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At least 559 records · Page 31Linked to original sources
PubMed1993

Dopamine modulates in a differential fashion T- and L-type calcium currents in bass retinal horizontal cells.

White bass (Roccus chrysops) retinal horizontal cells possess two types of voltage-activated calcium currents which have recently been characterized with regard to their voltage dependence and pharmacology (Sullivan, J., and E. M. Lasater. 1992. Journal of General Physiology. 99:85-107). A low voltage-activated transient current was identified which resembles the T-type calcium current described in a number of other preparations, along with a sustained high threshold, long-lasting calcium current that resembles the L-type calcium current. Here we report on the modulation of horizontal cell calcium channels by dopamine. Under whole-cell voltage clamp conditions favoring the expression of both calcium currents, dopamine had opposing actions on the two types of voltage-sensitive calcium currents in the same cone-type horizontal cell. The L-type calcium current was significantly potentiated by dopamine while the T-type current was simultaneously reduced. Dopamine had no effect on calcium currents in rod-type horizontal cells. Both of dopamine's actions were mimicked with the D1 receptor agonist, SKF 38393, and blocked by application of the D1 specific antagonist, SCH 23390. Dopamine's actions on the two types of calcium currents in white bass horizontal cells are mimicked by the cell membrane-permeant cyclic AMP derivative, 8-(4-chlorophenylthio)-cyclic AMP, suggesting that dopamine's action is linked to a cAMP-mediated second messenger system. Furthermore, the inhibitor of cAMP-dependent protein kinase blocked both of dopamine's actions on the voltage-dependent calcium channels when introduced through the patch pipette. This indicates that protein phosphorylation is involved in modulating horizontal cell calcium channels by dopamine. Taken together, these results show that dopamine has differential effects on the voltage-dependent calcium currents in retinal horizontal cells. The modulation of these currents may play a role in shaping the response properties of horizontal cells.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1993

Identification of a 5-hydroxytryptamine (5-HT2) receptor on guinea pig small intestinal crypt cells.

Radioligand labeling of [3H]ketanserin was examined in suspensions of dispersed guinea pig small intestinal mucosal cells prepared by modification of the EDTA-chelation method described by M. M. Weiser (J. Biol. Chem. 248: 2536-2541, 1973). Preferential incorporation of [3H]thymidine was used to confirm that suspensions were enriched in crypt cells. At 25 degrees C, binding of [3H]ketanserin to dispersed enterocytes was rapid, maximal by 5 min, saturable (dissociation constant = 1.5 nM), 65 +/- 5% specific, stable, and reversible. The maximal number of binding sites per cell was 92,000 (range 86,000-105,500). Binding was temperature dependent, with maximal binding at 37 degrees C, and was inhibited by 5-hydroxytryptamine (5-HT) (half-maximal inhibition of [3H]ketanserin binding observed in response to 1 microM 5-HT) and ketanserin (half-maximal inhibition of [3H]ketanserin binding observed in response to 1 nM ketanserin) but not by the 5-HT1P antagonist N-acetyl-5-hydroxytryptophyl 5-hydroxytryptophan amide (5-HTP-DP) or the 5-HT3 antagonist 3-tropanyl-indole-3-carboxylate methiodide (ICS-205-930). The second messenger system coupled to the putative mucosal 5-HT2 receptor was examined. 5-HT stimulated a concentration-dependent production of inositol 1,4,5-trisphosphate (IP3) in the dispersed enterocytes. This was maximal at 1 min and was inhibited in a concentration-dependent manner by ketanserin. 5-HTP-DP and ICS-205-930 had no effect on 5-HT-stimulated production of IP3. These data provide evidence for the existence of a mucosal 5-HT2 receptor located on guinea pig small intestinal crypt cells.

Animals↗
PubMed1995

Effects of fatigue of rat EDL in situ on metabolism of phosphoinositides.

The study was conducted to determine the effect of persistent fatigue in situ on the inositol phosphate second messenger system proposed to constitute a step in excitation-contraction coupling. Rat EDL, after stimulation in situ for 1 hr (100 Hz for 330 ms, 1/s), showed increased incorporation of myo-[3H]inositol into membrane phosphoinositides during a subsequent 4-h incubation period. The rate of hydrolysis of this pool resulting from 10 sec of tetanic stimulation, as well as the rate of production of inositol phosphates InsP, InsP2, and InsP3, were significantly reduced in fatigued muscles. These results suggest that the metabolic changes that parallel the alteration in contractile response with fatigue reflect a disruption in E-C coupling.

