BETA-ADRENERGIC-RECEPTOR STIMULATED PROSTACYCLIN SYNTHESIS IN RABBIT CORONARY ENDOTHELIAL-CELLS IS MEDIATED BY SELECTIVE ACTIVATION OF PHOSPHOLIPASE-D - INHIBITION BY ADENOSINE 3'5'-CYCLIC MONOPHOSPHATE

Activation of beta adrenergic receptors in the isolated rabbit heart b y catecholamines stimulates prostacyclin (PGI(2)) synthesis, which is inhibited by adenosine 3'5'-cyclic monophosphate (cAMP). The purpose o f this study was to determine if activation of beta adrenergic recepto rs in cultured coronary endothelial cells (CEC) of rabbit heart with i soproterenol (ISOP) stimulates PGI(2) synthesis and if cAMP inhibits t he synthesis of this prostanoid and to investigate the underlying mech anism. Incubation of CEC with ISOP increased production of cAMP and PG I(2), measured as immunoreactive cAMP and 6-keto-prostaglandin F-1 alp ha, (6-keto-PGF(1 alpha)), respectively. Forskolin, an activator of ad enylyl cyclase, increased cAMP accumulation and inhibited ISOP-stimula ted 6-keto-PGF(1 alpha) synthesis, 8-(4-chlorophenylthio) cAMP also in hibited ISOP-induced 6-keto-PGF(1 alpha) production. However, miconazo le, an inhibitor of adenylyl cyclase, reduced cAMP accumulation and en hanced ISOP-stimulated 6-keto-PGF(1 alpha) synthesis in CEC. ISOP-indu ced 6-keto-PGF(1 alpha) synthesis was attenuated by C-2-ceramide, an i nhibitor of phospholipase D (PLD) by propranolol, a beta-AR antagonist that also inhibits phosphatidate phosphohydrolase and by the diacylgl ycerol lipase inhibitor 1,6-bis-(cyclohexyloximinocarbonylamino)-hexan e (RHC 80267), Acetylcholine (ACh) induced 6-keto-PGF(1 alpha) synthes is was also inhibited by these agents. Both ISOP and ACh increased PLD activity, which was inhibited by C-2-ceramide but not by RHC 80267 or propranolol. ACh but not ISOP increased phospholipase A(2) activity i n CEC, ISOP- but not ACh-induced increase in PLD activity was attenuat ed by forskolin and 8-(4-chlorophenyl-thio)-adenosine 3'-5'-cyclic mon ophosphate and augmented by miconazole. These data suggest that beta a drenergic receptors activation promotes PGI(2) synthesis in the CEC by selective activation of PLD and that cAMP decreases PGI(2) synthesis by decreasing PLD activity. Moreover, beta adrenergic receptors activa ted PLD appears to be distinct from that stimulated by ACh.