The role of A- and B-type natriuretic peptides (ANP and BNP) in cardiac pathophysiology are of increasing interest. Isolated neonatal mouse cardiac myocytes express increased levels of ANP mRNA in the absence of growth factors in culture. Expression of ANP and BNP mRNA has not been studied in isolated adult mouse cardiac myocytes (AMCM). We examined expression of ANP and BNP mRNA in isolated AMCM with and without stimulation with beta-adrenergic receptor agonists and antagonists. AMCM were isolated and maintained in culture for 24-48 h with and without stimulation with the beta-adrenergic receptor agonist isoproterenol (Iso), the beta1-antagonist CGP20712A (CGP), or the beta2-antagonist ICI-118,551 (ICI). Northern blot analysis was performed using probes for mouse ANP and BNP mRNA. TUNEL assay was performed after beta-adrenergic receptor stimulation of AMCM. BNP mRNA expression was increased fivefold (P < 0.001) after 48 h in culture without adrenergic stimulation. BNP mRNA expression was reduced (P < 0.0001) after stimulation with Iso while ANP expression remained similar to unstimulated cells. CGP prevented the Iso reduction in BNP mRNA. Iso stimulation at doses that reduced BNP mRNA expression increased TUNEL positive nuclei, an effect blocked by the beta1-antagonist CGP. In conclusion, we have demonstrated differential gene expression of ANP and BNP in AMCM in culture. Expression of BNP mRNA increases in AMCM in culture and beta1-adrenergic receptor stimulation attenuates increased BNP gene expression and results in apoptosis.