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

In order to elucidate the mechanism of prostaglandin F2 alpha (PGF2 alpha) action to onset of labor, the author observed the changes in maternal peripheral plasma oxytocin, progesterone, estradiol and cystine-aminopeptidase (CAP) activity around the onset of labor by PGF2 alpha. For the investigation, 66 normal pregnant women from 6 to 10 gestational months and same numbers from 39 to 41 gestational weeks were chosen. The blood samples for the latter were drawn just before drip infusion of PGF2 alpha, 5-minutes interval, 3-minutes interval of pain and just after labor. PGF2 alpha administered for labor induction intravenously, and 55 pregnant delivered. 1) The maternal peripheral mean plasma concentrations of them showed increase during pregnancy. There were positive correlations between oxytocin and progesterone, estradiol, CAP. 2) During labor, oxytocin levels increased significantly (p less than 0.01) and progesterone levels decreased significantly (p less than 0.01). On the other hand estradiol levels did not change significantly. CAP levels showed irregular changes. Estradiol-progesterone ratio showed gradual increase. 3) Then during labor, progesterone levels showed negative correlation with oxytocin levels. From this study, the results indicate that significant changes in oxytocin and progesterone and gradual increase estradiol-progesterone ratio are concerned in the onset of labor caused by PGF2 alpha, so labor may progress dynamically.
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PMID:[Changes of oxytocin, progesterone, estradiol and CAP around the labor by prostaglandin F2 alpha (author's transl)]. 694 20

To determine if oxytocin and estradiol were effected by pelvic neurectomy (PN), utero-ovarian vein blood was collected from PN rats during the preparturient period and assayed for these hormones. Radioimmunoassayable oxytocin levels were not significantly different in any groups of sham operated (S) or PN animals on days 21 and 22 or PN animals on days 23 and 24. Estradiol (E2) levels rose significantly on day 22 in S animals but there was no significant change in E2 in PN rats throughout the time period studied, although E2 levels were generally high. These results indicate that the blocked parturition characteristic of PN animals cannot be attributed to altered oxytocin levels. The lack of a significant E2 surge on day 22 in PN rats may contribute to the failure of utero-ovarian vein prostaglandin F levels to rise in these animals during the preparturient period.
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PMID:Plasma oxytocin and estradiol in pelvic neurectomized rats with blocked parturition. 712 50

It is not known whether the equine preovulatory follicle produces oxytocin or is a target tissue for oxytocin, as has been reported for other species, especially ruminants. Bovine granulosa cells secrete oxytocin, and oxytocin modulates the production of progesterone by granulosa cells in vitro. We examined whether oxytocin plays a comparable role in the equine preovulatory follicle. To test the hypothesis that the equine preovulatory follicle produces oxytocin during estrus and that its production increases in late estrus, preovulatory follicles were isolated during early (Days 1 to 2; n = 4) and late (Days 4 to 5; n = 4) estrus. Granulosa cells, pieces of theca interna and pieces of follicle wall (theca with attached granulosa cells) were cultured for 3 d with or without equine gonadotropins. Culture media were collected, replaced at 3, 6, 12, 24, 48, and 72 hr of culture, and assayed for oxytocin. Granulosa cells from preovulatory follicles secreted negligible amounts of oxytocin during 3 d of culture, irrespective of gonadotropin treatment or stage of estrus. Likewise, negligible amounts of oxytocin were measured in theca and follicle wall cultures at both developmental stages, in the presence or absence of gonadotropins. Furthermore, follicular fluid from early or late estrous follicles contained only negligible amounts of oxytocin. To determine if oxytocin affects steroidogenesis by equine granulosa cells, granulosa cells from follicles obtained on Day 2 of estrus were cultured with graded doses of oxytocin (0, 1, 10, 100, and 1,000 ng/ml) in defined medium supplemented with testosterone (0.5 microM) and culture media were assayed for estradiol-17 beta and progesterone. Estradiol was secreted throughout the culture period, and its production was not significantly affected by oxytocin treatment (P > 0.05). Progesterone secretion was relatively low during the first 24 hr of culture, increased dramatically on the second day of culture, and remained high through the third day. No dose of oxytocin had a significant effect on progesterone secretion (P > 0.05). In conclusion, the results indicate that equine preovulatory follicles, isolated during early or late estrus, are neither a source of oxytocin nor a target for oxytocin action on steroidogenesis. Although ovarian oxytocin appears to play a role in regulating follicular function in some other mammalian species, our data provide no support for such a role for oxytocin in mares.
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PMID:Oxytocin in mares: lack of evidence for oxytocin production by or action on preovulatory follicles. 760 Jul 64

