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

The modification by magnesium of the excitatory effect of oxytocin (10(-5)-10(-2) U/mL) on electrical and mechanical activities of pregnant human myometrium was examined. The excitatory effect of oxytocin was enhanced by external magnesium, and the dose-response curve between oxytocin and relative tension in the presence of 118 mM potassium in tiny muscle strips shifted to the left with increases in magnesium from 0 to 2.4 mM. Oxytocin potentiates spontaneous contractions by enhancing the plateau part of action potentials, and the plateau potential induced in 2.4-mM magnesium was larger than that in magnesium-free solution. In potassium contracture experiments, the muscle contraction was potentiated in accordance with the concentration of preloaded magnesium when 10(-3) U/mL oxytocin was added at the tonic phase. These results suggest that magnesium might primarily potentiate the excitatory effect of oxytocin in electrical and mechanical activities of pregnant human myometrium at superficial sites of the plasma membrane, allowing the possibility of its intracellular action.
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PMID:Modification by magnesium of the excitatory effect of oxytocin in electrical and mechanical activities of pregnant human myometrium. 237 Oct 22

The effects of intraventricular injection (ICV) of oxytocin (OT) and antioxytocin serum (AOTS) on the pain threshold and electroacupuncture (EA) analgesia in rats were investigated in this study. The potassium iontophoresis induced tailflick was used to measure the pain threshold. An increase of 20-38% in the pain threshold was observed within 80 min after OT injection (50 ng), while the OT administration (50 ng) in combination with EA produced a dramatic increase of 139-234% in the pain threshold, which was much higher than that in the saline-EA group (P less than 0.05 or 0.01). The OT effect was dose-related in the range between 25-100 ng. Although ICV of AOTS did not change the pain threshold, the EA analgesia became weakened significantly. After injection of AOTS, EA only produced an increase of 47-61% in the pain threshold, while following ICV injection of normal rabbit serum instead of AOTS the EA could cause a rise of 104-123% in the pain threshold. There was a significantly statistical difference between the above two groups (P less than 0.05-0.01). The data indicate that ICV of OT not only elevates the pain threshold, but also enhances the EA effect, and that AOTS attenuates the EA analgesia. These results suggest that endogenous oxytocin in the central nervous system may play a role in the electroacupuncture analgesia.
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PMID:[The role of central oxytocin in electroacupuncture analgesia]. 237 36

We developed a technique to obtain very thin myometrial muscle strips that allowed comparison of characteristic features of contraction from the same strip under intact and membrane-permeable ("skinned") conditions. Absolute tension development per unit of cross-sectional area induced by high potassium and oxytocin concentrations in the intact condition, or by Ca2+ in the skinned condition, markedly increased in human myometrium at term compared with the nonpregnant state. The maximum tension in skinned strips was 8.3 mN/mm2 in nonpregnant strips and 47.5 mN/mm2 at term (both obtained at 10 mumol/L Ca2+). The Ca2+ sensitivity of the contractile proteins in skinned strips also increased at term compared with the nonpregnant state; the half-maximal response of Ca2+ sensitivity was 0.7 mumol/L in the nonpregnant state and 0.3 mumol/L at term. These results suggest that in human myometrium both the amount of contractile proteins and their sensitivity to Ca2+ may increase at term compared with the nonpregnant state.
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PMID:Gestational changes in mechanical properties of skinned muscle tissues of human myometrium. 238 56

The direct action of biologically active substances on the smooth muscle cells tone was studied in isolated segments of the cow diencephalic arteries. The serotonin, histamine, vasopressin, potassium ions were found to induce a dose-dependent increase of the smooth muscles tone. Weak responses to oxytocin and noradrenaline were revealed.
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PMID:[Effect of various biologically active substances on the tonus of smooth muscle cells of the arteries of the diencephalon]. 242 95

