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

This literature review, which describes the structure of myometrial muscle and the regulation of its contractility, cites research from 1971 to 1989. The functions of the myometrium and the cervix are interrelated and coordinated during pregnancy and labor. The structure of smooth muscle, by allowing contraction in any direction, permits the uterus to assume the shape and size necessary to accommodate the fetus. Myometrial smooth muscle cells communicate via gap junctions, which synchronize myometrial function via conduction of electrophysiological stimuli during labor. These junctions increase in number prior to labor. This is regulated by estrogen, progesterone, and prostaglandins (PGs). The structures of myosin and actin and their movement during contraction are described. Estrogen, via alpha adrenergic receptors, causes a decrease in cAMP levels. It also increases the number of oxytocin receptors. Progesterone, via beta adrenergic receptors, causes an increase in cAMP levels. While estrogen leads to increased production of PGF2alpha, progesterone stimulates the production of prostacyclin synthase, Mifepristone, which blocks progesterone at the receptor level, increases uterine activity and sensitivity to PG. Human amnion and chorion produce mainly PGE2. The decidua produces PGE2 and PGF2alpha. Prostaglandins induce uterine activity at all stages of gestation when they are administered exogenously. Their production by uterine tissues increases during pregnancy, as does their concentration in amniotic fluid and in maternal blood and urine. Their roles in labor, whether natural or induced, include the softening of the cervix, the induction of gap junctions, and the direct stimulation of myometrial contractions. Although PGE2 and PGF2alpha relax cervical smooth muscle, they contract the myometrium by acting as calcium ionophpores. The production of PGE2, PGF2alpha, and other eicosanoids by the fetoplacental production of PGE2, PGF2alpha, and other eicosanoids by the fetoplacental unit is related to increased contractile activity during labor. What is produced in the eiconsanoid pathway changes dynamically with the phases of the reproductive cycle and the local concentrations of enzymes. Because of the rise in arachidonic acid in amniotic fluid during labor, fetal membranes may be involved with the initiation of regular uterine contractions. In addition, any stimulus facilitating PGE2 synthesis in the fetal membrane (hypoxia, infection, exposure to oxytocin, hypertonic solutions, prostaglandins, or arachidonic acid) would induce the same series of steps leading to formation of PGF2alpha in the decidua and the myometrium. Since natural prostaglandins are rapidly metabolized, and induction of abortion requires a longer presence, analogues have been developed for this use. These include gemeprost, sulprostone, and minprostin. Their action is more prolonged and specific to uterine tissue than their parent compounds.
Baillieres Clin Obstet Gynaecol 1992 Dec
PMID:Biochemistry of myometrial contractility. 133 53

The effect of vasopressin analogues on plasma adenosine 3',5'-cyclic monophosphate (cAMP) concentration was examined in a group of five conscious dogs instrumented for the measurement of arterial pressure and cardiac output (electromagnetic flowmeter). These dogs were infused for 20 min with a selective antidiuretic (V2) agonist, desamino-8-D-arginine vasopressin (DDAVP, 10 ng.kg-1 x min-1). This infusion was repeated on another day in the presence of the combined V1-V2 antagonist d(CH2)5-D-Tyr(Et)-4-valine,8-arginine vasopressin. The dogs also received an infusion of the selective V1 agonist 2-phenylalanine,8-ornithine oxytocin (Phe-OrnOT) at a rate of 10 ng.kg-1 x min-1. The effect of these infusions was compared with those of an isotonic saline infusion. Plasma cAMP measured in the aorta remained unchanged during all infusions but that of the selective V2 agonist DDAVP alone, during which it increased significantly from 22.4 +/- 0.8 to 32.6 +/- 4.6 and 37.0 +/- 4.1 pmol/ml after 10 and 20 min, respectively. In the plasma sampled from the inferior vena cava caudal to the renal veins, cAMP increased during DDAVP infusion from 22.2 +/- 2.5 to 39.2 +/- 3.8 and 36.0 +/- 4.0 pmol/ml after 10 and 20 min, respectively. The infusion of DDAVP was later given to the same dogs under anesthesia after bilateral nephrectomy, which did not modify the effect of DDAVP on arterial plasma cAMP. In another group of four conscious dogs, infusion of DDAVP at the same rate did not induce significant changes in plasma catecholamines.(ABSTRACT TRUNCATED AT 250 WORDS)
Am J Physiol 1992 Dec
PMID:cAMP and extrarenal vasopressin V2 receptors in dogs. 133 16

