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

The secretion of oxytocin by the corpus luteum is thought to stimulate the episodic release of PGF-2 alpha from the uterus, thereby contributing to luteolysis. In pregnancy corpus luteum function is maintained, and secretion of oxytocin, or its actions on the uterus, appear to be inconsistent with the successful establishment of gestation. Protection against the effects of oxytocin is ensured by a number of mechanisms, including the cessation of luteal oxytocin secretion, which is evident by Day 20 after mating in sheep, and the maintenance of low levels of the oxytocin receptor in the uterus.
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PMID:Ovarian oxytocin and the maternal recognition of pregnancy. 300 1

The nature of the neurohypophyseal peptide receptor in the anococcygeus muscles from male mice was investigated. The rank order of potency of naturally occurring peptides was oxytocin greater than Arg-vasotocin greater than Arg-vasopressin greater than Lys-vasopressin, which is similar to that found in the uterus and mammary gland. Selective agonists on the oxytocin (OT) receptors of the uterus and mammary gland (Thr4-OT; Gly7-OT; Thr4-Gly7-OT) were also potent agonists in the mouse anococcygeus. Competitive antagonists of uterine responses to oxytocin (dP-TyrMe-Thr4-OT; dP-TyrMe-OT; dP-Thr4-OT; dp-Orn8-OT) were also competitive antagonists of oxytocin-induced contractions of the mouse anococcygeus. It is concluded that the neurohypophyseal peptide receptor of the male mouse anococcygeus is of the oxytocin type; antagonist pA2 values suggest that this receptor resembles, but may not be identical to, the uterine oxytocin receptor. Possible physiological and pharmacological implications of these observations are discussed.
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PMID:An oxytocin receptor in anococcygeus muscles isolated from male mice. 301 Nov 70

We examined the relation between increased uterine oxytocin receptor concentration and increased in vivo sensitivity of the rabbit uterus to oxytocin at the end of gestation. We determined oxytocin receptor concentrations in myometrium and decidua on different days near term of gestation and postpartum. We also examined the in vitro contractile response to oxytocin on days 30 and 5 days postpartum, when the uterus is unresponsive in vivo, and on day 31 (term), when the uterus is exquisitely sensitive to this hormone in vivo. In addition, we tested the role of endogenous eicosanoids and decidual oxytocin receptors in the myometrial contractile response to oxytocin by examining the contractile response in the presence of the cyclooxygenase/lipoxygenase inhibitor sodium meclofenamate or in muscle strips from which the decidua had been removed by scraping. The concentration of specific binding sites for [3H]oxytocin in myometrial and also decidual membrane preparations was determined. We demonstrate that contractile sensitivity to oxytocin increases at least 4-fold between days 30 and 31 (term) of gestation, and this is accompanied by a nearly 10-fold increase in the concentration of oxytocin-binding sites in both decidua and myometrium. The lesser sensitivity to oxytocin on day 30 was, however, only apparent in the presence of meclofenamate, which suggests that endogenous eicosanoids contribute to the preterm response to oxytocin measured in vitro. The maximal response to oxytocin (integrated area) increased 2-fold between day 30 and term. Thus, an increase in both sensitivity and maximal response to oxytocin could be demonstrated at term in vitro. Five days after parturition, maximal response and uterine sensitivity measured in the presence of meclofenamate had returned to those of the preterm uterus, and the concentration of oxytocin-binding sites had declined. In contrast, sensitivity and maximal response to the cholinergic agonist carbamylcholine declined between day 30 and term. These results support a highly regulated physiological role for oxytocin in parturition which depends primarily on changes in receptor concentration.
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PMID:Rabbit uterine oxytocin receptors and in vitro contractile response: abrupt changes at term and the role of eicosanoids. 301 54

Steroid-primed, ovariectomized ewes were treated intravenously with 2 doses of 1 microgram oxytocin at intervals of 1, 2, 4 or 6 h. The initial dose resulted in increases in 13,14-dihydro-15-keto-PGF-2 alpha in the peripheral circulation from 173 to 667 pg/ml within 5 min; subsequent doses caused responses of 23 +/- 1, 23 +/- 6, 54 +/- 12 and 62 +/- 10% respectively of the initial dose. Concentrations of oxytocin receptor in myometrium, caruncular endometrium and intercaruncular endometrium were, respectively, 185 +/- 33, 128 +/- 7 and 105 +/- 14 fmol/mg protein at 2 h after saline injection and 147 +/- 27, 195 +/- 52 and 170 +/- 50 fmol/mg protein at 2 h after administration of 1 microgram oxytocin. The dose of oxytocin administered was shown to raise circulating concentrations to levels characteristic of those observed during spontaneous episodes of release of oxytocin at luteolysis. Oxytocin administration therefore results in transitory uterine refractoriness which may be due to failure of a post-receptor response and this may contribute to the episodic nature of uterine prostaglandin secretion.
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PMID:Transient uterine refractoriness after oxytocin administration in ewes. 301 57

