Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The involvement of calcium and calmodulin in the regulation of juvenile rat ovarian adenylate cyclase activity was investigated. Both basal and LH-stimulated cAMP production were inhibited by adding Ca2+ to the incubation medium at concentrations higher than 10(-5) M. Conversely, up to 10(-3) M concentrations of EGTA increased cAMP production (basal, stimulated by LH, FSH, NaF and Gpp(NH)p); higher concentrations of the chelator led to an inhibition of cAMP formation. However, when the homogenates were previously deprived of Ca2+ by treatment with buffer containing EGTA, a biphasic response to LH and Gpp(NH)p stimulation was obtained in the presence of increasing concentrations of added Ca2+:cAMP production was first enhanced at low concentrations and then inhibited at higher concentrations. These observations suggest that the optimal concentration of Ca2+ needed to obtained maximal stimulation of the enzyme was much lower than the Ca2+ content in the homogenates and that a minimal concentration of Ca2+ was required to activate it. In the presence of micromolar concentrations of trifluoperazine and pimozide, two potent inactivators of calmodulin, LH-stimulated cAMP production was markedly decreased. Reactivation was obtained by adding exogenous calmodulin to the assay medium. The addition of Ca2+-free exogenous calmodulin (10(-6) M) caused a specific and significant enhancement of cAMP accumulation induced by an optimal dose of LH. These results suggest that calcium ions regulated the adenylate cyclase activity in the rat ovaries and had a dual effect that was first stimulatory at low concentration and mediated by calmodulin and then inhibitory at high (non-physiological) concentration.
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PMID:Modulation of juvenile rat ovarian adenylate cyclase activity by calcium and calmodulin. 301 Apr 4

The effects of spent media from seminiferous tubules (STM) on Percoll-purified rat Leydig cells were investigated. Intracellular and extracellular cyclic AMP (cAMP) accumulation and testosterone production were measured. After a 5 h incubation period, STM reduces both the basal and LH-dependent cAMP levels (38 and 20%, respectively for intra- and extracellular cAMP) while, simultaneously, a stimulation of testosterone production is observed (47 to 50%, respectively in the absence or presence of LH). The reduction of cAMP levels observed after 5 h is likely to be due to the potentiating effect of the STM factor on the LH-dependent initial rise of the cAMP level which, in turn, induces a desensitization of the Leydig cell adenylate cyclase. This substance is a thermolabile protein (Mr greater than 50 000) produced by the Sertoli cell, independent of FSH and testosterone controls, and different from the LHRH-like substance.
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PMID:Effects of seminiferous tubule secreted factor(s) on Leydig cell cyclic AMP production in mature rat. 301 82

Sertoli cell-enriched cultures derived from 19-day old rats were exposed to FSH, L-isoproterenol, glucagon and dbcAMP for 24 up to 96 h. The influence of primary stimulation with these agonists on the response of the cells to subsequent stimulation with the homologous or heterologous agonists was investigated. Particular attention was paid to the response of the aromatase system defined as the ability of the cells to convert testosterone into 17 beta-estradiol. The responsiveness of this system was compared with the responsiveness of two other systems: adenylate cyclase and phosphodiesterase. It could be demonstrated that preincubation with the mentioned agonists results in a decreased responsiveness (maximal response) and a decreased sensitivity (ED50) upon re-stimulation with the homologous agonists. Preincubation with FSH also provokes partial desensitization for glucagon and L-isoproterenol. This heterologous desensitization can be mimicked by dbcAMP. The mentioned desensitization reactions are accompanied by a marked decrease in the accumulation of cAMP in the medium. Whereas desensitization of the adenylate cyclase occurs rapidly, desensitization of the aromatase response requires protracted stimulation for 3-4 days. In contrast with the adenylate cyclase and the aromatase system, the responsiveness of phosphodiesterase to FSH, L-isoproterenol, glucagon and dbcAMP is not affected by repeated stimulation for 96 h. It is concluded that hormonal desensitization affects both early (cAMP) and late (aromatase) responses of the Sertoli cell. However, some responses, such as phosphodiesterase activity seem to escape the desensitization process.
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PMID:Desensitization of Sertoli cell-enriched cultures by FSH, L-isoproterenol and glucagon. Influence on subsequent stimulation of 17 beta-estradiol production. 301 70

