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

The ruminant conceptus secretes proteins during early pregnancy which maintain the corpus luteum. These trophoblast proteins are related to the alpha II-interferons and prevent luteolysis indirectly by disrupting the secretion of endometrial prostaglandin. Although trophoblast interferons appear to be largely confined to the uterine lumen, it remains possible that they also act peripherally. This report describes in vitro studies which suggest that interferon may influence hormone secretion by the ovary directly. The study employed i) a well defined serum-free culture model in which bovine granulosa cells secrete the luteal hormones progesterone and oxytocin, and ii) serum-free and serum-supplemented cultures of cells from early CL. Dose-response experiments were performed using bovine recombinant alpha-interferon (brIFN). Progesterone and oxytocin secretions were measured over 4-5 days of culture and DNA content was also determined. Low concentrations of brIFN (10(-15) mol/l to 10(-11) mol/l) stimulated progesterone secretion by granulosa cells by up to three fold, without significantly affecting oxytocin concentrations or culture DNA content. Concentrations of 10(-10) mol/l to 10(-1) mol/l suppressed progesterone secretion in a log dose-related manner (r = 0.97) with evidence of toxicity (lower oxytocin concentrations and significantly reduced DNA compared with controls). Progesterone secretion by luteal cells in serum-free culture was stimulated in the presence of 10(-15) mol/l brIFN, whilst high concentrations again caused inhibition. The data show that ovarian cells can respond directly to low concentrations of interferon-like proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Direct stimulation of bovine ovarian progesterone secretion by low concentrations of alpha-interferon. 147 25

The function of oxytocin receptors in the corpus luteum of pregnant ewes was investigated by infusing saline or oxytocin (100 ng/min) into the utero-ovarian artery of pregnant ewes (62 +/- 5 days, n = 12). During a 4-h infusion, plasma oxytocin (OT) concentration increased to 268 +/- 80 pg OT/ml in the OT-infused group and remained unchanged at 2.5 +/- 1.5 pg OT/ml in the saline-infused group. Progesterone concentration in jugular venous plasma (17 +/- 9 ng/ml) rapidly decreased during oxytocin infusion to 59 +/- 10% and 26 +/- 9% of control at 1.5 and 2 h, respectively; the utero-ovarian venous concentration of 64 +/- 38 ng/ml decreased by a similar magnitude during oxytocin infusion. Electron microscopy of corpora lutea, removed at the end of the experiments, showed no indication of luteolytic changes following oxytocin infusion. It was concluded that oxytocin markedly and rapidly reduces progesterone secretion in pregnant ewes.
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PMID:Effect of intra-ovarian infusion of oxytocin on plasma progesterone concentrations in pregnant ewes. 165 57

In recent years, considerable progress has been made in our understanding of the endocrine mechanisms that control the pattern and timing of uterine secretion of prostaglandin F2 alpha (PGF2 alpha) during luteolysis in ruminants. Oxytocin may be important in establishing a pulsatile pattern of secretion. Neurohypophyseal oxytocin appears to be released in a pulsatile fashion and may initiate each episode of PGF2 alpha secretion from the uterus. Uterine PGF2 alpha stimulates release of oxytocin from the corpus luteum. Luteal oxytocin further stimulates secretion of PGF2 alpha from the uterus and may induce a transient refractoriness of the uterus to subsequent stimulation with oxytocin. Uterine refractoriness subsides after approximately 6 h. A similar desensitization phenomenon occurs in response to PGF2 alpha at the level of the corpus luteum. Together, uterine and luteal refractoriness may account for the interval between pulses of PGF2 alpha observed during luteolysis. Uterine secretory responsiveness to oxytocin increases at luteolysis, when endogenous, pulsatile secretion of PGF2 alpha normally begins. Thus, the acquisition by the uterus of responsiveness to oxytocin may determine when endogenous secretion of PGF2 alpha occurs during the estrous cycle. Uterine secretory responsiveness to oxytocin develops slowly, in the presence of progesterone. Progesterone exerts two types of effects that contribute to the regulation of PGF2 alpha secretion. First, prolonged exposure to progesterone appears to promote uterine accumulation of arachidonic acid, prostaglandin endoperoxide synthase, and other substances needed for synthesis of PGF2 alpha. Second, progesterone exerts a suppressive effect on secretion, which wanes after prolonged exposure. Together, these effects of progesterone ensure that PGF2 alpha is secreted only at the appropriate time to induce luteolysis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Hormonal regulation of uterine secretion of prostaglandin F2 alpha during luteolysis in ruminants. 175 3

