiotensin II; Animals; Atrial Natriuretic Factor; Blood Volume; Circadian Rhythm; Corticosterone; Dehydration; Male; Oxytocin; Photoperiod; Pituitary Gland, Posterior; Pituitary Hormones, Posterior; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Sodium; Vasopressins

Topics: Animals; Chronic Disease; Dehydration; Female; Immunohistochemistry; Nerve Endings; Oxytocin; Pituitary Gland, Posterior; Rats; Vasopressins

Male rats were deprived of water for 5 days, and then given water ad libitum for 3, 7, 10 or 14 days. Plasma osmolarity returned to normal in less than 3 days, while pituitary vasopressin (AVP) and oxytocin (OXT) only returned to control levels after 14 days. Sections of the supraoptic nucleus (SON) were hybridized with 35S-labelled cDNA (OXT) or oligonucleotide (AVP) probes. Relative AVP and OXT mRNA contents were quantitated by counting the number of silver grains on a large standard area of the SON, then extrapolating this value to the volume of the whole SON (deduced from surface areas of all the sections). Dehydration significantly enlarged the volume of the SON (x 1.54) and increased the AVP and OXT mRNAcontent (x 2). During rehydration, both SON volume and density of silver grains were higher than normal for at least 7-10 days, although levels started to fall by day 3. The distribution of individual cells according to their silver grain densities remained unimodal during the dehydration-rehydration sequence with an extension, then a return to normal of the distribution range. Maximum sizes of AVP and OXT mRNAs on Northern blots of RNAs extracted from 5 pooled SONs were observed on dehydration day 5. The size of these species fell progressively, reaching control values by rehydration day 14. We conclude that during rehydration, at a time when most of the putative inducers of gene transcription are no longer activated, the peptidergic deficit was accompanied by an increased level of AVP and OXT mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine Vasopressin; Blotting, Northern; Dehydration; DNA; DNA Probes; Gene Expression; Histocytochemistry; In Situ Hybridization; Male; Osmolar Concentration; Oxytocin; Pituitary Gland, Posterior; Radioimmunoassay; Rats; Rats, Wistar; RNA, Messenger; Silver Staining; Supraoptic Nucleus

Rats euhydrated and dehydrated for two or four days were given intracerebroventricularly (i.c.v.) thyrotropin-releasing hormone (TRH) in a daily dose of 200 ng dissolved in 10 microliters of 0.9% sodium chloride.) A single dose of TRH administered to euhydrated animals was followed by a significant increase of the vasopressin content in the neurohypophysis and hypothalamus as well as of the hypothalamic oxytocin content. On the contrary, a single dose of TRH decreased the oxytocin content in the neurohypophysis. Under conditions of dehydration TRH distinctly restrained the decrease of vasopressin and oxytocin in the hypothalamus. In animals dehydrated for two or four days the decrease of oxytocin in the neurohypophysis, brought about by stimulation of osmoreceptors, was distinctly more marked under treatment with TRH. On the contrary, the depletion of neurohypophysial vasopressin was significantly less apparent under such conditions. 28 nmol/L TRH markedly increased vasopressin release but inhibited that of oxytocin from the neurointermediate lobes incubated in vitro both under basal conditions as well as during stimulation with excess (56 mmol) potassium.

Topics: Animals; Dehydration; Hypothalamus; In Vitro Techniques; Injections, Intraventricular; Male; Oxytocin; Pituitary Gland, Posterior; Potassium; Rats; Rats, Wistar; Thyrotropin-Releasing Hormone; Vasopressins

Topics: Animals; Biopterins; Body Water; Dehydration; Hypothalamus; Male; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Wistar; Reference Values; Vasopressins

The effect of CCK-8 (50 ng, i.c.v.) on the neurohypophysial vasopressin and oxytocin storage was estimated in haemorrhaged (1 ml per 100 g b.w.) male Wistar rats. In another experimental series rats dehydrated for three days were given CCK-8 in a daily i.c.v. dose of 50 ng. The neurohypophysial vasopressin and oxytocin content was bioassayed by pressor effect following Dekański or milk-ejection activity in vitro following van Dongen and Hays, respectively. The decrease of neurohypophysial vasopressin and oxytocin content, brought about by dehydration, was significantly less marked in animals treated with CCK-8. The depletion of neurohypophysial vasopressin and oxytocin content in haemorrhaged animals could be completely inhibited by earlier i.c.v. administration of CCK-8. It is suggested that hypothalamic cholecystokinin may serve as a modulator of neurohypophysial function.

Topics: Animals; Bloodletting; Dehydration; Disease Models, Animal; Hemorrhage; Injections, Intraventricular; Male; Models, Biological; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Wistar; Sincalide; Vasopressins

Experiments were performed to test a possible role of (6R)-5,6,7,8-tetrahydro-alpha-biopterin dihydrochloride (BH4) in the neurohypophysial vasopressin and oxytocin content in euhydrated and dehydrated rats. Chronic treatment with BH4, administered to not dehydrated animals, was followed by a significant decrease of neurohypophysial vasopressin, but not of neurohypophysial oxytocin. In dehydrated animals the neurohypophysial vasopressin content decreased progressively; this process was not affected significantly by BH4. In rats dehydrated and treated simultaneously with BH4 the decrease of neurohypophysial oxytocin content was distinctly less marked.

Topics: Animals; Biopterins; Dehydration; Male; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Wistar; Vasopressins

Intracerebroventricular hANP (50 nmol) inhibits release of vasopressin and oxytocin following dehydration as well as after haemorrhage. 10 nmol/L hANP markedly inhibits vasopressin and oxytocin release in vitro from the neurointermediate lobes both under basal condition as well as during stimulation with excess (56 mM) potassium. It is suggested that ANP may serve as a modulator of vasopressin and oxytocin release. The respective processes are localized, at least in part, at the neurohypophysial level.

