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

The neurohypophysial hormone oxytocin has previously been found in the ovaries of several animal species. In ruminants ovarian oxytocin is postulated to have a luteolytic function, because of its high concentrations in the corpus luteum. In primates the role of ovarian oxytocin is not known. In the present study we measured the immunoreactive oxytocin and oxytocin-neurophysin content in paired ovaries removed from cynomolgus monkeys (Macaca fascicularis) during the late luteal phase of the cycle (Days 12-14 of the luteal phase or Days 26-28 of a menstrual cycle). Each animal was pulsed with synthetic gonadotropin-releasing hormone to maintain normal menstrual cyclicity. The concentration of oxytocin and its neurophysin during the late luteal phase was greater in the non-corpus luteum than corpus luteum-bearing ovary. By high pressure liquid chromatography and bioassay the oxytocin in both the corpus luteal and non-corpus luteal ovaries was similar to synthetic and posterior pituitary oxytocin. The finding of high concentrations of immunoreactive oxytocin in the non-corpus luteum-bearing ovary suggests that the function of ovarian oxytocin in primates may not be confined specifically to the corpus luteum.
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PMID:Ovarian oxytocin and neurophysin concentrations in the cynomolgus monkey (Macaca fascicularis). 232 7

Previous studies have suggested the subfornical organ (SFO) to be the CNS site at which circulating angiotensin (ANG) acts to influence a variety of regulatory control mechanisms. We have utilised electrophysiological techniques: 1. to examine the neural connections through which the SFO exerts such control over hypothalamic regulatory control centres; 2. to investigate the responsiveness of neurons in a second circumventricular organ, the area postrema (AP), to circulating peptides. In accordance with previous endocrine studies we have demonstrated excitatory influences of SFO efferents on hypothalamic neurosecretory neurons putatively identified as vasopressin, oxytocin, CRH, and LHRH secreting. In addition systemic ANG increased the activity of the former three groups of these neurons, an effect which was abolished by destruction of the SFO. Single unit recordings from AP neurons have demonstrated subpopulations of cells in this regions to be sensitive to either circulating ANG or changes in blood pressure.
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PMID:Circumventricular structures: CNS sensors of circulating peptides and autonomic control centres. 236 60

Characterization of specific vasopressin binding sites was investigated in purified mouse Leydig cells using tritiated arginine-vasopressin. Binding of radioligand was saturable, time- and temperature-dependent and reversible. (3H)-AVP was found to bind to a single class of sites with high affinity (Kd = 2.20 +/- 0.18 nM) and low capacity (Bmax = 17.4 +/- 1.8 fmol/10(6) Leydig cells). Binding displacements with specific selective analogs of AVP indicated the presence of V1 subtype receptors on Leydig cells. The ability of AVP to displace (3H)-AVP binding was greater than LVP and oxytocin. The unrelated peptides, somatostatin and substance P, were less potent, while neurotensin and LHRH did not displace (3H)-AVP binding. The time-course effects of AVP-pretreatment on basal and hCG-stimulated testosterone and cAMP accumulations were studied in primary culture of Leydig cells. Basal testosterone accumulation was significantly increased by a 24 h AVP-pretreatment of Leydig cells (P less than 0.001). This effect was potentiated by the phosphodiesterase inhibitor (MIX) and was concomitantly accompanied by a slight but significant increase in cAMP accumulation (P less than 0.01). AVP-pretreatment of the cells for 72 h had no effect on basal testosterone accumulation, but exerted a marked inhibitory effect on the hCG-stimulated testosterone accumulation (P less than 0.001). This reduction of testosterone accumulation occurred even in the presence of MIX and was not accompanied by any significant change of cAMP levels. We conclude from these data that AVP is capable of modulating steroidogenesis in Leydig cells through specific and functionally V1 receptor subtype and postulate that this effect may be part of an intratesticular paracrine/autocrine control mechanism.
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PMID:Modulation of mouse Leydig cell steroidogenesis through a specific arginine-vasopressin receptor. 245 54

