Role of endothelium in responses of vascular smooth muscle.

Nitric oxide gas (NO) increased guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] activity in soluble and particulate preparations from various tissues. The effect was dose-dependent and was observed with all tissue preparations examined. The extent of activation was variable among different tissue preparations and was greatest (19- to 33-fold) with supernatant fractions of homogenates from liver, lung, tracheal smooth muscle, heart, kidney, cerebral cortex, and cerebellum. Smaller effects (5- to 14-fold) were observed with supernatant fractions from skeletal muscle, spleen, intestinal muscle, adrenal, and epididymal fat. Activation was also observed with partially purified preparations of guanylate cyclase. Activation of rat liver supernatant preparations was augmented slightly with reducing agents, decreased with some oxidizing agents, and greater in a nitrogen than in an oxygen atmosphere. After activation with NO, guanylate cyclase activity decreased with a half-life of 3-4 at 4° but re-exposure to NO resulted in reactivation of preparations. Sodium azide, sodium nitrite, hydroxylamine, and sodium nitroprusside also increased guanylate cyclase activity as reported previously. NO alone and in combination with these agents produced approximately the same degree of maximal activation, suggesting that all of these agents act through a similar mechanism. NO also increased the accumulation of cyclic GMP but not cyclic AMP in incubations of minces from various rat tissues. We propose that various nitro compounds and those capable of forming NO in incubations activate guanylate cyclase through a similar but undefined mechanism. These effects may explain the high activities of guanylate cyclase in certain tissues (e.g., lung and intestinal mucosa) that are exposed to environmental nitro compounds.

https://www.pnas.org/content/pnas/74/8/3203.full.pdf

Nitric oxide activates guanylate cyclase and increases guanosine 3':5'-cyclic monophosphate levels in various tissue preparations.

Article de synthese traitant de la pharmacologie de l'oxyde nitrique, du facteur EDRF et du GMP cyclique dans les vaisseaux sanguins et les thrombocytes, de l'isolation et de l'identification du facteur EDRF comme de l'oxyde nitrique, et de la formation, de la liberation et du metabolisme de l'endothelium derived NO (EDNO)

Biological actions and properties of endothelium-derived nitric oxide formed and released from artery and vein.

The present study investigates the hypothesis that endothelium-dependent relaxation of vascular smooth muscle may be mediated through the formation of cGMP. Relaxation of the rat thoracic aorta to acetylcholine, histamine, and Ca++ ionophore A23187 was associated with increased levels of cGMP in a time- and concentration-dependent manner, whereas cAMP levels were unaltered. Removal of the endothelium prevented relaxation to these agents and prevented the increased levels of cGMP. Removal of the endothelium after exposure to acetylcholine only partially decreased the elevated levels of cGMP, suggesting that the changes in cGMP occurred within the smooth muscle cells. Eicosatetraynoic acid, an inhibitor of lipoxygenase and cyclooxygenase, and quinacrine, an inhibitor of phospholipase, prevented and reversed acetylcholine-induced relaxation, respectively, and inhibited acetylcholine-induced increased levels of cGMP. In contrast, sodium nitroprusside-induced relaxation and increased levels of cGMP were independent of the presence of the endothelium, exposure to eicosatetraynoic acid, and quinacrine. The present results support the hypothesis that vascular smooth muscle relaxation induced by some agents is dependent on the presence of the endothelium and is mediated through the formation of an endothelial factor that increases cGMP levels in smooth muscle.

Agonist-induced endothelium-dependent relaxation in rat thoracic aorta may be mediated through cGMP.

Several years ago we accidentally discovered that relaxation of isolated prepa­ rations of arteries (rings, transverse strips, or helical strips) by acetylcholine (ACh) was strictly dependent on the presence of endothelial cells on the intimal surface of the preparations (1-3). This discovery helped resolve the paradox that ACh, a potent vasodilator of arteries in vivo, often produced no relaxation or even contraction of isolated preparations of arteries in vitro (4, 5). Apparent­ ly those isolated preparations that had failed to relax had had their endothelial cells unintentionally rubbed off during the course of their preparation for experiments. This discovery also led to the finding that a number of other agents, including some but not all of the most potent known endogenous vasodilators, also require endothelial cells to produce relaxation in isolated arteries. A number of laboratories are now engaged in research on various aspects of the endothelium-dependent relaxation of blood vessels by various agents. This review attempts to bring together the more important findings in this new area of research. A fuller description of early experimental results in this area obtained by the author and others is available in another recent review (6). The reader is also referred to that review for a discussion of a postulated role for endothelial cells in mediating or facilitating contractions of some blood vessels under special conditions.

The role of endothelium in the responses of vascular smooth muscle to drugs

The effects of various agents on cyclic 3',5'-AMP and cyclic 3',5'-GMP levels and mechanical activity of bovine tracheal smooth muscle were examined. Carbachol, acetylcholine, and histamine caused muscle contraction and increased cyclic GMP levels several fold in a dose-dependent manner; contraction preceded the increase in cyclic GMP. Serotonin and high K+ concentrations contracted muscle to the same degree as carbachol, while cyclic GMP increases were smaller than that due to carbachol. The effects of carbachol and histamine were blocked by atropine and diphenhydramine, respectively. The calcium ionophore A-23187 also increased cyclic GMP levels and caused contraction. Guanylate cyclase activators-sodium azide, hydroxylamine, sodium nitrite, nitroglycerin, and sodium nitroprusside-increased cyclic GMP levels and relaxed tracheal smooth muscle. None of these agents had any effect on cyclic AMP levels. The presence of Ca2+ in the incubation medium was not required for cyclic GMP increases with these latter agents. However, it was required in order to see increases in cyclic GMP with carbachol, histamine, and A-23187. Adremergic agonists relaxed muscle preparations and increased cyclic AMP levels 2-3-fold. Both these effects were blocked by propranolol. Inhibitors of cyclic nucleotide phosphodiesterases relaxed muscle preparations and were associated with increases in both cyclic AMP and cyclic GMP. Prostaglandins E1 and F2α had little or no effect on mechanical activity or cyclic nucleotide levels. The addition of 1 mM 8-bromo-cyclic GMP or 8-bromo-AMP relaxed muscle preparations. A variety of other nucleotides had no effect. These results support the hypothesis that cyclic AMP plays a role in relaxation of tracheal muscle induced by adrenergic agents. However, with a variety of other agents, we found that contraction or relaxation occurred with increases either in cyclic GMP alone or in both cyclic AMP and cyclic GMP. Thus the roles of cyclic AMP and cyclic GMP in smooth muscle mechanical activity remain obscure.

ACKNOWLEDGMENTS We thank Daniel Macklin and Joanne Holmes for their technical assistance, and Cathy Bostron for typing this manuscript.

Shoji Katsuki

Papers

Regulation of adenosine cyclic 3',5'-monophosphate and guanosine cyclic 3',5'-monophosphate levels and contractility in bovine tracheal smooth muscle.