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)

Rat GH-releasing hormone (GHRH), mainly contained in hypothalamic neurons, has also been identified in several extraneural tissues, including the gastrointestinal tract, placenta, ovary, and testis. In the testis, GHRH mRNA is ontogenically regulated, and GHRH immunoreactivity can be observed in interstitial cells and tubules, suggesting an intratesticular role for the peptide. Leydig cells in culture are able to produce hypothalamic releasing hormones, i.e. CRH, which acts as an autocrine negative regulator of Leydig cell function. In this study we investigated whether GHRH is present in Leydig cells and evaluated the role of the peptide in Leydig cell function. Adult Leydig cells in culture produced considerable amounts of immunoreactive GHRH [23.9 +/- 2.1 (+/- SE) pg/10(6) cells.30 min], and the release of the peptide was acutely stimulated by hCG. HPLC analysis of GHRH in media from basal and hCG-treated cultures showed the presence of a single peak eluting at the same retention time as that of hypothalamic rat GHRH. Radioligand binding and activation studies revealed a common receptor for vasoactive intestinal peptide (VIP) and rat GHRH in Leydig cell membrane. Specific binding of [125I]VIP to Leydig cell membranes showed the presence of a single site, with high affinity and low binding capacity. The relative potencies of VIP-related peptides for inhibition of radioligand binding were: VIP > rat GHRH > secretin > human GHRH. In cultured Leydig cells, GHRH and VIP stimulated cAMP production, consistent with coupling of the receptor to the adenylate cyclase system. VIP displayed a lower ED50 than GHRH in stimulating cAMP production (P < 0.01), comparable with the higher binding potency of this peptide. No additive effects of VIP- and GHRH-stimulated cAMP generation were observed, suggesting that both peptides compete for the same receptor protein. GHRH and VIP had no effect on basal steroidogenesis, indicating a lack of tonic actions and compartmentalization of the peptides' effect. On the other hand, GHRH acted as a potentiator of the acute gonadotropin stimulation of testosterone production and cAMP generation. [125I]hCG binding to the Leydig cells in culture showed that GHRH was unable to affect the number or affinity of binding sites for hCG, indicating that the GHRH-sensitizing effect on LH action is beyond the level of gonadotropin binding and possibly is through the facilitation of LH receptor coupling functions.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Growth hormone-releasing hormone is produced by rat Leydig cell in culture and acts as a positive regulator of Leydig cell function. 133 49

Pituitary adenylate cyclase-activating peptide (PACAP), a novel hypothalamic peptide that has been shown to exist in several tissues including the testis, was examined for its effects on cultured rat Sertoli cells. PACAP stimulates cAMP accumulation in Sertoli cells cultured from 15-day-old rats in the presence or absence of methylisobutylxanthine, a phosphodiesterase inhibitor, and in the presence of pertussis toxin, a blocker of the adenylate cyclase inhibitory pathway. Maximal stimulation, which is 20-40% of that attainable with FSH, occurs at PACAP concentrations of 10 nM: the ED50 is approximately 100 pM. The ability of PACAP to stimulate Sertoli cell cAMP declines with increasing age of donor animals (15-60 days of age) in a fashion similar to the FSH effect. PACAP stimulation of Sertoli cell cAMP accumulation is additive with submaximal, but not maximal, concentrations of FSH or forskolin. PACAP also stimulates the secretion of lactate, estradiol, and inhibin in a concentration-dependent manner. The stimulation of Sertoli cell cAMP accumulation by PACAP is not altered by a vasoactive intestinal peptide antagonist, and vasoactive intestinal peptide alone does not stimulate cAMP accumulation, indicating that PACAP is not acting via vasoactive intestinal peptide receptors. Further experiments are needed to determine whether PACAP is synthesized within the testis and if so, in which cell types; however, the present data clearly demonstrate that PACAP can modulate Sertoli cell function in vitro.
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PMID:A novel hypothalamic peptide, pituitary adenylate cyclase activating peptide, modulates Sertoli cell function in vitro. 133 66

In homogenates of female rat anterior pituitary, the azepine derivative B-HT 920 inhibited the forskolin-stimulated adenylate cyclase activity with an EC50 value of 0.35 microM. In male rat anterior pituitary, B-HT 920 curtailed the stimulation of adenylate cyclase activity by vasoactive intestinal peptide with an EC50 of 0.20 microM. In synaptic plasma membranes of rat striatum, B-HT 920 significantly reduced basal adenylate cyclase activity with an EC50 of 0.68 microM. Both in pituitary and striatum, the B-HT 920 inhibition was counteracted by the dopamine (DA) D2 receptor antagonist 1-sulpiride, but not by the alpha 2-adrenergic antagonist yohimbine. These results indicate that B-HT 920 is capable of activating DA D2 receptors negatively coupled to adenylate cyclase activity.
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PMID:B-HT 920 activates dopamine D2 receptors coupled to inhibition of adenylate cyclase activity. 135 80

