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)

To determine whether oxytocin (OT) could alter the release of PRL and other hormones from the anterior pituitary gland, the effects of OT were examined in two in vitro and two in vivo test systems. Cells dispersed from anterior pituitary glands of intact adult male rats were incubated in medium containing OT at doses of 10(-8), 10(-7), 10(-6), and 10(-5) M in two trials. OT stimulated PRL release 1.5-fold (P less than 0.01) and 2- to 3-fold (P less than 0.001) above control levels at 10(-8) and 10(-7) M doses, respectively, thus indicating a dose-dependent relationship. Higher doses did not produce a further elevation above that obtained with 10(-7) M OT. Arginine vasopressin (AVP) caused a slight decrease in PRL release from dispersed cells while TRH produced a small (25%), significant, but nondose-related increase in PRL release. Hemipituitary glands from adult male rats, incubated with 10(-6) and 10(-5) M OT, released twice as much PRL (P less than 0.01) into the medium as paired controls, but 10(-7) M OT was ineffective. The iv injection of 1 or 10 micrograms OT into conscious male rats elevated plasma PRL by 50% (P less than 0.05) or 500% (P less than 0.001), respectively, above basal values at 5 min only. Vehicle or 0.1 microgram OT were without effect. When 0.1 microgram OT was microinjected into the third ventricle (3V) of conscious male rats, it paradoxically reduced plasma PRL by 40% at 30 min (P less than 0.05), whereas 1 microgram OT significantly lowered PRL at 5-60 min, with the maximum suppression (60%, P less than 0.001) occurring at 30 min. These latter findings may indicate that an ultrashort loop feedback mechanism exists whereby exogenous OT decreases hypothalamic OT secretion, thereby reducing the OT stimulus for PRL release. The specificity of the OT effect on PRL was attested to by the failure of OT to alter significantly FSH, LH, and TSH in each system. GH was unchanged except that 3V-injected OT (1 microgram only) elevated (P less than 0.001) plasma GH at 15-30 min. These results support the view that OT acts directly on the cells of the anterior pituitary gland at low to high doses to release PRL specifically and in a dose-related fashion. In contrast, 3V injection of OT reduces PRL secretion, thereby suggesting that OT may decrease its own neurosecretion by ultrashort loop feedback and thus reduce an OT stimulus for PRL release.
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PMID:Hypothalamic and pituitary sites of action of oxytocin to alter prolactin secretion in the rat. 640 33

A glycoprotein of neurohypophysial origin was found to have cofractionated with FSH prepared from pituitary glands of the green turtle, Chelonia mydas. Antiserum raised against this preparation contained high antibody titres and affinity for the neurohypophysial component and allowed development of a specific radioimmunoassay to monitor its purification and distribution in the brain. Immunocytochemistry revealed that the glycoprotein was concentrated in the pars nervosa and associated nerve tracts passing through the median eminence to the supraoptic and paraventricular nuclei; similar distributions were observed in turtles and rats. The antiserum to the turtle material bound radiolabelled rat vasopressin (VP)-neurophysin and precipitated precursors of this neurophysin, but it did not cross-react with rat oxytocin-neurophysin. An amino-terminal alanine was also consistent with the structure of rat VP-neurophysin, but the turtle molecule was larger than the corresponding rat molecule. Limited tryptic digests of the turtle glycoprotein contained two components, one of which bound to lysine VP. Both components contained carbohydrate, but only the one which bound to VP cross-reacted in a radioimmunoassay for rat VP-neurophysin. The apparent surge in plasma immuno-FSH at the time of oviposition previously described in the turtle probably represented release of a neurophysin-like 'carrier' molecule associated with secretion of the neurohypophysial hormone (e.g. arginine vasotocin; AVT) responsible for oviduct contractility. These data suggest that the neurohypophysial glycoprotein represents a partially processed AVT precursor and provide the first biochemical evidence of a mammalian-like biosynthetic pathway for neurohypophysial hormones in a non-mammalian species.
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PMID:Presence of a neurophysin-like precursor in the green turtle (Chelonia mydas). 643 86

