The Bio 14.6 cardiomyopathic Syrian hamster is an animal model of human idiopathic cardiomyopathy. The pathogenesis of the disease in this animal has not yet been clearly elucidated. It is well known that alpha- and beta-adrenergic receptors are increased in the myocardium of this animal, but that isoprenaline does not produce an augmented response. We examined the activity of cardiac stimulatory GTP-binding protein (Gs), which couple with beta-adrenergic receptors to stimulate adenylate cyclase, in Bio 14.6 cardiomyopathic hamsters at 90 and 160 days of age. The cardiac norepinephrine concentration was significantly increased in Bio 14.6 hamsters compared with control hamsters (F1B) at 90 days of age (1,739 +/- 120 vs 1,470 +/- 161 ng/g wet tissue weight, p less than 0.05). Cardiac forskolin-stimulated adenylate cyclase activities at 90 and 160 days of age were lower in the cardiomyopathic hamsters than in the F1B controls (90 days old: 98 +/- 24 vs 122 +/- 29 pmol/min/mg protein, p less than 0.05; 160 days old: 74 +/- 13 vs 124 +/- 28 pmol/min/mg protein, p less than 0.01). Cardiac Gs activities at 90 and 160 days of age were significantly lower in Bio 14.6 hamsters than those in F1B hamsters (90 days old: 204 +/- 42 vs 259 +/- 49 pmol/min/mg protein, p less than 0.05; 160 days old: 156 +/- 39 vs 211 +/- 60 pmol/min/mg protein, p less than 0.05). We thus demonstrated functional defects in cardiac Gs protein and adenylate cyclase activity in the Bio 14.6 cardiomyopathic hamsters at 90 to 160 days of age (the hypertrophic stage of cardiomyopathy).(ABSTRACT TRUNCATED AT 250 WORDS)