Simultaneous Activation of Adenylyl Cyclase and Protein Kinase C Induces Production of Nitric Oxide by Vascular Smooth Muscle Cells

Rat aortic smooth muscle cells produced large quantities of nitric oxide (NO) after exposure to interleukin-1 fi, and this was do-pressed in the presence of the protein kinase C inhibitor bisin-dolylmaleimide. Intracellular cAMP levels were elevated mildly in cytokine-treated smooth muscle cells, and the presence of for-skolin enhanced both the cAMP levels and NO production. Inhibition of GTP:cyclohydrolase I by 2,4-diamino-6-hydroxypy-nmidine attenuated NO production by interleukin-1 fl-treated cells. GTP:cyclohydrolase is the regulatory enzyme for de novo tetrahydrobioptenn synthesis, and the latter is a required cofactor for NO synthase activity. Treatment of smooth muscle cells with forskolin induced GTP:cyclohydrolase mRNA expression, and simultaneous treatment of cells with forskolin and phorbol esters elicited NO production. Angiotensin II and arginine-vasopressin, acknowledged agonists for protein kinase C, elicited productio