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

We have investigated the influence of endogenous opioids on oxytocin secretion during pregnancy. In blood-sampled conscious rats on days 18 and 21 of pregnancy plasma oxytocin concentration, measured by radioimmunoassay, was significantly increased compared to non-pregnant or post-partum rats. On days 15, 18 and 21 of pregnancy but not in non-pregnant, early pregnant or post-partum rats, the opioid antagonist naloxone caused a significant increase in plasma oxytocin compared to vehicle injection, indicating activation of an endogenous opioid restraint over oxytocin secretion. Electrically stimulated neural lobes isolated from 16- and 21-day pregnant rats released more oxytocin than those from non-pregnant rats. However, naloxone (10(-5) M) was less effective at potentiating, and the kappa-opioid agonist U50,488 (10(-5)M) was less effective at inhibiting, stimulated release at the end of pregnancy than in non-pregnant rats suggesting desensitization of oxytocin nerve terminals to actions of endogenous opioids. Neural lobes from male rats drinking 2% saline for 4 days also showed desensitization of oxytocin nerve endings to naloxone. Neither neural lobe content of dynorphin A(1-8), an endogenous kappa-opioid, nor prodynorphin mRNA expression, measured by in situ hybridization histochemistry in the supraoptic nucleus altered during pregnancy. However, neural lobe content of Met5-enkephalin significantly decreased by day 21 of gestation suggesting enhanced release.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Endogenous opioid regulation of oxytocin secretion through pregnancy in the rat. 810 Apr 68

Anorexia nervosa is associated with vasopressin, oxytocin and serotonin abnormalities. Because of the relationship between exercise and anorexia nervosa, we explored the weight-loss syndrome produced by wheel running in food-deprived rats. Its effects on regional vasopressin and oxytocin concentrations were determined under basal conditions and following systemic fluoxetine. Weight-matched, exercised and unexercised rats served as controls. Fluoxetine caused abnormalities in suprachiasmatic vasopressin and dynorphin A content and in thymus oxytocin content that did not occur in weight-matched or exercised controls. No syndrome-specific anomalies occurred in the hypothalamo-neurohypophysial system or dorsal vagal complex (DVC). However, weight reduction and fluoxetine increased circulating vasopressin; moderate exercise caused fluoxetine-induced elevations in posterior pituitary vasopressin and oxytocin; and, unlike the other groups, fluoxetine increased DVC oxytocin in freely fed unexercised rats. It was concluded that syndrome-specific vasopressin and oxytocin abnormalities occur that are not secondary to weight loss or moderate exercise; that weight loss or fluoxetine increases circulating vasopressin; that moderate exercise alters neurohypophysial vasopressin and oxytocin content; and that weight loss or exercise inhibits a fluoxetine-stimulated increase in DVC oxytocin. Finally, it was argued that the fluoxetine abnormalities indicate possible serotonin dysfunction in the syndrome.
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PMID:Fluoxetine induces vasopressin and oxytocin abnormalities in food-restricted rats given voluntary exercise: relationship to anorexia nervosa. 810 Nov 30

Following our recent demonstration of metrazole-induced immediate-early gene expression in the hypothalamic supraoptic nucleus (SON), we have now performed a mRNA and transcription analysis to determine the consequences of metrazole treatment for neurohypophyseal peptide gene expression in male rats. Levels of hypothalamic vasopressin (VP) and oxytocin (OT) mRNA were significantly reduced at 2 and 4 h after metrazole (50 mg/kg, i.p.), whereas pro-dynorphin mRNA was significantly elevated at 2 h. No changes in mRNA levels were found at 8, 24 or 48 h after treatment. Another convulsant (kainic acid, 8 mg/kg, i.p.) elicited similar effects on VP and OT mRNAs at 2 h. Specific analysis of the SON, following metrazole, revealed an equivalent effect on VP and OT mRNA levels but a nuclear run-on assay did not detect any change in SON VP gene transcription at 0.5, 1 and 2 h after treatment. The results provide evidence of a novel mechanism which may provide an additional level of control in the regulation of neuropeptide gene expression.
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PMID:Acute down-regulation of oxytocin and vasopressin mRNA levels following metrazole-induced seizure in the rat. 824 43