The evidence for a paracrine, progonadotropic role of adenosine in ovarian cells is summarized along with a capsule review of the origin and mechanisms of release and action of adenosine in other tissues. Briefly, adenosine markedly amplified rat and human luteal cell cyclic AMP and progesterone accumulation in the presence, but not the absence, of LH. The site of action of adenosine was found to be intracellular, linked to its phosphorylation, which resulted in increased levels of ATP. In rat luteal cells, adenosine blocked the acute antigonadotropic (luteolytic) action of PGF2 alpha. In the follicle, adenosine release from granulosal cells appeared to be stimulated by FSH. Adenosine and a nonmetabolized adenosine analog, augmented FSH-dependent inhibition of oocyte maturation in the presence or absence of an adenosine transport inhibitor. Inhibition of oocyte maturation by adenosine thus appears to be mediated by extracellular purinergic receptors. Paracrine, antigonadotropic agents also appear to regulate ovarian function. For example, GnRH elicits antigonadotropic activity in rat granulosal and luteal cells. We describe a novel, GnRH-like, ovarian hormone (GLOH) which may be the physiological ligand whose action GnRH mimics in rat ovarian cells. This protein was shown to be distinctly different from GnRH and a variety of other cyclic and noncyclic peptides. PGF2 alpha is a well known leutolytic agent and a summary of the antigonadotropic mechanism of PGF2 alpha action in rat luteal cells is presented. In these cells, the action of GnRH (or possibly the GnRH-like protein) and PGF2 alpha are mediated by separate membrane receptors but they appeared to share the same intracellular second messenger. Evidence for a role of products of phosphoinositol as a mediator of these antigonadotropic agents is summarized. We suggest that the ultimate mediator of antigonadotropic agents is Ca2+ which is released in the luteal cell in response to the intracellular mediator of antigonadotropic agents. For example, pharmacological agents which increase intracellular levels of Ca2+, mimicked the antigonadotropic action of GnRH and PGF2 alpha in rat luteal cells. Also, Ca2+ directly inhibited LH-sensitive adenylate cyclase activity in isolated luteal membranes, a paradigm in which GnRH and PGF2 alpha were inactive. The mechanism of Ca2+ action appeared to be linked to interference with GTP activation of adenylate cyclase. However, removal of extracellular Ca2+ did not abrogate the action of either GnRH or PGF2 alpha.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Purines, prostaglandins and peptides--nature and cellular mechanisms of action of local assist and assassin agents in the ovary. 302 1

The hormonal regulation of inhibin production by cultured granulosa cells from immature hypophysectomized, estrogen-treated rats was examined using a specific RIA which detects the N-terminal portion of the inhibin alpha-chain. The RIA measured bioactive inhibin of Mr about 32,000 in granulosa cell conditioned media fractionated by fast protein liquid chromatography. In the presence of 10(-7) M androstenedione, FSH stimulated inhibin production in a dose-dependent manner during a 2-day culture. Inclusion of a phosphodiesterase inhibitor decreased the EC50 for FSH from 2.6 to 0.8 ng/ml (n = 3). The stimulatory effect of FSH could be mimicked with forskolin (an adenyl cyclase activator) and with a cAMP analog, (Bu)2cAMP, consistent with FSH action mediated through a cAMP dependent pathway. Intracellular levels of inhibin were unmeasureable, suggesting that inhibin is not stored to any great extent by the granulosa cells. This finding was consistent with in vivo studies which showed that whereas FSH treatment for 2 days doubled serum inhibin levels when compared with basal levels, there was no increase in the concentration of extractable inhibin in ovarian tissue. Granulosa cells which had been exposed to 20 ng/ml FSH for 2 days to induce LH receptors produced inhibin in response to both LH and human CG during the subsequent 2-day culture, with the levels of inhibin equalling the amount inducible by FSH. In contrast, neither PRL nor terbutaline, a beta 2-adrenergic agonist, had any effect on inhibin production even though receptors for these hormones are also induced by FSH. GnRH was found to inhibit the FSH-stimulated production of inhibin (IC50, 10(-7) M), consistent with previous observations that GnRH can act at the ovarian level to inhibit granulosa cell differentiation. This inhibition by GnRH could be reversed by inclusion of a specific GnRH antagonist. On the other hand, another regulatory peptide, vasoactive intestinal peptide, slightly stimulated inhibin production. The effect of several growth factors was also tested. Insulin-like growth factor I raised not only FSH-stimulated inhibin levels, but basal levels as well. Insulin was also effective, but only at 100-fold higher concentration. Epidermal growth factor inhibited FSH-stimulated inhibin production (IC50 = 0.1 ng/ml), whereas fibroblast growth factor had no effect. Thus, granulosa cell inhibin secretion is regulated by FSH and LH but not by PRL, presumably via a cAMP-mediated pathway.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Hormonal regulation of granulosa cell inhibin biosynthesis. 302 19

