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

Experimental conditions and parameters involved in high performance liquid chromatography (HPLC) separations of the peptide hormone oxytocin and seven of its diastereoisomers, namely [1-hemi-D-cystine]-, [2-D-tyrosine]-, [4-D-glutamine]-, [5-D-asparagine]-, [6-hemi-D-cystine-], [7-D-proline]-, and [8-D-leucine]-oxytocin, on reverse phase columns were investigated. The effects of solvent, pH, and salt concentration were studied. Using the solvent systems 10% tetrahydrofuran-ammonium acetate buffer or 18% acetonitrile-ammonium acetate buffer and the muBondapak C18 support, oxytocin was separated from each of its diastereoisomers under all conditions studied, but the order of elution of diastereoisomers was highly dependent on solvent and to a lesser extent on pH. Separations of the hormone and its diastereoisomers on reverse phase HPLC and on classical partition chromatography on Sephadex G-25 were compared. The results are discussed in terms of the interactions of the solute with the reverse phase column and the solvent system. Implications of these findings in terms of the different solution conformations of the peptides are discussed.
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PMID:The separation of peptide hormone diastereoisomers by reverse phase high pressure liquid chromatography. Factors affecting separation of oxytocin and its diastereoisomers--structural implications. 3 28

In a preliminary report we described the effects of rat prolactin on the incorporation of [14C]acetate into lipids by a cell line from a dimethylbenz(a)anthracene-induced rat mammary tumor. The characteristics of the response to prolactin were very similar to those described for the normal rat mammary gland; namely, insulin was required for full expression of the response, maximal activity was not seen until 36 hr after the addition of the hormones, and growth hormone was able to elicit the same response. However, we were unable to detect binding of 125I-labeled prolactin to these cells, and furthermore, other more purified prolactin preparations were inactive. Upon further investigation we discovered that the activity resided in a low-molecular-weight fraction of the rat prolactin B-1 preparation and was probably either vasopressin or oxytocin or both. These data suggest the possibility that vasopressin may play a role in rodent mammary tumorigenesis.
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PMID:Vasopressin stimulation of acetate incorporation into lipids in a dimethylbenz(a)anthracene-induced rat mammary tumor cell line. 10 Feb 17

Treatment of unanesthetized castrated adult male rats every 3 h for 48 h with either 5 microgram of arginine vasotocin (AVT) and/or 1 microgram luteinizing hormone-releasing hormone (LRH) caused a significant inhibition of plasma levels of luteinizing hormone (LH) and compared to castrated control rats receiving diluent only. However, the intravenous (iv) injection of 1 microgram of AVT into urethane-anesthetized male rats which had been castrated for 0, 24 or 48 h did not affect plasma levels of LH at 10, 20 or 60 min following injection compared to their respective diluent-treated castrated control rats. Similarly, the iv injection of either 100 ng, 1 microgram or 10 microgram AVT was unable to acutely affect plasma levels of LH in intact male rats. Following the iv injection of 2 doses of 50 ng LRH spaced 1 h apart in anesthetized castrated male rats, 2 peaks of equal magnitude in plasma LH were noted. Castrated rats treated with 2 injections spaced 1 h apart of LRH + AVT had significantly higher plasma levels of LH than did rats treated with LRH alone. In subsequent studies, both AVT and arginine vasopressin were observed to augment the plasma response of LH to an injection of LRH whereas oxytocin had no effect. A single injection of AVT + LRH significantly augmented the plasma titers of LH compared to levels observed in LRH-treated control rats as did a second injection 1 h later. The administration of cyproterone acetate sc for 2 days by itself had no effect on plasma LH but in conjunction with LRH caused a marked rise in plasma LH compared to intact rats treated with LRH alone. AVT in combination with LRH and cyproterone acetate caused a significant elevation in plasma LH at 60 min post-injection when compared to plasma levels of rats treated with LRH alone or the combination of LRH and cyproterone acetate. It is concluded that acute intravenous injections of AVT augment the LH-releasing activity of LRH; chronic treatment for 48 h, however, with LRH + AVT leads to a significant depression of plasma LH perhaps due to an exhaustion of the releasable pool of LH in the anterior pituitary.
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PMID:Interaction of luteinizing hormone-releasing hormone, cyproterone acetate and arginine vasotocin on plasma levels of luteinizing hormone in intact and castrated adult male rats. 37 36

