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

Oxytocin receptors were measured in myometrium and intercaruncular endometrium of cows during pregnancy and parturition. Concentrations of estradiol-17 beta, estrone, and progesterone in peripheral blood were also measured. Receptor concentrations in the endometrium rose almost 200-fold from Day 20 to term (p < 0.0001, ANOVA), from 40 +/- 11 to 7300 +/- 1430 fmol/mg protein. Myometrial receptor concentrations increased 10-fold from 180 +/- 36 fmol/mg on Day 20 to 1850 +/- 360 fmol/mg protein at term (p < 0.0001, ANOVA). During labor, endometrial receptors (6600 +/- 1300 fmol/mg) remained at prelabor values, whereas myometrial receptor concentrations had decreased to 1190 +/- 316 fmol/mg (not significant) and declined further postpartum. Plasma concentrations of progesterone declined from 4-5 ng/ml to about 2 ng/ml between Days 250 and 282 and dropped to < 0.2 ng/ml shortly before delivery. Plasma concentrations of estrone and estradiol-17 beta were below 10-20 pg/ml until Day 230. Estrone concentrations were significantly (p < 0.05) increased by Day 250 and estradiol-17 beta by Day 270, and then both rose rapidly. During labor, plasma estrone was 1135 +/- 245 pg/ml and plasma estradiol-17 beta was 226 +/- 131 pg/ml. The molar ratio of estrone and estradiol-17 beta to progesterone rose from less than 0.01 to 4.4 during labor, and was correlated with oxytocin receptor concentrations in endometrium (r = 0.5160, p < 0.001), but not those in myometrium (r = 0.0122). The regulation of oxytocin receptors by ovarian hormones in the two tissues may therefore differ.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Oxytocin and bovine parturition: a steep rise in endometrial oxytocin receptors precedes onset of labor. 133 77

Oxytocin infusions were initiated on day 10 of the oestrous cycle in ewes, and luteal regression was induced by injection of 100 micrograms cloprostenol on day 12. Blood samples were collected at frequent intervals via an indwelling jugular vein cannula to measure concentrations of progesterone and luteinizing hormone (LH) during the luteal and follicular phases in saline (n = 6) and oxytocin (n = 5) infused animals. The oxytocin infusion maintained peripheral plasma concentrations of 53 +/- 3.2 pg oxytocin ml-1 (mean +/- SEM) compared with values of about 1 pg ml-1 during oestrus in control ewes. Oxytocin infusion had no effect on luteal phase progesterone concentrations, the timing of luteolysis, basal luteinizing hormone (LH) secretion, LH pulse frequency, or the timing or height of the LH surge. Treated ewes came into oestrus significantly earlier than controls (P < 0.05) but ovulated normally. Uterine samples collected 96 h after cloprostenol injection (approximately day 2 of the cycle) showed that oxytocin receptor concentrations were significantly higher in the endometrium in ewes that had been given a 5 day oxytocin infusion than in control animals (556 and 262 fmol mg-1 protein, respectively: geometric means from ANOVA, P < 0.001), whereas myometrial receptor concentrations were not affected (113 and 162 fmol mg-1 protein, respectively). We conclude that the previously reported delay in luteal development caused by oxytocin infusion (Wathes et al., 1991) is not due to the inhibition or delay of ovulation, but must instead occur via a direct influence on the developing corpus luteum.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of oxytocin infusion on secretion of progesterone and luteinizing hormone and the concentration of uterine oxytocin receptors during the periovulatory period in cloprostenol-treated ewes. 133 45

