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

Six heifers with normal oestrous cycles were treated i.m. with 100 i.u. oxytocin on 3 consecutive days, commencing on Days 1-6 after oestrus, and the levels of prostaglandin (PG) F in posterior vena cava plasma were compared with pretreatment values. An increase of PGF in response to oxytocin was significantly influenced by day, with the greatest response occurring on Day 3 after oestrus. In an ovariectomized heifer the levels of PGF in posterior vena cava plasma increased 24 h after priming with oestradiol, but no further increase occurred after oxytocin injection. Peak levels of PGF were higher in the plasma of the posterior vena cava than in the jugular vein. Various storage conditions of the blood before centrifugation and freezing (--20 degrees C) produced significant differences in plasma levels of endogenous PGF, but storage experiments with added labelled PGF-2alpha indicated that the PG was stable in plasma and whole blood.
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PMID:The effect of oxytocin treatment on the levels of prostaglandin F in the blood of heifers. 55 71

1. Extracellular action potentials were recorded from forty antidromically identified single units in the supraoptic nucleus of lactating, urethane-anaesthetized female rats. The activity was monitored both during reflex milk ejection and during an increase of 10-15 m-osmole/kg in plasma osmotic pressure induced by intraperitoneal injection of 1 ml. of 1.5 M-NaCl solution.2. About half (eighteen) the cells showed a burst of activity before reflex milk ejection and were dubbed oxytocin cells. Oxytocin cells responded to a hypertonic injection with a smooth sustained threefold increase in firing rate.3. The remainder (twenty-two) showed no burst of activity before reflex milk ejection and were dubbed vasopressin cells. Vasopressin cells doubled their firing rate as plasma osmotic pressure increased. Neither cell type increased its firing rate after injections of isotonic NaCl.4. A phasic firing pattern was rarely seen in slow firing vasopressin cells (< 2 spikes/sec) but was seen in almost all vasopressin cells (twelve out of fourteen) firing between 3 and 8 spikes/sec. Above 8 spikes/sec, some vasopressin cells fired continuously. Phasic firing was only once encountered in an oxytocin cell.5. The firing rate of both oxytocin and vasopressin cells decreased when plasma osmotic pressure was reduced 10-15 m-osmole/kg by an intragastric water load of 10 ml.6. Hypothalamic cells lying just outside the supraoptic nucleus did not show a consistent response to injection of hypertonic NaCl.7. Clearly, both oxytocin and vasopressin cells are osmoresponsive, but phasic firing is characteristic of stimulated vasopressin cells. Thus, osmotic activation allows discrimination between oxytocin- and vasopressin-secreting neurones.
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PMID:Characterization of the responses of oxytocin- and vasopressin-secreting neurones in the supraoptic nucleus to osmotic stimulation. 56 5

Intraventricular injection of arginine-8-vasopressin and its analogues vasotocin and lysine-8-vasopressin into rat brain evoked a special rotational behavior resembling somatostatin-induced barrel rotation [1]. Oxytocin and oxypressin were less active while vasopressin fragments had no effect. Vasopressin-induced barrel rotation was accompanied by pathological symptoms indicating a disturbance of muscle tone regulation and is considered to be a non-specific and toxic effect. This rotational behavior was not prevented by atropine, propranolol, phentolamine, methylsergide or haloperidol but was reduced by chlorpromazine, probably due to the latter's muscle relaxing activity.
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PMID:Barrel rotation induced by vasopressin and related peptides in rats. 56 83