Topics: Animals; Atrial Natriuretic Factor; Dehydration; Femoral Vein; Hemorrhage; Injections, Intraventricular; Male; Oxytocin; Pituitary Gland, Posterior; Pituitary Hormones, Posterior; Potassium; Rats; Rats, Wistar; Vasopressins

It has been shown that during physiological stimuli, such as dehydration, supraoptic nucleus (SON) neurons undergo profound morphological changes. However, little is known about how much each type of cell, oxytocin (OT) or vasopressin (VP), contributes to this plasticity during dehydration. Using postembedding immunogold cytochemistry for both OT and VP hormones at the electron microscopic level, we address this question. Rats were chronically dehydrated (given 2% saline to drink for 10 days) and their SON neurons were studied morphologically. The results were compared to control animals with free access to water. Both VP and OT somata showed an enlargement in size in dehydrated animals. Percentage of somasomatic/dendritic membrane contact increased significantly in both VP and OT neurons, with no significant changes in percentage of coverage of the cells by astrocytic membrane. Only the VP cells had a lesser amount of axosomatic membrane contact after dehydration, possibly due to an increase in cell size rather than a decrease in synaptic contact. Multiple synapses (MSs) (i.e., terminals that form more than one synapse with adjacent somata and or dendrites) occurred only between positively labeled cells and between negatively labeled cells, but not between positively and negatively labeled cells. The number of MSs per 100 microns OT somatic membrane or per 100 OT cells was significantly higher in dehydrated rats but was unchanged with regard to VP neurons. These findings indicate that both VP and OT neurons undergo morphological changes during chronic dehydration and, thus, that plasticity is not limited to OT cells as some earlier reports have suggested.

Topics: Animals; Dehydration; Female; Immunohistochemistry; Male; Microscopy, Electron; Neuronal Plasticity; Oxytocin; Rats; Supraoptic Nucleus; Vasopressins

Magnocellular neurons synthesize vasopressin (VP) or oxytocin (OT) and release these hormones preferentially from the neural lobe during physiological stimulation. In the rat, VP is secreted preferentially during dehydration and hemorrhage, whereas OT is released without VP by suckling, parturition, stress, and nausea. Vasopressinergic neurons also synthesize and release dynorphin-related peptides--alpha- and beta-neoendorphin, dynorphin A (1-8) or (1-17), dynorphin B--which are agonists selective for kappa opiate receptors in the neural lobe. We proposed that one mechanism for preferential secretion of neurohypophysial hormones is that a dynorphin-related peptide(s) coreleased with VP inhibits selectively OT secretion from magnocellular neurons. We tested this hypothesis in conscious adult male Sprague-Dawley rats which were stimulated by either hypertonic saline administered intraperitoneally (2.5%, 20 ml/kg) or subcutaneously (1 M, 15 ml/kg) or by 24 h of water deprivation. Two approaches were used: (1) dynorphin-related peptides (0.02-20.4 mM) were injected intracerebroventricularly 1 min before decapitating the animal, and (2) the action of endogenous opioid peptides was blocked by injecting subcutaneously or intracerebroventricularly either naloxone or a selective kappa receptor antagonist, Mr 2266 or nor-binaltorphimine. VP and OT were measured by radioimmunoassay. After 24 h of water deprivation, the elevation in plasma [OT] but not [VP] was attenuated (p less than 0.05) by alpha-neoendorphin. Dynorphin A (1-8) also inhibited the release of OT and not VP after intraperitoneal administration of hypertonic saline. Blocking the action of endogenous opioid peptides at kappa receptors with Mr 2266 given peripherally (s.c.) elevated plasma [OT] but not [VP] after stimulation with hypertonic saline administered intraperitoneally or subcutaneously.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Benzomorphans; Dehydration; Dynorphins; Endorphins; Hypertonic Solutions; Injections, Intraventricular; Male; Naloxone; Naltrexone; Narcotic Antagonists; Neurons; Osmolar Concentration; Oxytocin; Peptide Fragments; Pituitary Gland, Posterior; Protein Precursors; Radioimmunoassay; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Vasopressins

In rats euhydrated or dehydrated for two or four days the neurohypophysial vasopressin and oxytocin content was estimated. Rats were given intracerebroventricularly (i.c.v.) isoprenaline in a daily dose of 10 micrograms dissolved in 10 microliters of 0.9% sodium chloride. The neurohypophysial vasopressor and oxytocic activity diminished progressively during deprivation of water. A single dose of isoprenaline diminished the neurohypophysial content of vasopressin in euhydrated rats. In animals dehydrated for two or four days the depletion of neurohypophysial vasopressin storage (as brought about by osmoreceptor stimulation) was distinctly less marked under treatment with isoprenaline. The neurohypophysial oxytocin storage was diminished by a single dose of isoprenaline; on the contrary, during dehydration isoprenaline distinctly intensified the oxytocin depletion in the neurohypophysis.

Topics: Adrenergic Fibers; Animals; Dehydration; Isoproterenol; Male; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Inbred Strains; Synaptic Transmission; Vasopressins

1. The effect of 96 hrs of water deprivation on plasma electrolytes, osmolarity, arginine vasotocin (AVT), mesotocin (MT), and on AVT and MT content in the neurohypophysis, anterior hypothalamic area (AHA) and proventriculus, was studied at 24 hrs intervals, in adult White Leghorn cockerels. 2. Plasma AVT increased three fold during the first 24 hrs but there was no further change during the next 48 hrs. In the last 24 hrs, plasma AVT decreased in about 25%. Plasma MT did not change during the entire period of dehydration. 3. Plasma sodium and osmolarity gradually increased during that time. 4. Neurohypophysial AVT content was depleted by 95% during the period of dehydration while MT content did not change. 5. In the AHA there was no change in AVT levels during dehydration while the levels of MT increased while in the proventriculus there was no change in either AVT or MT levels. 6. For the data collected during the entire experimental period, no correlation was found between plasma osmolarity and plasma AVT, but there was a highly significant negative correlation between plasma osmolarity and neurohypophysial AVT content. 7. It may be suggested that the depletion in AVT content in the neurohypophysis during progressive water deprivation resulted in an insufficient level of AVT in circulation to enable the cockerels to counter the dehydration. This may explain the death of those cockerels which were dehydrated for a further 24 hr period.

