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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Nitric oxide-dependent and -independent mechanisms are involved in TNF--induced depression of cardiac myocyte contractility

¹Section of Critical Care Medicine, Division of Cardiovascular Diseases and Critical Care Medicine, Cooper Hospital/University Medical Center, Robert Wood Johnson Medical School, University of Medicine and Dentistry, New Jersey, Camden, New Jersey; ²Section of Critical Care Medicine, Department of Medicine, University of Manitoba, Winnipeg, Manitoba; and ³Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada

Submitted 1 March 2006 ; accepted in final form 17 January 2007

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, 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 min of cardiac myocyte exposure. This effect was blocked by N-methyl-arginine (NMA), a nitric oxide synthase inhibitor, in all studies. Contractile and cAMP response to increasing concentrations of isoproterenol was deficient in cardiac myocytes exposed to TNF- regardless of the presence of NMA. In contrast, increasing concentrations of forskolin (a direct stimulant of adenylate cyclase) and dibutyryl cAMP (a metabolically active membrane-soluble analog of cAMP) completely reversed TNF--mediated depression, though only in the presence of NMA. Forskolin-stimulated cAMP generation remained intact regardless 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.

sepsis; septic shock; adrenoreceptor; myocardial depression; myocyte; heart; myocardial depressant substance; cytokine

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