Animals↗
PubMed1991

Further confirmation of the role of adenyl cyclase and of cAMP-dependent protein kinase in primary afferent hyperalgesia.

Recent evidence has suggested that cAMP plays a role as a second messenger in the decrease in nociceptive threshold (or hyperalgesia) produced by agents acting on primary afferent terminals. In support of this hypothesis we report that intradermal injection of a direct activator of adenyl cyclase, forskolin, produces a dose-dependent hyperalgesia in the rat. The duration of this hyperalgesia was prolonged by the phosphodiesterase inhibitors, isobutylmethylxanthine and rolipram. Forskolin hyperalgesia was antagonized by the Rp isomer of cyclic adenosine-3'5'-monophosphothioate, an analog of cAMP that prevents the phosphorylation of the cAMP protein kinase. The Rp isomer of cyclic adenosine-3'5'-monophosphothioate also inhibited the hyperalgesia induced by a membrane-permeable analogue of cAMP, 8-bromocyclic adenosine monophosphate, as well as the hyperalgesia induced by agents that are presumed to act directly on primary afferent nociceptors: prostaglandin E2, prostaglandin I2, (8R,15S)-dihydroxyicosa(5E-9,11,13Z)tetraenoic acid; and the adenosine A2-agonist 2-phenylaminoadenosine. Although the cAMP second messenger system contributes to primary afferent hyperalgesia, we found no evidence for a contribution of protein kinase C. Thus, hyperalgesia induced by prostaglandin E2, prostacyclin (prostaglandin I2), (8R,15S)-dihydroxyicosa(5E-9,11,13Z)tetraenoic acid, the adenosine A2-agonist 2-phenylaminoadenosine, 8-bromocyclic adenosine monophosphate and the direct activator of adenyl cyclase, forskolin, were not significantly attenuated by the selective inhibition of protein kinase C by the 19-31 fragment of protein kinase C. Two other inhibitors of protein kinase C, sphingosine and staurosporine, also failed to attenuate prostaglandin E2-induced hyperalgesia.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Contrasting effects of inflammatory stimuli on neutrophil and monocyte adherence to endothelial cells.

Leukocyte adherence to endothelial cells (EC) is an important early event in inflammatory responses, which are often characterized by a predominance of either neutrophils (PMN) or monocytes. However, there is little information concerning the molecular events important in leukocyte adherence to EC. Intracellular activation of protein kinase C and the calcium-second messenger system leads to the stimulation of a number of important functions in PMN and monocytes. We compared the effects of members of these pathways on human PMN and monocyte adherence to cultured bovine aortic EC. We observed that phorbol myristate acetate, phorbol, 12,13-dibutyrate, L-alpha-1-oleoyl-2-acetoyl-sn-3-glycerol, and ionomycin each induced significant dose-dependent increases in PMN adherence to EC monolayers. In contrast, similar concentrations of each of these agents induced significant decreases in EC adherence of monocytes enriched by countercurrent centrifugal elutriation. Separate experiments determined that the differences in PMN and monocyte adherence to EC were not related to differences in oxidant production because 1) phorbol myristate acetate and L-alpha-1-oleoyl-2-acetoyl-sn-3-glycerol caused similar marked increases in both PMN and monocyte superoxide anion and hydrogen peroxide production and 2) ionomycin, which had opposing effects on PMN and monocyte adherence, had no effect on PMN and monocyte superoxide anion or hydrogen peroxide release. We conclude that activators of protein kinase C and the Ca-second messenger pathway have opposite effects on PMN and monocyte adherence to EC and that these effects are mediated by O2 radical-independent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Methods for studying neurotransmitter transduction mechanisms.

This review describes the methodologies used to study the transduction mechanisms that are activated in excitable cells by G-protein-coupled agonists. In view of the complexity of second-messenger systems, it is no longer relevant to ask, "What is the transduction mechanism involved in the action of a given neuromodulator?" because, in many cases, a variety of transduction mechanisms and physiological responses are invoked following receptor activation. This means that a single aspect of the physiological response must be selected for study in order to address the question of transduction mechanism. This review is therefore concerned with a description the use of patch- and voltage-clamp procedures to study transduction mechanism because they are designed to isolate one aspect of the physiological response: the change in activity of a single type of membrane ion channel.

