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

We conducted this study to determine what receptor mediates the effect of oxytocin to increase osmotic water permeability (Pf) in the rat inner medullary collecting duct (IMCD). Reverse transcription-polymerase chain reaction (RT-PCR) experiments demonstrated that mRNA for both the oxytocin receptor and the V2 receptor is present in the rat terminal IMCD. In isolated perfused IMCD segments, we found that the V2 vasopressin receptor antagonist [d(CH2)5(1),D-Ile2,Ile4,Arg8]vasopressin, but not oxytocin receptor antagonists, blocked the hydrosmotic response to 200 pM oxytocin. The selective oxytocin receptor agonist [Thr4,Gly7]oxytocin did not increase water permeability. Oxytocin also increased urea permeability in IMCD segments. Studies in IMCD suspensions showed that oxytocin increases adenosine 3',5'-cyclic monophosphate production in a dose-dependent fashion with a half-maximal (EC50) response at 5.2 nM. The dose-response curves were virtually identical for IMCD suspensions from Sprague-Dawley rats and Brattleboro rats. The oxytocin dose-response curve was displaced to the right of the vasopressin dose-response curve (EC50, 0.44 nM). From these results, we conclude that the V2 receptor mediates the hydrosmotic action of oxytocin in rat IMCD.
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PMID:Oxytocin as an antidiuretic hormone. II. Role of V2 vasopressin receptor. 763 34

The effect of the neurohypophysial hormones oxytocin and arginine vasopressin (AVP) on testicular steroidogenesis was reevaluated by use of short-term (< 10 h) cultures of isolated adult rat Leydig cells. Oxytocin at 10(-9), 10(-7), and 10(-5) M concentrations significantly increased basal testosterone production in a dose-dependent manner but had no effect on LH-stimulated testosterone production. The specificity of the effect was determined by use of the specific oxytocin receptor antagonist (OTA). OTA from 10(-9) to 10(-5) M concentrations inhibited the oxytocin-stimulated increase in testosterone production. Furthermore, the oxytocin agonist Thr4 Gly7 oxytocin also induced a dose-dependent increase in basal testosterone production. In contrast, AVP from 10(-9) to 10(-5) M concentrations did not consistently affect basal testosterone production by isolated Leydig cells, but significantly decreased LH-stimulated testosterone production. Inclusion of 10(-7) and 10(-5) M OTA with 10(-7) M AVP did not alter the inhibitory effect of the AVP. These data show that oxytocin and AVP have different effects on testosterone production by Leydig cells in vitro and support the hypothesis that oxytocin acts in the testis through a specific oxytocin receptor.
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PMID:Effect of oxytocin on testosterone production by isolated rat Leydig cells is mediated via a specific oxytocin receptor. 763 35

We have investigated changes in endometrial oxytocin receptor concentrations and prostaglandin F2 alpha release in response to exogenous oxytocin treatment in ovariectomized cows treated with progesterone and oestradiol, and made comparisons with similar treatment in cyclic cows. In long-term ovariectomized cows, endometrial oxytocin receptors were present (300 fmol mg-1 protein), but no prostaglandin F2 alpha was released in response to oxytocin treatment until after the administration of progesterone. Subsequent administration of a concentration of oestradiol sufficient to induce oestrus resulted in the downregulation of these receptors and the loss of oxytocin responsiveness, which did not reappear within 20 days in the absence of further hormone treatment. When induced oestrus was followed by further treatment with luteal phase concentrations of progesterone and oestradiol, both oxytocin receptors and oxytocin-stimulated release of prostaglandin F2 alpha reappeared by day 16 after oestrus, in a pattern similar to that seen during the luteal phase of cyclic cows. These results demonstrate how progesterone and oestradiol control the development and responsiveness of endometrial oxytocin receptors in cows, and provide a valuable model in which to investigate further the precise control of the oxytocin receptor in this species.
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PMID:Control of endometrial oxytocin receptors and prostaglandin F2 alpha production in cows by progesterone and oestradiol. 770 3

