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

It was found that 10(-7)-10(-8) mol/l oxytocin (OT) or arginine-vasopressin (AVP) applications produced effects on functional properties of three types of acetylcholine (ACh) receptors on various neurons identified in the ganglia of Helix pomatia under voltage clamp conditions. OT and AVP depressed ACh-induced sodium-potassium-calcium current in neuron RBc3 without shift of reversal potential. Our data show that there are two types (subtypes) of ACh receptors which are connected with chloride current in neurons of Helix pomatia. OT decreased ACh-induced chloride current in neuron D4 and enhanced ACh-induced chloride current in neuron D5. These effects of OT were mimicked by the intracellular injection of cyclic AMP or application of isobutylmethylxanthine and an active cyclic AMP analog. AVP as a rule mimicked the effects of OT on functional properties of ACh receptors, but in neuron F8 effects of OT and AVP were independent. The present results suggest that cyclic AMP may be the second messenger mediating the OT- and AVP-induced modulations of functional properties of three types of ACh-receptors.
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PMID:Modulatory effect of oxytocin and arginine-vasopressin on functional properties of three types of acetylcholine receptors in molluscan neurons. 171 16

The ability of vasopressin to elevate cytosolic Ca2+ in small cell lung cancer (SCLC) cells was investigated. Ten nanomolar vasopressin elevated the cytosolic Ca2+ in 6 of 8 SCLC cell lines that were loaded with Fura-2 AM. Using SCLC cell line NCI-H345, the effect of vasopressin was dose dependent, being maximal at 100 nM, where the cytosolic Ca2+ was elevated from 150 to 210 nM. Because addition of 1 mM EGTA had no effect on the vasopressin response, vasopressin released Ca2+ from intracellular pools. Also, oxytocin weakly elevated the cytosolic Ca2+. The response to vasopressin was strongly blocked by [(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)1,O-MeTyr2,Arg8]vasopressin and weakly blocked by [(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)1,O-MeTyr2,Orn8]vasotocin. These data suggest that V1 vasopressin receptors are present on SCLC cells.
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PMID:Vasopressin elevates cytosolic calcium in small cell lung cancer cells. 172 21

Longitudinal muscle cells were successfully isolated from pregnant rat myometrium (21 days of gestation) with more than a 95% survival rate. The approximate size of relaxed cells was 232.2 +/- 74 microns in length and 16.2 +/- 7.0 microns in width. Using the fluorescent indicator Fura-2, the concentration of intracellular free calcium ([Ca2+]i) in resting state cells was calculated to be 116 +/- 18.5 nM. The isolated cells responded well to K+, acetylcholine and oxytocin in terms of contraction as well as the increase in [Ca2+]i. The increase in [Ca2+]i induced by acetylcholine and K+ appeared to be mainly due to an influx of extracellular Ca2+. On the other hand, the oxytocin-induced increase in [Ca2+]i was mainly due to a release of Ca2+ from intracellular storage sites in the isolated cells. Isolated longitudinal muscle cells can serve as a useful tool in establishing the relationship between [Ca2+]i and regulation of the uterine contraction at the final stage of pregnancy.
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PMID:Intracellular calcium of longitudinal muscles isolated from pregnant rat myometrium. 174 99

The obstetrician does not pay attention to electrolytes in the amniotic fluid inspite of its great significance in the fetal homeostasis since its disturbance causes quick death of the fetus. In the presented article we aimed not only to describe reference values of sodium potassium, chloride and calcium but to examine their changes in prepathological and pathological states. 135 women with changes in the course of pregnancy of various character were investigated as well as 200 control women with normally progressing pregnancy. The results showed that there was steady state in the concentration of the indicated electrolytes during the whole pregnancy. There were no statistically significant changes in electrolyte concentrations neither in preterm or prolonged pregnancy, nor in acute or chronic fetal asphyxia, in meconial and hematinic mexures samples as well as in oxytocin infusions with a medium of saline. There was only highly significant lowering of the amount of calcium ions in the amniotic fluid of women with pre-eclampsia. Analysis of the results show that the kidney, finding itself in functional correlation with the placenta, is reliable regulator of the internal and external homeostasis of the fetus.
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PMID:[Electrolyte studies of the amniotic fluid]. 178 66

