ROLE OF PROSTAGLANDIN-MEDIATED CYCLIC-AMP FORMATION IN PROTEIN-KINASEC-DEPENDENT SECRETION OF ATRIAL-NATRIURETIC-PEPTIDE IN RAT CARDIOMYOCYTES

The role of endogenous prostaglandin production in phorbol diester-ind uced myocardial atrial natriuretic peptide (ANP) secretion was investi gated in cultured spontaneously beating ventricular rat cardiomyocytes . Incubation of cells with 4 beta-phorbol 12-myristate 13-acetate (PMA ; 0.1 mu M) led to a rapid response in ANP release, a response accompa nied by increases in cellular prostacyclin (PGI(2)) production, cyclic AMP (cAMP) formation and spontaneous contraction frequency. Although PMA-induced ANP secretion exhibited the pharmacological profile of a p rotein kinase C (PKC)-mediated event, the response was abolished in th e presence of the cyclo-oxygenase inhibitors indomethacin (10 mu M) an d diclofenac (1 mu M), indicating that endogenous prostaglandin produc tion is responsible for PMA-induced ANP secretion in this system. Conf irming this, PMA-induced ANP secretion was strongly correlated with en dogenous formation of 6-oxo-prostaglandin F-1 alpha (r = 0.93, P < 0.0 005, n = 11), and exogenously applied PGI(2), prostaglandin E(2) (PGE( 2)) or prostaglandin F-2 alpha (PGF(2 alpha)) elicited simultaneous in creases in cAMP formation, contraction frequency and ANP secretion in these cells. Furthermore, PMA-induced cAMP formation was abolished in the presence of either diclofenac or indomethacin, whereas the cAMP-el evating agent forskolin (0.1 mu M) mimicked the secretory and chronotr opic effect of PMA in these cells. A role for cAMP in PMA-induced ANP secretion was also apparent insofar as PMA-induced ANP release was sub stantially decreased in the presence of the R(p)-diastereomer of 3',5' -cyclic adenosine monophosphorothioate (R(p)-cAMPS; 10 mu M), whereas the cAMP-mimetic agent dibutyryl cAMP(10 mu M) provoked a rapid increa se in ANP secretion in this system. Finally, the Ca2+-channel antagoni st nifedipine (0.1 mu M) severely decreased PGI(2)-, PGE(2)- and PMA-i nduced ANP secretion without affecting PGF(2 alpha)-induced peptide re lease, suggesting that PGI(2) and/or PGE(2), but not PGF(2 alpha), are the prostanoids involved in PMA induced ANP release. Taken together, these results suggest that PKC activation induces ANP secretion in spo ntaneously beating rat ventricular cardiomyocytes via an autocrine pat hway involving increased PGI(2) and/or PGE(2) formation, a response le ading to the activation of a myocardial adenylate cyclase and, subsequ ently, to that of a nifedipine-sensitive Ca2+ channel.