A steroid-treated ovariectomized ewe model was used to investigate the role of progesterone pretreatment in the control of functional oxytocin receptor concentrations during the early luteal phase. Ovariectomized ewes (n = 28) were injected with oestradiol for 2 days (final injection = day 0) with or without progesterone pretreatment (progestagen sponge for 10 days). Ewes were then given high or low concentrations of progesterone combined with high, low or zero concentrations of oestradiol in a pattern known to simulate the early luteal phase profile (n = 4 per group). Ewes were given 1 microgram oxytocin (i.v.) on day 4 and plasma was collected to assay 13,14-dihydro-15-keto PGF2 alpha. The concentration of progesterone and oestradiol administered had no effect on the concentration of 13,14-dihydro-15-keto PGF2 alpha following oxytocin administration (P > 0.05). However, the group that was not pretreated exhibited a small but significant 13,14-dihydro-15-keto PGF2 alpha response in comparison with the equivalent pretreated group (P < 0.05). In a subsequent study, ewes were divided into groups pretreated and not pretreated with progesterone; both groups were given oestrous concentrations of oestradiol and high concentrations of progesterone and oestradiol together. On day 0, 2, 3 or 4, ewes from each group (n = 3, 3, 4 and 4, respectively) were given 1 microgram of oxytocin i.v., and the endometrium was collected to measure the binding of oxytocin receptors. Oxytocin caused a significant (P < 0.05) increase in the concentration of 13,14-dihydro-15-keto PGF2 alpha in all ewes on day 0 but not on days 2, 3 or 4. Oxytocin receptor concentrations were maximal on day 0 and basal by day 4.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of progesterone pretreatment on the oxytocin receptor concentration and the response to oxytocin during the simulated early luteal phase in the ovariectomized ewe. 779 26

The multiple hormonal and neurotransmitter functions of the nonapeptide oxytocin are mediated by specific oxytocin receptors (OTRs). In most target tissues, the number of OTRs is strongly regulated. Specifically, in the uterus, a dramatic OTR upregulation precedes the onset of parturition. To study the molecular mechanisms underlying OTR regulation, we have isolated and characterized recombinant bacteriophage lambda EMBL3 genomic clones containing the rat OTR gene, using sequence information derived from a human myometrial OTR cDNA. The rat OTR gene spans > 20 kb and contains three exons. A 97-bp intron is in the 5' untranslated region and a > 12-kb intron interrupts the coding region between transmembrane domains 6 and 7. The promoter region lacks an apparent TATA or CCAAT box but contains multiple putative interleukin-response elements [six NF-IL6 (C/EBP beta) and four APRF (STAT3) binding motifs], supporting the notion that interleukins may mediate labor induction via transcriptional activation of the OTR gene. The predicted amino acid sequence is 93% identical to the human OTR sequence but only 48% and 38% identical to the rat V1 and V2 vasopressin receptor sequences, respectively. At parturition, the OTR gene is highly expressed in the rat uterus and gives rise to at least three transcripts (2.9, 4.8, and 6.7 kb) which differ in the length of their 3' untranslated regions.
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PMID:Structure, characterization, and expression of the rat oxytocin receptor gene. 781 17

In situ hybridization techniques were used in the present study to detect hypothalamic expression of the oxytocin receptor (OR) gene. Binding studies have localized OR to various brain regions and have detected a high density of receptors in the ventromedial hypothalamus (VMH), a documented target of estrogen action. This study was designed to compare levels of OR messenger RNA (mRNA) in the VMH of male and female rats and to study the effects of estrogen treatment on mRNA levels in the VMH of female rats. After cloning a rat OR gene from a genomic testes library, a probe was generated for use in in situ hybridization assays to evaluate sex differences in OR mRNA expression in the VMH. In addition, ovariectomized females were treated with estrogen, and VMH OR mRNA expression was compared with that in ovariectomized or intact females. The results of these studies showed that male rats expressed higher levels of OR mRNA in the VMH than females. Estrogen-treated ovariectomized females exhibited significantly greater expression in the VMH than either oil-treated or intact females. These results support binding studies that have shown oxytocin binding in the VMH to be regulated by gonadal steroids and suggest that estrogen may either directly or indirectly regulate transcription of the OR gene.
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PMID:Sex differences in and effects of estrogen on oxytocin receptor messenger ribonucleic acid expression in the ventromedial hypothalamus. 782 41