Eighty-four Holstein cows were used to determine effects of exogenous oxytocin on 305-d milk production and health. Cows were assigned at parturition by parity group to treatments: 1) oxytocin group, animals received an injection of 1 ml (20 IU) of oxytocin at each milking throughout lactation and 2) control group, animals received no injection. Oxytocin injections were given in the thigh region within 3 min following the initiation of udder preparation and immediately prior to machine attachment. Udder preparation consisted of forestripping and manual cleaning (10 to 20 s) and drying (5 to 10 s) of teats. Cows were milked in a parlor, and milk yield was recorded at each milking. Milk samples were collected from each cow biweekly for milk fat, protein, and somatic cell count determination. Individual lactations were modeled using Woods' lactation equation; resulting coefficients were analyzed using ANOVA. The oxytocin group produced 849 kg more milk during the lactation than the control group, with a significant difference occurring after peak milk yield. This suggests that exogenous oxytocin maintained greater persistency during lactation. No significant differences existed for milk fat or protein percentages. The use of exogenous oxytocin at milking increased lactation milk production with no apparent effect on health.
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PMID:Effects of daily exogenous oxytocin on lactation milk yield and composition. 189 7

The effect of administration of estradiol (E2) alone or combined with progesterone upon the circadian rhythm of oxytocin concentrations in cerebrospinal fluid (CSF) was examined in adult ovariectomized rhesus monkeys bearing temporary subarachnoid catheters and maintained in a constant photoperiod (lights on 06.00-18.00 h). Animals were subcutaneously implanted with silastic capsules containing 17 beta-E2 for 6 days and progesterone for the last 3 days of E2 administration. Hourly samples of CSF were collected before, during and after gonadal steroid administration and measured for oxytocin by RIA and reverse-phase high-performance liquid chromatography (RP-HPLC). A significant increase in the serum concentration of E2 and the plasma concentration of oxytocin neurophysin, but not the plasma concentration of oxytocin, was found during gonadal steroid administration. Each animal displayed a dirunal pattern of secretion of oxytocin in CSF with peak and trough levels during light and dark hours, respectively. No significant differences were found across experimental conditions in the following CSF oxytocin parameters: mean level of oxytocin in CSF during the light, dark, or light and dark hours combined; the daily phase or amplitude of the CSF oxytocin rhythm; the peak or nadir concentration of oxytocin in CSF; or the total amount of oxytocin secreted into the CSF as expressed as the area under the curve (multivariate repeated measures ANOVA). The CSF oxytocin parameters in the animals that were restudied using empty silastic implants were not significantly different across time (multivariate repeated measures ANOVA).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of estradiol and progesterone administration upon the circadian rhythm of oxytocin in the cerebrospinal fluid of rhesus monkeys. 211 31

Calcium channel blockers inhibit myometrial contractility by preventing the increase in intracellular free calcium which follows stimulation. They could thus be useful in treating premature labour. The effect of nitrendipine, a dihydropyridine calcium channel antagonist, on the contractile response of strips of pregnant human myometrium to oxytocin, angiotensin II (AII) and ergometrine has been examined. A total of 68 tissue strips were studied, with random allocation to treatment group. Initial concentration: response curves to one of the three agonists were determined; the concentration:response determinations were repeated in the presence or absence of nitrendipine at 10(-9)M. The initial EC50S for tissues exposed to oxytocin and AII were 8.2 X 10(-10)M and 3.4 X 10(-8)M respectively. The contractile response to both agonists was significantly blunted in the presence of nitrendipine (ANOVA; P less than 0.001 for both agents). This effect was greatest at high agonist concentrations. The initial EC50S for tissues exposed to ergometrine was 3.9 X 10(-8)M. Exposure to nitrendipine blunted the response (ANOVA; P less than 0.001), an effect most marked at low concentrations of ergometrine. The effect of nitrendipine on myometrial responses to the naturally occurring hormones oxytocin and AII supports suggestions of a role for it in inhibiting premature labour.
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PMID:Studies on the effects of nitrendipine on oxytocin-, angiotensin II- and ergometrine-induced contraction of pregnant human myometrium in vitro. 316 51

