oxytocin and Hypovolemia

Topics: Animals; Cerebral Ventricles; Cholecystokinin; Female; Hypothalamus; Hypovolemia; Lactation; Median Eminence; Neurons; Neurosecretory Systems; Oxytocin; Pregnancy; Subfornical Organ; Vasopressins; Water-Electrolyte Balance

We generated a transgenic rat line that expresses oxytocin (OXT)-monomeric red fluorescent protein 1 (mRFP1) fusion gene to visualize the dynamics of OXT. In this transgenic rat line, hypothalamic OXT can be assessed under diverse physiological and pathophysiological conditions by semiquantitative fluorometry of mRFP1 fluorescence intensity as a surrogate marker for endogenous OXT. Using this transgenic rat line, we identified the changes in hypothalamic OXT synthesis under various physiological conditions. However, few reports have directly examined hypothalamic OXT synthesis under hyperosmolality or hypovolemia. In this study, hypothalamic OXT synthesis was investigated using the transgenic rat line after acute osmotic challenge and acute hypovolemia induced by intraperitoneal (i.p.) administration of 3% hypertonic saline (HTN) and polyethylene glycol (PEG), respectively. The mRFP1 fluorescence intensity in the paraventricular (PVN) and supraoptic nuclei (SON) was significantly increased after i.p. administration of HTN and PEG, along with robust Fos-like immunoreactivity (co-expression). Fos expression showed neuronal activation in the brain regions that are associated with the hypothalamus and/or are involved in maintaining water and electrolyte homeostasis in HTN- and PEG-treated rats. OXT and mRFP1 gene expressions were dramatically increased after HTN and PEG administration. The plasma OXT level was extremely increased after HTN and PEG administration. Acute osmotic challenge and acute hypovolemia induced upregulation of hypothalamic OXT in the PVN and SON. These results suggest that not only endogenous arginine vasopressin (AVP) but also endogenous OXT has a key role in maintaining body fluid homeostasis to cope with hyperosmolality and hypovolemia.

Topics: Animals; Hypothalamus; Hypovolemia; Luminescent Proteins; Male; Osmoregulation; Osmotic Pressure; Oxytocin; Rats; Red Fluorescent Protein; Transgenes; Up-Regulation

To analyze outcomes after second-stage labor beyond 3 hours and determine if prolonged second stages were intentional.. Retrospective cohort analysis of maternal and neonatal outcomes in nulliparous women based on second-stage duration. Medical records were reviewed for management decisions in women with second stages ≥4 hours; all other outcomes were accessed via computerized obstetric database.. Second stage exceeding 3 hours occurred in 1489 (7%) of 21,991 pregnancies analyzed. Of the 427 (2%) with second stages ≥4 hours, 315 (74%) reached 4 hours unintentionally, after a decision for operative delivery had been made. Only 34 (8%) women were intentionally allowed to continue second-stage labor beyond 4 hours, and half of these ultimately required cesarean. Indices of maternal and neonatal morbidity were significantly increased when second stages exceeded 3 hours.. Most second stages reaching 4 hours are unintentional, occurring while awaiting an previously decided upon operative delivery. Maternal and neonatal morbidities are significantly increased with second stages beyond 3 hours.

Topics: Adolescent; Adult; Analgesia, Epidural; Analgesia, Obstetrical; Blood Transfusion; Cesarean Section; Chorioamnionitis; Cohort Studies; Female; Fetal Monitoring; Fever; Heart Rate, Fetal; Humans; Hypovolemia; Hysterectomy; Labor Stage, Second; Lacerations; Oxytocics; Oxytocin; Parity; Perineum; Pregnancy; Retrospective Studies; Time Factors; Young Adult

Previous studies demonstrated the inhibitory participation of serotonergic (5-HT) and oxytocinergic (OT) neurons on sodium appetite induced by peritoneal dialysis (PD) in rats. The activity of 5-HT neurons increases after PD-induced 2% NaCl intake and decreases after sodium depletion; however, the activity of the OT neurons appears only after PD-induced 2% NaCl intake. To discriminate whether the differential activations of the 5-HT and OT neurons in this model are a consequence of the sodium satiation process or are the result of stimulation caused by the entry to the body of a hypertonic sodium solution during sodium access, we analyzed the number of Fos-5-HT- and Fos-OT-immunoreactive neurons in the dorsal raphe nucleus and the paraventricular nucleus of the hypothalamus-supraoptic nucleus, respectively, after isotonic vs. hypertonic NaCl intake induced by PD. We also studied the OT plasma levels after PD-induced isotonic or hypertonic NaCl intake. Sodium intake induced by PD significantly increased the number of Fos-5-HT cells, independently of the concentration of NaCl consumed. In contrast, the number of Fos-OT neurons increased after hypertonic NaCl intake, in both depleted and non-depleted animals. The OT plasma levels significantly increased only in the PD-induced 2% NaCl intake group in relation to others, showing a synergic effect of both factors. In summary, 5-HT neurons were activated after body sodium status was reestablished, suggesting that this system is activated under conditions of satiety. In terms of the OT system, both OT neural activity and OT plasma levels were increased by the entry of hypertonic NaCl solution during sodium consumption, suggesting that this system is involved in the processing of hyperosmotic signals.

