Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.2 (guanylate cyclase)
 8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Crude preparations of secretin or pancreozymin increased and at higher concentrations decreased guanylate cyclase (GTP pyophosphate-lyase, EC 4.6.1.2) activity from soluble and particulate fractions of rat liver homogenates. Partially purified and synthetic secretin were without effect as was the biologically active octapeptide fragment of pancreozymin. The active contaminants in these preparations survived boiling, saponification, and treatment with phospholipase A, trypsin and neuraminidase C. The activity was extractable with chloroform/methanol and did not survive ashing. Eight bile salt contaminants in crude secretin were obtained with thin-layer chromatography. Two of the contaminating bile salts that increased liver particulate guanylate cyclase activity were identified as taurodeoxycholate and either glycochenodeoxycholate or glycodeoxycholate; taurocholate was inhibitory. The sodium salts of cholate, deoxycholate, chenodeoxycholate and their glycine-or taurine-conjugated forms either increased or decreased particulate and soluble rat liver guanylate cyclase activity depending upon their concentration. Thus, the previously reported stimulatory and inhibitory effects of secretin and pancreozymin preparations on guanylate cyclase activity are probable attributable to their bile salt contaminants.
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PMID:Activation of liver guanylate cyclase by bile salts and contaminants in crude secretin and pancreozymin preparations. 1 19

Ethanol decreases hepatic protein and albumin synthesis, and inhibits pancreatic water, bicarbonate, and protein secretion. Since these actions of ethanol are opposite to those reported for secretin, cholecystokinin-pancreozymin, and pentagastrin which may be mediated through increases in cyclic GMP, it appeared possible that the inhibitory actions of ethanol might be mediated through inhibition of guanylate cyclase, the enzyme that catalyzes the production of cyclic GMP. Ethanol inhibited soluble preparations of guanylate cyclase from rat liver, pancreas, stomach, and ileum. Maximal inhibition was observed at 5.0 and 2.5 percent ethanol. The inhibitory effects of ethanol on the guanylate cyclase-cyclic GMP system of these tissues provide a possible explanation for some of the diverse effects of ethanol on these tissues.
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PMID:Ethanol-induced inhibition of guanylate cyclase in liver, pancreas, stomach and intestine. 1 94

Guanylate cyclase in the guinea pig fundic mucosa occurred in two enzymatic forms: a "soluble" form and a particulate form. The mean basal activity of the soluble fraction measured in the presence of 300 micrometer guanosine-5'-triphosphate and 5 mM MnCl2 was 72.6 +/- 5.3 pmoles of cyclic GMP per mg of protein per min. Guanylate cyclase activity was dependent on Mn2+; it was increased by sodium azide (NaN3), CaCl2, cysteine, secretin, and cholecystokinin, but it was not influenced by gastrin, histamine, cholinergic esters, prostaglandins E1 and A1. NaN3 (1 mM) decreased the apparent Km for MnCl2 and potentiated the effects of MgCl2. The activity of the particulate fraction represented about 14% of that of the supernatant fraction. The guanylate cyclase activity of that fraction was not modified by NaN3, gastrin, cholinergic agents, secretin, or cholecystokinin. Cysteine inhibited its activity. These data do not support the hypothesis that cyclic GMP acts as a second messenger for the action of cholinergic agents and gastrin in the guinea pig gastric mucosa.
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PMID:Effect of Ca2+, Mg2+, NaN3, cholinergic agents, and gastrointestinal hormones on the guanylate cyclase from guinea pig gastric mucosa. 2 35

The response of the cyclic nucleotide system (cAMP, cGMP, adenylate cyclase, guanylate cyclase, and specific phosphodiesterases) to two gastric acid secretagogues, histamine and acetylcholine, and two secretory inhibitors, prostaglandin E2 and secretin, was studied in vivo and in vitro in canine gastric fundic mucosa. Histamine and acetylcholine in vivo failed to stimulate cAMP but significantly increased cGMP; in vitro they affected neither adenylate cyclase nor guanylate cyclase. Prostaglandin E2 and secretin, however, increased cAMP in vivo and significantly stimulated adenylate cyclase in vitro. Specific phosphodiesterases were unaffected by these compounds. The changes, while not specifically localized to the acid-producing cells, are consistent with the suggestion that the control of canine gastric acid secretion may be mediated by changes in mucosal cAMP and cGMP.
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PMID:Cyclic nucleotides and the regulation of canine gastric acid secretion. 3 56

