Previous studies have demonstrated the presence of myocardial depression in clinical and experimental septic shock. This response is mediated, in part, through circulating TNF-induced, nitric oxide-dependent, early (< 1 hr) depression of basal myocyte contractility. Other mechanisms of early myocardial dysfunction involving decreased response to adrenergic stimulation may exist. This study evaluated the presence and nitric oxide-dependence of impaired adrenergic response to TNF in in-vitro cardiac myocytes. The contraction of electrically-paced neonatal rat cardiac myocytes in tissue culture was quantified using a closed loop video tracking system. TNF induced depression of baseline contractility over the first 20 minutes of cardiac myocyte exposure. This effect was blocked by N-methyl-arginine (NMA), a nitric oxide synthetase inhibitor, in all studies. Contractile and cyclic AMP response to increasing concentrations of isoproterenol was deficient in cardiac myocytes exposed to TNF irrespective of the presence of NMA. In contrast, increasing concentrations of forskolin (a direct stimulant of adenylate cyclase) and dibutyryl cyclic AMP (a metabolically active membrane-soluble analogue of cyclic AMP) completely reversed TNF-mediated depression, though only in the presence of NMA. Forskolin-stimulated cyclic AMP generation remained intact irrespective of NMA. Increasing concentrations of exogenous calcium chloride, unlike other inotropic agents, corrected TNF-mediated defects of contractility independent of the presence of NMA. These data suggest that TNF exposure is associated with a second nitric oxide-independent but calcium-dependent early depressant mechanism that is manifested by reduced contractile and cAMP response to -adrenergic stimulation.