Myometrium from rats in varying stages of pregnancy (from 17 to 22 days) was treated with oxytocin (0.1-10 microM) and plasma membranes and sarcoplasmic reticulum were isolated using a Percoll gradient. When the myometrium had been treated with oxytocin, Ca2+ uptake was reduced by 29.4% in the plasma membrane and by 32.6% in the sarcoplasmic reticulum. The inhibitory action of oxytocin was highly dependent upon the stage of gestation: Only membranes from rats close to term (21-22 days) exhibited reduced Ca2+ transport activity after hormone treatment. This effect correlated highly with a significant decrease in the serum progesterone level of these animals. In plasma membrane vesicles, oxytocin reduced the maximal velocity of the Ca2+ pump without significantly affecting the affinity for Ca2+. Oxytocin did not affect the passive permeability of the plasma membranes, nor their proportion of sealed inside-out vesicles nor the amount of Ca2(+)-pump protein in these membranes. In addition, oxytocin caused no change in the passive permeability of the membrane nor in the rate of inositol trisphosphate-induced Ca2+ release from the sarcoplasmic reticulum. These results suggest that there is a specific action of oxytocin on the activity of the myometrial plasma membrane and sarcoplasmic reticulum Ca2+ pumps which may contribute to the maintenance of an elevated intracellular calcium level during parturition.
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PMID:Oxytocin pretreatment of pregnant rat uterus inhibits Ca2+ uptake in plasma membrane and sarcoplasmic reticulum. 182 13

The effect of arginine vasopressin (AVP) on its own septal release was evaluated using an in vitro superfusion procedure. As compared to basal release from septal fragments, pulses of synthetic AVP (15 pg/5 min) resulted in a 25-fold augmented release of endogenous AVP, indicating a positive feedback action. Both the basal and stimulated AVP release were significantly increased by 60 mM potassium and markedly reduced by omission of calcium. Preincubation of the septal fragments with the V2/V1 AVP receptor antagonist d(CH2)5 [D-Tyr (Et)2,Val4]AVP resulted in a dose-dependent inhibition of the positive feedback action of AVP which was nearly completely blocked at doses between 1.25 and 5 ng per 100 microliters incubation medium. As compared to this effect, the V1 antagonist d(CH2)5 Tyr (Me)2 AVP as well as oxytocin were significantly less potent. The results suggest that the positive feedback action of AVP on its own release from septal fragments is potassium-stimulated, calcium-dependent and mainly V2 receptor-mediated. The physiological significance of this phenomenon remains to be shown.
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PMID:The positive feedback action of vasopressin on its own release from rat septal tissue in vitro is receptor-mediated. 183 May 7

Arginine vasopressin (AVP), oxytocin (OT), and angiotensin-II (AII) elicit a biphasic ACTH secretory response by perifused anterior pituitary cells consisting of an initial transient (less than 3-min) spike phase and a subsequent sustained plateau phase. In contrast, CRF produces a monophasic sustained plateau type of ACTH secretory response. We have previously demonstrated that 1) influx of extracellular Ca2+ (Cae2+) via L-type voltage-sensitive Ca2+ channels is involved in both the response to CRF and the sustained phase of the response to AVP and OT; 2) release of intracellular Ca2+ (Cai2+) is involved in the spike phase of the response to AVP, OT, and AII; and 3) activation of protein kinase-C is required for the sustained phase, but not for the spike phase, of the response to AVP. CRF action is mediated by activation of protein kinase-A. In this study we further examined the role of Cai2+ by exploiting the fact that a low concentration (1 microM) of ionomycin, a potent Ca2+ ionophore, releases Cai2+ from nonmitochondrial inositol-1,4,5-trisphosphate (IP3)-sensitive Cai2+ stores without causing Cae2+ influx. Pretreatment with ionomycin for 10 min decreased the spike phase of the response to 100 nM AVP, OT, and AII, but had no effect on the response to 10 nM CRF or the sustained phase of the responses to the other agonists. The combination of CRF plus AVP induced a biphasic and synergistic release of ACTH. Ionomycin pretreatment reduced the spike phase, especially the first 1 min, without any effect on the sustained phase. These results indicate that Cai2+ release, but not Cae2+ influx, is involved in the spike phase of the response to AVP, OT, and AII and that Cai2+ is not involved in the synergistic effect of the combination of CRF plus AVP. Having established these relationships, we examined the effect of 2-h perifusion with 100 nM dexamethasone (DEX) on stimulated ACTH release. DEX pretreatment reduced the total response to CRF, the sustained phase of the responses to AVP and OT, and the sustained phase of the synergistic response to CRF plus AVP. However, DEX had no effect on the spike phase of the responses to AVP, OT, or AII or the spike phase of the response to CRF plus AVP. These results indicate that DEX inhibits ACTH release mediated by activation of either protein kinase-A or protein kinase-C, but does not affect inositol-1,4,5-trisphosphate/Cai2(+)-mediated ACTH release.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Effects of intracellular Ca2+ depletion and glucocorticoid on stimulated adrenocorticotropin release by rat anterior pituitary cells in a microperifusion system. 184 62

