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

Receptors for oxytocin were identified in a particulate fraction from the myometrium of the pregnant ewe. Specific binding of [3H]-oxytocin was rapid, reversible, and saturable. It showed an absolute requirement for Mg2+ and the selectivity among oxytocin analogues expected for the receptor. On fractionation of the myometrium by differential and discontinuous gradient centrifugation, [3H]-oxytocin binding showed a fractionation pattern which was similar to that for plasma membrane markers, but different from those for endoplasmic reticulum or mitochondrial markers. It is concluded that oxytocin receptors are located in the plasma membrane of the ewe myometrium. This subcellular fraction is a useful preparation for the study of receptor mechanisms and the regulation of myometrial contractility.
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PMID:Identification and characterization of receptors for oxytocin in the myometrium of the pregnant ewe. 629 Mar 51

The supraoptic (SON) and paraventricular (PVN) nuclei of the lizard Liolaemus cyanogaster c. were studied by use of histochemical, immunocytochemical and electron microscopic methods. The immunofluorescence staining for neurophysin was applied to methacrylate-embedded material before and after treatment of the sections with urea and trypsin. Pseudoisocyanine was applied to sections previously used for immunocytochemistry. The ultrastructural study showed that the SON and PVN neurons posses neurosecretory granules (nsg), distributed throughout the perikaryon, and large (2 to 12 micrometers) electron-dense droplets located within dilatations of the cisternae of the rough endoplasmic reticulum. Whereas the perikaryon (nsg) and the secretory droplets are stainable with pseudoisocyanine, only the former displays immunoreactivity for neurophysin. However, after treating the sections with urea and trypsin, the same secretory droplets become immunoreactive. It is suggested that the secretory droplets are sites of storage for the precursor of neurophysin, and that the tryptic digestion either triggers its conversion into neurophysin or exposes its immunoreactive sites. Based on the ultrastructure and the histochemical behavior of the secretory droplets, it is also postulated that they contain, in addition to peptides, a glycoprotein component.
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PMID:Ultrastructure and immunocytochemistry of neurons in the supraoptic and paraventricular nuclei of the lizard Liolaemus cyanogaster. Evidence for the intracisternal location of the precursor of neurophysin. 699 86

Phasic myometrial contractions utilize mechanisms involving the cycling of calcium into and out of intracellular calcium stores. These studies were performed to determine the effects of 2,5-di(tert-butyl)-1,4-hydroquinone (tBHQ), an endoplasmic reticulum Ca(2+)-ATPase inhibitor, on in vitro isometric myometrial contractions. These studies demonstrated that low concentrations of tBHQ (eg. 10 microM) appear to inhibit intracellular calcium cycling, whereas higher concentrations also inhibit extracellular calcium influx. These combined tBHQ effects markedly suppressed myometrial contractions stimulated in response to various agonists including oxytocin, PGF2 alpha, KCl, ionomycin, and Bay K 8644.
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PMID:Effects of 2,5-di(tert-butyl)-1,4-hydroquinone, an endoplasmic reticulum Ca(2+)-ATPase inhibitor, on agonist-stimulated phasic myometrial contractions. 753 6

Thimerosal inhibits calcium uptake and IP3-induced calcium release from IP3-sensitive endoplasmic reticulum; this study sought to evaluate the effects of thimerosal on agonist-stimulated phasic myometrial contractions. Thimerosal was found to significantly inhibit phasic contractions stimulated by oxytocin, aluminum fluoride, potassium chloride, ionomycin, and Bay K 8644. These observations provide support for the hypothesis that calcium uptake and IP3-induced calcium release are important events during agonist-stimulated phasic myometrial contractions.
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PMID:The effects of thimerosal, a sulfhydryl reagent, on phasic myometrial contractions. 753 99