The cyclic GMP level in the ductus deferens is elevated by acetylcholine, norepinephrine, KCl, and the phosphodiesterase inhibitor SC-2964. The presence of extracellular Ca++ is required for the effects of all of these agents on cyclic GMP levels. In addition, Ca++ appears to be an important factor for the basal turnover of cyclic GMP in this tissue, but it may be less important in other tissues. These observations have led us to the following working hypothesis (Fig. 5): The interactions of some hormones or neurotransmitters with membrane receptors secondarily increase cyclic GMP formation after primarily increasing the influx of extracellular Ca++ or changing the distribution of Ca++ among intracellular pools or compartments. However, in addition to this possibility, other hormonal effects on particulate and/or soluble guanylate cyclase that do not involve Ca++ mediation must also be considered. Some agents that are known to increase cyclic GMP in tissues have been reported in preliminary communications to activate cell-free preparations of guanylate cyclase (Amer and McKINNEY, 1973; White, Ignarro, and George, 1973), but these reports have not yet been confirmed by other laboratories. Secretin has been reported to stimulate guanylate cyclase activity from several tissues (Thompson, Johnson, Lavis, and Williams, 1974), but the significance of this report is unclear since secretin has not yet been shown to increase cyclic GMP levels in any tissue. Thus, although not convincingly established, some hormones may increase particulate guanylate cyclase activity in a manner similar to that by which hormones increase adenylate cyclase activity. Alternatively, some hormones may increase soluble guanylate cyclase activity with mediating factors other than Ca++ being involved, or hormone-receptor interaction at the plasma membrane could conceivably induce a dislocation and change in effective activity of a reversibly bound, membrane-associated guanylate cyclase. Elucidating which or how many of these possibilities are operative will require thorough study and understanding of the fundamental behavior and properties of soluble and particulate guanylate cyclase activities.
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PMID:Regulation of cyclic GMP levels in the ductus deferens of the rat. 16 75

Exogenous cGMP can inhibit both basal and glucagon-stimulated production of glucose in liver slices from fed rats. Thus, cAMP and cGMP have opposite effects on the production of glucose in rat liver. Acetylcholine, an activator of guanylate cyclase (EC 4.6.1.2) in other systems, also inhibits the glucagon-stimulated production of glucose. No effect on glucose production was observed with secretin or exogenous GTP.
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PMID:Regulation of glucagon-stimulated production of glucose in rat liver by guanosine 3',5'-cyclic phosphate. 19 Nov 65

Adenylate cyclase from the guinea-pig pancreas was activated in a dose-dependent manner by both secretin and cholecystokinin-pancreozymin, but in contrast with results in other species the hormones were approximately equipotent. All other hormones and transmitter substances tested were without any effect on adenylate cyclase activity. Guanylate cyclase activity was shown to have both particulate and supernatant components in the guinea-pig pancreas. The particulate enzyme, but not the supernatant enzyme, was markedly activated by Triton X-100, and most of the induced activity was released into the supernatant. The supernatant enzyme was specifically Mn2+-dependent, but, even though Mn2+ was maximally effective at a concentration of 3 mM, activity could be raised further by increasing Ca2+ concentration. The particulate enzyme, by contrast, was relatively Mn2+-independent. Activity of the particulate guanylate cyclase was enhanced by phosphatidylserine. The supernatant enzyme displayed classical Michaelis-Menten kinetics, but the particulate enzyme deviated markedly from such kinetics. Under none of the conditions used was any significant activation of guanylate cyclase observed with any of the secretogen hormones or transmitter substances.
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PMID:The metabolism of cyclic nucleotides in the guinea-pig pancreas. Adenylate cyclase and guanylate cyclase. 610