Topics: Animals; Chickens; Dehydration; Hypothalamus, Anterior; Male; Oxytocin; Pituitary Gland, Posterior; Poultry Diseases; Proventriculus; Vasotocin; Water Deprivation

The influence of the dehydration treatment on the hypophysial neural lobe of the water snake Natrix maura, has been investigated. Whereas control animals stayed in fresh water, experimental snakes were immersed in a hypertonic solution of sodium chloride (35%) for 48 h. All specimens were fixed by vascular perfusion with Bouin fluid and the pituitaries embedded in paraffin. The sections were stained through histochemical procedures and immunocytochemistry by means of antisera against bovine neurophysins, vasotocin and mesotocin. The intensity of the immunoreaction was measured by microdensitometry. The osmotic stress significantly decreases the amount of stainable neurosecretory material in the neural lobe as well as the immunoreactivity to antineurophysin and antivasotocin sera. Contrariwise, there is no clear decrease in the immunoreactivity to antimesotocin serum. These results suggest that the osmotic stress in Natrix maura elicited an increase in the release of vasotocin.

Topics: Animals; Dehydration; Female; Hypertonic Solutions; Immunohistochemistry; Male; Neurophysins; Oxytocin; Pituitary Gland, Posterior; Snakes; Vasotocin

Rats dehydrated up to four days were given intracerebroventricularly insulin in a daily dose of 100 ng. Insulin decreased significantly the hypothalamic and neurohypophysial oxytocin content in euhydrated rats. In dehydrated animals the oxytocin activity in the hypothalamo-neurohypophysial system, markedly depleted after deprivation of water, could be further reduced by intracerebroventricular treatment with insulin. These results seem to suggest a possible regulatory role of brain insulin in the mechanisms of oxytocin release.

Topics: Animals; Dehydration; Hypothalamus; Injections, Intraventricular; Insulin; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Inbred Strains

To investigate the influence of various peptides on control of dehydration-induced drinking, water intake elicited by overnight water deprivation was analyzed in groups of male rats after intracerebroventricular (third ventricle, icv) injection of 2 microliters of normal rabbit serum or an equal volume of antiserum directed against angiotensin II (Ab-AII), atrial natriuretic peptide, vasopressin, or oxytocin. There was no difference in water intake after normal rabbit serum and antiserum injections when water was offered immediately after icv injections. Water intake was greatly reduced by Ab-AII when water was offered 1 hr and 3 hr after icv injection. The other antisera were partially effective only when water was offered 3 hr after icv injection. The dipsogenic effect of icv injection of AII in normally hydrated rats was reduced only by icv injection of Ab-AII 3 hr before and not by the other antisera. Ab-AII injected icv had no effect on the drinking that occurred just before and after the onset of darkness and that was associated with eating (prandial drinking). The results indicate that AII is primarily responsible for dehydration-induced drinking, and the other peptides may play a permissive role since their antisera were partially effective, with longer latencies after antiserum injection, which is perhaps the result of gradual diffusion to effective sites within the hypothalamus. In contrast, endogenous AII appears to play little, if any, role in prandial drinking.

Topics: Angiotensin II; Animals; Antigen-Antibody Reactions; Atrial Natriuretic Factor; Dehydration; Drinking Behavior; Hypothalamus; Male; Microinjections; Oxytocin; Rats; Vasopressins; Water-Electrolyte Balance

Topics: Animals; Dehydration; Female; Fluid Therapy; Male; Osmolar Concentration; Oxytocin; Swine; Water Deprivation

Rats euhydrated and dehydrated for two days were given intracerebroventricularly (i.c.v.) propranolol hydrochloride in a daily dose of 10 micrograms. In euhydrated rats the single dose of propranolol diminished significantly the vasopressin and oxytocin content in the neurohypophysis. On the contrary, in animals dehydrated for two days the depletion of the vasopressin and oxytocin neurohypophysial storage was distinctly less marked during i.c.v. treatment with propranolol.

Topics: Animals; Dehydration; Injections, Intraventricular; Male; Oxytocin; Pituitary Gland, Posterior; Propranolol; Rats; Rats, Inbred Strains; Vasopressins

Group housed, castrated rams (N = 10) were studied over a 2 day period. Water was available ad libitum during day 1 (control) but was withheld throughout day 2 (experimental). On both days, blood was collected by jugular venepuncture at 10.30 h, and then again 2, 4, 6 and 24 h later. Plasma samples were analysed by radioimmunoassay for arginine vasopressin (AVP), oxytocin and cortisol content and measurements were also made of the haematocrit and plasma osmolality and electrolyte (Na+, Cl-) concentrations. After 24 h water deprivation there was a significant increase in plasma AVP levels but no changes in oxytocin or cortisol concentrations. Dehydration also significantly depressed the haematocrit and increased plasma osmolality and electrolyte concentrations.

Topics: Animals; Arginine Vasopressin; Dehydration; Electrolytes; Hydrocortisone; Male; Orchiectomy; Osmolar Concentration; Oxytocin; Sheep

One physiological role for endogenous opioid peptides is to attenuate the release of oxytocin (OT) from the hypothalamo-neurohypophysial system during dehydration and hemorrhage when vasopressin maintains fluid balance and blood pressure. During lactation, OT, which stimulates milk ejection, is released without vasopressin. The influence of endogenous opioid peptides on OT release during suckling has been studied primarily in animals anesthetized with urethane. In addition to anesthesia, urethane dehydrates the animal by elevating plasma osmolality and reducing cardiovascular volume. Thus, we examined in lactating rats the response of the magnocellular neuroendocrine system to dehydration and the role of endogenous opioid peptides in regulating OT release during suckling under conditions of altered fluid balance in conscious and urethane-anesthetized rats. Release of OT in response to an increase in plasma osmolality or a decrease in blood volume was attenuated during lactation in both conscious and anesthetized rats. Blockade of opiate receptors with naloxone (5 mg/kg) did not alter suckling-induced release of immunoreactive OT in conscious, normally hydrated rats, but did augment hormone release after urethane (1.1 g/kg, ip) or after osmotic stimulation with hypertonic sodium chloride (2.5%; 20 ml/kg, ip). During dehydration, the combination of decreased responsiveness of oxytocinergic neurons to osmotic stimulation and inhibition of OT release by opioid peptides may be important in the lactating rat for conserving pituitary stores of OT needed for milk ejection.