Progesterone and estradiol interact to regulate secretion of prostaglandin (PG) F2 alpha from the ovine endometrium in response to oxytocin. Two experiments were conducted to determine if these effects were due to changes in activity of phospholipase C or in the second messenger responsive pathways that regulate production of PGF2 alpha. In both experiments, ovariectomized ewes were assigned to one of four treatment groups (control, estradiol, progesterone, progesterone and estradiol). Steroids were administered, in vivo, to mimic the changes that occur during the estrous cycle. On Day 16 of steroid treatment, endometrial tissue was collected and incubated, in vitro, to measure activity of phospholipase C and release of PGF2 alpha. Treatment with progesterone, in vivo, enhanced basal and oxytocin-induced activity of phospholipase C and release of PGF2 alpha, in vitro. Estradiol suppressed oxytocin-induced activity of phospholipase C, both in the presence and absence of progesterone. In contrast to its effects on phospholipase C, estradiol inhibited basal and oxytocin-induced release of PGF2 alpha when administered alone, but not when administered with progesterone. Steroids had similar effects on the release of PGF2 alpha induced by phorbol 12-myristate 13-acetate and A23187. It was concluded that progesterone and estradiol regulate endometrial release of PGF2 alpha by affecting both the activity of phospholipase C and its associated second messenger responsive pathways that may regulate production of PGF2 alpha.
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PMID:Activity of phospholipase C and release of prostaglandin F2 alpha by endometrial tissue from ovariectomized ewes receiving progesterone and estradiol. 201 59

To determine the effects of relaxin, oxytocin, and prostaglandin F2 alpha on progesterone secretion, bovine luteal cells from different stages of gestation were dispersed in Medium 199 with 200 units/ml penicillin, 1.0% kanamycin, 0.5% bovine serum albumin, and 400 units/ml collagenase. Cells (10(5) were cultured in 400 microliters of Dulbecco's modified Eagle's medium and Ham's F-12 medium containing fetal bovine serum and antibiotics, in Falcon multiwell plates, in a humidified environment of 95% O2 and 5% CO2 at 37 degrees C. Cells were cultured for 24 hr without treatment and thereafter with medium-hormone replacement every 24 hr. Progesterone was quantified from unextracted media by radioimmunoassay. Basal progesterone secretion after 24 hr was 1.81 +/- 0.14, 1.76 +/- 0.17, 0.54 +/- 0.49, and 0.57 +/- 0.21 pg/ml per viable luteal cell from 145-, 165-, 185-, and 240-day-old corpora lutea, respectively. Basal progesterone secretion increased (P less than 0.05) with time in culture. Relaxin induced a dose-dependent (greater than 100 ng/ml) increase in progesterone release, compared with the controls. Oxytocin and prostaglandin F2 alpha induced greater release (P less than 0.05) of progesterone than relaxin at all stages of gestation, but progesterone release was dependent on the stage of gestation and the duration in culture. Luteinizing hormone (100 ng/ml) stimulated whereas 17 beta-estradiol (50 ng/ml) inhibited progesterone secretion by luteal cells at all stages of gestation examined. Relaxin obliterated the prostaglandin- and oxytocin-induced progesterone secretion by bovine luteal cells from 145 to 214 days of gestation. Thus, relaxin, cloprostenol, and oxytocin regulate progesterone production by cultured bovine luteal cells, but hormone secretion was dependent on the stage of gestation.
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PMID:Relaxin, oxytocin, and prostaglandin effects on progesterone secretion from bovine luteal cells during different stages of gestation. 223 7

Current evidence suggests that oestrogens, progesterone, relaxin, the prostaglandins, and oxytocin are all hormones concerned to a major degree with the onset and maintenance of parturition. Oestrogens, relaxin, and the prostaglandins are particularly involved with cervical ripening, while prostaglandins, progesterone and oxytocin are more involved in regulating myometrial contractility. Catecholamines may also have some regulatory function in relation to uterine contractions. Progesterone dominance during pregnancy is associated with a firm closed cervix, few myometrial gap junctions, low calcium levels in the cells, and a quiescent myometrium. At term, a change in the oestrogen/progesterone balance favours cervical ripening and increased uterine activity. Of particular importance at the level of the muscle cell are changes in the number of oxytocin receptors; a complex interaction between cAMP and phosphoinositide metabolism governs the intracellular level of calcium, thus regulating contractile activity.
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PMID:The endocrinology of parturition in the human. 224 99

The aim was to examine the effect of activin on luteinization of preovulatory bovine granulosa cells in vitro. Bovine activin-A was found to inhibit the production of oxytocin (OT) and progesterone by bovine granulosa cells from individual preovulatory follicles cultured in serum-free medium. The minimal response on OT production (25% inhibition) occurred with 0.1-1 ng/ml activin-A, and the maximal inhibition (83%) occurred with 10 ng/ml activin-A after 2-3 days in culture. Progesterone showed a similar response (30% inhibition for 0.1-1 ng/ml and 74% for 10 ng/ml). Inhibin production was not consistently effected by activin-A. Inhibin (75 U/ml) had no detectable effect upon OT or progesterone production. When activin-A was withdrawn from the cell culture after 72 h and the incubation continued for a further 72 h, a recovery in OT was seen on day 4 and 5 after activin-A doses of 0.1-1 ng/ml, but not after higher doses (3 and 10 ng/ml). Progesterone did not show a recovery, but the levels remained constant for 3 days (0.1 and 0.3 ng/ml activin-A) or for 1 day (1-10 ng/ml activin-A) and then fell to control levels by day 6 of culture. We conclude that bovine activin-A has an autocrine action on bovine granulosa cells in vitro, to inhibit basal production of OT and progesterone, consistent with the role of activin-A in delaying the process of luteinization.
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PMID:Activin-A inhibits oxytocin and progesterone production by preovulatory bovine granulosa cells in vitro. 231 63