Catecholamines acting through beta 1- and beta 2-adrenoceptors cause positive inotropic and chronotropic effects in the human heart. In recent years, however, evidence has accumulated that in the human heart also other receptor systems can affect heart rate and/or contractility. Positive inotropic effects can be mediated by receptor systems acting through accumulation of intracellular cAMP (Gs-protein coupled receptors such as 5-HT4-like, histamine H2, and vasoactive intestinal peptide) or by receptor systems acting independent of cAMP possibly through the phospholipase C/diacylglycerol/inositol-1,4,5-trisphosphate pathway (such as alpha 1-adrenergic, angiotensin II, and endothelin). In the non-failing human heart, however, activation of all these receptor systems induces only submaximal positive inotropic effects when compared with those caused by beta-adrenoceptor stimulation, indicating that in humans the cardiac beta-adrenoceptor-Gs-protein-adenylate cyclase pathway is the most powerful mechanism to increase heart rate and contractility. On the other hand, at least three receptor systems acting through inhibition of cAMP formation (Gi-protein coupled receptors) exist in the human heart: muscarinic M2-, adenosine A1-, and somatostatin-receptors. Activation of M2- and A1-receptors causes negative inotropic effects in the non-failing human heart: in atria activation of both receptors causes decreases in basal as well as in isoprenaline-stimulated force of contraction, but in ventricles only isoprenaline-stimulated force of contraction is depressed.
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PMID:Receptor systems in the non-failing human heart. 135 55

Thyroliberin (TRH), vasoactive intestinal peptide (VIP) and somatostatin (SRIF) act through receptors that are coupled to guanine nucleotide-binding regulatory proteins (G proteins). Regulation of hormone action may occur at the level of G protein coupling to the receptor or effector systems. In this study we demonstrate that prolonged exposure (for up to 48 hr) of cultured rat pituitary adenoma GH3 cells to these hormones caused homologous and to some extent heterologous attenuation of the adenylyl cyclase (AC) (EC 4.6.1.1) responsiveness. In addition, TRH and SRIF diminished both TRH- and guanosine 5'-[beta gamma-imido]-triphosphate-enhanced phospholipase C (PLC) (EC 3.1.4.3) activity within the same time-course. Measurements of cells membrane levels of Gs protein alpha-subunit (Gs alpha), G(i)-1 alpha/G(i)-2 alpha, G(i)-3 alpha, G(o) alpha and G beta by immunoblotting were performed. TRH and VIP upregulated levels of all G proteins except G(o) alpha and G beta. In contrast, SRIF caused a marked reduction of G beta levels. Thus, TRH and VIP, both acting through Gs, both modulated the alpha-subunit levels of this signal transducer, whereas SRIF, which possibly acts through G(i)-2, did not change the steady state level of G(i)-2 alpha. The actions of TRH, VIP and SRIF are multifaceted at the G protein level, where modulations of subtypes not directly involved in their actions may occur. These findings emphasize the complexity expected to be found in the in vivo situation.
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PMID:Hypothalamic hormones modulate G protein levels and second messenger responsiveness in GH3 rat pituitary tumour cells. 135 62

Catecholamines acting through beta 1- and beta 2-adrenergic receptors cause positive inotropic and chronotropic effects in the human heart. However, recent evidence suggests that in the human heart other receptor systems can also affect heart rate and contractility. Positive inotropic effects can be mediated by receptor systems acting through accumulation of intracellular cyclic adenosine monophosphate (cAMP; Gs-protein-coupled receptors such as 5-hydroxytryptamine(5-HT)4-like, histamine H2, and vasoactive intestinal peptide) or by receptor systems acting independently of cAMP, possibly through the phospholipase C/diacylglycerol/inositol-1,4,5-trisphophate pathway (such as alpha 1-adrenergic, angiotensin II, and endothelin). In the nonfailing human heart, activation of all these receptor systems induces only submaximal positive inotropic effects compared with those caused by beta-adrenergic receptor stimulation, indicating that in humans the cardiac beta-adrenergic receptor/Gs-protein/adenylate cyclase pathway is the most powerful mechanism to increase heart rate and contractility. However, the human heart contains only a few spare receptors for beta-adrenergic receptor-mediated positive inotropic effects and nearly all beta-adrenergic receptors are needed to cause maximal inotropic effects. Thus any decrease in the number of beta-adrenergic receptors will automatically lead to a reduction in functional responsiveness of beta-adrenergic receptors. In chronic heart failure the number and responsiveness of cardiac beta-adrenergic receptors are reduced, presumably because of the enhanced sympathetic drive to the heart and hence endogenous down-regulation by an elevated release of (cardiac-derived) norepinephrine, and this loss in cardiac beta-adrenergic receptor function is strongly related to the severity of the disease. However, beta 1- and beta 2-adrenergic receptors are differentially changed in different forms of heart failure. In dilated cardiomyopathy and possibly in aortic valve disease the number of cardiac beta 1-adrenergic receptors is selectively reduced without alteration in the number of beta 2-adrenergic receptors (although beta 2-adrenergic receptors become somewhat uncoupled). In ischemic cardiomyopathy, mitral valve disease, and possibly tetralogy of Fallot, the number of both beta 1- and beta 2-adrenergic receptors is concomitantly decreased. Because of the lack of a substantial receptor reserve, such a decrease in the number of beta-adrenergic receptors is accompanied by reduced inotropic and chronotropic responses to beta-adrenergic receptor stimulation in vitro and in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Receptor systems affecting force of contraction in the human heart and their alterations in chronic heart failure. 135 62