Topics: Animals; Appetite; Hypernatremia; Hypovolemia; Immunohistochemistry; Male; Neurons; Osmolar Concentration; Oxytocin; Paraventricular Hypothalamic Nucleus; Peritoneal Dialysis; Raphe Nuclei; Rats; Rats, Wistar; Satiety Response; Serotonin; Sodium, Dietary; Supraoptic Nucleus; Water-Electrolyte Balance

To explore the role of oxytocin in the regulation of salt appetite and blood pressure, we conducted studies in oxytocin gene-knockout mice and determined (1) blood pressure and heart rate during day and night periods, (2) salt appetite after iso-osmotic volume depletion, and (3) salt appetite and blood pressure after central injection of angiotensin II. Long-term arterial catheters were inserted, and blood pressure and heart rate were recorded for 24 hours. There was a modest decrease in blood pressure and heart rate in knockout mice. Salt appetite was measured with a 2- bottle choice (water and 2% NaCl), with measurement of licking activity. Mice were injected subcutaneously with 30% polyethylene glycol (0.5 mL), and voluntary intakes were measured for 24 hours. Knockout mice consumed 3 times the amount of NaCl than did controls, 276+/-77 vs 90+/-38 licks/24 h (P<0.05). Water consumption was similar between groups. Angiotensin II (5, 50, and 200 ng/3 microL) injected intracerebroventricularly produced dose-related increases in intake, with no differences between the groups. The 50-ng dose of angiotensin II elicited salt and water intakes of 151+/-43 vs 160+/-33 licks and 250+/-53 vs and 200+/-51 licks, respectively (control vs knockout). The pressor response to angiotensin II was not different between the groups. Results suggest that oxytocin plays a role in the regulation of blood pressure and salt appetite, specifically as mediated by volume receptors, and that the renin-angiotensin system is not involved in these changes.

Topics: Administration, Oral; Angiotensin II; Animals; Appetite; Blood Pressure; Cerebral Ventricles; Drinking; Heart Rate; Hypovolemia; Injections; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Oxytocin; Polyethylene Glycols; Renin-Angiotensin System; Sodium Chloride

Medullary catecholamine and hypothalamic neurosecretory oxytocin cells are activated by hypotension, but previous studies have provided uncertain outcomes concerning their ability to respond to a purely hypovolaemic stimulus. In the present study, injections of PEG/water and pentolinium were used to elicit non-hypotensive, isosmotic hypovolaemia and isovolaemic, isosmotic hypotension, respectively, in conscious rats. Animals were sacrificed 2 h after treatment. Immunolabelling for Fos, tyrosine hydroxylase and oxytocin established that these two stimuli activate almost identical populations of catecholamine neurons in the ventrolateral and dorsomedial medulla, and very similar populations of oxytocin cells in the supraoptic and paraventricular nuclei of the hypothalamus.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Catecholamines; Hypotension; Hypovolemia; Medulla Oblongata; Neurons; Oxytocin; Paraventricular Hypothalamic Nucleus; Pentolinium Tartrate; Polyethylene Glycols; Proto-Oncogene Proteins c-fos; Rats; Rats, Wistar; Supraoptic Nucleus; Tyrosine 3-Monooxygenase; Vasopressins

To date, glucagon-like peptide 1(7-36) amide (tGLP-1) has been found to affect the neurohypophysial and cardiovascular functions in normotensive and normovolaemic rats. The aim of the present study was to investigate possible effects of tGLP-1 on the mean arterial blood pressure and the release of vasopressin and oxytocin under conditions of blood volume depletion in the rat. In the first series of experiments, the animals were injected i.p. with either 0.15 M saline or 30% polyethylene glycol (PEG). PEG caused an 18% reduction of blood volume 1 h after injection. No significant changes in the mean arterial blood pressure were found in either normo- or hypovolaemic rats during the experiment. tGLP-1 injected i.c.v. at a dose of 1 microg/5 microl 1 h after the i.p. injection increased similarly the arterial blood pressure in normo- and hypovolaemic rats. The plasma vasopressin/oxytocin concentrations were markedly elevated in hypovolaemic animals and tGLP-1 further augmented the release of both hormones. In the second study, hypovolaemia was induced by double blood withdrawal. The haemorrhage resulted in a marked decrease of the mean arterial blood pressure and in the elevated plasma vasopressin/oxytocin concentrations. tGLP-1 injected immediately after the second blood withdrawal increased the arterial blood pressure. In parallel, tGLP-1 enhanced significantly vasopressin and oxytocin secretion when compared with haemorrhaged, saline-injected rats. The results of this study indicate that tGLP-1 may affect the arterial blood pressure and the secretion of neurohypophysial hormones under pathological conditions brought about by blood volume depletion.

Topics: Analysis of Variance; Animals; Arginine Vasopressin; Blood Pressure; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptides; Hypovolemia; Male; Oxytocin; Peptide Fragments; Pituitary Gland, Posterior; Rats; Rats, Wistar