This study investigated the underlying mechanisms of oxytocin (OT)-induced increases in intracellular Ca2+ concentrations ([Ca2+]i) in acutely dispersed myometrial cells from prepartum sows. A dose-dependent increase in [Ca2+]i was induced by OT (0.1 nM to 1 microM) in the presence and absence of extracellular Ca2+ ([Ca2+]e). [Ca2+]i was elevated by OT in a biphasic pattern, with a spike followed by a sustained plateau in the presence of [Ca2+]e. However, in the absence of [Ca2+]e, the [Ca2+]i response to OT became monophasic with a lower amplitude and no plateau, and this monophasic increase was abolished by pretreatment with ionomycin, a Ca2+ ionophore. Administration of OT (1 microM) for 15 sec increased inositol 1,4,5-trisphosphate (IP3) formation by 61%. Pretreatment with pertussis toxin (PTX, 1 microgram/ml) for 2 hr failed to alter the OT-induced increase in [Ca2+]i and IP3 formation. U-73122 (30 nM to 3 microM), a phospholipase C (PLC) inhibitor, depressed the rise in [Ca2+]i by OT dose dependently. U-73122 (3 microM) also abolished the OT-induced IP3 formation. Thapsigargin (2 microM), an inhibitor of Ca(2+)-ATPase in the endoplasmic reticulum, did not increase [Ca2+]i. However, it did time-dependently inhibit the OT-induced increase in [Ca2+]i. Nimodipine (1 microM), a voltage-dependent Ca2+ channel (VDCC) blocker, inhibited the OT-induced plateau by 26%. La3+ (1 mM), a nonspecific Ca2+ channel blocker, abrogated the OT-induced plateau. In whole-cell patch-clamp studies used to evaluate VDCC activities, OT (0.1 microM) increased Ca2+ current (ICa) by 40% with no apparent changes in the current-voltage relationship.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Oxytocin induced a biphasic increase in the intracellular Ca2+ concentration of porcine myometrial cells: participation of a pertussis toxin-insensitive G-protein, inositol 1,4,5-trisphosphate-sensitive Ca2+ pool, and Ca2+ channels. 761 2

This study describes ultrastructural and morphometric changes in the arginine vasopressin (AVP)-like immunoreactive and oxytocin (OT)-like immunoreactive neurons in the hypothalamic paraventricular nuclei (PVN) and supraoptic nuclei (SON) of streptozotocin-induced diabetic rats at 1-12 months post-diabetes. At 1-6 months post diabetes, both AVP-immunoreactive and OT-immunoreactive neuronal somata were hypertrophied in the PVN and SON. These neuronal somata contained highly dilated rough endoplasmic reticulum in the cytoplasm. The reaction product for AVP as well as OT localization was dispersed throughout the cytoplasm and cell nucleus, but not within the nucleolus. Moreover, the reaction product appeared to be studded onto the ribosomes on dilated cisterns of the endoplasmic reticulum. At 9-12 months post-diabetes, both AVP-immunoreactive and OT-immunoreactive dendrites contained dilated endoplasmic reticulum, autophagic vacuoles, lipid bodies, microtubules, membranous bodies and occasionally swollen mitochondria. Labelled hypertrophied axonal profiles containing neurosecretory granules, autophagic vacuoles, membranous bodies and tubulovesicular elements were also observed in the neuropil. Morphometric study showed that both AVP-immunoreactive and OT-immunoreactive neuronal somata of the PVN and SON in the diabetic rats were markedly hypertrophied at all the time intervals examined. It is concluded that the morphometric changes observed represent hyperactivity of both AVP- and OT-immunoreactive neurons, while the concurrent ultrastructural changes observed at later stages may be indicative of degeneration.
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PMID:Arginine vasopressin- and oxytocin-like immunoreactive neurons in the hypothalamic paraventricular and supraoptic nuclei of streptozotocin-induced diabetic rats. 773 75

Molecular biological and immunocytochemical data demonstrate nonhomologous crossing-over between the closely linked vasopressin (VP) and oxytocin (OT) genes in rat hypothalamic neuroendocrine neurons. Reverse transcription of hypothalamic total RNA from wild-type or homozygous Brattleboro aged rats combined with polymerase chain reaction (PCR) amplifications in the presence of appropriate 5' forward and 3' reverse primers deduced from the VP and OT cDNA sequences yielded PCR products that, upon cloning and sequencing, revealed several hybrid transcripts. They encode the N-terminal part of the VP precursor fused to the C-terminal part of the OT precursor (VP/OT transcripts) and vice versa (OT/VP transcripts). VP/OT hybrid precursor proteins have been identified immunocytochemically in enlarged cisternae of the rough endoplasmic reticulum, yet there is no evidence that the products can be secreted from affected cells. Recombination appears to be a rather frequent genetic event affecting about 0.06-0.1% of the rat vasopressinergic magnocellular neurons in aged rats.
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PMID:Somatic nonhomologous crossing-over between neuropeptide genes in rat hypothalamic neurons. 797 73

Immunoreactive oxytocin is expressed by thymic epithelial cells, which share properties with neuroendocrine cells. In order to investigate the assumed paracrine secretion of oxytocin, we studied the subcellular localization of immunoreactive oxytocin within thymic tissue and cultured thymic epithelial cells of the male mouse. Three types of immunoreactive cells were distinguished with the electron microscope. Immunoreactive oxytocin was found to be restricted to the cytoplasm by the use of pre- and postembedding methods. Some epithelial cells, especially in the cortex, showed a pronounced labelling of vesicular membranes and membrane tubules of the endoplasmic reticulum. In some cells, keratin filaments were associated with the electron-dense stain. Under culture conditions immunoreactive cells of different shapes were found, all displaying similar patterns of labelling. The contents of different types of vacuoles were only rarely labelled. A special class of immunoreactive exocytotic vesicles could not be identified. Thus, our results do not support neuroendocrine secretion of oxytocin via vesicles of thymic epithelial cells but offer alternative modes of secretion.
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PMID:Subcellular localization of immunoreactive oxytocin within thymic epithelial cells of the male mouse. 836 64