Topics: Anesthesia; Animals; Blood; Dehydration; Female; Lactation; Naloxone; Osmolar Concentration; Oxytocin; Pregnancy; Rats; Rats, Inbred Strains; Saline Solution, Hypertonic; Urethane; Vasopressins; Water-Electrolyte Balance

Rats euhydrated or dehydrated up to eight days were given intraperitoneally indomethacin (IM) twice daily in a dose of 0.2 mg/100 g of initial body weight. A single dose of IM injected to euhydrated animals did not affect the neurohypophysial oxytocic activity but decreased that potency in the hypothalamus. When IM was administered repeatedly during four or eight days, the hypothalamic oxytocic activity did not differ from the respective controls; under such conditions the oxytocic activity in the neurohypophysis increased progressively. Under conditions of dehydration the known depletion of hypothalamic and neurohypophysial oxytocin storage was not affected by indomethacin. It is therefore suggested that impulses of osmoreceptor origin are of distinct importance in determining the function of oxytocinergic neurones under conditions of inhibited prostaglandin synthesis.

Topics: Animals; Cyclooxygenase Inhibitors; Dehydration; Hypothalamus; Indomethacin; Male; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Inbred Strains; Water-Electrolyte Balance

We have shown, using the opiate receptor antagonist naltrexone, that endogenous opioid peptides inhibit the release of oxytocin (OT), but not of vasopressin (AVP), from the hypothalamo-neurohypophysial system during dehydration. The stimulus for the release of neurohypophysial hormones during dehydration is both hypovolemia and increased plasma osmolality. The aims of this study were to determine whether opioid peptides inhibit OT secretion during an osmotic stimulus alone and, if so, to study the ontogeny of opiate inhibition of OT and AVP release during osmotic stimulation. Effects of endogenous opioid peptides were evaluated by injecting naloxone into immature and adult rats. Hypertonic saline was used as the osmotic stimulus. Adult male rats were injected sc with normal saline (0.85%; 1 ml/kg BW) or naloxone (5 mg/kg BW), followed 5 min later by normal or hypertonic (1 M) saline (15 ml/kg BW). After 170 min, a second injection of saline or naloxone was given; animals were decapitated 10 min later. Immature male and female rats at 2, 8, 21, and 30 days of age received 0.85% saline (1 ml/kg BW) or naloxone (5 mg/kg BW) ip 5 min before normal or hypertonic (2.5%) saline (20 ml/kg BW, ip). Pups were decapitated 15 min later. AVP and OT were measured by RIA in extracts of plasma, pituitaries, and hypothalami. In control rats, the contents of AVP and OT increased with age in both the pituitary and hypothalamus, attaining adult levels by day 21 for AVP and by day 30 for OT. In contrast, plasma concentrations of both AVP and OT were highest in 8-day-old rats and decreased thereafter to adult levels by 30 days of age. Hypertonic saline raised plasma osmolality 9-16 mosmol/kg H2O, increased AVP and OT concentrations in plasma of adults and immature rats at 2, 8, 21, and 30 days of age, and reduced pituitary stores of OT in adult animals. Blocking the action of opioid peptides with naloxone during osmotic stimulation augmented the rise in plasma OT in rats of all ages but further elevated plasma AVP only in immature rats. In adult animals, blocking opiate receptors with naloxone enhanced the depletion of OT stores from the pituitary, but did not affect the AVP content. We conclude that in the adult rat, endogenous opioid peptides inhibit OT release during osmotic stimulation, thereby allowing preferential release of AVP.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Animals; Dehydration; Endorphins; Hypertonic Solutions; Hypothalamus; Male; Naltrexone; Osmosis; Oxytocin; Pituitary Gland, Posterior; Rats; Rats, Inbred Strains; Sodium Chloride; Vasopressins

After dehydration, oral rehydration causes a fall in plasma arginine vasopressin (AVP) that precedes changes in plasma osmolality. To investigate further the stimulus for this effect, its specificity, and association with thirst, six volunteers were deprived of water for 24 h and given a salt load on two separate occasions. On each study day they then drank rapidly 10 ml/kg of either tap water or hypertonic saline (360 mosmol/kg). There was a significant fall in plasma AVP from 2.0 +/- 0.3 to 1.2 +/- 0.4 pmol/l (P less than 0.05) 5 min after drinking water and from 1.8 +/- 0.3 to 0.9 +/- 0.2 pmol/l (P less than 0.05) after hypertonic saline. Plasma osmolality fell 30-60 min after water and was unchanged after saline. Plasma renin activity, oxytocin, and total protein all remained unchanged. All subjects reported diminished thirst after hypertonic saline. Gargling with water reduced thirst but did not affect plasma AVP. There appears to be a drinking-mediated neuroendocrine reflex that decreases plasma AVP irrespective of the osmolality of the liquid consumed. The sensation of thirst did not correlate with plasma osmolality and was not always related to plasma AVP concentration.