Neuroactive steroid modulation of GABAA receptors was investigated in the peptidergic nerve terminals of the posterior pituitary using patch clamp techniques. In common with GABAA receptors in cell bodies, the nerve terminal GABAA receptor was potentiated by the synthetic steroid alphaxalone and by physiological concentrations of the progesterone metabolite allopregnanolone. Both of these agents enhanced Cl- currents elicited by GABA. Estradiol-17 beta had a weak inhibitory effect on GABA responses of nerve terminals, but only at high concentrations. The potentiating action was manifest as an increase in the probability of channel opening, with no effect on the rate of desensitization of the GABAA receptor. Neuroactive steroids enhanced GABA-gated Cl- channel activity in cell-free membrane patches, thus demonstrating a membrane delimited response. These results indicated that with regard to allosteric modulation by neuroactive steroids, the nerve terminal GABAA receptor is similar to the GABAA receptors of nerve cell bodies and endocrine cells. Neuroactive steroids are thus capable of altering the chemosensitivity of nerve terminal membranes by enhancing GABA inhibition at this location. The neuroactive steroid sensitivity of nerve terminal GABAA receptors provides a pathway by which gonadal steroid derivatives could regulate peptide secretion from neurosecretory neurons. Such a pathway could participate in the coordination of neuropeptide secretion during complex neuroendocrine functions. With specific regard to the neurohypophysis, neuroactive steroid-induced changes in the sensitivity of nerve terminal GABAA receptors could play a role in the initiation of oxytocin secretion during the transition between pregnancy and parturition.
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PMID:Neuroactive steroids modulate GABAA receptors in peptidergic nerve terminals. 782 23

Human myometrium contains hCG/LH receptors. There are fewer of these receptors during labor compared to no labor at preterm or term deliveries. Exogenous hCG can directly inhibit oxytocin-stimulated human myometrial contractions. These findings suggest that hCG may directly maintain myometrial quiescence during pregnancy. As maintenance of uterine quiescence may involve down-regulation of myometrial gap junctions, we investigated the effect of hCG on connexin-43 (CX-43) gene expression from RNA to protein and morphological gap junctions. The addition of 5 or 10 nM highly purified hCG to subconfluent cultures of pregnant myometrial smooth muscle cells resulted in a significant decrease in CX-43 protein levels. Higher hCG concentrations (100 and 1000 nM), however, had no effect. The maximal effect of hCG was seen at 4-8 h of culture, followed by recovery after a longer duration of culture. hCG treatment also concomitantly decreased CX-43 messenger RNA and morphological gap junctions. The hCG effect on CX-43 protein levels is hormone specific and mediated by protein kinase-A signaling. Estradiol and oxytocin increased, whereas progesterone decreased, CX-43 protein levels and morphological gap junctions. The oxytocin-induced increase was reversed by cotreatment with hCG. Although RU 486 alone had no effect on CX-43 protein levels, it prevented the down-regulating action of hCG and progesterone. In summary, our results demonstrate that hCG can directly decrease CX-43 messenger RNA, protein, and morphological gap junctions in cultured pregnant human myometrial smooth muscle cells. The hCG action is concentration and time dependent, hormone specific, and mediated by protein kinase-A signaling and appears to involve progesterone receptors. These data lend support to the concept that hCG could be one of the hormones responsible for maintaining uterine quiescence by down-regulating myometrial gap junctions during pregnancy.
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PMID:Novel regulation of pregnant human myometrial smooth muscle cell gap junctions by human chorionic gonadotropin. 798 70