Adult rat Leydig cell aromatase activity is stimulated 2.5 fold by LH or dbcAMP. Spent media prepared from seminiferous tubules or Sertoli cells of immature rats depress both the basal and the LH stimulated estradiol syntheses (25 and 20% decreases, respectively). These inhibitory effects are further enhanced when FSH is added to the culture medium of seminiferous tubules or Sertoli cells. Rat serum as well as culture media from other cell lines are ineffective while seminiferous tubule media from other immature animals (mouse, guinea-pig, calf) inhibit the aromatase activity. This Sertoli cell factor is a heat stable protein (molecular weight greater than 10 kDa), different from the LHRH-like Sertoli cell compound, which acts on the aromatase activity at a step beyond the adenylate cyclase.
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PMID:Spent media from immature seminiferous tubules and Sertoli cells inhibit adult rat Leydig cell aromatase activity. 303 Sep 13

GTP binding to Sertoli cell membranes has been investigated using [3H]5'-guanylyl-beta gamma-imidodiphosphate [[3H]Gpp(NH)p], a nonhydrolyzable analog of GTP. Binding of [3H]Gpp(NH)p Gpp(NH)p to membranes prepared from Sertoli cells in serum-free culture was proportional to membrane protein concentration in the range of 5-50 micrograms. Competitive displacement studies using adenine (ATP, ADP, and AMP) and guanine nucleotides [GTP, GDP, GMP, and Gpp(NH)p] indicated that only GTP, its analog Gpp(NH)p, and GDP were effective ligands. The relative potencies were Gpp(NH)p much greater than GTP greater than GDP, as characterized by ED50 values of 0.8, 2.5, and 4 microM, respectively. Competitive inhibition by GTP, however, was similar to that by Gpp(NH)p in the presence of a nucleoside triphosphate-regenerating system, suggesting the involvement of an active GTPase. Equilibrium binding studies indicated a single high affinity site for GTP with a Ka of 3.3 +/- 0.2 X 10(7) M-1. This value was supported by other studies in which an association rate constant of 1.8 X 10(6) M-1 min-1 and a dissociation rate constant of 2.4 X 10(-2) min-1 were estimated. Maximal binding of [3H]Gpp(NH)p to Sertoli cell membranes ranged from 30-55 pmol/mg protein. FSH enhanced [3H]Gpp(NH)p binding by about 50% (P less than 0.05), reflecting an increase in the number of available binding sites rather than an effect on Ka. When GDP was preincubated with membranes in the absence of FSH, the number of available binding sites for [3H]Gpp(NH)p was decreased. This reduction in available binding sites by pretreatment with GDP could be reversed by adding FSH during the equilibrium binding analysis. These studies have demonstrated specific high affinity binding of Gpp(NH)p to Sertoli cell membranes with an affinity comparable to that required for activation of FSH-sensitive adenylate cyclase. Furthermore, a potent GTPase activity associated with the Sertoli cell membrane is responsible for rapid hydrolysis of GTP to GDP and may participate in inactivation of GTP-dependent adenylate cyclase activity. The role of FSH in the regulation of nucleoside binding appears to be in facilitating exchange of GTP for GDP by enhancing the release of bound GDP.
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PMID:Guanine triphosphate-binding site regulation by follicle-stimulating hormone and guanine diphosphate in membranes from immature rat Sertoli cells. 309 3

The effect of forskolin on the hormonal (LH, FSH) activation and on the stimulation provided by other effectors (Gpp(NH)p,NaF) of the juvenile rat ovarian adenylate cyclase was investigated. Forskolin exhibited a synergistic action with LH, FSH and Gpp(NH)p but not with NaF. Addition of Ca2+ was inhibitory over a concentration range from 10(-5) to 10(-2) M whereas EGTA enhanced the response at 5.10(-5) M and inhibited it at higher concentration. The cAMP production was increased by addition of Mn2+ at low concentration (up to 5 mM) but markedly decreased at higher concentration (30 mM). FSH induced cAMP production was completely abolished at 30 mM Mn2+. The effect of vanadyl ion was very similar to that of Mn2+ Vanadate anion on the contrary was without effect on FSH stimulation.
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PMID:Action of Mn2+ and vanadium compounds on hormone and forskolin induced stimulation of juvenile rat ovarian adenylate cyclase. 309 97