The neurotransmitter gamma-aminobutyric acid (GABA) appears to be involved in the control of gonadotropin secretion. These studies were conducted 1) to evaluate the effect of GABAergic drugs on in vitro LHRH secretion and 2) to characterize the role of different types of GABA receptors (the GABA-A and GABA-B subtypes) in these actions. Arcuate nuclei-median eminence fragments were incubated in vitro, and the release of LHRH, prostaglandin E2 (PGE2), arginine vasopressin, and oxytocin was measured by RIA. Both GABA and muscimol at different concentrations induced an increase in LHRH release, but did not affect the release of arginine vasopressin and oxytocin. This stimulatory effect was blocked by the specific GABA antagonist bicuculline, suggesting the involvement of GABA-A type receptors. Muscimol-stimulated LHRH release was not affected by the presence of phentolamine, suggesting that the stimulatory effect of GABA-A receptors on LHRH release is not mediated by interactions with the noradrenergic system. PGE2 has been shown to be a potent secretagogue of LHRH from the median eminence in vitro, and in this model the stimulatory effect of PGE2 was enhanced by muscimol. Baclofen, a specific GABA-B type receptor agonist, had no effect on basal LHRH release, but completely suppressed naloxone-stimulated LHRH and PGE2 secretion. The inhibitory effect of baclofen was blocked by the presence of 5-aminovalerate, a drug that has been shown to block the inhibitory effect of baclofen on NE release from noradrenergic terminals. This suggests the possibility that GABA-B receptors interacting with noradrenergic terminals may be responsible for the inhibitory effect of baclofen on naloxone stimulation. This study uncovered both stimulatory and inhibitory effects of GABA on LHRH release after activation of GABA-A or GABA-B receptors, respectively. Further, the data show possible relationships among the GABAergic, endogenous opiate peptide, and noradrenergic systems in the control of LHRH release from the hypothalamus.
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PMID:Different gamma-aminobutyric acid receptor subtypes are involved in the regulation of opiate-dependent and independent luteinizing hormone-releasing hormone secretion. 254 12

As a first step to investigate whether gonadotropin releasing hormone (GnRH) analogs might be able to modulate directly the proliferation of human epithelial ovarian carcinomata, we checked if binding sites for GnRH are present in these malignancies. Specific binding of [125I][D-Ala6-des Gly10]-GnRH-ethylamide (GnRH agonist = GnRH-A) could be demonstrated in plasma membranes from 32 out of 40 ovarian carcinomata tested. This binding was dependent on temperature, time and plasma membrane concentration. Mathematical analysis of the binding data showed that the interaction of GnRH-A with the binding sites was consistent with a single class of low affinity, high capacity binding sites (Ka = 1.42 +/- 0.14 X 10(5) M-1; range: 0.3-3.8 X 10(5) M-1; R = 209 +/- 69 X 10(-12) M/mg membrane protein; range 16-400 X 10(-12) M/mg MP; means +/- S.E., n = 32). Native GnRH and the GnRH antagonist [D-p-Glu1, D-Phe2, D-Trp3,6]-GnRH had Ka values comparable to those of the GnRH-A used. [125I]GnRH-A binding could not be displaced by oxytocin, thyrotropin releasing hormone and corticotropin releasing factor in concentrations up to 10(-4) M. Somatostatin cross-reacted with binding sites from some carcinomata, while it did not displace GnRH-A binding in membranes from others. Though the functional role of this specific binding site for GnRH in human epithelial ovarian carcinomata is still obscure, it might be part of an autocrine regulatory system and provide a possible point of attack for therapeutic approaches using GnRH analogs in this malignancy.
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PMID:Gonadotropin releasing hormone binding sites in human epithelial ovarian carcinomata. 264 75

The ontogenic development of some hypothalamic neuropeptides: luteinizing hormone releasing hormone (LHRH); somatostatin (SRIF) and neurophysin (NF) and their localization in the hypothalamus of fetuses in different stages of the fetal life were studied by immunoperoxidase method. It was found that differentiation of the neurons which produce the examined hormones begins in the midstage of pregnancy. LHRH is stored in the nerve terminals of the median eminence (ME) and organum vasculosum of the lamina terminalis (OVLT) since 72 day of gestation and its amount gradually increases with the development of the embryo. In this stage a few immunoreactive (ir) LHRH perikarya appear but they are most numerous in the last days of pregnancy (110 day). They are localized in the most anterior periventricular parts of the hypothalamus, area preoptica, diagonal band of Broca and very rare in the medial-basal hypothalamus. Somatostatin is produced in the separate neuronal system and appears in the last days of fetal life. Neurophysin is present in both magnocellular nuclei in 72 day-old fetuses, but at the end of gestation it is seen also in some preoptico-septal region.
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PMID:Ontogeny of neuropeptidergic systems: luteinizing hormone releasing hormone (LHRH); somatostatin (SRIF) and neurophysin (NF) in the hypothalamus of the domestic pig by immunocytochemistry. 286 38