Animals↗
PubMed1998

Metabotropic glutamate receptors limit adenylyl cyclase-mediated effects in rat hippocampus via protein kinase C.

Glutamate receptors of the metabotropic type (mGluRs) activate protein kinase C in hippocampus, but few physiological functions of this pathway are known. The present data show that mGluRs utilize protein kinase C to inhibit another second messenger system, the adenylyl cyclase pathway, in neurons of the CA1 area of hippocampus. Activation of mGluRs prevented beta-adrenergic receptors, which couple to adenylyl cyclase, from blocking the slow Ca2+-dependent afterhyperpolarization (AHP). Since the afterhyperpolarization modulates neuronal responsiveness, crosstalk between protein kinase C and the adenylyl cyclase pathway is likely to have physiological consequences. Moreover, mGluRs themselves block the afterhyperpolarization, so the observed interference with the beta-adrenergic response constitutes a hierarchical relationship in which mGluRs are dominant over beta-adrenergic receptors.

Adenylyl Cyclases↗
PubMed1993

Muscarinic acetylcholine receptors in invertebrates: comparisons with homologous receptors from vertebrates.

The pharmacology, physiology and molecular biology of invertebrate muscarinic acetylcholine receptors are compared with current knowledge concerning vertebrate muscarinic acetylcholine receptors. Evidence for the existence of multiple receptor subtypes in invertebrates is examined, emphasizing what is presently known about the sensitivity of invertebrate preparations to subtype selective ligands previously defined in vertebrate studies. Other evidence for muscarinic receptor subtypes which is examined includes: heterogeneous responses to classical muscarinic ligands and evidence for coupling of invertebrate muscarinic receptors to several different classes of second messenger systems. Clues regarding possible functions for invertebrate muscarinic receptors are discussed, including evidence from both physiological studies and in situ localization studies which reveal patterns of receptor protein and mRNA expression. A detailed analysis of the structural similarities between a cloned Drosophila muscarinic receptor and vertebrate muscarinic receptors is also presented. Regions of the receptors that may be involved in ligand binding, effector coupling and receptor regulation are identified in this comparison. Future directions for invertebrate muscarinic receptor research are considered including: methods for cloning other receptor subtypes, methods for cloning homologous receptors from other species and genetic approaches for determining the physiological roles of muscarinic receptors.

Amino Acid Sequence↗
PubMed1996

Carbamazepine inhibits the potentiation by adenosine analogues of agonist induced inositolphosphate formation in hippocampal astrocyte cultures.

Carbamazepine (CBZ) resembles lithium in its beneficial effects in therapy and prophylaxis of affective disorders. Since lithium is presumed to act via an attenuation of the inositolphosphate/Ca(2+)-second messenger system, it is of particular interest whether or not CBZ might also have inhibitory effects on this type of signal transduction. CBZ is an antagonist of adenosine A1-receptor subtypes. We show here that activation of adenosine A1-receptors potentiates the phenylephrine induced formation of inositolphosphates in hippocampal astrocytes and that this potentiating effect is inhibited by CBZ at a therapeutically relevant concentration. These results indicate that CBZ can by antagonism of adenosine A1-receptors inhibit the inositolphosphate/Ca(2+)-signalling in neural pathways regulated by adenosine.

Adenosine↗
PubMed1997

Beta adrenergic sensitization of gamma-aminobutyric acid receptors to ethanol involves a cyclic AMP/protein kinase A second-messenger mechanism.

Previous studies have found that ethanol (EtOH) will consistently potentiate gamma-aminobutyric acid (GABA) receptor function in the cerebellum during beta adrenergic receptor activation. One consequence of beta adrenergic receptor stimulation is to increase cAMP levels, which, in turn, activate protein kinase A (PKA)-mediated phosphorylation of intracellular protein sites. In the present study, we investigated three cAMP analogues, two activators and one inhibitor of PKA to determine whether this cAMP-mediated second-messenger system may be one mechanism involved in the previously observed beta adrenergic interaction of EtOH with the GABA(A) receptor. Furthermore, because the phosphorylation state of the GABA(A) receptor may be an important determinant of function, we investigated the effect of the block of phosphatase activity on EtOH/GABA receptor interactions. We found that similar to the beta adrenergic agonist isoproterenol, local applications of the membrane-permeable cAMP analogues 8-bromo-cAMP and Sp-cAMP could modulate responses to iontophoretically applied GABA and that these modulated GABA responses were sensitized to the potentiative effects of EtOH. EtOH did not facilitate unmodulated GABA effects or GABA responses that were maximally modulated by 8-bromo-cAMP, suggesting that the cAMP mechanism mediates the observed EtOH interaction with GABA mechanisms. Furthermore, the PKA inhibitor Rp-cAMP reversed the EtOH-induced potentiation of the isoproterenol-modulated GABA responses. Finally, microcystin-LR and okadaic acid, which are type I and IIa phosphatase inhibitors, could also modulate and sensitize GABA responses to EtOH. These data suggest that beta adrenergic sensitization of GABA(A) receptors to EtOH involves the intracellular cAMP/PKA second-messenger cascade.

