UNIPROT:P01178 - FACTA Search

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

We examined the effects of several in vitro experimental systems on the apparent potencies of putative secretagogues for stimulating ACTH release from rat anterior pituitary cells. Cells were prepared by trypsin digestion and gentle mechanical dispersion. Aliquots of the same cell preparations were tested in 1) a microperifusion system immediately after dispersion (day 0), 2) the same microperifusion system after 4 days of static suspension culture on a layer of Sephadex G-10 gel particles (day 4), 3) a static suspension system after 4 days of static suspension culture, and 4) a static monolayer system after 4 days of monolayer culture. Ovine CRF stimulated release of similar amounts of ACTH in all of the systems on days 0 and 4, except in one experiment, in which the response was less on day 4. Arginine vasopressin (AVP), oxytocin, and angiotensin II all appeared to be more potent in day 4 than in day 0 cells in the perifusion system, and the synergism of AVP with ovine CRF was also increased. Dioctanoylglycerol, which directly activates protein kinase-C, and forskolin, which directly activates adenylate cyclase, both stimulated greater release in day 4 cells. The mechanism(s) responsible for the difference in the responses of day 0 and day 4 cells is unknown. Epinephrine had only a small effect in the microperifusion system, but both epinephrine and norepinephrine had potencies comparable to AVP in the static suspension and monolayer systems. This was not due to prolonged exposure to the catecholamines, suggesting that these agents may act on other anterior pituitary cells to release metabolic products that secondarily stimulate the corticotrophs to release ACTH. The same situation appears to be true for atrial natriuretic factor. Gastrin-releasing peptide, its bioactive COOH-terminal half, which was active in a rat urinary bladder smooth muscle assay, its amphibian analog, bombesin, and cholecystokinin (26-33) were devoid of ACTH-releasing activity in all of the systems, in contrast to the findings of others. Since 4-day culture of dispersed cells improved most of their responses and diminished none, we postulate that they may more closely resemble normal pituitary cells in function, and since cellular metabolites are unlikely to accumulate in the interstitial fluid of the pituitary gland, we propose that the secretory functions of cells in perifusion systems may more closely resemble those in the pituitary gland in situ than they do in static incubation systems.
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PMID:Effects of several in vitro systems on the potencies of putative adrenocorticotropin secretagogues on rat anterior pituitary cells. 283 88

In view of the presence of distinct oxytocin (OT) and vasopressin (VP) receptors in the male genital tract (porcine) we have reexamined the receptors for OT and AVP in the classical OT target tissue, female genital tract (rabbit). Neurohypophysial hormone receptors have been investigated in vagina, myometrium, and oviduct using quantitative ligand binding, adenylate cyclase, and contractility studies. Our results clearly indicate the presence of distinct OT and V1 VP receptors in the myometrium, while only the latter was detected in vagina and oviduct. In myometrium, estrogen treatment increases the density of OT and AVP receptors, while progesterone administration inhibits the estrogen effect. At the time of spontaneous delivery a dramatic (17-fold) increase was observed for the OT sites, while the AVP sites were unchanged. AVP receptors in vagina were sensitive to sex steroid administration and were reduced during pregnancy and delivery. Isometric contractility studies suggest that not just OT, but AVP can stimulate uterine strips, an effect that is partially reversible by the V1 antagonist d(CH2)5TyrMeAVP. In vagina only AVP is effective in inducing contractions at nanomolar concentrations. These results suggest a role for AVP as well as OT in regulation of the motility of female genital tract.
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PMID:Vasopressin and oxytocin receptors in vagina, myometrium, and oviduct of rabbits. 283 78

