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Query: UNIPROT:P01178 (oxytocin)
 15,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:A functional role for opioid peptides in the differential secretion of vasopressin and oxytocin. 654 Oct 75

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)
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PMID:Effects of pinealectomy on neurohypophysial hormones in the SFO and plasma of dehydrated rats exposed to 12 hours of light. 666 81

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.
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PMID:Vasopressin and oxytocin in cerebrospinal fluid and plasma of conscious rabbits--response to dehydration and haemorrhage. 667 74

We have developed small-scale methods for the isolation and biochemical characterization of subcellular fractions from single guinea-pig posterior-pituitary glands. Secretory vesicles and coated microvesicles produced in this way were of similar purity to those isolated from large amounts of tissue by conventional ultracentrifugation. [35S]Cysteine injected into the hypothalamus was found in the soluble contents of secretory vesicles isolated from the neural lobes 24 h later. High-pressure liquid-chromatographic analysis revealed that the radiolabel was incorporated into the expected neurosecretory products (oxytocin, vasopressin and neurophysin) and also into a biosynthetic intermediate in the vasopressin system. The membranes of secretory vesicles were labelled with [3H]choline 24 h after its hypothalamic injection. Little or no [3H]choline could be demonstrated in coated microvesicles at this time, although these structures were labelled 5 days after injection. Stimulating hormone secretion by chronic dehydration produced a significant fall in [3H]choline content of the secretory-vesicle membranes without any transfer of label into coated microvesicles, suggesting that coated microvesicles are not involved in membrane retrieval in the neurohypophysis.
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PMID:Membrane retrieval in the guinea-pig neurohypophysis. Isolation and characterization of secretory vesicles and coated microvesicles after radiolabel incorporation in vivo. 671 33

The neuropil located ventral to the SON was investigated by the use of immunoperoxidase staining for neurophysins, oxytocin and vasopressin, and electron microscopy. The study was performed in six groups of rats: 1) control; 2) infusion of isotonic saline into the CSF; 3) infusion of hypertonic saline into the CSF; 4) drinking hypertonic saline for 4 days; 5) same as group 4 but injection of colchicine into the CSF on second day of dehydration; 6) salt loading for 3 months. In the control rats the ventral neuropil contained a few immunoreactive processes, the general morphology of which was completely different from that of the neurosecretory axons emerging from the SON at its dorsal aspect. In rats of groups 3 to 6 the ventral processes (VP) became loaded with neurosecretory granules, whereas the perikarya and axons were depleted. Based on their general morphology and reactivity pattern it is suggested that the VP are dendrites. Most of these "dendrites" were embedded in a glial cushion formed by the processes of a particular type of marginal glia. Some of these "dendrites" enveloped an arteriole penetrating the optic tract. All VP were rich in synaptic contacts. The possibility that the VP of neurosecretory cells may be functionally related to the subarachnoid CSF and the arteriolar blood flow is discussed.
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PMID:Immunocytochemistry and ultrastructure of the neuropil located ventral to the rat supraoptic nucleus. 671 4

Extracts of cerebral and pleuro-pedal ganglia from two terrestrial slugs, Ariolimax columbianus and Limax maximus, and from the marine opisthobranch, Aplysia californica, contain immunoreactivity resembling that of a vasotocin or vasopressin. Radioimmunoassays using several antisera indicate that the immunoreactivity is not due to vasotocin, vasopressin, or any other known naturally occurring neurohypophyseal peptide. Immunoreactivity of extracts on a relatively nonspecific vasopressin antiserum is well correlated with activity on antidiuretic assays on rats. Both immunoreactivity and antidiuretic activity are adsorbed onto bovine neurophysin affinity columns. Thus these extracts contain one or more peptides that closely resemble the vertebrate antidiuretic hormones, vasotocin and vasopressin, both immunologically and pharmacologically. The amounts of immunoreactivity and antidiuretic activity in ganglion extracts do not appear to change during dehydration and rehydration. Although both ganglionic extracts and vasotocin stimulate exudation of fluid across the slug body wall, the present experiments provide no evidence that the vasotocin-like material(s) in these ganglia may participate as neurotransmitters or hormones in the regulation of fluid balance. This remains an attractive hypothesis.
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PMID:Immunological and biological characteristics of the vasotocin-like activity in the head ganglia of gastropod molluscs. 672 97

