The effect of urocortin (UCN), a recently characterized mammalian member of corticotropin-releasing factor (CRF)-related peptide and a putative endogenous ligand for CRF type 2 beta receptor in the regulation of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) release, was investigated using cultured neonatal rat cardiomyocytes. Treatment with UCN (10(-10)-10(-6)M) resulted in significant increase in ANP and BNP secretions, and the effect of UCN on ANP and BNP secretions was more potent than that of CRF on an equimolar basis. The effect of UCN (10(-7)M) was completely blocked by alpha-helical CRF (9-41), a specific CRF type 2 receptor antagonist. The effect of UCN (10(-7)M) was not only blunted by cAMP-dependent protein kinase A (PKA) inhibitor, H-89 (10(-5)M), but also diltiazem (10(-7)M), a voltage-dependent Ca2+ channel blocker. Further, UCN stimulated cAMP production in cardiomyocytes. Also, UCN (10(-7)M) itself stimulated [3H]leucine uptake into neonatal rat cardiomyocytes and potentiated endothelin-1-induced increase of [3H]leucine uptake. These results suggest that activation of CRF type 2 receptor, especially type 2 beta receptor, with UCN induces ANP and BNP secretions, at least in part, via PKA pathway during cardiac hypertrophy.