Oxytocin, vasopressin, melanostatin, bradykinin, LHRH-like peptide in different ways affected the spontaneous outflow and release of adrenaline and noradrenaline induced with central and peripheral nervous stimuli as well as with acetylcholine in the superfusate of the dog isolated inferior mesenteric ganglion.
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PMID:[Peptide modulation of spontaneous and evoked catecholamine release in the caudal mesenteric ganglion of the dog]. 287 2

1. We have reviewed recent studies in which in situ hybridization histochemistry (ISHH) was used to investigate the regulation of expression of neurohypophysial peptides and hypothalamic releasing hormones. 2. ISHH is a technique in which the presence and quantity of a specific mRNA can be determined in tissue sections with a high degree of resolution and sensitivity. 3. ISHH has been used to measure changes in cellular levels of mRNAs encoding vasopressin, oxytocin, corticotropin-releasing factor, gonadotropin-releasing hormone, thyrotropin-releasing hormone and somatostatin in response to various physiological challenges. 4. A theme emerging from these studies is that changes in levels of mRNA encoding neuroendocrine peptides reflect changes in biosynthesis and secretion.
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PMID:Neuroendocrine gene expression in the hypothalamus: in situ hybridization histochemical studies. 289 79

The effects of oxytocin (OT) on gonadotropin-releasing hormone (GnRH) release from the adult male rat mediobasal hypothalamus and median eminence were studied in an in vitro incubation system. OT induced a dose-related (10(-13) to 10(-9) M) inhibition of both basal and KCl-stimulated GnRH release from the mediobasal hypothalamus. OT, but not arginine vasopressin, also inhibited GnRH release from the isolated median eminence, and this inhibition was blocked by treatment with an OT receptor antagonist. Moreover, antagonist alone stimulated GnRH release from the isolated median eminence. These results demonstrate that OT can inhibit in vitro release of GnRH by an OT receptor mediated mechanism at the level of neurosecretory terminals in the median eminence and suggest that the hypothalamic OT neuronal system may play an inhibitory role in the modulation of GnRH secretion.
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PMID:GnRH release from the mediobasal hypothalamus. In vitro regulation by oxytocin. 300 97

The binding sites for [125I]LHRH were characterized in membranes from the hypthalamus and the effect of estrogen on the binding characteristics was studied in ovariectomized female rats. The radioligand, [125I]LHRH, was found to bind specifically to membranes from the hypothalamus at a maximal level, with an optimal temperature of 0 degrees C and a pH between 7 and 8. The binding was enhanced by NaCl at a concentration of 0.1-0.2 M. The specifically bound [125I]LHRH was only displaced by LHRH, but not by sodium iodide (NaI), bovine serum albumin and other hormones, such as thyrotropin-releasing hormone, bradykinin, oxytocin, prolactin, luteinizing hormone and growth hormone. The divalent metal ions, copper (Cu2+) and mercury (Hg2+), inhibited the specific binding of [125I]LHRH completely, whereas magnesium (Mg2+) and calcium (Ca2+) caused a decrease in binding. As revealed from Scatchard plot analysis, the binding sites for [125I]LHRH in the hypothalamus had a dissociation constant of 0.40 +/- 0.03 microM and the maximum number of binding sites was 98.55 +/- 4.34 pmol/mg protein. Treatment of female rates (ovariectomized for 3 weeks) with 4 micrograms of estradiol benzoate caused a statistically significant decrease in the maximal number of binding sites without any significant effect on the dissociation constant. However, the direct addition of estradiol hemisuccinate to the membrane preparations had no statistically significant effect on the specific binding of [125I]LHRH. The present study provides the evidence that estrogen decreases the density of binding sites for [125I]LHRH in the hypothalamus in vivo.
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PMID:The effect of estrogen on luteinizing hormone-releasing hormone binding sites in hypothalamic membranes. 331 92


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