pituitrin and alpha-neoendorphin

The source and topography of neuropeptide-containing axons in the median eminence are summarized. Several of these neuropeptide-containing neurons (thyrotropin-releasing hormone, corticotropin-releasing hormone, vasopressin, oxytocin, cholecystokinin) are localized in the paraventricular nucleus. The periventricular and medial preoptic nuclei constitute the main sources of somatostatin and luteinizing hormone releasing hormone axons in the median eminence, respectively. Dynorphins and alpha-neo-endorphin-synthetizing neurons in the supraoptic nucleus also project to the median eminence. Wherever they originate, the projections may follow a common organization pattern and use a common gate--the lateral retrochiasmatic area--to enter the median eminence.

Topics: Animals; Cholecystokinin; Corticotropin-Releasing Hormone; Dynorphins; Endorphins; Gonadotropin-Releasing Hormone; Medial Forebrain Bundle; Median Eminence; Nerve Fibers; Nerve Tissue Proteins; Neural Pathways; Neurons; Optic Chiasm; Oxytocin; Protein Precursors; Somatostatin; Thyrotropin-Releasing Hormone; 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

Arginine (AVP) and lysine vasopressin induce a weak but statistically significant increase in the water permeability of Amoeba proteus plasmalemma. Vasotocin and deaminovasopressin, which share the hydroosmotic properties of AVP on classical vertebrate systems, are without effects on Amoeba while SKF 101926, a synthetic AVP antagonist, is even more effective than the parent compound. Theophyllin and dibutyryl-cAMP do not affect AVP action on Amoeba. Lithium, oxytocin, and carbachol are also without effect. Thus, it is unlikely that either V2 (cAMP) or V1 (phosphatidylinositol choline) receptors are involved. A clear correlation has been found between the amphiphilic character of tested peptides and their effect on Amoeba water permeability. Classical amphiphilic peptides, melittin, mastoparan, and fragment 1-8 of alpha-neoendorphin, also increased water permeability in Amoeba. It is known that vasopressin can interact with artificial lipid membranes, increasing their permeability to water. We propose that amphiphilic members of the AVP family interact directly with the lipid phase of the Amoeba membrane. Their incorporation within the lipid bilayer may cause local disruptions or may create micellar water channels as shown for other amphiphilic proteins. Our observations provide a model for the early evolution of peptide hormone systems, preceding the appearance of specific membrane receptors and associated second messenger amplifying mechanisms.

Topics: Amoeba; Animals; Arginine Vasopressin; Cell Membrane; Cell Membrane Permeability; Deamino Arginine Vasopressin; Endorphins; Intercellular Signaling Peptides and Proteins; Lipid Metabolism; Lypressin; Melitten; Oxytocin; Peptides; Protein Precursors; Receptors, Angiotensin; Receptors, Vasopressin; Vasopressins; Wasp Venoms; Water

The content of vasopressin, oxytocin, neurophysin, leucine-enkephalin, methionine-enkephalin, dynorphin-(1-13), and alpha-neoendorphin in the rat neurohypophysis was measured after different periods of dehydration and after depolarisation of isolated neural lobes and of neurosecretory nerve endings. The rates at which the amount of neurohypophysial hormone and opioid peptides decreased, and the changes in the ratios between the amount of vasopressin or oxytocin and opioid peptide in the neurohypophysis after dehydration and in the incubation medium after depolarization in vitro cast some doubt on, and can be explained by mechanisms other than co-localisation of the different peptides.

Topics: Animals; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalin, Methionine; Histological Techniques; Neurophysins; Oxytocin; Peptide Fragments; Pituitary Gland, Posterior; Protein Precursors; Radioimmunoassay; Rats; Rats, Inbred Strains; Vasopressins

Specific radioimmunoassays were used to measure the effects of hypertonic saline (salt loading), water deprivation, and trichothecene mycotoxin (T2 toxin) on the content of methionine enkephalin (ME), leucine enkephalin (LE), alpha-neoendorphin, dynorphin A, dynorphin B, vasopressin, and oxytocin in the rat posterior pituitary. Concentrations of vasopressin and oxytocin decreased in response to both osmotic stimuli and treatment with T2 toxin, but the decrease was greater with osmotic stimulations. Similarly, concentrations of LE and dynorphin-related peptides declined after salt loading and water deprivation; LE concentrations also decreased after treatment with T2 toxin. The concentration of ME decreased after water deprivation, did not change after salt loading, and increased after T2 toxin treatment. The differentiating effects of these stimuli on the content of immunoreactive LE and ME are consistent with the hypothesis that LE and ME may be localized in separate populations of nerve endings with different roles in the posterior pituitary.

Topics: Animals; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalin, Methionine; Male; Osmosis; Oxytocin; Pituitary Gland, Posterior; Protein Precursors; Rats; Rats, Inbred Strains; Saline Solution, Hypertonic; Sesquiterpenes; T-2 Toxin; Vasopressins; Water Deprivation