Previous reports have suggested that gonadotropins, estradiol, and prostaglandin F2 alpha (PGF2 alpha) have varying effects on progesterone and oxytocin synthesis or secretion in cultured granulosa and luteal cells collected at different stages of the estrous cycle. The experiments reported here were designed to investigate whether effects of these agonists on secretion of hormones and their coupling to second messenger systems changed around the time of ovulation. Granulosa cells and Day 2 luteal cells of the ewe were cultured for three days and then treated for 30 min with varying doses of PGF2 alpha, LH, or estradiol. LH increased intracellular cAMP at both stages, but granulosa cells were more responsive in terms of both minimum effective dose (10 compared with 100 ng/ml) and degree of stimulation. LH caused no change in intracellular inositol phosphate levels. Both granulosa and early luteal cells responded to LH treatment by an increase in progesterone output in a dose-responsive fashion. PGF2 alpha increased inositol phosphate accumulation in cells collected at both stages of the cycle. All doses tested (10(-6)-10(-8) M) stimulated the release of oxytocin into the culture medium from both granulosa and luteal cells. Progesterone secretion was also increased, but only at the highest dose (10(-6) M). Estradiol treatment (10(-6) M) did not affect either the inositol phosphate or cAMP second messenger systems, but it did inhibit the secretion of oxytocin from granulosa cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Acute effects of prostaglandin F2 alpha, luteinizing hormone, and estradiol on second messenger systems and on the secretion of oxytocin and progesterone from granulosa and early luteal cells of the ewe. 819 57

The peptide hormone oxytocin (OT) and its mRNA are synthesized by bovine granulosa cells. Bovine granulosa cells isolated before the preovulatory LH/FSH surge secrete low amounts of OT and respond to gonadotropins with an increase in OT secretion. After the LH/FSH surge, basal OT secretion increases 20-fold. At the same time, dramatic changes in steroidogenesis occur in the preovulatory follicle. Estradiol-17 beta production is high before and declines after the LH surge. The objective of this study was to determine whether steroid hormones, particularly estradiol-17 beta, influence OT secretion by bovine granulosa cells. Heifers (n = 5) were injected with prostaglandin F2 alpha (PGF2 alpha) on Day 7 of the estrous cycle to induce luteolysis. Preovulatory follicles were obtained during the ensuing follicular phase, 24 h after PGF2 alpha injection (about 24-36 h before the expected time of the preovulatory LH/FSH surge). Granulosa cells were isolated and cultured for 5 days in defined medium containing graded doses (0, 0.001, 0.01, 0.1, 1, 10 micrograms/ml) of estradiol-17 beta, testosterone, or progesterone. Media were collected daily and assayed for OT by radioimmunoassay. Addition of 0.001 or 0.01 micrograms estradiol-17 beta/ml stimulated OT secretion by granulosa cells by about 75% during the last 2 days of culture (p < 0.01). In contrast, estradiol-17 beta at high doses (1 and 10 micrograms/ml) inhibited OT secretion by 45-85% (p < 0.01). Therefore, estradiol-17 beta had a biphasic effect on OT secretion by granulosa cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Estradiol-17 beta has a biphasic effect on oxytocin secretion by bovine granulosa cells. 831 93