1. In the intact guinea-pig myometrium, carbachol and oxytocin stimulated a specific receptor-mediated phospholipase C activation, catalysing the breakdown of PtdIns(4,5)P2 with the sequential generation of InsP3, InsP2 and InsP. Stimulation of muscarinic receptors also triggered an inhibition of cyclic AMP accumulation caused by prostacyclin. 2. NaF plus AlCl3 mimicked the effects of carbachol and oxytocin by inducing, in a dose-dependent manner, the generation of all three inositol phosphates as well as uterine contractions. AlCl3 enhanced the fluoride effect, supporting the concept that A1F4- was the active species. Under similar conditions, fluoroaluminates activated the guanine nucleotide regulatory protein Gi, reproducing the inhibitory effect of carbachol on cyclic AMP concentrations. 3. Both carbachol- and oxytocin-mediated increases in inositol phosphates, as well as contractions, were insensitive to pertussis toxin, under conditions where the expression of Gi was totally prevented. Cholera toxin, which activates Gs and enhances cyclic AMP accumulation, failed to affect basal or oxytocin-evoked inositol phosphate generation, but induced a slight, though consistent, attenuation of the muscarinic inositol phosphate response, which was similarly evoked by forskolin. 4. The data provide evidence that, in the myometrium, (a) a G protein mediates the generation of inositol phosphates and the Ca2+-dependent contractile event, (b) the relevant G protein that most probably couples muscarinic and oxytocin receptors to phospholipase C is different from Gi and Gs, the proteins that couple receptors to adenylate cyclase, and (c) cyclic AMP does not seem to control the phosphoinositide cycle, but rather exerts a negative regulation at the muscarinic-receptor level.
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PMID:Fluoroaluminates mimic muscarinic- and oxytocin-receptor-mediated generation of inositol phosphates and contraction in the intact guinea-pig myometrium. Role for a pertussis/cholera-toxin-insensitive G protein. 284 25

We have previously demonstrated in pregnant sheep that ritodrine infusion for 24 hours reduces myometrial beta-adrenergic receptor density and isoproterenol-stimulated adenylate cyclase activity. These receptor-associated changes were accompanied by an increasing inability of ritodrine to inhibit uterine contractility induced by a bolus of oxytocin. In the present study, we evaluated whether these ritodrine-induced effects could be altered by dexamethasone. Ten pregnant sheep at gestational ages of 92 to 130 days received ritodrine 2 micrograms/kg/min for 24 hours. Five animals also received dexamethasone 10 mg intravascularly twice during the ritodrine infusion. Before and at 4 and 24 hours of ritodrine infusion, the animals were given an identical dose of oxytocin as a bolus, and the area under the uterine pressure-time curve was quantified. Myometrial biopsy specimens were obtained before and after ritodrine infusion. Dexamethasone treatment prevented ritodrine-induced reductions in beta-adrenergic receptor density and isoproterenol-stimulated adenylate cyclase activity. Despite these receptor-associated effects, dexamethasone did not prevent the loss of tocolytic efficacy associated with prolonged ritodrine infusion.
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PMID:Dexamethasone effects on ritodrine-induced changes in myometrial contractility and beta-adrenergic receptor function. 284 80

We have developed a model in pregnant sheep to investigate pharmacological agents used for suppression of preterm labor. This model allows repetitive determinations of uterine contractility and simultaneous measurements of myometrial receptor and postreceptor events. We used the model to study the beta-adrenergic agent ritodrine. We infused 11 pregnant sheep with ritodrine and 3 with physiological saline for 24 h. Oxytocin boluses were given before and at 5 and 22 h after onset of the infusion. Myometrial biopsies were obtained before and immediately after the infusion. After 22 h of ritodrine infusion, uterine contractility in response to the same oxytocin bolus was 50% greater than at 5 h (P less than 0.02). Myometrial membrane beta-adrenergic receptor density decreased 49% (P less than 0.005), and catecholamine-stimulated adenylate cyclase activity was reduced 70% (P less than 0.005). The model thus demonstrates that use of the beta-adrenergic agonist ritodrine in a clinically relevant manner results in tachyphylaxis of its effects on both physiological parameters and the receptor cascade system.
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PMID:Myometrial desensitization after ritodrine infusion. 288 62

