MODULATION BY CYCLIC-AMP OF BETA-ADRENERGIC RECEPTOR-STIMULATED PROSTACYCLIN SYNTHESIS IN RABBIT VENTRICULAR MYOCYTES

The purpose of the present study was to determine the possible interac tion of cyclic AMP (cAMP) and the synthesis of prostacyclin [measured as immunoreactive 6-keto-prostaglandin (PG)F-1 alpha] elicited by the beta adrenergic receptor agonist isoproterenol (ISOP), in freshly diss ociated rabbit ventricular myocytes. ISOP (10(-13) to 10(-11) M) incre ased 6-keto-PGF(1 alpha) synthesis without altering the level of cAMP. Increasing the concentration of ISOP from 10(-10) to 10(-7) M enhance d accumulation of cAMP, which was associated with a decline in 6-keto- PGF(1 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 8-keto-PGF(1 alpha) synthesis. 8-(4-chlorophenylthio) (cpt)-c AMP (10(-7) M) also inhibited ISOP-induced 6-keto-PGF(1 alpha) product ion. On the other hand, miconazole (10(-4) M), an inhibitor of adenyly l cyclase, reduced cAMP accumulation and enhanced ISOP-induced 6-keto- PGF(1 alpha) synthesis in myocyies. Miconazole also attenuated ISOP-, forskolin- and cpt-cAMP-induced increases in protein kinase A activity . The protein kinase A inhibitor H-89 omocinnamylamino)ethyl]-5-isoqui nolinesulfonamide} attenuated the ISOP (10(-7) M)-induced increase in the activity of this enzyme and minimized the decline in 6-keto-PGF(1 alpha) synthesis produced by 10(-7) M ISOP and the inhibitory effect o f cpt-cAMP and forskolin on 6-keto-PGF(1 alpha) production. 3-Isobutyl -1-methylxanthine, forskolin and cpt-cAMP did not alter the conversion of exogenous arachidonic acid to 6-keto-PGF(1 alpha). These data indi cate that beta adrenergic receptor activation promotes prostacyclin sy nthesis in rabbit ventricular myocytes and that GAMP acts as an inhibi tory modulator. This action is mediated via activation of protein kina se A, probably by decreasing the activity of the lipase,involved in be ta adrenergic receptor induced arachidonic acid release.