The present study examines the influences of selective destruction of the locus coeruleus (LC) or of the ventral noradrenergic bundle (VB) upon discrete CNS and pituitary pools of vasopressin, dynorphin and related opioid peptides in the rat. The selectivity of the lesions was indicated by the fact that destruction of the LC strongly depressed levels of noradrenaline in the cortex in contrast to the hypothalamus, whereas destruction of the VB decreased noradrenaline in hypothalamus but not cortex. Rats sustaining VB lesions displayed a parallel depletion in neurointermediate, but not anterior, lobe levels of immunoreactive-(ir-dynorphin (DYN), ir-DYN, ir-alpha-neo-endorphin (ir-alpha-NE) and ir-vasopressin (ir-VP) whereas those of ir-Met-enkephalin (ir-ME) were unaffected. In the hypothalamus, the content of ir-DYN and ir-VP tended to rise and that of ir-DYN and ir-alpha-NE was significantly elevated, whereas that of ir-ME was not altered. LC destruction failed, in contrast, to modify levels of ir-VP, ir-DYN, ir-DYN, ir-alpha-NE or ir-ME in any of the above structures. It was found to, however, result in a depression in levels of ir-DYN and ir-alpha-NE, but not of ir-ME or ir-VP, in both the hippocampus and striatum whereas VB lesions were, in this respect, ineffective. Further, in the spinal cord, LC lesions resulted in a significant elevation in levels of ir-DYN and ir-alpha-NE in comparison to those of ir-DYN, ir-VP and ir-ME. Neither type of lesion significantly altered the content of any opioid peptide examined in thalamus, cortex, septum or midbrain. These data indicate that: the LC as compared to the VB interact differently with discrete pools of ir-DYN, ir-DYN, ir-alpha-NE and ir-VP in brain, pituitary and spinal cord; it is the VB rather than the LC which modulates the activity of magnocellular neurones projecting to the neural lobe of the pituitary; ir-DYN, ir-DYN and ir-alpha-NE are, in all tissues, regulated independently of ir-ME; levels of ir-DYN, ir-DYN and ir-alpha-NE are co-regulated with those of ir-VP in the hypothalamus-neural lobe axis but not in extrahypothalamic brain tissues nor the spinal cord; and DYN, DYN and alpha-NE might, in certain cases, be modulated differentially of one another, possibly reflecting alterations in precursor processing.

Topics: Animals; Brain; Cerebral Cortex; Corpus Striatum; Dynorphins; Endorphins; Enkephalin, Methionine; Hippocampus; Hypothalamus; Locus Coeruleus; Neural Pathways; Norepinephrine; Peptide Fragments; Pituitary Gland; Protein Precursors; Rats; Spinal Cord; Vasopressins

The postnatal development of several pro-enkephalin-B-derived opioid peptides - dynorphin 1-17, dynorphin 1-8, dynorphin B, alpha-neo-endorphin and beta-neo-endorphin - was examined in rat pituitary lobes. The concentrations of pro-enkephalin-B-derived peptides from the anterior pituitary were between 4- and 12-fold and those from the neurointermediate pituitary between 17- and 122-fold lower in newborn as compared to adult rats. Similarly, the concentrations of vasopressin in the neurointermediate pituitary increased 50-fold between birth and adulthood; those of oxytocin, however, increased more than 540-fold over this period. The molecular weight pattern of dynorphin 1-17, dynorphin 1-8, dynorphin B, alpha- and beta-neo-endorphin-immunoreactive peptides in the anterior and neurointermediate pituitary did not differ between 3-day-old pups and adult rats. In the neurointermediate pituitary, the major immunoreactive components had the same chromatographic properties as synthetic dynorphin 1-17, dynorphin 1-8, dynorphin B, alpha- and beta-neo-endorphin, respectively, on gel filtration and high-performance liquid chromatography (HPLC). This indicates that neonatal rats were already capable of processing the precursor pro-enkephalin B into these various opioid peptides. In newborn rats, however, the amount of dynorphin 1-8 in the neurointermediate pituitary was three times lower than that of its putative intermediate precursor peptide dynorphin 1-17. Similarly, the amount of beta-neo-endorphin was almost four times lower than that of its putative precursor alpha-neo-endorphin. In contrast, in the neurointermediate pituitary of adult rats, dynorphin 1-17 and dynorphin 1-8, in addition to a alpha- and beta-neo-endorphin, occurred in equimolar amounts.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Animals, Newborn; Cell Differentiation; Chromatography, High Pressure Liquid; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalins; Female; Male; Molecular Weight; Oxytocin; Peptide Fragments; Peptides; Pituitary Gland, Anterior; Pituitary Gland, Posterior; Pregnancy; Protein Precursors; Rats; Rats, Inbred Strains; Vasopressins

Bilateral, radiofrequency destruction of the hypothalamic paraventricular nucleus resulted in a pronounced depression in levels of immunoreactive (ir-) vasopressin (VP) in the medulla-pons of rats. The contents of ir-dynorphin1-17 (DYN), ir-DYN1-8 and ir-alpha-neo-endorphin (alpha-NE) therein were not, in contrast, affected. Exposure of naive rats to acute foot-shock stress was associated with an elevation in levels of ir-VP in the medulla-pons whereas those of ir-DYN, ir-DYN1-8 and ir-alpha-NE were not significantly altered. The data indicate that the paraventricular nucleus is a major source of ir-VP but not of ir-DYN, ir-DYN1-8 or ir-alpha-NE in the medulla-pons, and that these pools of ir-VP, in contrast to those of ir-DYN, ir-DYN1-8 and ir-alpha-NE, are involved in the response to stress. It is concluded that ir-DYN, ir-DYN1-8 and ir-alpha-NE exist in (a) neuronal network(s) independent of that of ir-VP in the medulla-pons of the rat.

Topics: Animals; Dynorphins; Electroshock; Endorphins; Male; Medulla Oblongata; Paraventricular Hypothalamic Nucleus; Pons; Protein Precursors; Rats; Rats, Inbred Strains; Stress, Physiological; Vasopressins

Topics: Animals; Endorphins; Histocytochemistry; Hypothalamus; Immunochemistry; Neurons; Protein Precursors; Staining and Labeling; Vasopressins

Topics: Animals; Endorphins; Immunoenzyme Techniques; Male; Neurons; Oxytocin; Pituitary Gland, Posterior; Protein Precursors; Rabbits; Rats; Vasopressins