Despite the widespread clinical use of oxytocin (OT) as a potent and specific stimulant of labor, previous research data have not supported a role for OT in the physiology of normal human parturition. We have demonstrated synthesis of OT mRNA in amnion, chorion, and decidua using Northern blot analysis, ribonuclease protection assays, and in situ hybridization. Probes directed towards both the 3' and 5' ends of the gene have been used. Levels were highest in decidua with considerably less in chorion and amnion and very low levels in placenta. The transcript size in decidua appears to be 60-80 nucleotides smaller than the transcripts in amnion and chorion. OT gene expression in chorio-decidual tissues increased three- to fourfold around the time of labor onset. Estradiol stimulated synthesis of OT mRNA during in vitro incubation. These results support the hypothesis of a paracrine system involving OT and sex steroids within intrauterine tissues wherein significant changes could occur without being reflected in the maternal circulation. Such a paracrine system could rationalize a long-sought role for oxytocin in the physiology of human labor. These data may lead to novel approaches towards prevention or treatment or preterm labor.
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PMID:Synthesis of oxytocin in amnion, chorion, and decidua may influence the timing of human parturition. 842 17

We have studied oxytocin (OT) gene expression, secretion, and action in bovine preovulatory follicles during the follicular phase of the estrous cycle. OT is secreted in vitro by follicular granulosa cells, but not by theca cells. Both OT content of granulosa cells and their ability to secrete OT in culture increased dramatically when follicles were obtained after the gonadotropin surge (LH surge) that triggers ovulation. These changes were correlated with increased levels of messenger RNA (mRNA) for OT in granulosa cells obtained after vs. before the LH surge. When granulosa cells were obtained before the surge, both OT secretion and OT mRNA levels increased with time in culture, and the increases were greatly enhanced in the presence of LH. Estradiol, at concentrations found in follicular fluid of preovulatory follicles before the LH surge, inhibited OT secretion in vitro, whereas concentrations found in follicular fluid after the LH surge were not inhibitory. Progesterone, at physiological concentrations, stimulated OT secretion in vitro. We have shown previously that OT increases progesterone secretion by granulosa cells obtained before the LH surge. Taken together these results show that, during the follicular phase in cattle, OT secretion and gene expression are coordinately regulated and suggest that they are regulated by both gonadotropins and intrafollicular steroids. Increases in OT after the LH surge may play a role in the follicular/luteal phase shift in steroidogenesis from estradiol/androgen to progesterone.
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PMID:Oxytocin gene expression and action in bovine preovulatory follicles. 851 53

Using in situ hybridization methods that discriminate mRNAs encoding rat vasopressin V1a, V1b, V2 and oxytocin receptors in hepatic, brain and renal tissues, experiments were done to determine whether estrogen and/or progesterone influence renal vasopressin receptor (VR) or oxytocin receptor (OTR) transcripts. Estrogen induced OTR gene expression in the outer stripe of the outer medulla and increased expression of OTRs in macula densa cells. Outer stripe OTR mRNA peaked with 4 days of estrogen treatment, and decreased to undetectable levels with 31 days of treatment of ovariectomized females. Estradiol's induction of outer stripe OTR mRNA expression was blocked by the antiestrogen, tamoxifen, but was not affected by high levels of circulating oxytocin. A role for OTRs in regulating renal function independently of adrenal steroids was suggested by findings that adrenalectomized males showed high levels of OTR transcripts in outer stripe proximal tubule and cortical macula densa cells after 5 and 10 micrograms/100g of estradiol. Consistent with specialized roles for OTRs during female reproduction, OTR transcripts could not be detected in renal tissues of peri-parturient females, at times when OTR mRNA levels were very high in uterus. OTR gene expression in macula densa cells reappeared 4-8 days into lactation and attained control levels by day 20. Physiological experiments showed that estrogen + oxytocin decreased plasma [Na+] levels in ovariectomized rats at a time when proximal tubule OTR expression is maximal. These data are consistent with 1) cell-specific regulation by estrogen of renal OTR gene expression and 2) the possibility that OTRs may be important mediators of steroid-induced alterations in renal fluid and/or solute reabsorption.
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PMID:Oxytocin receptor gene expression in female rat kidney. The effect of estrogen. 871 83


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