Neurohypophysial hormones stimulate the motility of tunica albuginea, epididymis, and vas deferens acting through oxytocin (OT) and V1 vasopressin receptors. To test the hypothesis that these hormones are involved also in the regulation of seminal vesicle physiology, we studied binding of [3H]OT and [3H] arginine vasopressin ([3H]AVP) to porcine seminal vesicle membranes. Neurohypophysial hormones bind to two different classes of sites. The first class shows low capacity (35 fmol per mg of protein) and a very high affinity (Kd less than 1 nM) for both the labeled ligands. The second class is characterized by a high capacity (2000 fmol per mg of protein) and a high affinity for AVP (Kd approximately equal to 2.5 nM), whereas OT has 160 times lower affinity. Lysine vasopressin and the V1 antagonist [1-deaminopenicillamine, 2-(O-methyl)tyrosine]Arg8-vasopressin compete with high affinity with [3H]AVP binding, whereas the V2 agonist [1-deamino,4-valine]D-Arg8-vasopressin (dVDAVP) is 110 times less potent than AVP. The OT agonist [Thr4,Gly7]OT and the OT antagonist [1(beta-mercapto-beta, beta-cyclopentamethylene propionic acid), 2-(O-ethyl)tyrosine, 8-ornithine]vasotocin failed to affect [3H]AVP binding. These findings seem to suggest that AVP interacts with the V1 vasopressin isoreceptor in porcine seminal vesicle membranes. However, AVP stimulates adenylate cyclase activity in a dose-dependent fashion with an EC50 of 14 nM, whereas OT or dVDAVP has no effect at 100 nM. Moreover, a well-characterized V1 vasopressin antagonist, [1-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid),2-(O-methyl)tyrosine]Arg8-vasopressin [d(CH2)5Tyr(Me)AVP], competes with [3H]AVP binding with an IC50 of 0.17 microM. These pharmacological properties are distinct from the previously described V1 and V2 vasopressin receptors and indicate the presence of a new class of AVP receptors. Although this vasopressin isoreceptor shares some pharmacological characteristics with the V1 (pressor) isoreceptor, it has low affinity for the V1 antagonist d(CH2)5-Tyr(Me)AVP and is linked to the adenylate cyclase system. The extremely high density of AVP receptors in porcine seminal vesicles (2 pmol per mg of protein) is comparable to the density of V2 vasopressin receptors in porcine renal medulla, suggesting a physiological role for vasopressin in the seminal vesicle.
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PMID:Identification and characterization of a vasopressin isoreceptor in porcine seminal vesicles. 294 37

Synaptic plasma membranes containing binding sites for (3H) oxytocin and (3H) arginine vasopressin were isolated from rat amygdala, olfactory bulb and hippocampus. In the hippocampus, two specific binding sites have been characterized: an "oxytocic" binding site, which has a high affinity for oxytocin, arginine vasopressin and arginine vasotocin, and a "vasopressic" binding site, which has a high affinity for arginine vasopressin, arginine vasotocin and a low affinity for oxytocin. The specificity of these binding sites were tested in competition experiments. The affinity of different antidiuretic and vasopressic analogues for the vasopressic site was similar to that observed for the V1 type of vasopressin receptors present in the hepatocytes and vascular smooth muscle cells. The affinity of several analogues for the oxytocic site shows some similarities with their corresponding relative activities in increasing the firing rate of non pyramidal neurones in hippocampal slices. Arginine vasopressin and oxytocin did not change the activity of adenylate cyclase present in the hippocampal synaptic plasma membranes. The properties of these specific binding sites for the neurohypophyseal hormones are compared with the receptors present on the peripheral targets.
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PMID:[Vasopressin and oxytocin receptors in the central nervous system of the rat]. 300 28