All hormones were determined in blood samples collected simultaneously from the caudal vena cava and jugular vein at 20-min intervals for 12 h during the early (Day 4) and mid- (approximately Day 11) luteal phases of the oestrous cycle in 7 cows. Mean concentrations of oestradiol, progesterone and oxytocin were greater (P less than 0.01) in the vena cava than in the jugular vein. Pulses of these hormones were also more easily identifiable in the vena cava. The frequency of LH pulses was higher (P less than 0.01) during the early luteal than during the mid-luteal phase (8.0 versus 3.6 pulses/12 h). During both phases, 90-96% of all LH pulses were followed within 60 min by a pulse of oestradiol. Basal concentration and amplitude of oestradiol pulses were greater (P less than 0.05) during the early than during the mid-luteal phase. The frequency of FSH pulses was similar to that of LH during the early luteal phase (8.5 and 8.0 pulses/12 h) but was greater (P less than 0.01) than that of LH during the mid-luteal phase (6.3 versus 3.6 pulses/12 h). Thus, 41% more (P less than 0.01) FSH pulses than LH pulses were observed during the mid-luteal phase. However, the separate FSH pulses were associated with low-amplitude short-duration pulses of LH as clarified by an additional study (in 3 cows) using 5-min sampling intervals: 90-100% of all LH/FSH pulses and separate FSH pulses were secreted either concomitantly with or followed by a pulse of progesterone. However, no separate FSH pulses were associated with a pulse of oestradiol. Basal concentration and amplitude of progesterone were greater (P less than 0.01) during the mid-luteal than during the early luteal phase. The frequency of oxytocin pulses was similar to that of progesterone during the mid-luteal but not during the early luteal phase. During the mid-luteal phase 97% of all oxytocin pulses were associated with a pulse of progesterone. It is concluded that (1) separate FSH pulses are secreted in addition to parallel LH and FSH pulses during the mid-luteal phase; therefore, the frequency of secretion of LH may be modulated to a greater extent by ovarian steroids than is FSH pulse frequency; (2) pulses of progesterone are probably a result of stimulation by pulses of FSH and/or LH whereas pulses of oestradiol are caused by LH pulses; (3) ovarian oxytocin and progesterone are secreted concomitantly during the mid-luteal phase of the oestrous cycle.
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PMID:Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during the luteal phase of the oestrous cycle in the cow. 654 Mar 9

An injection of 500 micrograms prostaglandin (PG) analogue was given on Day 12 (mid-luteal phase) of the oestrous cycle to 8 cows. An LH surge occurred 59 +/- 2 h later. LH, FSH, prolactin, oestradiol-17 beta, progesterone and oxytocin concentrations were determined in blood samples collected from the caudal vena cava and/or the jugular vein at 20-min (5 cows) or 5-min (3 cows; only LH and FSH concentrations were determined) intervals for 24 h, beginning 48 h after the PG injection. Oxytocin concentrations were low and similar in the vena cava and the jugular vein. In blood samples collected every 5 min the interpulse interval for LH and FSH during the period before the LH surge was 38-40 min. In the 20-min samples the interpulse interval for oestradiol was similar to that for LH and FSH, but pulse amplitude and basal concentrations steadily increased to reach maximum concentrations 6-8 h before and again during the LH surge. A decrease in oestradiol concentrations, lasting at least 60 min, occurred just before the start of the LH surge. Progesterone concentrations also increased at the same time as the LH surge. The magnitude of the LH surges varied from 7 to 32 ng/ml, but all cows ovulated and had oestrous cycles of normal length. Distinct pulses of LH and FSH were observed throughout the LH and FSH surges. Pulsatile secretion of LH was not detected for a period of up to 6-12 h following the LH surge, but then low-amplitude pulses occurred. In contrast, the pulsatile secretion of FSH remained at a frequency similar to that observed during the descending phase of the FSH surge. Furthermore, a second increase in FSH concentrations occurred, beginning 4-12 h after the LH-surge. It is concluded that: (1) the frequent, high-amplitude pulses of oestradiol that occur before and during the LH surge are probably due to stimulation by pulses of LH; (2) the LH surge is the result of an increase in frequency and amplitude of the LH pulses; (3) the second increase in FSH that follows the LH and FSH surges appears to be the result of an increase in the amplitude (not frequency) of the FSH pulses; and (4) very little, if any, oxytocin is secreted from the ovary during the periovulatory phase of the oestrous cycle.
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PMID:Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during the periovulatory phase of the oestrous cycle in the cow. 674 58