This study demonstrates the dual regulation by somatostatin of vasoactive intestinal peptide (VIP)-stimulated and forskolin-stimulated cyclic AMP accumulation by isolated rat intestinal epithelial cells. Somatostatin non-competitively inhibited (IC50 = 1 microM) the stimulatory effect of VIP on cyclic AMP accumulation, suggesting that the two neuropeptides act through separate receptors. The cyclic AMP accumulation produced by forskolin (a diterpene that stimulates directly the catalytic subunit of adenylate cyclase) was also inhibited by somatostatin in a dose-dependent manner. However, somatostatin did not modify the stimulatory effect of VIP on adenylate cyclase activity in a membrane preparation from the same cells, making it difficult to explain the mechanism of somatostatin action at this level. The data presented here suggest that somatostatin may play a physiological role in the regulation of nutrient absorption and the release of gut hormones or exocrine secretions by intestinal epithelial cells through the modulation of cyclic AMP production.
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PMID:Somatostatin inhibits VIP- and forskolin-stimulated cyclic AMP accumulation in enterocytes from rat jejunum. 136 40

This study was designed to test the hypothesis that stimulation of adenylate cyclase and elevation of cAMP is involved in the signal transduction process for substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, cholecystokinin or gastrin releasing peptide in myenteric ganglia. Enzymatically dissociated ganglia from the myenteric plexus of the guinea-pig small intestine were used to study changes in levels of cAMP in response to application of the brain-gut peptides in the presence and absence of forskolin. Application of substance P and calcitonin gene-related peptide were found to increase intraganglionic cAMP in a dose-dependent fashion when a phosphodiesterase inhibitor was present. The ED50 values for substance P and calcitonin gene-related peptide were 5 microM and 0.75 microM, respectively. The presence of forskolin in the incubation medium resulted in significant upward shifts of the dose-response curves for both peptides. Neither vasoactive intestinal peptide, cholecystokinin nor gastrin releasing peptide stimulated increases in intraganglionic cAMP under the same experimental conditions used for substance P and calcitonin gene-related peptide.
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PMID:Effects of brain-gut related peptides on cAMP levels in myenteric ganglia of guinea-pig small intestine. 137 54

The muscarinic stimulation of adenylate cyclase activity in rat olfactory bulb was characterized, with the aim of elucidating the nature of the molecular mechanism involved. Carbachol (CCh) stimulated the enzyme activity in either crude or purified cell membrane preparations and increased cyclic AMP accumulation in miniprisms of olfactory bulb. The CCh stimulation of adenylate cyclase activity displayed a fast onset and was rapidly reversed by addition of atropine. The stimulation was associated with an increase in the apparent Vmax of the enzyme, with no change in the Km for Mg-ATP. The affinity of the enzyme for Mg2+ was enhanced by CCh. The muscarinic effect required GTP at concentrations higher than those needed for enzyme stimulation with either l-isoproterenol or vasoactive intestinal peptide. Moreover, contrary to the beta-adrenergic stimulation, the muscarinic effect disappeared when guanosine 5'-O-(3'-thiotriphosphate) was substituted for GTP. In vivo treatment of olfactory bulbs with pertussis toxin completely prevented the muscarinic stimulation of adenylate cyclase, whereas cholera toxin was without effect. These results indicate that in rat olfactory bulb muscarinic receptors increase adenylate cyclase activity by interacting with a pertussis toxin-sensitive GTP-binding protein different from the stimulatory GTP-binding protein.
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PMID:Properties of muscarinic-stimulated adenylate cyclase activity in rat olfactory bulb. 137 77

We have compared the effects of vasoactive intestinal peptide (VIP) and of the VIP-related peptides pituitary adenylate cyclase activating peptide (PACAP) 1-27 and 1-38, helodermin, helospectin I and helospectin II, on the electrically evoked twitches in the isolated vas deferens of the rat. While VIP was virtually without effect, PACAP 1-38 suppressed the electrically evoked twitches effectively and in a concentration-dependent manner (pIC50 value 7.5). The naturally occurring N-terminal fragment PACAP 1-27 was less effective than PACAP 1-38 (Imax values 37.2% suppression compared to 76.5%) and less potent. The C-terminal fragment PACAP 16-38 was virtually inactive. Also helodermin and helospectin I+II suppressed the electrically evoked twitches effectively and in a concentration-dependent manner (pIC50 values 6.9; 7.2; 6.8, respectively). The three peptides produced similar maximum reduction of the twitches (74-80%). The findings suggest that PACAP, helodermin and helospectin suppress the electrically evoked contractions in the rat vas deferens via receptors distinct from VIP receptors.
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PMID:Unlike VIP, the VIP-related peptides PACAP, helodermin and helospectin suppress electrically evoked contractions of rat vas deferens. 143 78


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