Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01178 (oxytocin)
 15,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Membrane fractions prepared from the uterine endometrium of untreated ovariectomized sheep contained a 41 x 10(3) Mr protein that was [32P]ADP-ribosylated by pertussis toxin in the presence of [32P]NAD. Progestin and progestin plus oestrogen treatment in vivo increased the concentration of this protein 2.7- and 3.6-fold respectively. Endometrial extracts from untreated or progestin-treated sheep also contained proteins of Mr 69 x 10(3) and 120 x 10(3) which were ADP-ribosylated in the absence of pertussis toxin; these proteins were not ADP-ribosylated in sheep receiving oestrogen. Incubation of endometrial slices from progestin plus oestrogen-treated sheep with oxytocin in vitro increased phosphoinositide hydrolysis 11-fold. This effect was not altered by prior incubation with pertussis toxin, although toxin treatment reduced by 64% subsequent labelling of the 41 x 10(3) Mr protein when membrane fractions prepared from pretreated slices were incubated with pertussis toxin and [32P]NAD. Thus the endometrium contains a pertussis toxin-sensitive protein which is induced by steroid treatment, but this protein is not involved in the phosphoinositide response to oxytocin.
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PMID:Pertussis toxin-catalysed ADP-ribosylation of endometrial proteins in sheep. 339 97

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

The expression of heterotrimeric (alpha beta gamma subunits) GTP-binding regulatory proteins (G proteins) and the activation of G protein-linked receptors in human granulosa cells were investigated. The cells were obtained from stimulated follicles in women undergoing in vitro fertilization and were cultured in serum-supplemented medium. Immunoblotting with specific antibodies showed that granulosa cell membranes express alpha s, alpha i3 alpha i1,2, alpha q,11 and beta subunits. Three antibodies against alpha o failed to detect this protein. The cells responded to hCG and to prostaglandin E2 with a dose-dependent increase in cAMP formation, confirming the functional activation of G alpha s. The alpha 2 adrenoceptor agonist, clonidine, inhibited hCG-stimulated cAMP formation and this effect was blocked with pertussis toxin, thus involving a Gi-type protein, most likely G alpha i2. Oxytocin provoked an increase in formation of inositol phosphates and intracellular calcium concentration, which was partly pertussis toxin resistant, providing evidence of G alpha q,11 activation. However, a significant component of the response to oxytocin could be blocked by pertussis toxin, indicating Gi-mediated phospholipase C activation (by either alpha i or beta gamma subunits). These data demonstrate the presence of G proteins in granulosa cells and suggest a complex regulation of hormonal signalling. The concentration of cAMP in these cells depended on the balance of G alpha s:G alpha i activation, whereas activation of the inositol phospholipid pathway and rises in intracellular calcium involved both Gq,11 and Gi pathways.
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PMID:G protein expression and second messenger formation in human granulosa cells. 763 9

The role of oestradiol in the control of uterine responsiveness to oxytocin was investigated by measuring oxytocin-induced phospholipase C activation in [3H]inositol-labelled cultured human myometrial cells. Addition of oestradiol to steroid-free culture medium (10% (v/v) fetal calf serum treated with dextran-coated charcoal in phenol red-free medium) enhanced formation of inositol phosphates and this effect was completely abolished by the anti-oestrogen tamoxifen. The inhibitory effect of tamoxifen on oxytocin-induced phospholipase C activation occurred in both steroid-free and complete culture medium; it was time- and concentration-dependent and was only partly reversed by oestradiol. When phospholipase C was activated with PGF2 alpha or fluoroaluminate instead of oxytocin, oestradiol and tamoxifen had the same stimulatory and inhibitory effects, respectively. The inhibitory effect of tamoxifen could not be prevented by treating the cells with pertussis toxin. Moreover, the effect of tamoxifen was not mediated by inhibition of protein kinase C, since the use of staurosporine (a protein kinase inhibitor) resulted in potentiation of phospholipase C activation by oxytocin. Both oestradiol and tamoxifen increased [3H]inositol incorporation into cellular lipids and cell proliferation. These results suggest that oestradiol enhances myometrial responsiveness to oxytocin and other agonists by facilitating phospholipase C activation at a post-receptor level. This effect is antagonized by tamoxifen; however, tamoxifen also has oestrogen-independent inhibitory effects.
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PMID:Effects of oestradiol and tamoxifen on oxytocin-induced phospholipase C activation in human myometrial cells. 770 87