Sections of neurosecretory cells fixed in glutaraldehyde and osmium tetroxide were studied by means of an EMMA-4 analytical microscope. Secretory granules in neurosecretory cells of the corpus cardiacum and of the brain, both in the desert locust Schistocerca and in the blowfly Calliphora, as well as neurosecretory granules in posterior pituitaries of the frog Rana and of the albino rat all contain a high concentration of calcium. A distinct sulphur peak was also a constant feature. In neurosecretory cells of the corpus cardiacum of Schistocerca the chromatin contained a high concentration of calcium. The mitochondria also contained much calcium, but part of this disappeared during preparation except when fixative and wash contained calcium chloride. By block staining with uranyl acetate most calcium is displaced from the mitochondria, whereas most of the calcium remains in the neurosecretory granules. Since the calcium peaks in spectra from neurosecretory granules appear of similar size, regardless of variations in the preparative procedure, this calcium must be firmly bound. The possible role of the calcium bound to the neurosecretory substance is discussed. The presence of sulphur in insect neurosecretory granules indicated the presence of a protein besides the hormone, i.e., an insect neurophysin.
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PMID:Calcium and sulphur in neurosecretory granules and calcium in mitochondria as determined by electron microscope x-ray microanalysis. 62 26

Cytochemical methods using silver proteinate, silver methenamine an potassium ferrocyanide + OsO4 for ultrastructural detection of glycoproteins allow, in the posthypophysis and the magnocellular nuclei of the rat, differentiation of two types of fibres and neurons: one type containing negative granules with a homogenous content of low electron density, the second type containing granules which demonstrate a ring shaped deposit either of silver or of potassium ferrocyanide-osmium complex, likely to be related to a glycoprotein component. The difference between these two types is increased by prestaining "en bloc" with uranyl acetate before the silver proteinate reaction. A similar investigation was carried out on the vasopressin deficient Brattleboro rat; the neurosecretory material, present in some endings and neurons only, is of the nonreactive type, so that it appears justified to correlate the reactivity of granules with vasopressin, consequently to distinguish neurones and fibres containing vasopressin from those in which oxytocin is quantitatively the main hormonal peptide. This conclusion is strongly supported by the fact that percentages of reactive and negative endings, as determined on this basis in the posthypophysis of normal rats from two different strains, are in good agreement with biochemical data reported in the literature.
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PMID:Cytochemical duality of neurosecretory material in the hypothalamo-posthypophysial system of the rat as related to hormonal content. 87 84

Virgin female Wistar rats were ovariectomized and 2 days later were given a single .2 ml dose of steroid im. Medroxyprogesterone acetate, 100 mg/kg of body weight or estradiol valerate 100 mcg were used. Group 1 (controls) received only solvents, Group 2 received progestogen in saline, Group 3 received the estrogen in oil, and Group 4 received both steroids. On selected days after treatment a rat from each group was killed, the uterus removed, and 2 myometrial strips were suspended in isolated organ baths on Statha G10B strain gauges for isometric recording. After 30 minutes, a dose of either 10 mcg/ml of acetylcholine or .25 mcg/ml of oxytocin was added to each bath. Tension was recorded for 10 minutes followed by a 15-minute wash. These doses were supramaximal. Responses began with a brief contraction and then became a series of fast powerful contrations which continued for 30-60 minutes. Each strip was later removed, prepared for sectioning, and length and cross-section were measured. Controls responded similarly to saline and to oil injections. There was a significnt initial increase in the response to both acetylcholine (p less than .05) and oxytocin (p less than .01). From Days 6 to 20 the responses did not change significantly. After Day 20 the response to acetylcholine declined significantly (p less than .01) but the response to oxytocin was unchanged for the 60 days of the test. With estrogen treatment, increase in response to both spasmogens was highly significant (p less than .001) in the first 18 days at which time it reached a plateau and remained the same for 60 days. With the progestogen treatment the mean response to acetylcholine increased significantly for the first 2 days (p less than .01) then maintained a plateau for the next 3 days equal to the control group and subsequently declined slowly (p less than .001). The contractile response to oxytocin remained constant for 60 days. With estrogen plus progestogen treatment there was a significant increase in contractility up to Day 5 (p less than .001). From Days 5 to 9 plateau levels were maintained with acetycholine and at a lower level with oxytocin. After Day 9 there was a significant decline in both spasmogens effect (p less than .001). With controls and all steroid treatments there was a highly significant difference in responses to acetylcholine and to oxytocin, with acetylcholine consistently giving stronger responses (p less than .001) than oxytocin. Results indicated that medroxyprogesterone acetate required the presence of estrogen for its myometrial action. There was also evidence that estrogen actions were modified by progestogen. It is concluded that single doses of estrogen and progestogen had depot actions of adequate intensity and duration for prolonged studies in myometrial contractility and that there was significant interaction between them when given together. Rat myometrium retained a significant response to spasmogens for at least 60 days after ovariectomy without steroid replacement, perhaps from adrenocortical steroid secretion.
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PMID:Sustained effects on synthetic ovarian steroids of rat myometrial contractility. 96 82