Myometrial and endometrial cells of sheep, rat, and calf in monolayer cell culture display at least three populations of binding sites for oxytocin, with dissociation constants (Kd) of approximately 5 X 10(-9), 4 X 10(-7), and greater than 10(-5) mol/liter, respectively. Binding of the tritium-labeled oxytocin (concentration range, 10(-11) to 5 X 10(-4) M) to the first two sites is displaceable by cold oxytocin. The ratio of binding capacities of the high to medium affinity site appears to average 1:18. Dissociation rate constants for these sites (22 degrees C) are roughly 10(-4) and 2 X 10(-3) s-1, respectively. The capacity of the low affinity site varies in individual cell preparations and is between 5 and 66 times that of the medium affinity site. The low affinity binding sites may not be fully saturable and may follow a nonasymptotic binding isotherm. Logarithms of Kd and binding capacity for individual binding sites are linearly correlated. The coexistence of the three sites was also proven by cluster analysis based on similarities between Kd, binding capacity, and Hill coefficient. Only minor systematic species and cell type differences occur in these properties. The value of Kd for the oxytocin receptor in rat myometrium, derived recently from a stepwise irreversible inhibition of uterotonic response to oxytocin, is close to 2.5 X 10(-7) mol/liter. Additional pharmacological data (pA2 values of structural analogues of oxytocin acting as competitive inhibitors) also reveal a Kd value of 3 X 10(-7). It is, therefore, concluded that the receptors for oxytocin in rat myometrium are identical with the medium affinity site.
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PMID:Binding of oxytocin to uterine cells in vitro. Occurrence of several binding site populations and reidentification of oxytocin receptors. 302 77

Both myometrial oxytocin and alpha 2-adrenergic receptors are induced by estrogen. To compare the regulation of these two receptor populations by progesterone, we measured myometrial receptor concentration in ovariectomized steroid-treated and in pregnant rabbits. To control for the effects of estrogen withdrawal, we used concomitant rather than sequential presentation of estrogen and progesterone in ovariectomized rabbits. Estradiol increased both myometrial oxytocin and alpha 2-adrenergic receptor concentrations in ovariectomized rabbits after 8 days of treatment. Simultaneous progesterone administration during the last 4 days of estradiol treatment reversed the induction of oxytocin, but not alpha 2-adrenergic, receptors. Similarly, administration of the antiprogestin RU 38486 to pregnant rabbits on day 27 of gestation resulted in premature delivery and evoked an increase in myometrial oxytocin receptor concentration mimicking that observed at term (day 31). However, RU 38486 did not significantly affect alpha 2-adrenergic receptor concentration. Our data provide further support for involvement of oxytocin receptors in parturition, but do not indicate a comparable function for myometrial alpha 2-adrenergic receptors.
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PMID:Rabbit myometrial oxytocin and alpha 2-adrenergic receptors are increased by estrogen but are differentially regulated by progesterone. 302 88

Administration of oestradiol-17 beta benzoate on Days 9 and 10 of the oestrous cycle resulted in episodic secretion of PGF-2 alpha (as indicated by elevated circulating concentrations of 13,14-dihydro-15-ketoprostaglandin F-2 alpha) and a decline in circulating progesterone. Release of PGF-2 alpha began 35 +/- 3 h after first injection of oestrogen and progesterone concentrations declined from 42 +/- 3 h. Secretion of oxytocin, which was first observed 26 +/- 3 h after oestrogen treatment, preceded secretion of PGF-2 alpha; 69% of pulses of oxytocin coincided with episodes of PGF-2 alpha secretion. Uterine oxytocin receptor concentrations were raised in ewes treated with oestrogen, increases occurring in caruncular endometrium and myometrium by 12 h after treatment and in intercaruncular endometrium by 24 h. Raised receptor concentrations were followed at 24 h by increases in the incorporation of [3H]inositol into phosphatidylinositol and in the hydrolysis of labelled tissue phosphoinositides in response to oxytocin in slices of caruncular endometrium incubated in vitro. The following sequence of events is therefore suggested to occur at oestrogen-induced luteolysis: induction of the oxytocin receptor; increased turnover of phosphoinositides; onset of episodic secretion of PGF-2 alpha; and functional luteolysis.
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PMID:Effects of a luteolytic dose of oestradiol benzoate on uterine oxytocin receptor concentrations, phosphoinositide turnover and prostaglandin F-2 alpha secretion in sheep. 303 33