In several models of salt appetite in the rat, stimulated NaCl intake can be severely blunted by treatments associated with pituitary release of oxytocin (OT). Central administration of the potent dipsogen angiotensin II (ANG II) is known to elicit a limited salt appetite as well as thirst, but it has also been reported to stimulate pituitary OT secretion. These results suggest the possibility that the expression of ANG II-induced salt appetite in rats may be inhibited by a simultaneous central release of OT in response to this stimulus. To investigate this possibility, rats were given intracerebroventricular injections of OT-receptor antagonists before administration of 5 ng ANG II intracerebroventricularly in a 1-h two-bottle (water and 0.3 M NaCl) drinking test. This pretreatment resulted in a three- to fourfold potentiation of ANG II-induced saline ingestion, which was most prominent during the first 15 min of the test. OT-receptor antagonism did not, however, interfere with the dipsogenic properties of ANG II, nor did it stimulate saline ingestion alone in the absence of ANG II. Immunocytochemical studies demonstrated that central administration of ANG II at this dose caused pronounced c-fos expression in hypothalamic magnocellular OT and vasopressin neurons and also in OT neurons in parvocellular subdivisions of the paraventricular nucleus. These results therefore demonstrate that central administration of small doses of ANG II activates both magnocellular and parvocellular OT neurons in rats and indicate that some of the activated central OT pathway(s) may mediate an inhibitory effect that limits the salt ingestion induced by this treatment.
Am J Physiol 1992 Dec
PMID:Central oxytocin inhibition of angiotensin-induced salt appetite in rats. 133 19

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)
Biol Reprod 1992 Dec
PMID:Oxytocin and bovine parturition: a steep rise in endometrial oxytocin receptors precedes onset of labor. 133 77

There is increasing evidence for the existence of substances in ovarian tissues and fluids which are able to act locally, either alone or by modulating the actions of the gonadotropins, thus modifying the functions of ovarian cells. There are now clear data for oxytocin (OT), insulin-like growth factor-1 (IGF-1) and basic fibroblast growth factor (bFGF) in luteal tissue, with regard to specific expression of mRNA, secretion of peptid and receptors. Biological effects of these growth factors and others on luteal tissue were determined during the estrous cycle using two different in vitro systems; a novel microdialysis system (MDS) of intact luteal tissue and culture of luteal cells. The concentrations of secreted progesterone and OT were used as parameters. MDS; OT was most stimulative during the early luteal phase (days 5-7) and decreased continuously from days 8-12 to days 15-18. During early and mid stages bFGF was the most potent stimulator and at the late stage IGF-1 and IGF-2 were most stimulatory. Transforming growth factor beta (TGF-beta) stimulated the release of OT most effective at the early luteal stage. Results from the cell culture system (where no cell to cell contact exists) showed a different pattern. IGF-1 and IGF-2 had a stimulatory effect during long and short term stimulation, bFGF only during short term and OT showed no effect. Receptors were found for all peptides examined of luteal cells. A model of an intraovarian cascade-like system for the amplification of luteal function is presented.
J Physiol Pharmacol 1992 Dec
PMID:Regulation of bovine intra-luteal function by peptide hormones. 134 64