A highly sensitive and specific radioimmunoassay for LRF was applied to the measurement of endogenous LRF in various hypothalamic extracts. Specific antiserum was obtained by injecting LRF conjugated to human serum albumin with glutaraldehyde. Thyrotropin-releasing hormone, lysine vasopressin, oxytocin, noradrenaline, LH, FSH and cortical extracts did not appear to affect the assay, and the maximum cross-reaction observed with the LRF analogs tested was 8.5 p. 100 with LRF 2-10. The best detection limit (0.4 pg/tube) was usually obtained when the labelled LRF had been purified by polyacrylamide gel electrophoresis. Within and between-assay coefficients of variation were 8.0 and 12.6 p. 100, respectively (from B/Bo = 20 to 80 p. 100). Synthetic LRF administered to rams by intravenous injection was readily detectable in the peripheral plasma. However, the direct measurement of plasma endogenous LRF may give misleading results due to non-specific interference by plasma factors. No endogenous LRF could be detected in plasma methanol or acetone extracts obtained from rats and rams in various physiological conditions. The inhibition curves parallel to the synthetic LRF curve were obtained by diluting the crude hypothalamic extracts of rams and rats, and a good correlation (r = 0.997) with the Ramirez-McCann bioassay resulted, indicating that using radioimmunoassay to determine hypothalamic LRF content may be fruitful in studying hypothalamo-pituitary gonad interactions. The LRF content of rat and ovine hypothalami ranged from 2-8 to 20-80 ng of LRF, respectively.
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PMID:Reassessment of LRF radioimmunoassay in the plasma and hypothalamic extracts of rats and rams. 676 Feb 82

Serial plasma oxytocin (OT), PRL, TSH, FSH, LH, estrone, estradiol, and progesterone were measured by RIA in 12 women before and during a 30-min breast-feeding period on the third or fifth postpartum day. Plasma OT increased significantly from 10.8 +/- 3.4 to 22.4 +/- 3.5 pg/ml (mean +/- SE) within 2 min of suckling (P = less than 0.05) to reach the mean peak level of 53.2 pg/ml at 10 min. The increase in plasma OT was bimodal. Plasma PRL and TSH also increased significantly from baseline levels of 192 +/- 39 ng/ml and 16.9 +/- 5.6 microU/ml, respectively, to reach maximum levels of 427 +/- 91 ng PRL/ml at 10 min (P = less than 0.025) and 281.5 +/- 56.6 microU TSH/ml at 25 min (P = less than 0.005). Plasma FSH-beta (range of means, 3.5-4.6 ng/ml), LH (range of means, 1.7-2.6 mIU/ml), and estradiol (range of means, 29.8-38.2 pg/ml) were low and remained unchanged throughout breast feeding. Plasma progesterone was 6.0 +/- 0.4 ng/ml before breast feeding and did not alter significantly during breast feeding. The significance of these findings is discussed in relation to the milk let-down reflex and the relationship of TSH to PRL.
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PMID:Oxytocin release and plasma anterior pituitary and gonadal hormones in women during lactation. 678 15

Plasma oxytocin (OT), FSH, and LH were measured by specific RIA in eight healthy adult males before, during, and after stopping iv infusions of OT. With a constant infusion of 132 mU OT/min for 60 min, plasma OT reached a steady state concentration of 228-241 pg/ml at 30-60 min. When the dose of oxytocin infused was doubled every 15 min, plasma OT increased from 81.0 +/- 17.9 pg/ml (mean +/- SE) with 32 mU/min to reach a steady state concentration of 378 +/- 73.4 pg/ml with 256 mU/min (1 muU = 2 pg OT). The curve of disappearance of plasma OT could be resolved into a single exponential curve in all of the subjects, with a mean calculated half-life of 10.3 +/- 1.6 min (range, 5.3-17.3 min). The mean MCR of OT was 21.5 +/- 3.3 ml/kg.min, and the mean apparent volume of distribution was 305 +/- 46 ml/kg. Plasma FSH and LH showed no significant change throughout OT infusion and for up to 60 min after stopping the OT infusion. The findings demonstrate that in man 1) plasma OT concentration achieved is closely related to the infusion rate, 2) OT infusion does not affect plasma FSH and LH, and 3) the apparent volume of distribution of OT suggests that infused OT is distributed into space or spaces other than the circulating plasma volume.
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PMID:Oxytocin levels and disappearance rate and plasma follicle-stimulating hormone and luteinizing hormone after oxytocin infusion in men. 735 23