Isolated porcine luteal cells from d 10 and 15 of the estrous cycle (estrus = d 0) were incubated with or without combinations of FSH (0, 10, 10(2), 10(3) ng), LH (0, 10, 10(3) ng), oxytocin, or prostaglandin F2 alpha (PGF2 alpha) (each at 0, 10, 10(3), and 10(5) pg). Progesterone (P4) content was determined after overnight incubation (0 h) then at 2 and 24 h of incubation. The basal (0 h) P4 production of large cells (LC) from d 10 corpora lutea (CL) was 31-fold higher than that by small cells (SC) at 0 h. The LC and SC from d 10 but not those from d 15, were stimulated to a small extent by LH (P < .05). The FSH inhibited P4 production (P < .05) by SC at 24 h on d 10 and by LC after 2 or 24 h of incubation on d 15. There was no interaction between LH and FSH on P4 production. Oxytocin and PGF2 alpha decreased P4 production by d 15 LC at 2 h of incubation (P < .05) and by d 15 SC after 2 or 24 h of incubation (P < .05 and P < .01). The morphology of cells from CL of the cycle or early or mid pregnancy were examined using scanning and transmission electron microscopy (EM). Freshly isolated LC (using scanning EM) from d 10 contained many microvilli arranged in apparent networks on their membranes, but SC had smooth surfaces and contained only a few microvilli. Internally, LC had more small mitochondria than did SC and a different organization of smooth endoplasmic reticulum (SER). The SC from CL of pregnant (d 30 to 60) gilts contained more mitochondria than SC from CL of cyclic gilts. The results indicate that FSH, oxytocin, and PGF2 alpha can have a direct cellular luteolytic effect in the late luteal phase in pigs. The FSH influenced LC, whereas oxytocin and PGF2 alpha effected a more pronounced decrease in P4 from SC. The lower amount of P4 produced overall by SC may be associated with fewer microvilli, mitochondria, and SER in SC.
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PMID:Responsiveness of porcine large and small luteal cells to luteotropic or luteolytic hormones and cell morphologic changes during the estrous cycle and pregnancy. 844 Jun 70

Most magnocellular hypothalamic neurons synthesize the precursor for either vasopressin (AVP) or oxytocin (OT). The AVP precursor is cleaved to give AVP, AVP-associated neurophysin (AVP-NP) and a glycopeptide (GP), whereas the OT precursor gives OT and OT-NP. In Brattleboro rats a frame-shift mutation in the AVP-NP-encoding region of the gene prevents the secretion of AVP by the cells and, in most AVP neurons, AVP itself is virtually undetectable. A small number of magnocellular neurons in homozygous Brattleboro rats contain very large accumulations of peptide in distended saccules of rough endoplasmic reticulum (RER), and this peptide is immunoreactive for AVP and C-terminal OT-NP, but not for OT, AVP-NP or GP (Pow et al., 1992). We have now shown that this results from somatic non-homologous crossing over of the AVP and OT genes, resulting in the production of hybrid mRNA molecules with the 5'end of the AVP sequence and the 3' end of the OT sequence (AVP/OT transcripts). In most cases, the crossing over occurs within the highly homologous B exons (Mohr et al., 1994). In addition to the production of AVP/OT hybrid transcripts, polymerase chain reaction (PCR) amplification of mRNA from the hypothalami of homozygous rats also reveals OT/AVP hybrid transcripts, with 5' OT sequences and 3' AVP sequences. Furthermore, both types of hybrid transcript are not restricted to homozygous Brattleboro rats but can also be found in normal Long Evans animals. To date, we have not been able to locate cells in which the OT/AVP hybrids are produced; all the magnocellular neurons with hybrid peptide accumulations in the RER so far studied have been shown by immunocytochemistry to be of the AVP/OT type. In both normal and homozygous Brattleboro rats large accumulations of peptide do occur in the RER of OT-producing neurons but the peptide is immunoreactive for OT and OT-NP but not for AVP, AVP-NP or GP. Such cells increase in number 10-fold after injection of 20 micrograms estradiol daily for 7 days (Pow et al., 1991). Why this apparently normal gene product accumulates within the RER remains to be determined.
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PMID:Production of hybrid oxytocin/vasopressin precursors and accumulation of oxytocin precursors in the rough endoplasmic reticulum of rat magnocellular neurons. 871 51


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