The facilitation of peptide secretion from the neurohypophysis induced by increasing stimulation frequency is accompanied by action potential (AP) prolongation. One hypothesis argues that inactivation of potassium channels in the neural lobe terminal membranes, under these conditions, is the underlying mechanism which leads to AP prolongation, and, therefore, increased calcium entry and secretion per AP. Therefore, factors which are known to cause AP prolongation, such as stimulus frequency and potassium channel blocking agents, were studied and compared with regard to their ability to augment electrically evoked release of oxytocin (OT) and vasopressin (VP) from isolated rat neurointermediate lobes (NILs). OT release (to a constant applied stimulus of 600 spikes) was maximally facilitated by increasing frequency up to a rate of 30 Hz, whereas VP release in the same stimulus paradigm was maximal between 12 and 20 Hz. Tetraethylammonium (TEA), 4-aminopyridine (4AP) and barium each caused a significant augmentation of AP-dependent, electrically stimulated hormone release, without affecting basal levels. The magnitude of the effect of the K channel blocking agents was inversely related to the frequency of the applied stimulus. Application of either 4AP or TEA caused a shift in the range of frequency dependence for OT such that maximal release was seen at a stimulus frequency of 12 Hz, but there was no comparable change in the pattern of VP release. The maximal effects of TEA and 4AP were additive indicating that the NIL terminals have two types of K channels which appear to be involved in the regulation of secretion. Addition of the three agents together produced maximal release at a stimulus frequency of 4 Hz, which was not facilitated further by the increase of stimulus frequency to 20 Hz. These data demonstrate the importance of potassium channels in the regulation of VP and OT secretion, and provide indirect support for the spike prolongation hypothesis of frequency facilitated secretion in the neural lobe.
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PMID:Effects of stimulus frequency and potassium channel blockade on the secretion of vasopressin and oxytocin from the neurohypophysis. 244 64

Increasing concentrations of nitrendipine were found to inhibit various types of muscular activation (electrical stimulation, acetylcholine, oxytocin, potassium chloride), as well as the spontaneous rhythmic activity of the isolated rat uterus. The degree of the inhibitory effect of nitrendipine depends on the type of activation. Nitrendipine showed an exceptionally high efficacy in inhibiting contractions induced by electrical stimulation and of spontaneous rhythmic activity. For inhibition of these contractions even osmolar concentrations of nitrendipine were sufficient. The relaxant effect of nitrendipine depended on the concentration of extracellular calcium and the time of incubation of nitrendipine in the bathing medium. Nitrendipine showed high selectivity for the uterine smooth muscle because in a very high concentrations is exerted an insignificant relaxation of the other isolated smooth muscles (oesophagus, urinary bladder). Our experiments indicate that nitrendipine might have a role in therapy of premature delivery and abortion because of its great selectivity for the uterine smooth muscle. Addition of calcium into the medium restores completely all types of muscular activation after the inhibitory action of nitrendipine except its depressive action on the phasic component of oxytocin-induced contractions. These findings that individual types of activation, after inhibitory action of nitrendipine, are reestablished in various degrees by the addition of calcium into the medium, are also an additional confirmation about the existence of various types of calcium channels.
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PMID:[Effect of nitrendipine on isolated uterus and other smooth muscles of the rat]. 253 Oct 21

Nerve endings from rat neural lobes isolated by homogenization were placed on a filter and constantly superfused. The effects of exogenous oxytocin and vasopressin (both added at 1 nM concentration) on basal and stimulated release of oxytocin and vasopressin were investigated. Stimulated release was evoked by 30 mM potassium and a simultaneous increase in osmolarity. A stimulatory effect of oxytocin on basal and evoked release of oxytocin was found while there was no effect on vasopressin release. The addition of vasopressin did not induce any change in the release of either hormone. The positive feedback mechanism observed with oxytocin might be active during the discharge of oxytocin which is known to occur in bursts.
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PMID:Oxytocin stimulates oxytocin release from isolated nerve terminals of rat neural lobes. 262 24