The indirect immunofluorescence technique was used to examine the pharmacology associated with reserpine-induced alterations in vasopressin and neurophysin (VP/NP) immunoreactivity in the external layer of the median eminence in the rat. Twenty-four hours after injection of reserpine, a selective, marked depletion of VP/NP immunoreactivity from the external layer is apparent. Pretreatment with the monoamine oxidase inhibitors, pargyline and tranylcypromine, prevents the depleting effect of reserpine, indicating that the acute effect of reserpine is mediated by monoamines. Acute intraventricular treatment with 6-hydroxydopamine, but not 5,7-dihydroxytryptamine, mimicked the reserpine effect, suggesting that catecholamines mediate reserpine depletion of VP/NP immunoreactivity from the external layer. The experimental results are consistent with a regulatory model in which catecholamines tonically inhibit VP/NP release from terminals in the external layer of the median eminence. Although the studies do not definitively determine the functional relationship between VP and ACTH, the anatomical location of these terminals, the dramatic change in the VP/NP content of these terminals in response to reserpine, and the lack of a response to dehydration suggest that this pool of vasopressin may contribute to ACTH hypersecretion in response to reserpine.
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PMID:Terminals of reserpine-sensitive vasopressin-neurophysin neurons in the external layer of the rat median eminence. 701 84

Experiments were performed to evaluate the effect of dehydration on neurohypophyseal hormone secretion, both vasopressin and oxytocin, fluid balance, and blood pressure in male spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar Kyoto (WKY). Metabolic studies showed that the antidiuretic response to dehydration (24 and 48 hours of water deprivation) was significantly depressed (p less than 0.01) in the hypertensive animals. They responded inappropriately to dehydration with a greater loss of water and sodium and a larger increase in hematocrit. In contrast, the vasopressin response (both urinary excretion and plasma levels) was increased. The peak plasma levels were 25.3 pg/ml (SHR) compared to 16.6 pg/ml (WKY), while the urinary excretion was 22.5 ng/24 hrs (SHR) vs 9.0 ng/24 hrs (WKY). Dehydration also elicited a stimulation of oxytocin secretion, with no differences observed in the responses of the groups. Blood pressure was significantly greater in the SHR and it did not change during dehydration. These results provide further support for the idea that hypertension is associated with abnormalities in the control of fluid/electrolyte balance.
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PMID:Neurohypophyseal response to dehydration in the spontaneously hypertensive rat. 706 Nov 23

1. The present study investigates the nature and magnitude of the renal response to plasma levels of oxytocin which might be induced by salt loading. 2. Increased plasma osmolality induced by loading with NaCl is an effective stimulus for oxytocin release in the unanaesthetized male rat. Plasma oxytocin concentration was positively correlated (r = 0-.77) with plasma osmolality. Plasma oxytocin (muu./ml.) = 0.37 x (plasma osmolality (m-osmole/kg) -297). 3. In anaesthetized Long Evans rats intra-atrial administration of oxytocin at rates of 0.05 and 0.15 m-u./ml. produced plasma hormone concentrations (5 +/- 1 and 16 +/- 2 mum./ml. respectively) within the range induced by salt loading. 4. Oxytocin administration at 0.15 and 1.5 m-u./min in Long Evans rats produced dose-related increases in urine flow and Na+ and Cl- excretion. Renal responses to 0.05 m-u. oxytocin/min were equivocal. 5. Oxytocin administration at 0.15 m-u./min was ineffective in Brattleboro rats but 1.5 m-u./min led to increased Na+ and Cl- excretion and a reduction in urine flow. 6. Plasma oxytocin levels similar to those induced by severe dehydration or salt loading are effective in increasing renal Na+ and Cl- excretion and urine flow. These effects on water and electrolyte excretion appear to be independent of each other and both may be modified by the presence or absence of vasopressin. 7. This study provides no evidence for a major role for oxytocin in the day to day regulation of salt or water balance under conditions of normal hydration in the male rat.
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PMID:Release of oxytocin induced by salt loading and its influence on renal excretion in the male rat. 723 26

Synthetic arginine-vasopressin (AVP), oxytocin (OXY) and arginine-vasotocin (AVT) were labelled with radioiodine at a moderate specific activity. The purity of the labelled octapeptides was checked by descendent paper chromatography in butanol-acetic acid-water (4 : 1 : 5 v/v) after a double filtration on a Sephadex G-25 column of the labelling mixtures. The rabbit anti-AVP serum bound 125I--AVP, the highest binding belling observed on the descendent eluates from the Sephadex column. The antiserum is specific to AVP, no binding being observed will AVT or oxytocin. The sensitivity of a RIA system using 125I--AVP, commercial anti-AVP serum and polyethyleneglycol separation technique, was of 5 pg/ml in terms of AVP with a biological activity of 385 IU/mg. The validity of the assay was tested on five patients (two with diabetes inspidus (DI) and three with other endocrine diseases) submitted to dehydration of hydration tests.
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PMID:Labelling of octapeptide neurohormones for in vitro studies. Radioimmunologic assay for arginine-vasopressin. 729 46


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