Abstract

The purpose of the present study was to determine the possible interaction of cyclic AMP (cAMP) and the synthesis of prostacyclin [measured as immunoreactive 6-keto-prostaglandin (PG)F1 alpha] elicited by the beta adrenergic receptor agonist isoproterenol (ISOP), in freshly dissociated rabbit ventricular myocytes. ISOP (10(-13) to 10(-11) M) increased 6-keto-PGF1 alpha synthesis without altering the level of cAMP. Increasing the concentration of ISOP from 10(-10) to 10(-7) M enhanced accumulation of cAMP, which was associated with a decline in 6-keto-PGF1 alpha synthesis. Forskolin (10(-6) M), an activator of adenylyl cyclase, and 3-isobutyl-1-methylxanthine (10(-5) M), an inhibitor of cAMP phosphodiesterase, increased cAMP accumulation and inhibited ISOP-induced 6-keto-PGF1 alpha synthesis. 8-(4-chlorophenylthio) (cpt)-cAMP (10(-7) M) also inhibited ISOP-induced 6-keto-PGF1 alpha production. On the other hand, miconazole (10(-4) M), an inhibitor of adenylyl cyclase, reduced cAMP accumulation and enhanced ISOP-induced 6-keto-PGF1 alpha synthesis in myocytes. Miconazole also attenuated ISOP-, forskolin- and cpt-cAMP-induced increases in protein kinase A activity. The protein kinase A inhibitor H-89 {N-[2-(p-bromocinnamylamino)ethyl] -5-isoquinolinesulfonamide} attenuated the ISOP (10(-7) M)-induced increase in the activity of this enzyme and minimized the decline in 6-keto-PGF1 alpha synthesis produced by 10(-7) M ISOP and the inhibitory effect of cpt-cAMP and forskolin on 6-keto-PGF1 alpha production. 3-Isobutyl-1-methylxanthine, forskolin and cpt-cAMP did not alter the conversion of exogenous arachidonic acid to 6-keto-PGF1 alpha. These data indicate that beta adrenergic receptor activation promotes prostacyclin synthesis in rabbit ventricular myocytes and that cAMP acts as an inhibitory modulator. This action is mediated via activation of protein kinase A, probably by decreasing the activity of the lipase, involved in beta adrenergic receptor-induced arachidonic acid release.