Topics: Administration, Oral; Adult; Arginine Vasopressin; Dehydration; Drinking; Female; Humans; Male; Oxytocin; Saline Solution, Hypertonic; Sodium Chloride; Thirst

Immunoreactive-vasopressin, -oxytocin, -dynorphin, -dynorphin-(1-8), -alpha-neo-endorphin and -[Met]enkephalin were, in each case, present in greater concentrations in dorsal as compared to ventral, and lumbo-sacral as compared to cervico-thoracic, spinal cord. These differences were significantly more pronounced for vasopressin and oxytocin than for the other peptides. Lesions of the hypothalamic paraventricular nucleus depleted levels of immunoreactive-vasopressin and -oxytocin throughout the cord whereas levels of the opioid peptides therein were unaffected. In contrast, destruction of either the supraoptic or suprachiasmatic nucleus failed to change the content of immunoreactive-vasopressin, -oxytocin or any of the opioid peptides in the cord. Dehydration for 3 days depressed levels of immunoreactive-vasopressin, -oxytocin and -dynorphin in the neurointermediate lobe of the pituitary. In distinction, the levels of these were not modified in the spinal cord. Further, treatment with the synthetic corticosteroid, dexamethasone, elevated levels of immunoreactive-vasopressin, -oxytocin and -dynorphin in the neurointermediate pituitary whereas these were unaffected in the spinal cord. It is concluded that vasopressin and oxytocin in the spinal cord are predominantly derived from the paraventricular nucleus, localized in dorsal lumbo-sacral regions of the cord and insensitive to endocrinological manipulations. These pools may, thus, be modulated differently from their counterparts in the neurohypophysis and have a differing role, possibly in the control of the primary processing, autonomic or motor junctions. Further, there is no evidence from these or our prior studies for a close interrelationship of spinal cord vasopressin with dynorphin-related peptides (or oxytocin with [Met]enkephalin), likewise in contrast to the neurohypophysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Brain Mapping; Dehydration; Dexamethasone; Dynorphins; Endorphins; Enkephalin, Methionine; Hypothalamus; Oxytocin; Rats; Spinal Cord; Vasopressins

The total Na+/K+ ATP-ase activity of the thick ascending limb of the loop of Henle may be stimulated by arginine-vasopressin (AVP). Lysine-vasopressin (LVP), oxytocin (OT), and arginine-vasotocin (AVT) produce less than 5% of the enzyme activity induced by the same concentration of AVP. Physiological concentrations of a mixture of other hormones with known activity on the kidney (T3, T4, aldosterone, angiotensin II, and OT) did not significantly increase total Na+/K+ ATP-ase activity. Specific AVP antiserum consistently removed greater than 90% of the stimulatory effect of plasma. The concentration of AVP in plasmas from dehydrated subjects was greater than 10 times that of the same subjects hydrated. Intra-assay coefficient of variation was 35% and 52% from 200 microliters and 20 microliters of plasma respectively. The interassay coefficient of variation was 53% and 55% from plasma pools with high and low AVP content.

Topics: Animals; Arginine Vasopressin; Biological Assay; Dehydration; Histocytochemistry; Humans; Immune Sera; Kidney Tubules; Loop of Henle; Lypressin; Oxytocin; Rats; Sodium-Potassium-Exchanging ATPase; Vasotocin

Despite the absence of vasopressin, Brattleboro homozygous (DI) rats concentrate their urine to hypertonic levels when deprived of drinking water for 24 h. Glomerular filtration rate (GFR) falls concurrently and might contribute to the increased concentrating ability. The present studies concerned the time course of the changes in concentrating ability and GFR during the early hours of dehydration. Experiments were performed in 10 chronically catheterized conscious DI rats in the normally hydrated control state and during 3 h of fluid deprivation. Urine osmolality (Uosmol) increased from 97 +/- 6 (SE) to 325 +/- 11 mosmol/kg H2O at 3 h. Averaged over the 3 h, neither GFR nor effective renal blood flow changed significantly (103 +/- 2 and 106 +/- 4% of control, respectively). Fractional excretion of sodium (FENa) rose markedly from 0.3 +/- 0.1 to 1.3 +/- 0.1% at its peak. Clearly, a fall in GFR cannot explain the rise in Uosmol during the first 3 h. Plasma oxytocin (OT) increased from 5.6 +/- 0.8 to 36.4 +/- 4.5 pg/ml after 3 h of dehydration. In additional experiments, d(CH2)5-D-Phe-VAVP, an antidiuretic antagonist (anti-ADH), was administered to eight DI rats after 3-h dehydration. Control, 3-h dehydration, and post-anti-ADH values were, respectively: for Uosmol, 102 +/- 7, 347 +/- 14, 145 +/- 11 mosmol/kg H2O; for GFR, 1,003 +/- 43, 1,042 +/- 59, 866 +/- 54 microliter X min-1 X 100 g body wt-1; for FENa, 0.4 +/- 0.1, 1.4 +/- 0.1, 0.5 +/- 0.1%. The decreases following anti-ADH were all statistically significant. We conclude that OT is released during the early hours of dehydration in the DI rat and has at least three renal effects. It causes a natriuresis, it maintains renal hemodynamics and GFR during the volume contraction, and it elicits a weak antidiuretic response.

Topics: Animals; Dehydration; Diuresis; Glomerular Filtration Rate; Hemodynamics; Homozygote; Kidney; Oxytocin; Rats; Rats, Brattleboro; Rats, Mutant Strains; Regional Blood Flow; Vasopressins

A sensitive and specific radioimmunoassay method for simultaneous measurement of plasma arginine vasopressin (AVP) and oxytocin (OT) has been developed utilizing an extraction technique on DEAE Sephadex A25. This procedure resulted in mean recoveries of 70.7% (AVP) and 65.4% (OT) in the peptide range of 5 to 100 pg/4 ml. The sensitivity of the assay is 0.5 pg/tube for AVP and 2 pg/tube for OT. The lower limit of detection for plasma extracts was 1.2 pg AVP/ml and 5 pg OT/ml plasma. Employing this method in normal human non smokers and ad libitum fluid the basal levels (mean +/- SE) of plasma AVP are 3.5 +/- 0.2 pg/ml in males and 4.6 +/- 0.4 pg/ml in females and the basal concentrations of plasma OT are 5.1 +/- 0.3 pg/ml in males and 5.4 +/- 0.3 pg/ml in females. Dehydration and water loading produced significant changes in plasma AVP and OT concentrations and a significant correlation exists between plasma AVP and plasma (r = 0.96, p less than 0.001) and urinary (r = 0.84, p less than 0.01) osmolality, but not between plasma OT concentrations and plasma (r = 0.11, NS) and urinary (r = 0.27, NS) osmolality. These results suggest that a wide range of physiological and pathophysiological changes in plasma AVP and OT can be simultaneously measured by the extraction procedure and the radioimmunoassay described.