The subject of the study was the development of follicular and luteal catecholamine responsiveness during the periovulatory period. Follicles and corpora lutea and granulosa cells were obtained from the PMSG ovulatory model and adenylate cyclase activity measured in membrane fractions. In the earlier part of the follicular phase (48 h and 26 h before ovulation) no response to noradrenalin on follicular and granulosa cell adenylate cyclase activity was seen. A small but significant response to noradrenalin was observed from 18 h before until 3 h after ovulation. The response to noradrenalin on luteal adenylate cyclase activity increased markedly with time and reached a maximum 39-57 h after ovulation. After this time the luteal response to noradrenalin decreased with luteal age. The effect of LH was less than that of noradrenalin during the early luteal phase, and in contrast to noradrenalin, increased with luteal age. The combined effects of LH and noradrenalin were not additive. In order to test whether gonadotropins could induce a noradrenalin response, injections of LH and FSH were given to the animals two days before ovulation. LH, but not FSH, induced a small but significant response to noradrenalin 16 h later. The present investigation has shown that ovarian responsiveness to catecholamines appears in preovulatory follicles followed by a marked increase in luteal catecholamine responsiveness. This development could at least partly occur under the influence of LH.
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PMID:Studies of the luteinization process in the rat: follicular and luteal adenylate cyclase responsiveness to catecholamines. 310 59

We have previously reported detergent (Triton X-100) solubilization of a follitropin (FSH) receptor-rich fraction from light membranes of bovine testis that responded to exogenous FSH by activation of adenylate cyclase (Dattatreyamurty, B., Schneyer, A., and Reichert, L. E., Jr. (1986) J. Biol. Chem. 261, 13104-13113). Upon gel filtration of the detergent-extract through Sepharose-6B, two fractions were separated. Each specifically bound [3H]guanosine 5'-imidotriphosphate (Gpp(NH)p) and had guaninetriphosphatase (GTPase) activity. Of these, one fraction (6B-Fraction-1) also bound radioiodinated human follitropin (hFSH), indicating a coelution of the nucleotide-binding protein with receptor. The other fraction (6B-Fraction-2) did not contain detectable FSH receptor activity. Several lines of evidence suggest that 6B-Fraction-1 is a complex consisting of FSH receptor and a guanine nucleotide regulatory protein, probably Ns. 1) The GTP-binding and FSH-binding activities of 6B-Fraction-1 were retained by a GTP-affinity column, and their retention by the affinity matrix could be prevented by simultaneous addition of free Gpp(NH)p. 2) When exogenous GTP was added to 6B-Fraction-1, binding of 125I-hFSH was reduced compared to controls lacking exogenous GTP. This effect of GTP was highly specific and noncompetitive, indicating that GTP did not bind to receptor. In addition, the affinity of receptor for FSH was decreased, and the rate and degree of dissociation of bound labeled FSH from receptor were increased in the presence of exogenous GTP, each in concentration-dependent manner. 3) Exposure of 6B-Fraction-1 to higher concentration of Triton X-100 reduced significantly the receptor-associated GTP-binding activity and also rendered the hormone-binding activity insensitive to GTP. 4) Treatment of highly purified testis membranes with cholera toxin plus NAD, but not pertussis toxin plus NAD, eliminated the ability of GTP to modulate the 125I-hFSH binding to receptor. 5) After cholera toxin-induced [32P]ADP-ribosylation of testis membranes, a major peak of radioactivity (presumably Ns) was coeluted with FSH receptor activity from the Sepharose-6B column. These results and the observation that the effect of GTP is noncompetitive at FSH receptor level suggest that FSH binding inhibition and the increased rate of hormone dissociation from receptor were the result of GTP interaction with a guanine nucleotide regulatory protein, probably Ns, which itself was functionally associated with the FSH receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Physical and functional association of follitropin receptors with cholera toxin-sensitive guanine nucleotide-binding protein. 311 50


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