Animals↗
PubMed1996

Alterations of local cerebral blood flow, phorbol 12,13-dibutyrate binding activity, and histological damage during acute focal ischaemia in rat brain. A pathophysiology of acute focal ischaemia: Part 1.

The alterations of the local cerebral blood flow (LCBF), 3H-phorbol 12,13-dibutyrate (PDBu) binding activity were measured, and histological findings were also examined during the closed time course (0, 1, 3, 5, 7 hour) after middle cerebral artery occlusion (MCAO) in rat brain to assess the complex pathophysiology of acute focal ischaemia. From 1 to 3 hours after the start of MCAO, significant (p < 0.01) hyperreactivity of the second messenger system involving PDBu binding may be present, despite low perfusion of LCBF, and severe damage in the striatum whereas sparing almost completely the cortex on histological examination. At 5 hours, the PDBu binding activity increased slightly but not significantly but is reduced markedly at 7 hours after MCAO compared with the control group. The measurement of PDBu binding activity, additionally to measuring the LCBF and observation of the histological change might be a useful indicator in determining the threshold and duration of ischaemia which cause functionally irreversible cell damage in the brain.

Animals↗
PubMed2001

Involvement of calcium, inositol-1,4,5 trisphosphate and diacylglycerol in the prothoracicotropic hormone-stimulated ecdysteroid synthesis and secretion in the prothoracic glands of Bombyx mori.

The objective of this study was to determine which intracellular second messenger systems are activated by prothoracicotropic hormone in the prothoracic glands (PGs) of Bombyx mori. Recombinant prothoracicotropic hormone (rPTTH) could stimulate ecdysteroid synthesis and secretion from day 6 PGs of the 5th instar of Bombyx mori within 30 min of in vitro incubation. However, rPTTH did not stimulate any increases in the glandular content of inositol 1,4,5-trisphosphate and cAMP during this short incubation period. Extracellular Ca2+ influenced the basal and rPTTH-stimulated ecdysteroid synthesis and release in a dose-dependent manner. The L-type Ca2+ channel antagonist, nitrendipine, inhibited the rPTTH-stimulated ecdysteroid synthesis and secretion (IC50-28 microM). The phospholipase C inhibitor, 2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate, inhibited the rPTTH-stimulated ecdysteroid synthesis (IC50-19 microM). The protein kinase C inhibitor, chelerythrine chloride, inhibited the rPTTH-stimulated ecdysteroid synthesis (IC50-14 microM). The protein kinase C activator, phorbol-12-myristate 13-acetate (PMA), could stimulate basal ecdysteroid synthesis and secretion (EC50-1 microM) and its inactive alpha-isomer (4 alpha-PMA) was ineffective. The combined results suggest that the PTTH-stimulated ecdysteroid synthesis and release in the PGs of Bombyx is dependent on extracellular Ca2+ and the bifurcating second messenger signalling cascade of inositol 1,4,5-triphosphate and diacylglycerol.

Alkaloids↗
PubMed2006

Integration of metabolic stimuli in the hypothalamic arcuate nucleus.

Integration of peripheral and central anabolic and catabolic inputs within the hypothalamic arcuate nucleus (ARC) is believed to be central to the maintenance of energy balance. In order to perform this complex task, neurons in the ARC express receptors for all major humoral and central transmitters involved in the maintenance of energy homeostasis. The integration of these inputs occurs at the cellular and circuit level and the resulting electrical output forms the origins for the activation of feeding and energy balance-related networks. Here, we discuss the role that active intrinsic membrane conductances, K(ATP) channels and intracellular second messenger systems play in the integration of metabolic stimuli at the cellular level in the ARC. We conclude that the research into the integration of hunger and satiety signals in the ARC has made substantial progress in the last decade, but we are far from unraveling the complex neuronal networks involved in the maintenance of energy homeostasis. The diverse range of inputs, neuronal integrative properties, targets, output signals and how these signals relate to the physiological output provides us with a colossal challenge for years to come. However, to battle the current obesity epidemic, target-specific drugs need to be developed for which the knowledge of neuronal pathways involved in the maintenance of energy homeostasis will be crucial.

