INDUCTION OF NITRIC-OXIDE SYNTHASE IN CULTURED VASCULAR SMOOTH-MUSCLE CELLS - THE ROLE OF CYCLIC-AMP

1 Interleukin-1 beta (IL-1 beta) is a potent stimulant of inducible nitric oxide synthase (iNOS) mRNA and nitric oxide (NO) production in vascular smooth muscle (VSM) cells in culture. These studies investigate the role of adenosine 3':5'-cyclic monophosphate (cyclic AMP) in this process. 2 Dibutyryl cyclic AMP (db cyclic AMP, 0.1-1 mM), forskolin (1-10 mu M) and the phosphodiesterase inhibitor, Ro 20-1724 (1-10 mu M), all of which increase intracellular cyclic AMP, had no effect on NO production when added alone but markedly enhanced NO production by IL-1 beta-stimulated VSM cells in a dose-dependent manner. Consistent with a cyclic AMP-mediated action, isoprenaline (1-10 mu M) increased NO production from IL-1 beta-stimulated cells. Dibutyryl cyclic GMP (db cyclic GMP) had no effect at concentrations up to 1 mM. 3 Pursuing these observations, iNOS protein levels were examined by Western blot analysis and iNOS mRNA levels were measured by reverse transcription and amplification of the resultant cDNA using the polymerase chain reaction. In addition to enhancing NO production, db cyclic AMP increased iNOS protein and mRNA above that produced by IL-1 beta alone. 4 These data demonstrate a major effect of cyclic AMP on cytokine-induced NOS activity in VSM cells, mediated at least in part by regulating synthesis of iNOS, and has implications for the pathogenesis and management of septic shock.