The importance of sympathetic innervation changed significantly during sexual maturation and in the course of the oestrous cycle in females. Basal secretion of progesterone is partly dependent on constant beta-adrenergic stimulation since local infusion of propranolol (beta-blocker) into the ovary decreased progesterone secretion by 20-30% of pre-treatment value. Noradrenaline given into the abdominal aorta in the moderate doses affected very quickly and dramatically the secretory function of the corpus luteum during the luteal phase in cattle and also in other species. Thus short-lasting mobilization stress protects and even supports corpus luteum function. This effect is exerted through the stimulation of beta-adrenoceptors which then activates specific intracellular enzymes. Additionally noradrenaline acts upon vascular alpha-receptors and increase ovarian blood flow allowing utilization of serum-derived lipoprotein as a source of cholesterol for steroidogenesis. The highest amount of specific beta-receptors in luteal membranes was found in the newly-formed corpus luteum which does appear to require noradrenergic support especially at that stage of its development. The mechanism of noradrenaline influence upon luteal cells resulting concomitant progesterone and ovarian oxytocin secretion is, however, obscure. It is suggested that intracellular second messengers (cAMP, Ca2+) involved in noradrenaline action can simultaneously affect the secretion of both these hormones and this indicates some functional relationship between them. The presented results are focused mainly upon cattle due to the importance of this species among other domestic animals. Nevertheless for comparison data from other species are also quoted.
J Physiol Pharmacol 1992 Dec
PMID:Role of the noradrenergic system in the secretory function of the corpus luteum. 134 65

A series of three large field trials was carried out to assess the effect of buserelin on fertility in dairy cows. In the first, 10 micrograms buserelin was injected on the day of insemination. There were no significant effects on fertility parameters compared to untreated controls. In the second trial cows were injected on day 12 after insemination. Mean pregnancy rates to first insemination were 53.4 and 65.4% for control and treated cows respectively (P < 0.01). Mean pregnancy rates to repeat inseminations were 52.9 and 59.4% for control and treated cows (NS). Mean calving to conception intervals were 91.4 and 85.3 days (P < 0.01) and the incidence of barren cows was 10.2 and 5.3% (NS). Overall the economic benefit of buserelin injection on day 12 was calculated to be 27.43 pounds per cow treated excluding the cost of the treatment. In trial 3 cows were injected with buserelin either on day 8 or 10 after insemination. There were no significant effects on fertility parameters compared to untreated control cows. In a fourth trial ewes were injected with 4 micrograms buserelin on day 12 after service. There were indications that both pregnancy rate and lambing percentage could be increased by buserelin treatment. Daily blood samples were collected from 5 dairy cows during a control cycle and a cycle in which 10 microgram buserelin was injected on days 11 and 13. Cycle length was unaffected by treatment and the concentration and pattern of progesterone secretion did not differ between control and treated cycles. Plasma oestradiol concentrations were similar in the control and treated cycles before day 11. However from day 12 to 16, equivalent to the time of maternal recognition of pregnancy, the mean concentration of oestradiol was significantly reduced in the treated cycle. As oestradiol stimulates both the development of uterine oxytocin receptors and the secretion of PGF2 alpha we suggest that any improvement in pregnancy rate after buserelin is due to a weakened luteolytic mechanism, resulting from a lower plasma oestradiol concentration.
J Physiol Pharmacol 1992 Dec
PMID:Experimental and practical approaches to the establishment and maintenance of pregnancy. 134 66