The effect of oxytocin on uterine estrogen and progesterone receptors (ER and PgR) was investigated in vivo in groups of immature female rats that were treated subcutaneously with oxytocin, 0.5 or 5 IU (1 and 10 micrograms) for 5 and 3 d, respectively. Receptor concentrations and affinities were estimated by Scatchard analysis, using radioactive hormones as ligands. Statistical analysis was performed by Student's t test and by ANOVA. Oxytocin did not alter the receptor affinity for either steroid hormone, but the lower dose significantly decreased the concentrations of receptors: ER = 486 +/- 76 fmol/mg vs 346 +/- 105 fmol/mg (P < 0.001) and PgR = 686 +/- 237 fmol/mg vs 433 +/- 236 fmol/fmol/mg (P < 0.01) (mean +/- SD values for control and treated animals, respectively). There were no significant effects on the plasma 17 beta-E and Pg concentrations. In in vitro studies with mature rats, uterine specific binding of estradiol and progesterone in the presence or the absence of oxytocin showed no modification. Oxytocin could be a negative modulator of ER and PgR in the uterus, even though the mechanism of its action remains unknown. It could have potential implications on reproductive capacity and fertilization.
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PMID:Effect of oxytocin on estrogen and progesterone receptors in the rat uterus. 755 Mar 99

Although GnRH is believed to be the primary secretagogue for LH, oxytocin has also been shown to stimulate LH release from the anterior pituitary. We investigated the possibility that the two secretagogues interact in the modulation of LH release. Anterior pituitaries were removed from adult female rats at pro-oestrus, and tissue pieces were pre-incubated in oxytocin for 3 h prior to being stimulated with 15 min pulses of GnRH. LH output over the 1 h period from the beginning of the GnRH pulse was determined. Control incubations were carried out in the absence of oxytocin, and background secretory activities without GnRH stimulation were also determined. Tissue which was pre-exposed to oxytocin (0.012-1.25 microM) had an increased LH response to GnRH (1.25 nM). The increase was larger than the sum of the LH outputs obtained with oxytocin and GnRH separately, revealing that oxytocin synergistically enhanced LH secretion elicited by GnRH (P < 0.05; ANOVA). If stimulation by GnRH was delayed for 2 h after incubation with oxytocin, an increase in LH secretion was still observed, indicating that oxytocin-induced modulation did not rapidly disappear. Oxytocin pre-incubation was observed to result in an increase of maximal GnRH-induced LH output (P < 0.001; t-test), as well as an increase of intermediate responses. The LH response of the anterior pituitary to subsequent pulses of GnRH was modified by the self-priming process. The effect of oxytocin pretreatment on the response of primed tissue to GnRH was also investigated.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Oxytocin modulates the luteinizing hormone response of the rat anterior pituitary to gonadotrophin-releasing hormone in vitro. 779 16

The established role of oxytocin (OT) in facilitation of steroid-modulated reproductive and affiliative behaviors led to the speculation that it may have anxiolytic actions under certain hormonal conditions. NIH-Swiss mice were tested for responsiveness to OT in two behavioral tests of anxiety, the holeboard apparatus and elevated plus-maze. Dose-response assessment indicated that 3 mg/kg was the optimal dose for peripherally administered (IP) OT on the elevated plus-maze. There were no consistent effects at any dose on the holeboard apparatus. In ovariectomized mice pretreated with estradiol (E2), peripherally administered OT increased the number of entrances onto the open arms, as well as the amount of time on the open arms compared to other groups (ANOVA; p < 0.05). There was little to no effect of OT in ovariectomized animals not pretreated with E2. When OT was administered intracerebroventricularly (ICV), there was an increase in entrances and time on the open arms compared to that of females infused with arginine vasopressin (AVP). This increase was apparent in ovariectomized females, but was further enhanced in those pretreated with E2 (ANOVA; p < 0.05). In contrast, the combination of E2 pretreatment and ICV AVP decreased the number of entrances and time spent on the open arms of the elevated plus-maze compared to those receiving OT, suggesting an estrogen-modulated anxiogenic action of AVP. Analyses of [125]I-OVTA binding density indicated a significant increase in binding density in the lateral septum of E2-treated females compared to OIL-treated controls (ANOVA; p < 0.05). There was no effect of E2 treatment on [125]I-OVTA binding density in the amygdala or ventromedial nucleus of the hypothalamus. Taken together, these data indicate that OT exerts an anxiolytic action that is enhanced in the presence of circulating estrogen. This behavioral effect may be mediated by estrogen-induced increases in OT binding density in the lateral septum and may be important to the facilitation of social interactions.
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PMID:An anxiolytic action of oxytocin is enhanced by estrogen in the mouse. 891 73

