CHARACTERIZATION OF CYCLIC-AMP ACCUMULATION IN CULTURED HUMAN CORPUS CAVERNOSUM SMOOTH-MUSCLE CELLS

Intracavernous pharmacotherapy relies heavily on the use of vasoactive agents which act by increasing intracellular cAMP levels in human cor pus cavernosum smooth muscle. Yet little is known about the cAMP gener ating system in this tissue, and how it may affect observed patient va riability. Thus, the goal of these studies was to better characterize the biochemistry of cAMP formation in human corpus cavernosum smooth m uscle, and thus provide more insight into the mechanisms of corporal s mooth muscle relaxation in vivo. We studied both receptor and nonrecep tor mediated increases in cAMP formation in short-term cultures of hum an corpus cavernosum smooth muscle cells. Both isoproterenol (ISO) and prostaglandin E(1) (PGE(1)) produced concentration-dependent increase s in cAMP, but histamine, serotonin and vasoactive intestinal polypept ide did not. Forskolin, a relatively specific activator of adenylate c yclase, was also a potent stimulant of cAMP formation in these cells. Moreover, there was a direct correlation between the degree of forskol in-induced cAMP accumulation in cultured corporal smooth muscle cells and the magnitude of the forskolin-induced relaxation response of prec ontracted isolated corporal smooth muscle strips. Prostaglandin E(1) a nd ISO concentration response curves (CRCs) were then assayed in the a bsence and presence of subthreshold forskolin (0.1 mu M.). In the pres ence of forskolin, the calculated maximal PGE(1)-induced cAMP accumula tion (E(max)) was significantly greater than that elicited by PGE(1) a lone, ISO alone, or ISO + forskolin (p less than or equal to 0.02). In addition, a fixed molar ratio (FMR) (PGE(1):ISO) protocol was used to demonstrate that both 80:20 and 70:30 FMRs (but not 95:5 or 90:10), w ere associated with significantly greater cAMP E(max) values than that observed for PGE(1) alone (p less than or equal to 0.01). These data provided direct evidence that the degree of cAMP formation in cultured corporal smooth muscle cells is strongly correlated with the magnitud e of relaxation of isolated corporal smooth muscle strips. In addition , since simultaneous activation of distinct components of the cAMP gen erating system produces significant increases in maximal intracellular cAMP accumulation, this suggests that such drug combinations may also augment corporal smooth muscle relaxation in vitro and in vivo.