Previous studies have indicated the existence of natriuretic factors of hormonal nature with the posterior pituitary gland as a possible site of origin. It was in this light that a series of experiments was designed to examine the posterior pituitary for such factors. Acetic acid extracts of porcine and bovine posterior pituitary lobe tissue were subjected to gel filtration on Sephadex G-25. Several fractions in the molecular size range of 1000 were obtained which possessed potent natriuretic activity as assayed in rats. The activity of these fractions maximally increased sodium excretion to 6-8 muequiv./min, a 10- to 40-fold increase above control, when administered intraperitoneally to hydropenic, conscious rats. However, oxytocin and vasopressin, present in the posterior pituitary are natriuretic. These hormones were measured by radioimmunoassay, and invariably only those fractions which contained vasopressin and (or) oxytocin possessed natriuretic activity. Moreover, the extent of the natriuresis could be accounted for by the vasopressin and (or) oxytocin content of the test fractions. The natriuretic property of this material was abolished by treatment with thioglycollate. Further purification of natriuretic fractions by ion exchange resins, thin-layer chromatography and isoelectric focusing failed to resolve natriuretic activity from vasopressin and oxytocin. Similar results were observed following analysis of fractions isolated by gel filtration of acetic acid extracts of ventral hypothalamus tissue. The natriuretic fractions isolated from hypothalamic tissue were indistinguishable from oxytocin and vasopressin. These experiments suggest that the natriuretic activity in neurohypophyseal extracts can be attributed to oxytocin and vasopressin.
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PMID:Characterization of natriuretic activity from posterior pituitary lobes. 97 83

1. The time course of changes in specific activities of citrate, lactose and fatty acids in milk during frequent milking, following the I.V. administration of labelled glucose, acetate and chylomicrons in goats has been studied. Peak specific activities of lactose and citrate in milk were reached at 2-3 hr, while peak specific activites of fatty acids were reached at 5-7 hr. 2. Following short I.A. infusions of 24Na, 36Cl, and 42K, peak specific activities in milk were reached in 1 hr or less. 3. The mammary epithelium of lactating goats was found to be virtually impermeable to labelled citrate in both directions. 4. Labelled citrate had an apparent volume of distribution in lactating guinea-pigs mammary slices in vitro similar to that of extracellular space markers. 5. Treatment of goats with large doses of oxytocin markedly increased the permeability of the secretory epithelium to labelled citrate. 6. In the goat mammary gland, citrate, protein and calcium failed to enter milk which had been diluted with isosmotic lactose by intraductal injection, whereas Na, K and Cl did enter, thus tending to restore the concentrations of these ions to normal. 7. It is suggested that citrate, which is formed within the sucretory cell, enters milk not by passage across the apical cell membrane but, in common with lactose and milk protein, by exocytosis of Golgi vesicles. It appears that citrate is held at high concentrations in milk by virtue of the impermeability of the mammary epithelium to the forms in which it occurs in milk.
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PMID:The secretion of citrate into milk. 97 74