Animals↗
PubMed1994

Preliminary characterization of a transformed cell strain derived from human trabecular meshwork.

Cells isolated from the trabecular meshwork (TM) of a male glaucoma patient were transformed by transfection with an origin defective mutant of SV40 virus. Transformation dramatically increased the growth rate of these cells (designated HTM-3 cells), allowing biochemical and pharmacological characterization. The HTM-3 cells had cytoskeletal components that were reported to be present in TM tissue and non-transformed TM cells. Vimentin, tubulin and smooth muscle specific alpha-actin, but not desmin, were localized in these cells by immunocytochemistry. The extracellular matrix components collagen types I, III and IV, fibronectin and laminin were found in HTM-3 cells as well as their non-transformed parental cells. As predicted, the protein profile of the HTM-3 cells revealed by two-dimensional gel electrophoresis was different from that of the non-transformed cells, probably due to the enhanced growth characteristics of these cells. Furthermore, HTM-3 cells had various intracellular second messenger systems that responded to pharmacological agents. Forskolin, prostaglandin E2, beta-adrenergic and adenosine A2 agonists stimulated the adenylyl cyclase in these cells, whereas muscarinic, serotonergic, dopaminergic and other agonists were ineffective. Sodium nitroprusside increased the intracellular concentration of cGMP, demonstrating the presence of a functional guanylyl cyclase. Phospholipase C activity in these cells was also detected. Muscarinic agonists, histamine and bradykinin, but not adrenergic, serotonergic agonists or prostaglandins, increased phosphoinositide turnover. These drug responses of HTM-3 cells agree with published data on primary TM cells and TM tissues, suggesting that the transformed cells may be a valid substitute for certain pharmacological studies of TM.

Aged↗
PubMed2003

Biochemical evidence for a P2Y-like receptor in Tetrahymena thermophila.

Extracellular nucleotides are ubiquitous signaling molecules. ATP signals through two receptor types: the ionotropic P2X receptors, and the metabotropic P2Y receptors. ATP acts as a chemorepellent in Tetrahymena thermophila, where it causes a distinct avoidance response. The intracellular mechanisms by which ATP causes avoidance in this organism, however, are unknown. In this study, we use in vivo pharmacological assays along with enzyme immuno-assays to obtain information about the ATP chemorepellent pathway and its associated second messenger systems. Our data show strong similarities between the presumed ATP receptor of T. thermophila and members of the P2Y family of receptors. The ATP response of T. thermophila appears to be coupled to phospholipase C, a defining characteristic of the P2Y receptor family. In addition, the ATP chemoresponse appears to be linked to a G(i/o) protein, nitric oxide synthase, and adenylyl cyclase, all of which are characteristic of some P2Y receptors. This is an important first step in describing the pathways involved in ATP chemoresponse of this organism.

Adenosine Triphosphate↗
PubMed2002

ERKs are the point of divergence of PKA and PKC activation by PTHrP in human skin fibroblasts.

Parathyroid hormone-related peptide (PTHrP) receptors, coupled to trimeric G proteins, operate in most target cells through at least three different transduction routes: Galpha s-mediated stimulation of adenylylcyclase (AC), Galpha q-mediated activation of phospholipase Cbeta (PLC) and mitogen-activated protein kinase (MAPK) activation. In this study we investigated the relative role of different pathways in human skin fibroblast proliferation. Using chemical inhibitors and activators of signal transduction, we demonstrated that: (i) AC/cAMP and PLC/1,4,5 inositol triphosphate/diacylglycerol second-messenger systems are simultaneously activated following PTHrP binding to its receptors; (ii) the mitogenic response to PTHrP derives from a balance between two counteracting pathways--an activating route mediated by protein kinase C (PKC) and an inhibitory route mediated by protein kinase A (PKA); (iii) PTHrP mitogenic effects are largely dependent on MAPKs, whose activity can be modulated by both PKA and PKC. Our results indicate that MAPKs are common targets of both transduction routes and, at the same time, their point of divergence in mediating PTHrP dual and opposite mitogenic effects.