In the ruminant ovary, synthesis and secretion of oxytocin begin in the granulosa cells of the preovulatory follicle and are markedly stimulated by the surge of LH and FSH. Luteinization of the granulosa cells results in a further increase in oxytocin gene expression, but translation of mRNA appears to be retarded because the peak concentration of luteal oxytocin occurs later than the maximal accumulation of the message. Several hormones have been shown to stimulate oxytocin secretion from granulosa and luteal cells in vivo or in vitro. However, the role of prostaglandin F2 alpha (PGF2 alpha) in regulating luteal oxytocin secretion has perhaps received more study than other hormones. The mechanism of action of PGF2 alpha has been shown to encompass a phosphoinositide cascade and activation of protein kinase C, events that are associated with luteal secretion of oxytocin. Protein kinase C phosphorylation of the actin-binding protein myristolated alanine-rich C kinase substrate (MARCKS) may be required for exocytosis of oxytocin.
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PMID:Dynamics of molecular mechanisms underlying ovarian oxytocin secretion. 762 28

Mammalian preovulatory follicles produce primarily estradiol and androgens before the preovulatory gonadotropin surge. In cattle, the LH/FSH surge triggers a rapid decrease in estradiol and androgen production and a dramatic increase in progesterone and oxytocin biosynthesis. It is unclear how changes in gonadotropin concentrations in vivo regulate this follicular/luteal phase shift in hormone production. To address this question, theca interna and granulosa cells were isolated from preovulatory follicles of Holstein heifers approximately 24 h before the expected time of the LH/FSH surge and cultured in defined medium containing insulin (1 microgram/ml), with varying doses of LH or FSH (0, 1, 2, 4, 8, 16, 32, 64, or 128 ng/ml). Media were collected and replaced every 24 h for 3 days, and assayed for androstenedione and progesterone in theca interna cultures, and for estradiol, progesterone and oxytocin in granulosa cell cultures. After the first day of culture (24-72 h), only very low doses of LH (2 or 4 ng/ml) enhanced (p < 0.05) androstenedione secretion by theca interna cultures above control levels, whereas progesterone secretion was increased by a wide range of LH concentrations (p < 0.05), with maximal progesterone secretion at high doses of LH. Likewise, after the first day of culture (24-72 h), estradiol secretion by granulosa cells was stimulated only by low doses of FSH and was inhibited at higher concentrations relative to control cultures (p < 0.05), whereas the production of oxytocin and progesterone was enhanced maximally by high concentrations of FSH (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Low and high concentrations of gonadotropins differentially regulate hormone production by theca interna and granulosa cells from bovine preovulatory follicles. 763 41

The genes for the alpha subunit of inhibin and for the nonapeptide hormone oxytocin are both expressed in the granulosa cells of the ruminant follicle as well as in the Sertoli cells of the ruminant testis. Northern hybridization of mRNA from both ovary and testis indicate that in both gonads the expression of the two genes is inversely regulated. In the luteinizing granulosa cells, in vitro as in vivo, the alpha-inhibin gene is down-regulated when the oxytocin gene is up-regulated. In the Sertoli cells of the bull and sheep testis, the situation is similar, with the alpha-inhibin gene being up-regulated in the prepubertal gonad and down-regulated concomitantly with an up-regulation of the oxytocin gene in early puberty. The gene for the bovine alpha-inhibin subunit was cloned and characterized. Assessment of transcriptional initiation by primer extension and ribonuclease protection assays showed that several different sites were used in both granulosa cells and testis. Transient transfection of primary bovine granulosa cells with alpha-inhibin/luciferase gene constructs indicated that a major promoter element resided in the region -178 to -245 respective to the methionine start codon of translation, a region that contains a cAMP response element. The ability of forskolin to up-regulate the transcription of transfected gene constructs also depended on the integrity of this region. In contrast, transfection of TM4 cells led to transcriptional initiation from an unusual site in the alpha-inhibin gene and to a lack of forskolin regulation. Comparison of the alpha-inhibin and oxytocin genes indicates that although both can be up-regulated by FSH or by forskolin within the same cells, different mechanisms of signal transduction are involved to explain the temporal differences in expression. Together the results indicate that a differentiation step occurring in Sertoli cells at early puberty and in granulosa cells at luteinization involves comparable regulation of genes through the sequential action of different cAMP-linked transcription factors.
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PMID:Structure of the alpha-inhibin gene and its regulation in the ruminant gonad: inverse relationship to oxytocin gene expression. 814 57

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