Single- and double-immunohistochemical staining methods were used to assay the effect of estrogen on the expression of co-existing peptides in the magnocellular neurosecretory system of the female rat. It was confirmed in colchicine-treated, ovariectomized animals that immunoreactive corticotropin-releasing factor and cholecystokinin co-exist in subsets of oxytocinergic neurons; in addition, dynorphin immunoreactivity was detected in a substantial majority of oxytocin containing magnocellular neurons. Consistent with previous studies, magnocellular vasopressinergic cells were found to display angiotensin II-, dynorphin- and galanin-immunoreactivities. Comparable results occurred in colchicine-treated ovariectomized rats independent of whether or not the animals received replacement injections of estradiol benzoate or vehicle. Ovariectomized rats that were not pretreated with colchicine showed enhanced staining (increased cell number and staining intensity of both cell bodies and terminals in the posterior pituitary) for each of the peptides that was found to co-exist in vasopressinergic neurons after treatment with estradiol; staining for vasopressin was similar in steroid- and oil-treated animals. Perikaryal staining for peptides co-localized with oxytocin was not discernibly different in estradiol- vs vehicle-treated animals, while in the posterior lobe, differential effects of hormone replacement on oxytocin, cholecystokinin, and corticotropin-releasing factor immunostaining of terminals were apparent. Perikaryal staining for co-existing peptides in gonadally intact animals killed at the estrus or the diestrus II phases of the estrous cycle provided a pattern of results compatible with those seen in ovariectomized animals treated with estradiol or oil, respectively. These observations suggest that circulating gonadal steroids affect co-existing peptide expression differentially in oxytocinergic vs vasopressinergic neurons. All peptides examined that could be co-localized in vasopressinergic cells showed evidence of enhanced expression in the presence of estrogen, while at least two of these co-localized with oxytocin appeared driven in the opposite direction. The results in normally cycling rats indicate that this kind of influence may be manifest under normal physiological conditions.
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PMID:Neuropeptide co-expression in the magnocellular neurosecretory system of the female rat: evidence for differential modulation by estrogen. 834 19

Opioid peptides are present in nerve terminals in the rat neural lobe where they partially coexist with vasopressin. Morphological findings suggest that these neuropeptides are released onto pituicytes, which is in agreement with a possible role for the pituicyte in oxytocin and vasopressin release from the neural lobe. Pituicytes in culture respond to vasopressin with a mobilization of calcium from intracellular stores. In the present study this vasopressin induced increase in intracellular free calcium levels was both delayed and decreased by pre-exposure to dynorphin 1-17, while dynorphin 1-17 by itself did not affect basal calcium levels. All effects of dynorphin 1-17 could be blocked with naloxone. The present results suggest that opioid receptors are present on pituicytes and are coupled to a second messenger pathway by which opioid peptides may inhibit inositol phosphate dependent calcium mobilization by other neuropeptides, such as vasopressin.
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PMID:Dynorphin 1-17 delays the vasopressin induced mobilization of intracellular calcium in cultured astrocytes from the rat neural lobe. 868 Apr 28

The magnocellular oxytocin neurons within the paraventricular and supraoptic nuclei (PVN and SON) of the hypothalamus are important relays in the milk ejection reflex in lactating animals, and are activated by suckling. It has been suggested that proto-oncogene transcription factors such as Fos/Jun act as early nuclear transducers of sensory stimuli in neurons. Therefore, we have studied with immunohistochemistry Fos-related antigens (FRAs) as a marker for neuronal activity in the PVN and SON during suckling in lactating rats. In nonlactating rats, only few cells exhibiting FRAs were observed in these nuclei. Also in lactating rats subjected to continuous suckling Fos-like activity was low. In contrast, lactating rats separated from their pups for 4 h and then exposed to suckling for 1 h expressed strong Fos-like immunoreactivity, both in vasopressin and oxytocin neurons. Using in situ hybridization and immunohistochemistry we have also investigated the expression of the mRNAs for oxytocin, dynorphin, galanin and galanin message-associated peptide and of oxytocin and dynorphin in the PVN of lactating and nonlactating rats. In lactating rats, an increase in oxytocin and dynorphin and their mRNAs was observed, whereas mRNAs for galanin and galanin message-associated peptide were downregulated. With the help of immunohistochemistry and double-staining methods, a substantial coexistence between oxytocin- and dynorphin-like immunoreactivities was shown in magnocellular neurons. These results indicate that FRAs are activated in the PVN in the beginning of a suckling period, while this response cannot be seen after continuous stimulation. Furthermore, in the PVN of lactating rats, an upregulation of oxytocin and dynorphin occurs while galanin expression decreases. Finally, the coexistence between oxytocin and dynorphin is more pronounced in lactating rats and nonlactating female rats than has previously been described in male rats.
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PMID:Expression of Fos-related antigens, oxytocin, dynorphin and galanin in the paraventricular and supraoptic nuclei of lactating rats. 873 91

Oxytocin plays a physiological stimulatory role on sexual behavior. Conversely, opioid neuropeptides play a physiological inhibitory role. Here we show that in sexually impotent rats there is a reduced expression of oxytocin mRNA and an increased expression of proenkephalin and pro-dynorphin mRNA in the paraventricular nucleus of hypothalamus (PVN), a brain structure of key importance for sexual behavior. These data suggest that an imbalance in the production of oxytocin and of opioid peptides in the PVN, with prevalence of opioid peptides, may underlie a condition of sexual impotence.
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PMID:Sexual impotence is associated with a reduced production of oxytocin and with an increased production of opioid peptides in the paraventricular nucleus of male rats. 935 Aug 33