Mesotocin (MT), the oxytocin-like peptide of the tammar wallaby (Macropus eugenii) is important for delivery of live young. The tammar mesotocin receptor (MTR) was first characterized using the iodinated oxytocin receptor antagonist [125I]d(CH2)5 [Tyr(Me)2, Tyr4, Orn8, Tyr-NH(2)9]-vasotocin. MTR concentrations were then measured in matched samples of gravid and nongravid myometrium and median vagina at different stages of the 26-day pregnancy. MTR concentrations in both the gravid and nongravid myometrium changed significantly (ANOVA, p < 0.01) during pregnancy. There was no difference in MTR concentrations between uteri on Days 8-22. From Day 23 of pregnancy, MTR concentrations in the gravid myometrium increased (615.8 +/- 144.0 fmol/mg protein), whereas in the nongravid myometrium, they remained unchanged (248.6 +/- 65.5 fmol/mg protein). Receptor concentrations were high in the gravid myometrium during the last 3 days of pregnancy but decreased significantly in the nongravid myometrium. In the median vagina, MTR concentrations were low compared with myometrial tissues and did not increase at term. Changes in MTR concentrations paralleled changes in uterine responsiveness to exogenous MT in vitro. Our data show that MTR concentrations and the responsiveness to MT differ between the gravid and nongravid myometrium during pregnancy. The increase in MTRs in the gravid myometrium and the decrease in the nongravid suggest that different factors influence these receptors in the separate uteri, independent of systemic influence.
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PMID:Evidence for a local fetal influence on myometrial oxytocin receptors during pregnancy in the tammar wallaby (Macropus eugenii). 900 50

Neurohypophysial hormones are thought to be involved in alterations in fluid balance during pregnancy and delivery. In the course of normal pregnancy intravascular volume is increased whereas sodium restriction is thought to reduce plasma volume and cardiac output. In the present study, we measured the effect of long-term severe sodium restriction on vasopressin (AVP) and oxytocin (OT) levels during normal pregnancy and after delivery. Fifty-nine healthy nulliparous women were randomized either for a low sodium diet (20 mmol sodium daily) or for a normal diet from week 12 of pregnancy onwards. Circulating plasma levels and urinary excretion of AVP and OT, their neurophysins (Np-AVP and Np-OT) and AVP bound to platelets were determined at regular intervals during pregnancy and after delivery. After completion of the study, women on a sodium-restricted diet were compared with control women on a normal diet using repeated measurement ANOVA with adjustment for potentially confounding variables. After randomization, a reduction in urinary sodium excretion of, on average, 40-82% was found. In general, no effect of sodium restriction could be demonstrated on the various parameters (0.53 < P < 0.98) with the exception of a significantly lower 24-h urinary AVP excretion by non-smokers with sodium restriction compared with non-smokers having a normal diet (P = 0.018). For all parameters, clear changes were found in the course of pregnancy and puerperium (P < 0.0001 to P < 0.005). Platelet-bound AVP decreased and Np-OT increased during pregnancy. After birth, free plasma AVP, platelet-bound AVP, OT, osmolality, sodium and potassium increased, while Np-AVP and Np-OT decreased. Although elevated Np-AVP and Np-OT levels during pregnancy seem to indicate increased release of neurohypophysial hormones, pregnancy up to 36 weeks of gestation is accompanied by low circulating AVP and OT levels. Long-term severe sodium restriction diminishes urinary AVP excretion in (non-smoking) pregnant women, without changing circulating levels of AVP and OT, despite the known reduction in circulating volume. The reduced circulating (platelet-bound) AVP levels during pregnancy, whether or not in combination with severe sodium restriction, support the absence of significant non-osmotic stimulation of AVP during pregnancy.
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PMID:Vasopressin and oxytocin levels during normal pregnancy: effects of chronic dietary sodium restriction. 907 54


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