The respective roles of protein kinase C (PKC) and endogenous prostaglandin formation in angiotensin II (Ang II)-induced myocardial secretion of atrial natriuretic peptide (ANP) was studied in cultured, spontaneously beating, neonatal-rat cardiomyocytes. Incubation of cardiomyocytes with 0.1 microM Ang II led to a rapid but transient increase in particulate-bound PKC activity, a response accompanied by marked increases in cellular 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha) generation and ANP secretion. A role for PKC in Ang II-induced 6-oxo-PGF1 alpha formation and ANP secretion was apparent, insofar as both responses were suppressed in the presence of the PKC inhibitors staurosporine (1 microM) and CGP 41251 (1 microM), as well as in cells in which PKC had been previously down-regulated by pretreatment with phorbol diester. Furthermore, Ang II-induced 6-oxo-PGF1 alpha production was found to be strongly correlated with Ang II-induced ANP release (r = 0.87, P < 0.001, n = 6), indicating a role for prostacyclin (PGI2) in Ang II-induced ANP secretion in these cells. This hypothesis was confirmed by finding that both Ang II-induced 6-oxo-PGF1 alpha production and ANP release were abolished in the presence of the respective phospholipase A2 and cyclo-oxygenase inhibitors quinacrine (10 microM) and indomethacin (10 microM), whereas exogenously applied PGI2 (1 microM) and prostaglandin E2 (0.1 microM) mimicked Ang II-induced ANP secretion in this system. Taken together, these results suggest that Ang II induces ANP secretion in spontaneously beating rat cardiomyocytes via a PKC-dependent autocrine pathway involving a cyclo-oxygenase product and a yet-to-be-identified myocardial prostanoid receptor.