Vasopressin (AVP), the antidiuretic hormone, is a cyclic nonapeptide that acts through binding to G protein-coupled specific membrane receptors pharmacologically divided into three subtypes (V1a, V1b, and V2) linked to distinct second messengers. Within the family of human AVP receptors, the V2 AVP receptor has been cloned, but the structure of the human V1a and V1b AVP receptors remains unknown. We report here the structure and functional expression of a human V1a AVP receptor complementary DNA isolated from human liver cDNA libraries. Cloning and sequencing of a full-length clone isolated a 1472-nucleotide sequence encoding a 418-amino acid polypeptide with seven putative transmembrane domains typical of G protein-coupled receptors. Amino acid sequence identity with the rat liver V1a AVP receptor, the human and rat V2 AVP receptors, and the human oxytocin receptor was 72, 36, 37, and 45%, respectively. Functional characterization of the cloned receptor was done by transient expression in COS-7 cells and stable expression in Chinese hamster ovary cells. Localization of the expressed receptor at the cellular surface was illustrated by using the fluorescent linear analog phenylacetyl-D-Tyr(Et)-Phe-Gln-Asn-Lys-Pro-Arg-NH2 coupled to fluorescein-avidin by dodecabiotin. Competition binding experiments with phenylacetyl-D-Tyr(Et)-Phe-Val-Asn-Lys-Pro-[125I]Tyr-NH2 and AVP analogs revealed high affinity specific binding sites of the V1a subtype. Saturation binding experiments with [3H]AVP confirmed the presence of a single class of high affinity binding sites. Measurement of AVP-induced inositol phosphate production and calcium mobilization confirmed that the expressed V1a AVP receptor is coupled to phospholipase C via a pertussis toxin-insensitive pathway. Thus, the human V1a AVP receptor belongs to the superfamily of seven-transmembrane segment receptors with a significant sequence identity with the other members of the AVP-oxytocin family of receptors.
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PMID:Molecular cloning, sequencing, and functional expression of a cDNA encoding the human V1a vasopressin receptor. 810 69

We investigated the effects of intracerebroventricular (i.c.v.) pertussis toxin upon the sensitivity of supraoptic oxytocin neurones to intravenous morphine (1-5000 micrograms/kg) in urethane-anaesthetized rats. The maximal inhibitory capacity of morphine was diminished by prior administration of pertussis toxin. Some cells were tested with both morphine and with the kappa-opioid agonist U50,488 (1-5000 micrograms/kg): U50,488-induced inhibition of firing rate was apparently unimpaired by pertussis toxin pre-treatment. The opioid inhibition of firing rate seen in the absence of and after pertussis toxin pre-treatment was naloxone-reversible. Thus a pertussis toxin-sensitive G protein may mediate the inhibitory action of morphine upon supraoptic putative oxytocin neurones or inputs to them.
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PMID:A pertussis toxin-sensitive G protein mediates inhibition by morphine of spontaneous electrical activity of oxytocin neurones in anaesthetized rats. 835 40

Phosphoinositide hydrolysis is important in mediating the actions of oxytocin and prostaglandin (PG) F2 alpha on uterine contractions during labour. We have measured the effect of oxytocin, PGF2 alpha and other agents on the formation of inositol phosphates (IPs) in cultured human myometrial cells labelled with [3H]inositol and on changes in intracellular free Ca2+ concentration ([Ca2+]i) in cells loaded with Fura-2. Oxytocin induced the formation of [3H]IPs in a concentration-dependent manner with an EC50 (concentration of agonist producing 50% of the maximal response) of 1.4 +/- 0.5 nmol/l (mean +/- S.E.M.). The maximal response was obtained with 1 mumol oxytocin/l and represented a stimulation of 670% over basal. PGF2 alpha also stimulated the formation of [3H]IPs and the response at 1 mumol/l was a 204% stimulation over basal. The effects of PGF2 alpha were independent of extracellular Ca2+ but the effect of oxytocin was reduced with low extracellular Ca2+. Cyclic AMP formation, induced by forskolin or PGE2, had no effect on the stimulated levels of [3H]IPs. Pertussis toxin (PT) reduced the oxytocin-stimulated formation of [3H]IPs in a concentration-dependent manner. The maximal effect of PT resulted in an 80% reduction in the formation of [3H]IPs. However, PGF2 alpha stimulation was not affected by PT treatment. To analyse the action of PT further, we studied its effect on oxytocin-induced changes in [Ca2+]i. The basal [Ca2+]i was 112 +/- 4 nmol/l (n = 225 cells) and was not affected by PT treatment (109 +/- 3 nmol/l; n = 200 cells). In the absence of PT, 1 mumol oxytocin/l increased [Ca2+]i to a peak of 522 +/- 26 nmol/l, and in PT-treated cells, the [Ca2+]i peak was reduced to 348 +/- 16 nmol/l. Similar inhibitory effects of PT were obtained at oxytocin concentrations ranging from 1 to 100 nmol/l. Our data suggest that in human myometrial cells, the oxytocin-induced production of [3H]IPs and increase in [Ca2+]i are mediated by a PT-sensitive G-protein. However, a significant fraction of the oxytocin response appears to be mediated by a PT-insensitive G-protein, possibly a member of the Gq family.
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PMID:Oxytocin-stimulated phosphoinositide hydrolysis in human myometrial cells: involvement of pertussis toxin-sensitive and -insensitive G-proteins. 838 15