Topics: Adult; Arginine Vasopressin; Chromatography, Ion Exchange; Dehydration; Female; Humans; Male; Osmolar Concentration; Oxytocin; Radioimmunoassay; Urine

The presence of opioid peptides and opiate receptors in the hypothalamo-neurohypophysial system, as well as the inhibitory effects of enkephalins and beta-endorphin on release of oxytocin and vasopressin have been well documented. The physiological importance of opioid peptides in this classical neurosecretory system, however, has remained illusive. In the present study we tested the effects of naltrexone on the plasma concentrations of oxytocin and vasopressin during dehydration, hemorrhage and suckling in the conscious rat. We obtained evidence supporting the hypothesis that opioid peptides inhibit oxytocin release and thereby promote the preferential secretion of vasopressin when it is of functional importance to maintain homeostasis during dehydration and hemorrhage. Our data support the concept that the coexistence of a neuromodulator and a neurohormone in the same neuron, as demonstrated for vasopressin with dynorphin or leucine-enkephalin, serves to regulate the differential release of two biologically different, yet evolutionarily-related, neurohormones, e.g. oxytocin and vasopressin, from the same neuroendocrine system.

Topics: Animals; Arginine Vasopressin; Dehydration; Endorphins; Female; Hemorrhage; Hypothalamo-Hypophyseal System; Lactation; Male; Naltrexone; Oxytocin; Pregnancy; Rats; Rats, Inbred Strains

Serum concentrations of arginine vasotocin (AVT), mesotocin and prolactin were determined by radioimmunoassay in Rhode Island Red chickens during and after dehydration, haemorrhage and oviposition. During dehydration increased circulating levels of AVT, mesotocin and prolactin were found. As water deprivation proceeded, marked differences were observed. After an initial rise in serum AVT, mesotocin and prolactin levels during mild and moderate dehydration, concentrations of both AVT and prolactin tended to normalize during continued water deprivation, while those of mesotocin remained high throughout the whole dehydration experiment with the highest at the end of the water-deprivation period. Removal of 5 ml blood at intervals of 10 min during six consecutive time-periods did not affect serum osmolality and circulating levels of AVT and prolactin, but slightly increased mesotocin. These results suggest an osmoregulatory role for AVT and prolactin, whereas mesotocin may be involved in volume control. Finally, 1 min after oviposition, control values of 19.5 +/- 3.4 pmol AVT/1 (n = 9) were raised more than sevenfold to 142.9 +/- 12.5 pmol/l (n = 11). Thereafter, a decline occurred with a half-life for AVT of 13 min with raised serum levels up to 31 min after oviposition. In contrast, the serum concentrations of mesotocin and prolactin remained unaffected by oviposition.

Topics: Animals; Blood Volume; Chickens; Dehydration; Female; Hematocrit; Male; Osmolar Concentration; Oviposition; Oxytocin; Prolactin; Vasotocin; Water Deprivation

Topics: Adrenocorticotropic Hormone; Dehydration; Female; Humans; Hypothalamo-Hypophyseal System; Lactation; Learning; Memory; Neurophysins; Ovary; Oxytocin; Pituitary Gland, Anterior; Pregnancy; Thirst; Vasopressins

Magnocellular neurons in the supraoptic and paraventricular nuclei synthesize and release vasopressin and oxytocin in response to dehydration. Pinealectomy has been observed to decrease the distribution in the supraoptic nuclei of thiamine diphosphate-phosphohydrolase, an enzyme specific for the Golgi apparatus that correlates positively with neurosecretory activity. Based upon these studies we postulated that pinealectomy would alter the concentration of neurohypohysial hormones in plasma elevated by 48 hr of water deprivation. In addition, we investigated the possibility that pinealectomy would affect vasopressin concentration in another circumventricular organ, the subfornical organ (SFO) and in a adjacent fiber tract of the limbic system, the hippocampal commissure-fornix (HC-F). Adult, male, Sprague-Dawley rats exposed to a 12 hr light/dark cycle were either unoperated (controls; C), sham-operated (Sham; S) or pinealectomized (PX) three weeks prior to testing. Food and water consumption and urinary excretion of Na and K were measured for 7 days. On the fifth day, half of the animals in each treatment group (C, S, PX) were deprived of water for 48 hr. Animals were decapitated on day 8. Vasopressin and oxytocin in plasma were extracted using bentonite and acetone-ether, respectively, then quantified by radioimmunoassay. The SFO and HC-F were microdissected from each brain. Like tissues from 4 rats were pooled, homogenized in 0.1 N HCl, and centrifuged. The supernatant was neutralized and vasopressin was quantified by radioimmunoassay. Dehydration resulted in antidiuresis, increased urine concentrations of Na and K, a decreased ratio of Na:K in urine, and reduced food consumption of similar magnitudes in all groups (C, S, PX; p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Body Weight; Dehydration; Eating; Hematocrit; Hippocampus; Light; Male; Neurosecretory Systems; Oxytocin; Pineal Gland; Rats; Rats, Inbred Strains; Subfornical Organ; Time Factors; Vasopressins

Vasopressin and oxytocin were determined simultaneously by a radioimmunoassay in cerebrospinal fluid and plasma of conscious, unrestrained rabbits. An elevation of neuropeptide levels in plasma, but not in cerebrospinal fluid, in response to dehydration or haemorrhage suggests an independent regulation of vasopressin and oxytocin concentration in both body fluids.