Isolated uteri from rats with regular 4-day cycles were incubated in Krebs-Ringer bicarbonate buffer and the release of PGF into the medium was measured by radioimmunoassay after extraction of the incubation medium with ethyl acetate at pH 3.0-3.5. PGF was produced from endogenous precursors and accumulated in equal amounts in the medium during two successive 60 min periods on each day of cycle, but the magnitude of the production varied significantly during the cycle, being greatest in estrus. Oxytocin in doses up to 500 mU/ml had no effect on PGF accumulation in the incubation period at any stage of the cycle, while epinephrine (10(-3)) greatly stimulated PGF release from the estrous uterus but had no effect on PGF release from the diestrous uterus. Phentolamine, an alpha-blocking agent, had no effect on the epinephrine-induced release of PGF, while propranolol, a beta-blocking agent, not only prevented in increase in PGF production induced by epinephrine but also reduced the basal release of PGF by the estrous uterus. Since oxytocin contracts and epinephrine relaxes the nonpregnant rat uterus both in vivo and in vitro, it is unlikely that the effects of these two compounds on uterine contractility are mediated by the release of PGF2alpha.
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PMID:Effects of epinephrine and oxytocin on the release of prostaglandin F from the rat uterus in vitro. 56 31

Release of oxytocin and Substance P-like peptides from the rat posterior pituitary lobe incubated in situ after infusion of hypertonic solution into the third cerebral ventricle. Acta Physiol. Pol., 1978, 29 (1): 9-16. The experiments were carried out on male rats. Under general urethane and chloralose anaesthesia the ventral surface of the hypothalamus and the pituitary gland were exposed by a transpharyngeal approach and the anterior pituitary lobe was entirely removed. The posterior lobe with the remaining neural and partially vascular connections with the hypothalamus was incubated in situ. Oxytocin and Substance P-like peptides were assayed biologically in six 20-min samples of the fluid outflow from the posterior pituitary lobe incubated in situ. At the beginning of collection of the fourth sample a hypertonic solution was infused into the third ventricle through a micropipette. This infusion increased significantly the release of oxytocin and insignificantly that of Substance P-like pepides from the posterior pituitary lobe into the incubation fluid.
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PMID:Release of oxytocin and substance P-like peptides from the rat posterior pituitary lobe incubated in situ after infusion of hypertonic solution into the third cerebral ventricle. 56 6

Electromyograms were obtained from three different locations on the uterus of conscious, unrestrained rats during the 4 day estrous cycle. Intrauterine pressure changes were monitored simultaneously by means of indwelling intraluminal balloons (vol. 0.02 to 0.05 ml.). Electrical activity consisted of bursts of action potentials that were usually initiated at either end of the uterus. Propagated burst activity gave rise to cyclic intrauterine pressure changes, whereas bursts appearing at one electrode only did not elicit any measurable contractions. The rate of intrauterine pressure development depended on the propagation velocity, whereas the tension achieved was related to the duration of burst activity. All three parameters of electrical activity studied, namely, the duration and frequency of spike bursts, as well as their rate of propagation, varied significantly during the cycle. Regional differences were also subject to cyclic variations; thus, in proestrus the bursts originated predominantly at the cervical end, whereas in diestrus they were usually initiated at the ovarian end. Oxytocin stimulated the frequency and duration of bursts along the whole uterus and elicited corresponding changes in intrauterine pressure. Response to oxytocin was dose dependent and modified by cycle stage. Norepinephrine caused a transient prolongation of burst activity that was not dose dependent; epinephrine had a marked dose-dependent inhibitory action. The response to catecholamines did not vary significantly during the cycle. The variations in electrical and mechanical activity were characteristic for each stage of the ovarian cycle and could be correlated with the well-known hormonal changes. High circulating estrogen levels in proestrus are associated with infrequent but rapidly propagated spike bursts, whereas low levels in estrus are associated with frequent and sometimes nonpropaged bursts. The rise in plasma estrogen in diestrus coincides with a decrease in the frequency of burst activity, and the elevated progesterone levels are probably causally related to the significant drop in propagation velocity and the increase in duration of bursts observed in diestrus. These findings are consistent with the concept that estrogen withdrawal activates the estrogen-primed, quiescent myometrium, and that progesterone has an effect similar to that of estrogen withdrawal--at least in the rat.
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PMID:Electrical and mechanical activity of rat uterus in vivo during the estrous cycle. 56 83