Oxytocin stimulates phosphoinositide turnover in myometrium. To elucidate whether the coupling mechanism involves the interaction of oxytocin receptor with GTP-binding proteins, we examined oxytocin stimulation of guanosine triphosphatase (GTPase) activity and phospholipase-C activity in rat and human myometrial membranes. Oxytocin consistently stimulated both GTPase and phospholipase-C activities, and both stimulations were attenuated by an antibody directed against the carboxyl-terminals of the GTP-binding proteins, G alpha q and G alpha 11. Neutralization of the antibody by preincubation with antigenic peptide reversed this inhibition. [Thr4,Gly7]oxytocin, a specific oxytocin receptor agonist, stimulated both GTPase and phospholipase-C activities, and the stimulations were also inhibited by anti-G alpha q/11 IgG. Immunoreactive GTP-binding proteins, G alpha q and G alpha 11, and phospholipase-C beta 3 isoforms were present in myometrial membranes. These results indicate that stimulation of phospholipase-C activity by oxytocin in myometrium is mediated via G alpha q, G alpha 11, or a closely related GTP-binding protein, probably coupling to phospholipase-C beta.
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PMID:Oxytocin stimulates myometrial guanosine triphosphatase and phospholipase-C activities via coupling to G alpha q/11. 789 60

Estrogens have been implicated in the sodium and fluid imbalances associated with the menstrual cycle and late pregnancy. An estrogen-dependent role for renal oxytocin receptors in fluid homeostasis is suggested by the present findings which demonstrate that estradiol benzoate treatment increases the expression of the oxytocin receptor messenger ribonucleic acid and 125I-OTA binding to oxytocin receptors in the renal cortex and medullary collecting ducts of ovariectomized female rats. Moreover, estradiol induced high levels of oxytocin receptor expression in outer stripe proximal tubules of ovariectomized female and adrenalectomized male rats. Proximal tubule induction was inhibited in a dose-dependent manner by the antiestrogen tamoxifen, but cortical expression of oxytocin receptors in macula densa cells was unaffected by tamoxifen. These data demonstrate cell-specific regulation of oxytocin receptor expression in macula densa and proximal tubule cells, and suggest a important role for these receptors in mediating estrogen-induced alterations in renal fluid dynamics by possibly affecting glomerular filtration and water and solute reabsorption during high estrogen states.
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PMID:Estrogen increases renal oxytocin receptor gene expression. 789 93

Prairie voles (Microtus ochrogaster) are monogamous mammals that form male-female pair bonds. Partner preference formation, one component of the pair bond in prairie voles, occurs following male-female cohabitation and is facilitated by mating. The peptide hormone oxytocin is released during physical contact and particularly following vaginal stimulation. Oxytocin has been implicated in mother-infant bond formation. The present study tested the hypothesis that oxytocin participates in the partner preference component of pair bond formation in adult prairie voles. Ovariectomized female prairie voles were implanted with osmotic mini-pumps releasing oxytocin (1-100 ng/h) or artificial cerebrospinal fluid (CSF). Pumps were implanted intracerebroventricularly or subcutaneously and females then were housed for 6 h with a male partner, followed by a preference test in which females could elect to spend time with either the partner or an unfamiliar male. Females in groups that received centrally-administered oxytocin (10 or 100 ng/h), but not CSF, exhibited a significant preference for the partner present during infusion. The induction of a partner preference after oxytocin administration appeared specific for central oxytocin pathways as peripheral oxytocin administration was ineffective. Moreover, central administration of a selective oxytocin receptor antagonist inhibited the behavioral effect of exogenous oxytocin. These results suggest that oxytocin may be one factor contributing to the development of partner preferences in this monogamous rodent.
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PMID:Oxytocin administered centrally facilitates formation of a partner preference in female prairie voles (Microtus ochrogaster). 792 May 90

We describe here the binding and functional properties of a cloned human oxytocin receptor (OTR). We established a transient OTR expression system on COS-1 cells, which do not express vasopressin receptors. With the transfected cells and [3H]oxytocin, the dissociation constant (Kd) of OTR to oxytocin was 6.0 +/- 1.1 nmol/l; the binding properties of several oxytocin-related peptides were also examined. The functional properties of OTR were determined by an electrophysiological method, using a Xenopus laevis oocyte injected with in vitro transcribed OTR mRNA. These two methods showed that [Phe2,Orn8]vasotocin, a vasopressin agonist, was an OTR antagonist. A combination of these methods using cloned OTR cDNA is a novel and effective method for the investigation of oxytocin-related ligands.
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PMID:Molecular characterization of a cloned human oxytocin receptor. 792 Dec 28


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