Treatment of isolated rat adipocytes with epinephrine or isoproterenol caused a time- and concentration-dependent increase in phospholipid methyltransferase (PLMT) activity that was blocked by propranolol and unaffected by phentolamine. Forskolin mimicked the stimulatory effect on PLMT, and insulin inhibited this effect. In both the absence and presence of insulin, there was a linear relationship between PLMT activity and lipolysis. PLMT activity was also increased in response to oxytocin, which does not activate adenylate cyclase in adipocytes and does not stimulate lipolysis. The effects of oxytocin were inhibited by insulin and were additive with those of isoproterenol on PLMT. These data support the hypothesis that in adipocytes, PLMT is activated by a cAMP-dependent protein kinase and a cAMP-independent mechanism, both of which can be regulated independently, and both of which are sensitive to inhibition by insulin.
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PMID:Hormonal regulation of phospholipid methyltransferase by 3',5'-cyclic adenosine monophosphate-dependent and independent mechanisms. 303 90

Corpora lutea from sheep and cows as well as human and primates contain both large and small steroidogenic cells exhibiting distinct functional properties. Only the small cells seem to be able to respond in vitro to LH stimulation by raising their progesterone secretion. However, the entire progesterone secretion of the corpus luteum has been shown to be regulated in vivo by LH in the primate. The LH steroidogenic action involves the activation of membrane adenylate cyclase whose molecular mechanism has been elucidated. Then a rise in intracellular cyclic AMP induces phosphorylation by a cyclic AMP dependent protein kinase of steroidogenic protein targets which have not yet been completely identified. In sheep and cows, luteolysis is believed to be the consequence of a series of reciprocal interactions between the corpus luteum whose large cells secrete pulses of oxytocin in response to PGF2 alpha luteolysin and the endometrium which secretes pulses of PGF2 alpha in response to oxytocin. The secretion of endometrial PGF2 alpha can only begin after the induction of endometrial receptors by estradiol, from the preovulatory follicles. Similarly in women and primates luteolysis, which does not require the presence of the uterus, could be the consequence of local reciprocal paracrine interactions between luteal cells of different types. These interactions are likely to involve PGF2 alpha' oxytocin and estradiol. The biochemical mechanism responsible for the inhibition by PGF alpha of LH induced progesterone secretion in luteal cells could involve a stimulation in the cell membrane of protein kinase C and the rise of cytosolic Ca+.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Recent concepts concerning the corpus luteum]. 307 52

Normal corpus luteum function is determined by function in the follicular as well as the luteal phase. In the follicular phase adequate follicle-stimulating hormone (FSH) and oestrogen stimulation are required for granulosa cell mitosis and luteinizing hormone (LH) receptor synthesis. An increase in LH pulse frequency may also be necessary for adequate oestrogen synthesis and preparation of follicular cells for luteinization and secretion of progesterone. The nature of LH release may also influence luteal function and pre-ovulatory progesterone may increase the responsiveness of the follicle to gonadotrophins. The thecal vascular network becomes extensive around pre-ovulatory follicles and may influence access of gonadotrophins and/or the ability of follicular cells to respond to them. Further vascularization is an early feature of luteinization. Angiogenic factors are found in luteal tissue and prostacyclin increases luteal blood flow. The corpus luteum consists of large cells which secrete most of the progesterone and have prostaglandin F2 alpha receptors and small cells which are responsive to LH. In the luteal phase subnormal luteal function has not been associated with a reduction in LH concentration, pulse frequency or amplitude. The number and occupancy of LH receptors and adenylate cyclase activity do not appear to be altered by a reduction in luteal function. Low density lipoprotein provides the substrate and somatomedin C modulates among other hormones' influences, progesterone production. In addition to the cAMP second messenger system phosphatidyl inositol metabolism may also be associated with LH stimulation. Luteolysis is an active process; prostaglandin F2 alpha or lipoxygenase products and possibly an endogenous GnRH-like ovarian hormone may mediate it as also may oxytocin in some species.
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PMID:The corpus luteum. 328 62

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