Oxytocin (OT) is secreted during the final stages of bovine follicular development. To test OT's potential role as a regulator of follicular steroidogenesis, theca and granulosa cells were isolated from bovine preovulatory follicles 48 h after initiation of luteolysis with prostaglandin F2 alpha, and cultured with graded doses of OT (0, 0.5, 5, 50, and 500 mIU/ml). Granulosa cells were cultured with testosterone (0.5 microM) in either defined medium or medium containing 10% fetal bovine serum in the presence or absence of FSH (300 ng/ml); medium was collected and replaced daily for 5 days. In defined medium, oxytocin alone significantly increased progesterone production by granulosa cells (P less than 0.001) in a dose-dependent manner; over 5 days, doses of 0.5, 5, 50, and 500 mIU/ml OT caused 1.7-, 2.0-, 2.2-, and 2.6-fold increases. FSH enhanced progesterone 5-fold, but no dose of OT increased progesterone in the presence of FSH. OT also elevated progesterone in serum-containing medium (P less than 0.005), but the magnitude of its effects was lower (1.07-, 1.1-, 1.2-, and 1.4-fold increases with 0.5, 5, 50, and 500 mIU/ml OT). OT had little effect on estradiol secretion by granulosa cells cultured with or without FSH. To test the specificity of OT's effects on progesterone production by granulosa cells, granulosa cells were treated with graded doses of an OT antagonist (0, 1, 10, 100, and 1000 ng/ml) in the presence or absence of OT (5 and 50 mIU/ml). Progesterone production by granulosa cells in the presence of the antagonist alone was similar to production in control cultures. The stimulatory effects of 5 and 50 mIU OT were completely abolished in the presence of 100 or 1000 ng antagonist, respectively (P less than 0.01). Preparations of theca interna were cultured in defined medium with graded doses of OT (0, 0.5, 5, 50, and 500 mIU/ml) in the presence or absence of LH (300 ng/ml), with collection and replacement of medium at 3, 6, 12, 24, 48, and 72 h. LH alone increased both progesterone (12-fold) and androstenedione (4-fold) production over controls. However, no dose of OT significantly affected either progesterone or androstenedione production. These results show that OT stimulates progesterone production by granulosa cells, and thus, suggest that OT regulates steroidogenesis in bovine granulosa cells in vivo.
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PMID:Effects of oxytocin on steroidogenesis by bovine theca and granulosa cells. 237 62

A group of 14 ewes was actively immunized against oxytocin coupled to carrier protein, and comparisons of the reproductive status of these animals were made against ewes immunized against carrier protein only (N = 5) and untreated controls (N = 6). The last two groups were indistinguishable and were therefore combined as a single control group for analysis of the results. Oestrous cycle lengths were significantly extended in oxytocin-immunized ewes (P less than 0.005) with 42% of cycles lasting greater than 18 days. Cloprostenol treatment in the mid-luteal phase resulted in apparently normal luteal regression and re-ovulation, but luteal phase FSH concentrations and follicular phase LH concentrations were elevated in the immunized ewes, although surge levels of both hormones were unaffected. Measurements of free oxytocin concentrations in the blood suggested that these were significantly raised in treated animals. Progesterone concentrations in peripheral plasma were not altered by treatment. Mating resulted in a conception rate of 91% in control ewes compared with only 28% in oxytocin-immunized animals (P less than 0.01). There was no evidence of any conceptus material in the uteri of non-pregnant immunized ewes 25 days after service. Some had re-ovulated, whereas the ovaries of others contained mature corpora lutea which had been maintained. Ovarian histology appeared normal. We conclude that active immunization against oxytocin influences gonadotrophin secretion and reduces fertility. The site(s) of action for both of these effects needs to be determined.
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PMID:Effect of active immunization against oxytocin on gonadotrophin secretion and the establishment of pregnancy in the ewe. 250 10

Two ovarian hormones, estradiol and progesterone, which facilitate mating behavior in the female rat by acting on the ventromedial nuclei (VMN) of the hypothalamus, induce changes in oxytocin receptor binding in this brain region. Estradiol induced a 4-fold increase in the oxytocin receptor binding of the VMN and surrounding area and increased the number and immunostaining of oxytocin fibers in an area lateral to the ventral VMN. Progesterone, in estrogen-primed rats, caused the induced oxytocin receptors to spread over the area containing the oxytocin fibers. Infusion of oxytocin into the ventromedial hypothalamus increased the display of lordosis behavior only in females primed with both estradiol benzoate and progesterone. Thus, the sequential actions of two ovarian hormones bring a neuropeptide and its receptors into register and enable the neuropeptide to exert behavioral effects.
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PMID:Localized actions of progesterone in hypothalamus involve oxytocin. 254 47


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