The demonstration that endothelin (ET) induces rat uterine contraction, coupled with the observation that ET is present in human amniotic fluid, suggests that the myometrium may be an important target organ for this hormone. We show that in quiescent human myometrial cells ET produced a dose-dependent increase in cytosolic free Ca2+ (Cai2+), which was markedly attenuated when the cells were studied in Ca2(+)-free media. Preincubation with nicardipine, diltiazem, or verapamil reduced the ET-evoked Cai2+ transient by 30, 40, and 65%, respectively. The presence of voltage sensitive Ca2+ channels was demonstrated by Mn2+ quenching of fura-2. Activation of the Na+/H+ antiport could not be demonstrated with ET stimulation. In nonquiescent cells, the ET-evoked Cai2+ transient was significantly reduced, while the response to oxytocin was retained. This is at least partially explained by a reduction in Bmax (maximal binding capacity) for ET (mean +/- SEM) from 3,506 +/- 268 binding sites/cell in quiescent cells to 2,411 +/- 300 binding sites/cell, as well as 72% increase in Kd (equilibrium dissociation constant), in the nonquiescent cells. We conclude that, in human myometrial cells, ET and oxytocin modulate Cai2+ through independent receptors and propose that ET, like oxytocin, is an important endogenous modulator of uterine contractility.
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PMID:Endothelin- and oxytocin-induced calcium signaling in cultured human myometrial cells. 184 47

Oxytocin, the peptide well-known for its hormonal role in parturition and lactation, is present in several extrahypothalamic brain areas besides the neurohypophyseal system. The peptide is found in neurons which send their projections to brain areas containing specific oxytocin-binding sites. Oxytocin is also released from its synapses in a calcium-dependent fashion and may be the precursor of potent behaviorally active neuropeptides. These findings suggest that this ancient neuropeptide acts as a neurotransmitter in the central nervous system. We have attempted to review the most recent behavioral, morphological, electrophysiological and neurochemical studies providing evidence that oxytocin plays an important role in the expression of central functions, such as maternal behavior, sexual behavior (penile erection, lordosis and copulatory behavior), yawning, memory and learning, tolerance and dependence mechanisms, feeding, grooming, cardiovascular regulation and thermoregulation.
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PMID:Central functions of oxytocin. 185 13

Intracellular recording and labeling were combined with neurophysin immunohistochemistry to study neurons in the paraventricular nucleus region of the rat hypothalamus. Neuronal membrane properties were examined in hypothalamic slices, and cells were labeled by injecting biocytin or Lucifer yellow. Slices were then embedded, sectioned, and immunohistochemically processed for neurophysin. Immunoreactivity patterns, and in some cases counterstaining, enabled determinations of the cytoarchitectonic positions of recorded cells to be made. Recorded cells were divided into three types according to their electrophysiological characteristics. The first type lacked low-threshold Ca2+ spikes and displayed linear current-voltage relations, a short time constant, and evidence for an A current. These were relatively large cells that were typically immunoreactive for neurophysin and were situated near other neurophysin-positive neurons. The second type had relatively small low-threshold potentials that did not generate bursts of Na+ spikes. These cells had heterogeneous current-voltage relations and intermediate time constants. They did not label for neurophysin, and most were located in the parvicellular subregion of the paraventricular nucleus. The third type had large low-threshold Ca2- spikes that generated bursts of Na+ spikes, and these cells had nonlinear current-voltage relations and long time constants. These neurons were dorsal or dorsolateral to the paraventricular nucleus and were not immunoreactive for neurophysin. These results indicate that paraventricular magnocellular neurons lack low-threshold potentials, whereas paraventricular parvicellular neurons display low-threshold potentials that generate one or two action potentials. Neurons that fire spike bursts from low-threshold potentials are adjacent to the paraventricular nucleus, confirming earlier reports.
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PMID:Immunohistochemical differentiation of electrophysiologically defined neuronal populations in the region of the rat hypothalamic paraventricular nucleus. 185 30


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