We characterized oxytocin (OT) receptors in purified plasma membranes from amnion, decidua, and myometrium of late pregnant rabbits using an iodinated OT antagonist (OTA). Saturation studies showed similar Kd values for specific binding sites in the 100- to 250-pM range in all three tissues. OT receptor concentrations in decidua and myometrium did not change until the day of labor (day 31), when they rose about 2.5- and 18-fold, respectively. Increases in amnion receptors were first apparent on day 28 and continued to maximal levels on day 31. There was an increase of about 230-fold from day 26 to labor, reaching 9.5 pmol/mg protein. Competition studies using analogs showed that ligand specificities of amnion and decidual membranes were indistinguishable. Those of myometrial membranes were somewhat different, possibly owing to the presence of both AVP receptors and OT receptors in the myometrium. Binding of OTA corresponded to the OT-induced release of prostaglandin E2 (PGE2) by amnion cells in culture. The effects of OT were dose dependent, agonist specific, and selectively inhibited by OTA. Amnion cells from days 22 and 28 did not respond significantly to either OT or phorbol 12-myristate 13-acetate (PMA), but cells from day 30 pregnant rabbits responded strongly to both. In contrast, calcium ionophore stimulated comparable amounts of PGE2 release from cells cultured on day 22, 28, or 30. These studies show that specific, high affinity OT receptors are associated with the release of PGE2 from rabbit amnion cells. Increases in amnion OT receptor and protein kinase-C activity precede by several days the increases in receptor concentrations in decidua and myometrium, suggesting important roles for the amnion and OT in the initiation of labor in rabbits.
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PMID:Characterization of oxytocin receptors in rabbit amnion involved in the production of prostaglandin E2. 131 89

1. The characteristics of vasopressin-stimulated phosphatidylinositol 4,5 bisphosphate (PtdIns(4,5)P2) and phosphatidylcholine (PtdCh) hydrolysis were examined in A10 vascular smooth muscle cells (VSMC), by assessing the formation of [3H]-inositol phosphates ([3H]-IP) and the accumulation of the phospholipase D (PLD) specific product, [3H]-phosphatidylbutanol ([3H]-PtdBuOH). 2. Vasopressin ([Arg8]-VP) and a number of related analogues stimulated the accumulation of [3H]-IP and [3H]-PtdBuOH with similar EC50 values, generating the same rank order of potency for each response (Arg8-VP = vasotocin = Lys8-VP much greater than oxytocin). 3. Inhibition of vasopressin-stimulated [3H]-IP and [3H]-PtdBuOH accumulation by the V1a receptor antagonists, Des-Gly9[beta-mercapto-beta,beta,-cyclopentamethylene propionyl, O-Et-Tyr2,Val4,Arg8]-vasopressin generated similar IC50 values suggesting that both these responses are mediated through the activation of a single V1a receptor subtype. 4. The onset of vasopressin-stimulated inositol-1,4,5-trisphosphate (Ins(1,4,5)P3) mass formation preceded [3H]-PtdBuOH accumulation indicating that PtdCh hydrolysis was activated subsequent to PtdIns(4,5)P2 breakdown. 5. The protein kinase C (PKC) activator, tetradecanoylphorbol acetate (TPA) also stimulated [3H]-PtdBuOH accumulation. Preincubation with the PKC inhibitor Ro-31-8220 abolished both TPA- and vasopressin-stimulated [3H]-PtdBuOH, suggesting that the intermediate activation of protein kinase C is involved in the regulation of PLD by vasopressin. 6. Pretreatment of the A10 VSMC with Ro-31-8220 (100 microM) also potentiated vasopressin-stimulated Ins(1,4,5)P3 mass formation.Therefore stimulation of PKC may have opposing roles in the regulation of agonist activation of PLC and PLD.7. Preincubation of the cells with EGTA, verapamil, or the receptor-operated calcium channel antagonist, SK&F 96365, reduced vasopressin-stimulated [3H]-PtdBuOH accumulation by approximately 30%, suggesting that influx of calcium has a significant role to play in the regulation of vasopressinstimulated PLD activity.
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PMID:Vasopressin-stimulated [3H]-inositol phosphate and [3H]-phosphatidylbutanol accumulation in A10 vascular smooth muscle cells. 133 Jan 54


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