Studies were undertaken to investigate the effects of oxytocin induction on prolactin release in term (Group II) and preterm (Group III) mares and to compare these effects to spontaneously foaling mares (Group I). Since physiological concentrations of prolactin in blood have not been measured in the neonatal foal, experiments were designed to monitor prolactin in the cord artery and jugular blood of the foals from all groups of mares. Although prolactin levels varied in term mares (Group I and II) during the last 11 days of pregnancy, an increase was observed between Day -6 and Day 0 (2.7 and 11.9 ng/ml respectively; P less than 0.1). The average concentration of prolactin over the last 4 days (Days -3 to 0) had increased by 40% when compared to the average concentration on Days -6, -5, and -4. These findings indicate a rising trend which appears to occur concomitantly with changes in concentrations of 2 mammary components tested, sodium and potassium. Prolactin concentrations did not significantly increase in term mares after oxytocin treatment or in spontaneously foaling mares. However, the preterm induced mares had higher prolactin concentrations during the first stage of labor (19.3 +/- 7.2 ng/ml) than prior to treatment with oxytocin (4.7 +/- 2.0 ng/ml; P less than 0.01). Levels of prolactin in all groups significantly declined by 20-min post-placental expulsion. For the first 30 min after birth, prolactin concentrations in foals from oxytocin-induced mares appeared to be 2-fold higher than those from spontaneously foaling mares. Thereafter, prolactin values declined to baseline values by 48 hrs. When comparing cord arterial plasma with cord venous plasma in each group, prolactin concentrations were similar. However, the average prolactin levels in both the cord artery and vein appeared higher (ave: 1.1 ng/ml) in Group II and III than in Group I (less than 0.5 ng/ml). From these results, the authors suggest that 1) prolactin may have a role in regulating mammary secretory products in mares just prior to parturition; 2) oxytocin may increase prolactin secretion in preterm induced mares; 3) oxytocin induction may have a short term effect to increase circulatory prolactin concentrations in neonates in utero regardless whether their dams were treated preterm or term.
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PMID:Plasma prolactin concentrations in mares and their neonates after oxytocin induction of parturition. 273 12

The ability of lipoprotein lipase to move across the mammary epithelium by a paracellular route was investigated. Five goats were milked hourly to activate the paracellular pathway. Three goats responded to hourly milking with a fivefold increase in milk lipoprotein lipase activity as compared with nonresponding goats. Massage of the mammary gland was necessary in the two nonresponding goats too cause increased lipoprotein lipase activity in milk. Oxytocin treatment during hourly milking also increased enzyme activity in milk from a nonresponding goat. Activation of the paracellular pathway by hourly milking increased milk sodium and protein and decreased potassium and lactose concentrations. After a 12-h milking interval, lipoprotein lipase activity was distributed primarily in the serum (48%) and cream (40%) fractions and, to a lesser extent, in the casein (12%) fraction. Hourly milking increased enzyme activity distributed in the serum fraction (62%), whereas enzyme activity associated with the cream (32%) and casein (6%) fractions decreased. Possible mechanisms for the origin of lipoprotein lipase in milk are discussed.
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PMID:Paracellular leakage of lipoprotein lipase across the mammary epithelium of the goat. 274 24

Naloxone increased the electrically (15 Hz, 1 min) evoked release of oxytocin from isolated neural lobes of rats 3-4-fold. In the presence of 4-aminopyridine or tetraethylammonium ions the evoked release of oxytocin was increased 8-9-fold and remained unaffected by naloxone. Increasing the calcium concentration in the medium from 1.2 to 3 mM caused only a marginal increase of the evoked oxytocin release. In conclusion, blockade of potassium channels and/or the resulting prolongation of the action potential can surmount the opioid inhibition of oxytocin release.
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PMID:Tetraethylammonium ions and 4-aminopyridine prevent opioid inhibition of neurohypophysial oxytocin release. 282 94


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