There is a great variation in body weight loss during lactation among primiparous sows fed a standard diet that is adjusted based on the number of piglets nursed and the maintenance requirements. Energy and protein catabolism is more pronounced during the first 1 to 3 weeks of lactation and sows with low weight loss recover earlier from their negative energy balance during lactation than sows with high weight loss. Using continuous blood collection a decrease in plasma levels of oxytocin, prolactin, and insulin, and an increase in plasma levels and no of LH pulses during lactation were demonstrated. Prolactin levels gradually increased in response to each suckling while only 40-50% of recorded sucklings induced a significant rise in plasma oxytocin. Following a 24-h fast during lactation, levels of prolactin were very low but increased rapidly after refeeding. Even plasma levels of insulin and glucose decreased to very low levels during fasting, but the release of LH was similar before and after refeeding. Weaning resulted in decrease in plasma levels of prolactin and increase in plasma levels and no. of LH pulses. Plasma levels of cortisol showed a diurnal pattern of change which disappeared on the day of weaning. In response to weaning plasma levels of glucagon and gastrin decreased, whereas insulin and somatostatin increased. At weaning sows with low weight loss during lactation had higher plasma insulin and lower plasma cortisol levels than sows with high weight loss, but no differences in levels or no. of LH pulses were observed between the two groups of sows.
J Physiol Pharmacol 1992 Dec
PMID:Metabolic and reproductive hormones during lactation and the post-weaning period in sows. 134 70

With the inrush of new data the recent clear division of neural, hormonal and immunological regulation has been seriously complicated. Both central and peripheral neural tissue produce over 30 neuropeptides, among which are many classic peptide hormones. A steroid biosynthetic pathway has been demonstrated in oligodendrocytes. However, the distribution and role of peptydoergic neurons within the reproductive system are only superficially known among farm animals. Neurons have receptors for many hormones and interleukins. Cells of the immune system, in addition to secretion of many interleukins and interferons, produce neuropeptides locally and they possess specific receptors for them as well. Till now, the interaction between the nervous, hormonal and immunological systems has not been taken into account while investigating the functions of ovarian follicles, the corpus luteum, oviduct and uterus. The penetration of blood and lymphatic vessels by hormones, neuropeptides and cytokins has not been taken into consideration also. The counter current transfer of many steroid and peptide hormones from ovarian venous and lymphatic effluent to arterial blood supplying the ovary and through arterial anastomoses of the oviduct and uterus has been hithero shown. It has been demonstrated that thanks to this system, arterial blood supplying the uterus and oviduct has, in physiological conditions, a much higher level of some steroid hormones such as progesterone and androstendione, 37% and 36% respectively, than in systemic blood. Recently, a powerful exchange system for resupplying hormones to the brain which is dependent on the phase of the estrous cycle, has been discovered. It has also been demonstrated that neuropeptides LH-RH, beta-endorphin and oxytocin as well as the steroid hormone progesterone, were counter current transferred from venous to arterial blood at the perihypophyseal cavernous sinus and carotid rete in sheep and gilts, but only during specific periods of reproductive activity. The mechanism of this process is still unknown. The role of peptydoergic neurons and cytokins in vascular permeability during hormone counter current transfer in the broad ligament vasculature, perihypophyseal cavernous sinus and carotid rete has not been investigated. It is suggested that progress in this area may change our point of view on many basic regulatory mechanisms involved in animal reproductive physiology.
J Physiol Pharmacol 1992 Dec
PMID:New pathways in animal reproductive physiology frontiers and perspectives. 134 74

The present study tested the hypothesis that the attenuation by oxytocin of tolerance to ethanol-induced hypothermia relies upon an impairment of the putative conditioning processes underlying environment-specific tolerance. According to the conditioning model of tolerance, such tolerance occurs because an opposite compensatory response conditioned to ethanol-paired cues attenuates ethanol's effects. Tolerance to ethanol-induced hypothermia was established to a particular environment over 4 days by injecting mice (daily) with oxytocin 2 h before ethanol, outside the colony room. As controls, other mice were injected similarly but following testing in the animal room. We found that oxytocin suppressed the conditioned compensatory response, revealed by injecting saline to every group in the tolerance-associated environment. These results suggest that oxytocin acted, at least partly, via an inhibition of the associative learning processes that facilitate tolerance development.
Pharmacol Biochem Behav 1992 Dec
PMID:Oxytocin blocks the environmentally conditioned compensatory response present after tolerance to ethanol-induced hypothermia in mice. 136 94


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