In Exp. I oxytocin (60 micrograms/100 kg/day) was infused into the jugular vein of 3 heifers on Days 14-22, 15-18 and 16-19 of the oestrous cycle respectively. In Exp. II 5 heifers were infused with 12 micrograms oxytocin/100 kg/day from Day 15 of the oestrous cycle until clear signs of oestrus. Blood samples were taken from the contralateral jugular vein at 2-h intervals from the start of the infusion. The oestrous cycle before and after treatment served as the controls for each animal. Blood samples were taken less frequently during the control cycles. In Exp. III 3 heifers were infused with 12 micrograms oxytocin/100 kg/day for 50 h before expected oestrus and slaughtered 30-40 min after the end of infusion for determination of oxytocin receptor amounts in the endometrium. Three other heifers slaughtered at the same days of the cycle served as controls. Peripheral concentrations of oxytocin during infusion ranged between 155 and 641 pg/ml in Exp. I and 18 and 25 pg/ml in Exp. II. In 4 our of 8 heifers of Exps I and II, one high pulse of 15-keto-13,14-dihydro-prostaglandin F-2 alpha (PGFM) appeared soon after the start of oxytocin infusion followed by some irregular pulses. The first PGFM pulse was accompanied by a transient (10-14 h) decrease of blood progesterone concentration. High regular pulses of PGFM in all heifers examined were measured between Days 17 and 19 during spontaneous luteolysis. No change in length of the oestrous cycle or secretion patterns of progesterone, PGFM and LH was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of continuous infusion of oxytocin on length of the oestrous cycle and luteolysis in cattle. 339 43

The existing data on the hormonal factors involved in human parturition indicate that the steroid hormones, progesterone and the oestrogens, play only a facilitatory role in the initiation of labour. A definite role for fetal adrenal steroids in this process has yet to be established, and they too may serve only a facilitating function. The stimulation of the uterine muscle during labour results from an interaction of oxytocin and prostaglandin (PG) F2 alpha. Recent evidence suggests that oxytocin is most important for the initial phase of labour, whereas increased synthesis of PGF2 alpha is essential for the progression of labour. The role of PGE2 remains unclear, but this PG may play an important role in the ripening of the cervix which in turn is essential for successful parturition. The finding of maximal oxytocin receptor concentrations in the myometrium in labour adds strong support to the notion that oxytocin is the trigger for uterine contractions. The factors which control oxytocin receptor formation are therefore important; this may be one of the processes where the steroids play a crucial role. Oxytocin is also one of the stimuli that increase uterine PG synthesis; the coupling of oxytocin receptor occupancy and PG synthetase activity in uterine tissues may be another crucial factor in the mechanism of labour. The formation of gap junctions between the myometrial cells also seems essential for the synchronization and progression of myometrial activity. We propose, therefore, that the co-ordinating of oxytocin receptor formation, PG synthesis and gap junction formation is a key to the initiation and maintenance of human labour. The fetus may fulfil such a co-ordinating role through its influence on placental oestrogen production, through mechanical distention of the uterus, and through its secretion of neuro-hypophysial hormones and other stimulators of PG synthesis.
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PMID:Endocrinology of human parturition: a review. 609 29

We have determined the concentration and distribution of oxytocin receptors in myometrial and decidual tissues obtained at cesarean section or hysterectomy during pregnancy. Myometrial receptor concentration was low at 13 to 17 weeks but had risen about twelvefold by 37 to 41 weeks. After the onset of labor, either preterm or term, the receptor levels were maximal and significantly higher than before the onset of labor. In cases of failed induction of labor with oxytocin and in postterm pregnancies (43 to 46 weeks), the receptor concentration was significantly lower than in spontaneous labor. Myometrial receptor concentrations in the fundus and the corpus were similar and significantly higher than in the lower part of the uterine segment, and the cervix had the lowest concentration. The parietal decidua had oxytocin receptor concentrations of the same magnitude as the myometrium. These results are consistent with a functional role of endogenous oxytocin in the activation of the human uterus during pregnancy and parturition.
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PMID:Oxytocin receptors in the human uterus during pregnancy and parturition. 609 38


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