Topics: Animals; Arginine Vasopressin; Dehydration; Hemorrhage; Kinetics; Male; Oxytocin; Rabbits

Topics: Animals; Dehydration; Diabetes Insipidus; Diuresis; Female; Kidney Concentrating Ability; Male; Natriuresis; Oxytocin; Rats; Rats, Brattleboro; Rats, Mutant Strains

Arginine vasopressin (AVP) and oxytocin (OXT) were measured simultaneously in the same sample by specific and sensitive radioimmunoassay (RIAs). The antibodies used did not cross-react to a variety of analogues and related peptides. The extraction procedure using Vycor glass powder resulted in mean recoveries of 84.4% (AVP) and 64.6% (OXT). In both assays, the sensitivity was 1 to 2 pg/ml plasma. A preincubation procedure that depresses plasma levels of both AVP and OXT selectively, provided specific blank values for a given plasma sample. To confirm the validity of the RIAs, dehydration experiments were performed. In rats, the basal levels of plasma AVP and OXT (means: 2.63 pg/ml and 6.80 pg/ml, respectively) are increased significantly after 24 h, 48 h and 72 h of water deprivation. Relationships are presented between both neurohormones in the plasma and neurohypophyses of control and dehydrated animals. As shown in cows, a significant correlation exists between plasma AVP and plasma osmolality but not between plasma OXT and osmolality or plasma AVP and OXT. The conclusion is drawn that basal levels as well as physiological changes in plasma and neurohypophyseal AVP and OXT can be measured by the RIAs described.

Topics: Animals; Arginine Vasopressin; Cattle; Dehydration; Female; Male; Oxytocin; Pituitary Gland, Posterior; Radioimmunoassay; Rats; Rats, Inbred Strains

Rats dehydrated up to 12 days were given intraperitoneally propranolol hydrochloride in daily dose of 1.0 mg/100 g of initial body weight. In not dehydrated animals the only dose of propranolol increased significantly the vasopressin and oxytocin release from the neurohypophysis. In dehydrated animals propranolol restrained somewhat the decrease of vasopressin in the neurohypophysis, but intensified the vasopressin depletion in the hypothalamus. The oxytocic potency of both the neurohypophysis and hypothalamus decreased progressively in animals deprived of water. Propranolol potentiated this effect of osmoreceptor stimulation.

Topics: Animals; Dehydration; Hypothalamus; Male; Oxytocin; Pituitary Gland, Posterior; Propranolol; Rats; Vasopressins; Water Deprivation

Topics: Animals; Arginine Vasopressin; Body Weight; Carboxy-Lyases; Dehydration; Hematocrit; Kidney; Male; Mice; Mice, Inbred Strains; Ornithine Decarboxylase; Osmolar Concentration; Oxytocin; Time Factors; Water Deprivation

The activated hypothalamic magnocellular neurosecretory system of the rat was studied in tissue sections, double stained with the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique. The results indicate that in animals with an activated hypothalamic magnocellular neuroendocrine system, as well as in normal animals, vasopressin and oxytocin are exclusively synthesized in separate vasopressinergic and oxytocinergic neurons.

Topics: Animals; Dehydration; Diethylstilbestrol; Histocytochemistry; Hypothalamus; Immunoenzyme Techniques; Oxytocin; Rats; Stress, Physiological; Vasopressins

Antisera, with cross reactive antibodies removed by affinity chromatography, were used in the immunoperoxidase-bridge technique to study the distribution of oxytocin and vasopressin together with neurophysin in the hypothalamo-neurohypophysial system of the rat. The hormones were demonstrated in different areas of the supraoptic nucleus (SON) and paraventricular nucleus (PVN), in neurosecretory fibres of the hypothalamo-neurohypophysial tract, median eminence, and in nerve terminals of the neurohypophysis. Intact normal and rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain), and rats dehydrated by the administration of oral hypertonic saline were studied. In dehydrated rats the hormone concentration in the neurons, and the number of neurons containing hormone varied according to the time of dehydration stress. The observations support the hypotheses that: 1) oxytocin and oxytocin-neurophysin, and vasopressin and vasopressin-neurophysin are synthesised in different neurons and are transported along different axons; 2) the SON and PVN are functionally indistinguishable in that neurons containing oxytocin or vasopressin are present in both nuclei; and 3) the two types of neurons respond to osmotic stimulation in a way that is qualitatively the same but quantitatively different.

Topics: Animals; Dehydration; Diabetes Insipidus; Female; Fluorescent Antibody Technique; Hypothalamo-Hypophyseal System; Immunoenzyme Techniques; Median Eminence; Neurons; Neurophysins; Oxytocin; Paraventricular Hypothalamic Nucleus; Pituitary Gland, Posterior; Rats; Rats, Inbred Strains; Supraoptic Nucleus; Vasopressins

Vasopressin and oxytocin were measured by radioimmunoassay in rat posterior pituitary and microdissected hypothalamic areas after 3 and 10 days of oral 2 percent sodium chloride in place of drinking water. There was a significant decrease in concentration of both hormones in posterior pituitary and in specific areas of the hypothalamus. Supraoptic, paraventricular, and arcuate hypothalamic nuclei and the retrochiasmatic area had decreased concentration of one or both hormones following hypertonic saline, while hormone concentration in the suprachiasmatic nucleus and median eminence was unaffected.

Topics: Administration, Oral; Animals; Dehydration; Hypothalamus; Male; Oxytocin; Pituitary Gland, Posterior; Rats; Saline Solution, Hypertonic; Sodium Chloride; Time Factors; Vasopressins

In dehydrated rats both neurohypophysial hormones diminished in hypothalamus as well as in the neurohypophysis. Oxytocin disappearef from the hypothalamus and neurohypophysis at a more rapid rate than vasopressin did. The minimal content of vasopressin and oxytocin in the hypothalamus was observed during 3rd--4th day, but even in extreme dehydration it was found to be relatively high: 65 per cent of vasopressin and 27 per cent of oxytocin as compared with intact animals. At that time the neurohypophysial vasopressin and oxytocin content were almost fully exhausted. In dehydrated and additionally reserpinized animals (10 mg/kg intraperitoneally, then each 48 hr 5 mg/kg of initial body weight) the vasopressin and and oxytocin hypothalamus and neurohypophysis changed in a similar manner. In some experimental groups the decrease of neurohormones in both sites was more marked under reserpine treatment. The drug seems therefore rather to potentiate the effects of physiological stimulation of osmodetectors. So the existence of monoaminergic stimulatory synapses, directly involved in the neural pathway between the osmodetector and the neurosecretory cell, appears to be hardly probable.