Adult↗
PubMed1990

Activation in vitro of NF-kappa B by phosphorylation of its inhibitor I kappa B.

Nuclear factor kappa B (NF-kappa B), which was first detected by its binding to the kappa B site in the immunoglobulin kappa-gene enhancer, is important for the regulated expression of the kappa-gene and is partly responsible for the induction in appropriate cells of interleukin-2 (IL-2), IL-2 alpha receptor, beta-interferon and serum amyloid A protein. NF-kappa B is present as a nuclear DNA-binding protein in B lymphocytes and mature macrophages, but is found in the cytoplasm of many cells in a form unable to bind to DNA. The cytoplasmic form is bound to an inhibitor protein, I kappa B, from which it can be released in vitro by deoxycholate and other agents. Activation of cells by various agents, notably the phorbol esters that stimulate protein kinase C (PKC), leads to dissociation in vivo of the NF-kappa B/I kappa B complex and migration of NF-kappa B to the nucleus. Therefore, it acts as a second messenger system, transducing activation signals from the cytoplasm to the nucleus. To elucidate the mechanism of signal transfer, we have used an in vitro system in which addition of purified protein kinases to a partially purified NF-kappa B/I kappa B complex leads to the activation of the DNA-binding activity of NF-kappa B. Using gel retardation assays we found that PKC, cyclic AMP-dependent protein kinase (PKA) and a haem-regulated eIF-2 kinase (HRI) could activate NF-kappa B in vitro, whereas casein kinase II was ineffective. To determine the target for the protein kinases we purified and characterized both NF-kappa B and I kappa B and found that I kappa B is phosphorylated and inactivated in the presence of PKC and HRI but not PKA.

Adenosine Triphosphate↗
PubMed1995

A proposed role for oxytocin in regulation of endometrial prostaglandin F2 alpha secretion during luteolysis in swine.

Pulsatile secretion of endometrial prostaglandin (PG)F2 alpha is stimulated by oxytocin (OT) during late diestrus in domestic ruminants (i.e., cattle, sheep and goats) and results in corpus luteum (CL) regression leading to the onset of a new estrous cycle. Pulsatile PGF2 alpha release is also responsible for CL regression in swine, but the stimulus for its secretion from the uterine endometrium is not known. We propose that OT binds to specific OT receptors (OTR) on the endometrium to stimulate phosphoinositide (PI) hydrolysis, thereby activating the inositol trisphosphate (IP3)-diacylglycerol (DAG) second-messenger system to promote pulsatile PGF2 alpha secretion. Exogenous OT administered to cyclic gilts during late diestrus (days 10-16) decreased interestrous interval in three of four experiments. However, OT did not promote CL regression in hysterectomized gilts indicating that the effect of OT was uterine-dependent. Circulating concentrations of 13,14-dihydro-15-keto PGF2 alpha (the major stable metabolite of PGF2 alpha) were increased (p < 0.01) 10 min after i.v. injection of OT on days 14 and 16 in cyclic gilts and on days 10-16 in pregnant gilts, but the magnitude of the response to OT on all days in pregnant gilts was markedly reduced compared to the response in cyclic gilts on days 14 and 16. Mean density and Kd of OTR detected on endometrium of cyclic pigs 15 days post-estrus were 29.2 +/- 5.5 fmol/mg protein and 1.59 +/- 0.23 nM, respectively. Density of OTR was correlated with OT-stimulated PI hydrolysis (r = 0.83, p < 0.05) and PGF2 alpha secretion (r = 0.87, p < 0.10). Endometrial IP3 was increased within 30 seconds after OT treatment and preceded the increase in PGF2 alpha release stimulated by OT. Endometrial PI hydrolysis and PGF2 alpha secretion were similarly increased by AIF4-(phospholipase C activator), but not by cholera toxin (adenylyl cyclase activator). Although OT binding to OTR could be displaced by lysine-vasopressin and lysine-vasopressin stimulated PI hydrolysis, lysine-vasopressin did not stimulate PGF2 alpha release. Distinct receptors for OT and lysine-vasopressin on pig endometrium were confirmed by treatment with 100 nM OT + 100 nM lysine-vasopressin which stimulated PI hydrolysis more than 100-200 nM OT or lysine-vasopressin alone. These results support the hypothesis that OT stimulates phospholipase C to hydrolyze PI, yielding IP3 and DAG second-messengers which promote endometrial PGF2 alpha release during CL regression in pigs.

Animals↗