In the pregnant rat myometrium, an averaged 30% of inositol phosphate accumulation induced by carbachol and oxytocin was inhibited by oxodipine indicating that a part of receptor-mediated generation of inositol phosphates depended on Ca++ influx through voltage-gated Ca++ channels. In fura-2-loaded cells, carbachol and oxytocin caused a two-phase [Ca++]i response, made up of a transient [Ca++]i peak of about 700 nM followed by a sustained phase of about 120 nM. Oxodipine reduced the [Ca++]i peak by 40% and the plateau phase by 50%, pointing to a contribution of Ca++ influx in both the [Ca++]i peak and sustained phase. Isoproterenol reduced inositol phosphate response to carbachol and oxytocin to an amount equivalent to that elicited by oxodipine. No additional reduction could be obtained in a combination of isoproterenol and oxodipine. Isoproterenol decreased by 40% the [Ca++]i peak and by 70% the [Ca++]i plateau phase. Differently from isoproterenol, forskolin did not affect inositol phosphate accumulation induced by oxytocin and failed to attenuate the [Ca++]i peak. The inhibitory effect of isoproterenol on both inositol phosphate accumulation and [Ca++]i increase induced by oxytocin was abolished by pertussis toxin. These data suggest that beta adrenergic receptor activation is linked via a cAMP-independent, pertussis toxin-sensitive process to an activation of K+ channels, as revealed by use of selective K+ channel antagonists, with the consequent closure of voltage-gated Ca++ channels, resulting in the inhibition of the Ca(++)-associated generation of inositol phosphates.
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PMID:Beta adrenergic receptor activation attenuates the generation of inositol phosphates in the pregnant rat myometrium. Correlation with inhibition of Ca++ influx, a cAMP-independent mechanism. 855 22

PGE2 is a powerful modulator of uterine contractility, but there is uncertainty as to which receptor subtypes (EP1, EP2, EP3, or EP4), G proteins, and second messenger systems are activated by PGE2 in myometrium. Here we show that in cultured human myometrial cells, PGE2 (1-100 microM) activates phospholipase C (PLC) up to 500% over the control level and elevates intracellular calcium ([Ca2+]i) from the resting level of 60-90 nM up to 350 nM in a concentration-dependent manner. Stimulation by the receptor subtype-selective analogs GR63799X (EP3), sulprostone (EP3 > EP1), and misoprostol (EP3 > EP2 > EP1) indicates that these effects are transmitted through EP3 receptors. Both effects are resistant to pertussis toxin (PT). Lower concentrations of PGE2 (1-300 nM) increase [Ca2+]i via a PT-sensitive pathway, without PLC activation. This [Ca2+]i increase occurs after an inverse dose-related delay and is inhibited by the selective EP1 antagonist AH6809 and calcium channel blockers. By comparison, oxytocin stimulates PLC up to 1000% over the control level and elevates [Ca2+]i up to 800 nM in a concentration-dependent manner without any measurable delay; both effects are partly sensitive to PT. These data provide functional evidence for the presence of different stimulatory mechanisms for PGE2 in myometrium: 1) a low affinity receptor (probably EP3D) that activates PLC through a PT-insensitive pathway; and 2) a high affinity receptor (probably EP1), independent from PLC and involving a PT-sensitive G protein (G(i)?). Both pathways lead to elevation of [Ca2+]i.
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PMID:Prostaglandin E2 activates phospholipase C and elevates intracellular calcium in cultured myometrial cells: involvement of EP1 and EP3 receptor subtypes. 864 Dec 11

The entire coding region of an ovine endometrial oxytocin receptor (OTR) cDNA was generated by PCR, subcloned into the SV40 major late promoter expression vector pSVLJ and transiently expressed in Cos-7 cells. A specific OTR antagonist, 125I-labelled d(CH2)5 [Tyr(Me)2,Thr4,Tyr-NH2(9)]-vasotocin (OTA), was used to describe the binding kinetics of the expressed receptor which had a Kd of 4.5 nM and Bmax of 2.4 nM/mg protein (6.8 x 10(5) receptor molecules/transfected cell). The functional properties of the expressed OTR were determined by measuring oxytocin-induced phosphoinositide (PI) hydrolysis. Oxytocin increased PI turnover in OTR transfected cells fourfold in excess of residual endogenous activity, and stimulated phospholipase C (PLC) activity in a dose- and time-dependent manner, confirming that the expressed OTR cDNA was functional. Arginine vasopressin also stimulated PI turnover in a dose-dependent manner; thresholds of responses to oxytocin and arginine vasopressin were 10(-9) M and 10(-7) M respectively. OTA did not increase PI turnover and competitively inhibited the oxytocin-induced response. Direct activation of the pathway by aluminium fluoride and guanosine (3'-O-thio)-triphosphate (GTP gamma S) confirmed that the OTR was G-protein linked. Co-incubation of GTP gamma S with oxytocin shifted the PI-response threshold from 10(-7) M to 10(-9) M and significantly increased the level of response, suggesting that maximum PI turnover was agonist-dependent. The G-protein involved in mediating the signal transduction pathway was pertussis toxin-insensitive and, therefore, probably a member of the Gq subfamily. The PLC inhibitor, U73122, had no effect on oxytocin-induced PI turnover, consistent with the response in endometrial tissue. These data suggest that the signalling pathway mediated by expressed OTR is similar to that attributed to OTR occupancy in ovine endometrium.
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PMID:Functional characterisation of an ovine endometrial oxytocin receptor cDNA transiently expressed in Cos-7 cells. 869 Oct 97


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