Uterine responses to vasopressin and oxytocin were monitored in non-pregnant and 3- or 6-8-day-pregnant rabbits by recording the intrauterine pressure. Oxytocin stimulated uterine activity in all groups, but the effect of vasopressin was stimulatory in non-pregnant animals, inhibitory in those 3 days post coitum and weakly stimulatory in those later in pregnancy. Inhibition of prostaglandin (PG) synthesis, by the administration of indomethacin, reduced the spontaneous uterine activity as well as the responses to oxytocin and vasopressin in the non-pregnant rabbits, but had little effect in the pregnant animals. During infusion of PGF-2alpha, PGE-1 or PGE-2 in 6-8-day-pregnant rabbits, the stimulatory response to vasopressin, although slight before the infusion, was inhibited whereas the stimulatory response to oxytocin remained virtually unchanged. The results suggest that vasopressin and oxytocin under certain hormonal conditions, are able to activated the uterine contractions by mechanisms in which the involvement of PG is not obligatory.
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PMID:Differences in the effects of vasopressin and oxytocin on rabbit myometrial activity and a possible mediation of prostaglandins. 59 88

During the first 6 days after delivery the daily amount of mild secretion was measured in 300 nursing puerperae who had been treated with 0,2 mg of Methylergobrevin per day in combination with 100 IU Oxytocin. The milk let-down was compared with that of 300 untreated puerperae nursing under the same conditions. A significantly smaller milk let-down was found in treated old primiparae over 30 years, multiparae between 19-30 years and puerperae after premature delivery. In puerperae desiring to nurse their babies the routine post-partum treatment with Methylergobrevin should always be combined with Oxytocin. In women who had a premature delivery and in old primiparae a postpartum treatment with Methylergobrevin should be avoided.
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PMID:[Studies on the modification of puerperal lactation using methylergobrevin]. 61 Feb 38

The effect of intraventricular 6-hydroxydopamine on the content of oxytocin and vasopressin in the hypothalamus and pituitary gland of water deprived rats. Acta Physiol. Pol., 1977, 28 (6): 497-504. Rats received one infusion of 200 microgram 6-hydroxydopamine with 25 microgram of ascorbic acid into the lateral cerebral ventricle. After 57 days some rats were deprived of water for 4, 8 or 12 days. Then, the animals were sacrificed by decapitation. Oxytocin was determined in extracts from the posterior pituitary lobe and hypothalamus by the method of Van Dongen and Hays, while the vasopressin content was determined by the method of Dekanski. It was found that 6-hydroxydopamine injection into the cerebral ventricles causes a rise in oxytocin content in the hypothalamus and prevents its fall during--4--12 days of dehydration.
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PMID:The effect of intraventricular 6-hydroxydopamine on the content of oxytocin and vasopressin in the hypothalamus and pituitary gland of water-deprived rats. 61 34

A technique for the continuous superfusion of small tissue samples in vitro has been applied to the study of prostaglandin production by ovine intra-uterine tissues. Basal and oxytocin-stimulated production of prostaglandins was studied at 120-125 days of pregnancy and after dexamethasone-induced delivery. In general, the relative rate of prostaglandin production by tissues was: foetal cotyledon = maternal cotyledon greater than myometrium and in quantitative order the prostaglandins produced were prostaglandin E (PGE) greater than prostaglandin F (PGF) = 13,14-dihydro-15-oxo-prostaglandin F (PGFM). Considerable variations was found between the rates of prostaglandin production in individual sheep. Oxytocin had no effect on the production of prostaglandins by tissues obtained before labour but myometrium and maternal cotyledon obtained at delivery exhibited a significant increase in production of PGE and PGF (though not PGFM) in response to oxytocin. Administration of arachidonic acid increased the production of PGE and PGF by the foetal cotyledon.
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PMID:Prostaglandin production by intra-uterine tissues from periparturient sheep: use of a superfusion technique. 62 76


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