Proteolytic enzymes, which are synthesized and secreted by cells of the seminiferous tubule of the testis, have important functions in spermatogenesis. We performed metabolic studies using small peptide hormones as a substrate to investigate the activity of proteases in cultured Sertoli cells of the rat. High-performance liquid chromatographic analysis of the cell culture supernatants showed cleavage of met- and leu-enkephalin, substance P, and bradykinin. No peptidolysis was observed for the cyclic peptide oxytocin. The hormone cleavage pattern and the use of specific protease inhibitors in peptide degradation experiments demonstrated activities of several proteases in Sertoli cells. These are mainly metalloproteinases including neutral metalloendopeptidases, angiotensin-converting enzyme and aminopeptidases. In addition, activities of serine and aspartic proteases were detected. Only marginal proteolytic activities were observed in Sertoli cell conditioned supernatants, indicating that the investigated proteases are mainly located on Sertoli cell membranes. The peptide hormones used in this study have been found to play a potential role in the endocrine, paracrine or autocrine regulation of testicular cells. The membrane-associated proteases reported here may therefore be involved in the metabolism and inactivation of these peptides.
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PMID:Possible involvement of proteases in the regulation of spermatogenesis. 973 15

Magnocellular neurosecretory cells (MNCs) in the hypothalamo-neurohypophysial system that express and secrete the nonapeptides oxytocin (OT) and vasopressin (VP) were evaluated for the expression of multiple genes in single magnocellular neurons from the rat supraoptic nucleus using a single cell RT-PCR protocol. We found that all cells representing the two major phenotypes, the OT and VP MNCs, express a small, but significant, amount of the other nonapeptide's messenger RNA (mRNA). In situ hybridization histochemical analyses confirmed this observation. A third phenotype, containing equivalent amounts of OT and VP mRNA, was detected in about 19% of the MNCs from lactating female supraoptic nuclei. Analyses of these phenotypes for other coexisting peptide mRNAs (e.g. CRH, cholecystokinin, galanin, dynorphin, and the calcium-binding protein, calbindin) generally confirmed expectations from the literature, but revealed cell to cell variation in their coexpression. Our results also show that the high voltage-activated calcium channel subunit genes, alpha1A-D, alpha2, and beta1-4 are expressed in virtually all MNCs. However, the alpha1E subunit gene is not expressed at detectable levels in these cells. The expression of all of the beta-subunit genes in each MNC may account for the variations in physiological and pharmacological properties of the high voltage-activated channels found in these neurons. (Endocrinology 140: 5391-5401, 1999)
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PMID:Single cell reverse transcription-polymerase chain reaction analysis of rat supraoptic magnocellular neurons: neuropeptide phenotypes and high voltage-gated calcium channel subtypes. 1053 71

The relationship between the cloned kappa opioid receptor, dynorphin, and the neurohypophysial hormones vasopressin and oxytocin was analysed in the guinea-pig hypothalamic magnocellular neurosecretory neurons. This analysis was performed in order to understand better which population of neuroendocrine neurons in the guinea-pig is modulated by kappa opioid receptors and its endogenous ligand dynorphin. Extensive co-localization was observed between kappa opioid receptor immunoreactivity and preprodynorphin immunoreactivity in neuronal cell bodies in the paraventricular and supraoptic nuclei. Cells positive for either the kappa opioid receptor or both the kappa opioid receptor and preprodynorphin were restricted to the vasopressin expressing neuronal population and not found in the oxytocin expressing neuronal population. The kappa opioid receptor and dynorphin were examined in the posterior pituitary and both were found to be extensively distributed. Staining for the kappa opioid receptor and dynorphin B co-localized in posterior pituitary. In addition, immunogold electron microscopy confirmed that kappa opioid receptor and dynorphin B immunoreactivity were found in the same nerve terminals. Ultrastructural analysis also revealed that kappa opioid receptor immunoreactivity was associated with both nerve terminals and pituicytes. Within nerve terminals, kappa opioid receptor immunoreactivity was often associated with large secretory vesicles and rarely associated with the plasma membrane. Our data suggest that the cloned kappa opioid receptor may directly modulate the release of vasopressin but not oxytocin in guinea-pig hypothalamic magnocellular neurosecretory neurons and posterior pituitary. Furthermore, we propose that this receptor is an autoreceptor in this system because our results demonstrate a high degree of co-localization between kappa opioid receptor and dynorphin peptide immunoreactivity in magnocellular nerve terminals.
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PMID:The kappa opioid receptor and dynorphin co-localize in vasopressin magnocellular neurosecretory neurons in guinea-pig hypothalamus. 1068 77


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