Topics: Animals; Dehydration; Hypothalamo-Hypophyseal System; Male; Oxytocin; Rats; Reserpine; Vasopressins

The ultrastructural features of paraventricular (PVN) and supraoptic (SON) neurons and of their axons were studied in lactating and dehydrated rats. Under both conditions of stimulation, the PVN and SON neurons and their axons enlarge. The protein synthesizing apparatus of the neurons becomes activated, but the number of neurosecretory granules (NSG) is decreased. No differences are seen between the PVN and SON neurons during lactation or dehydration. The similarity and simultaneity of the response of the PVN and SON neurons to these two different stimuli is discussed in the light of the theory of nuclear and neuronal specialization for the production of only one hormone. After prolonged lactation of over 2 1/2 weeks' duration, neurons with extreme vacuolation of the rough endoplasmic reticulum (RER) appear in the PVN and SON; the vacuolated neurons appear earlier and predominantly in the PVN involving a maximum of 10-15% of all PVN neurons. Vacuolated neurons were never seen in either nucleus during dehydration of up to 6 days' duration. The vacuolation is suggested to represent an exhaustion phenomenon due to an intense, long-lasting stimulus for oxytocin synthesis. The predominant location of the vacuolated neurons in the PVN supports the theory that oxytocin is produced predominantly in the PVN. The decrease in the number of NSGs during these states of enhanced hormone secretion is considered to corroborate the proposed existence of an extragranular fast axoplasmic transport mechanism in PVN and SON neurons. The possible existence of a reuptake mechanism into NSGs, similar to that in the vesicles of monoaminergic nerve endings is discussed.

Topics: Animals; Axonal Transport; Axons; Cytoplasmic Granules; Dehydration; Endoplasmic Reticulum; Female; Golgi Apparatus; Hypothalamo-Hypophyseal System; Hypothalamus; Lactation; Male; Neurons; Neurophysins; Oxytocin; Paraventricular Hypothalamic Nucleus; Pregnancy; Rats; Supraoptic Nucleus; Vacuoles; Vasopressins

Topics: Animals; Antibody Specificity; Arginine; Chickens; Chromatography, Paper; Dehydration; Immune Sera; Iodine Radioisotopes; Oxytocin; Pituitary Gland; Rabbits; Radioimmunoassay; Rana catesbeiana; Rats; Time Factors; Vasopressins; Vasotocin

Topics: Adipose Tissue; Animals; Dehydration; Fatty Acids, Nonesterified; Female; In Vitro Techniques; Lipid Mobilization; Male; Oxytocin; Pituitary Hormones, Posterior; Rats; Vasopressins

Topics: Adipose Tissue; Animals; Catecholamines; Cycloheximide; Dehydration; Epididymis; Fasting; Fatty Acids, Nonesterified; Female; Male; Oxytocin; Phenoxybenzamine; Pituitary Hormones, Posterior; Propranolol; Rats; Uterus; Vasopressins

Topics: Animals; Cysteine; Dehydration; Electrophoresis, Disc; Hydrogen-Ion Concentration; Oxytocin; Pituitary Hormones, Posterior; Rats; Serum Albumin; Sulfur Isotopes; Vasopressins

1. Rat neurohypophysial extracts have been examined by polyacrylamide-gel electrophoresis. 2. Three of the proteins were tentatively identified as neurophysins by their acidic nature and their disappearance after dehydration of the animals. 3. These proteins were radioactive 24h after intracisternal injection of [(35)S]cysteine. 4. Two of the proteins were present in much greater quantities than the third, and these two were present in the gland in the same ratio as the hormones vasopressin and oxytocin. 5. One of these proteins was absent from glands of rats homozygous for diabetes insipidus but present in heterozygous animals. 6. It is suggested that these two proteins are the vasopressin-neurophysin and oxytocin-neurophysin of the rat.

Topics: Animals; Cysteine; Dehydration; Diabetes Insipidus; Electrophoresis, Disc; Heterozygote; Homozygote; Oxytocin; Pituitary Gland, Posterior; Protein Binding; Protein Biosynthesis; Proteins; Rats; Sulfur Isotopes; Swine; Vasopressins

Topics: Adipose Tissue; Animals; Dehydration; Epinephrine; Fatty Acids, Nonesterified; Lysine; Oxytocin; Phenoxybenzamine; Propranolol; Rats; Vasopressins

Topics: Age Factors; Animals; Animals, Newborn; Cattle; Dehydration; Female; Fetus; Hypertonic Solutions; Lactation; Oxytocin; Pregnancy; Protein Binding; Proteins; Radioimmunoassay; Sodium Chloride; Statistics as Topic; Vasopressins

Topics: Amphibians; Animals; Anura; Catechol Oxidase; Dehydration; Ethyl Ethers; Hemorrhage; In Vitro Techniques; Oxytocin; Peptides; Pituitary Hormones, Posterior; Sodium; Sodium Chloride; Trypsin; Urinary Bladder; Vasotocin; Water

Topics: Animals; Dehydration; Hypothalamus; Oxytocin; Peptide Hydrolases; Rabbits; Vasopressins; Water Intoxication

Topics: Animals; Blood Chemical Analysis; Body Weight; Dehydration; Hematocrit; Male; Osmolar Concentration; Oxytocin; Pituitary Gland; Rats; Vasopressins

Topics: Animals; Dehydration; Electrophoresis; Neurosecretion; Organ Size; Oxytocin; Peptides; Pituitary Gland, Posterior; Rats; Sodium Chloride; Vasopressins

Topics: Animals; Anura; Dehydration; Electrophoresis; Glycolates; Osmosis; Oxytocin; Pituitary Gland, Posterior; Pituitary Hormones, Posterior; Poultry; Reptiles; Sodium Chloride; Vasopressins

Topics: Animals; Anura; Biological Transport; Cell Membrane Permeability; Dehydration; Hypertonic Solutions; Osmosis; Oxytocin; Pharmacology; Research; Sodium Chloride; Solutions; Sucrose; Urea; Urinary Bladder