The release of somatostatin-like immunoreactivity was studied in isolated synaptosomes. A significant release of somatostatin-like immunoreactivity was observed in the presence of vasoactive intestinal polypeptide (VIP) (10(-6) M: 53.0 +/- 12.4 pg/mg, basal: 14.3 +/- 1.7 pg/mg, n = 5, P < 0.05), secretin (10(-6) M: 56.1 +/- 3.8 pg/mg, basal: 25.8 +/- 1.6 pg/mg, n = 6, P < 0.01) and isoproterenol (10(-5) M: 54.0 +/- 13.4 pg/mg, basal: 20.0 +/- 3.4 pg/mg, n = 8, P < 0.05). Forskolin, an unspecified activator of the adenylate cyclase, caused a significant release of somatostatin-like immunoreactivity (10(-6) M: 57.3 +/- 13.2 pg/mg, basal: 30.0 +/- 5.8 pg/mg, n = 13, P < 0.01) which was further augmented in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX 10(-4) M) (77.0 +/- 17.8 pg/mg, n = 13, P < 0.01). 3-Isobutyl-l-methylxanthine and N6, 2'-O-dibutyryladenosine-3',5'-cyclic monophosphate mimicked at effect of forskolin and VIP. The release of somatostatin was paralleled by an increase of cAMP immunoreactivity in the presence of VIP (10(-6) M: 37.1 +/- 9.4 pmol/mg, basal: 19.8 +/- 4.2 pmol/mg, n = 10, P < 0.05), isoproterenol (10(-5) M: 42.4 +/- 9.8 pmol/mg basal: 16.7 +/- 2.4 pmol/mg, n = 12, P < 0.01) and forskolin (10(-6) M: 47.1 +/- 12.4 pmol/mg, basal: 19.8 +/- 4.2 pmol/mg, n = 10, P < 0.01). The effect of nitric oxide (NO) which acts as an inhibitory neurotransmitter in the enteric nervous system was studied. NO is known to activate guanylate cyclase to induce transmitter release. The NO-generating compound sodium nitroprusside and bromoguanosine-3',5'-cyclic monophosphate (8-Br-cGMP) had no effect on the release of somatostatin-like immunoreactivity. These data demonstrate the stimulatory effect of VIP, secretin and isoproterenol on release of somatostatin-like immunoreactivity from enteric synaptosomes, which is presumably mediated by cAMP-dependent mechanisms. cGMP-dependent mechanisms seem to be of minor relevance.
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PMID:Presynaptic modulation by VIP, secretin and isoproterenol of somatostatin release from enriched enteric synaptosomes: role of cAMP. 895 33

C-type natriuretic peptide (CNP) is the major natriuretic peptide in the brain and its mRNA has been reported in the central nervous system, which supports local synthesis and its role as a neuromodulator. The aim of the present work was to study the effect of centrally applied CNP on pancreatic secretion. Rats were fitted with a lateral cerebroventricular cannula one-week before secretion studies. The central administration of CNP dose-dependently enhanced pancreatic fluid and protein output. CNP response was diminished by atropine and hexamethonium, but it was abolished by vagotomy. Neither adrenergic antagonists nor the administration of (D-p-Cl-Phe(6),Leu(17))-vasoactive intestinal peptide (VIP antagonist) or N(omega) Nitro-L arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor) affected CNP response. The effect induced by CNP was mimicked by 8-Br-cGMP but not by c-ANP-(4-23) amide (selective agonist of the natriuretic peptide receptor C). Furthermore, CNP interacted with cholecystokinin (CCK) and secretin in the brain to modify pancreatic secretion. Present findings show that centrally applied CNP enhanced pancreatic secretion through a vagal pathway and suggest that CNP response is mediated by the activation of natriuretic peptide guanylyl cyclase coupled receptors in the brain.
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PMID:C-type natriuretic peptide applied to the brain enhances exocrine pancreatic secretion through a vagal pathway. 1626 10

Atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) are members of the natriuretic peptide family best known for their role in blood pressure regulation. However, in recent years all the natriuretic peptides and their receptors have been described in the gastrointestinal tract, digestive glands and central nervous system, as well as implicated in the regulation of digestive gland functions. The current review highlights the regulatory role of ANP and CNP in pancreatic and other digestive secretions. ANP and CNP stimulate basal as well as induced pancreatic secretion and modify bicarbonate and chloride secretions. Whereas ANP and CNP exert effects directly on pancreatic cells, CNP also acts through a vago-vagal reflex. At high doses both peptides attenuate pancreatic secretion induced by high doses of secretin through the PLC/PKC pathway. With regards to other digestive secretions, ANP and CNP decrease bile secretion in the rat. ANP does not induce salivation by itself but enhances stimulated salivary secretion and modifies salivary composition in rat parotid as well as submandibular glands. In rat pancreatic, hepatic, parotid and submandibular tissues, the NPR-C receptor mediates mostly peripheral responses whereas NPR-A and NPR-B receptors, which are coupled to guanylate cyclase, likely mediate the central response. In addition, ANP modulates gastric acid secretion via a vagal-dependent mechanism. In the intestine, ANP and CNP decrease water and sodium chloride absorption through an increase in cGMP levels. Overall, these findings indicate that ANP and CNP are members of the large group of regulatory peptides affecting digestive secretions.
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PMID:Natriuretic peptides as regulatory mediators of secretory activity in the digestive system. 1923 31


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