NITRIC-OXIDE AS A POSITIVE INOTROPIC AGENT IN ISOLATED RAT HEARTS

The purpose of this study was to examine the inotropic effects of nitr oprusside (NP), a direct nitric oxide (NO) donor, in isolated rat hear ts. Langendorff-perfused hearts (n = 5), paced at 6 Hz, were subjected to 15 min of equilibration (EQ) followed by infusion of NP, producing a coronary artery concentration of 1 x 10(-5) M. Coronary flow, left ventricular developed pressure (DP), end-diastolic pressure, and contr actility and compliance (+/- dP/dt) were monitored throughout the expe riment by a computerized data acquisition system. Myocardial oxygen co nsumption (MVO(2)) was measured at the end of EQ and after 2 1/5 min o f NP infusion. Myocardial efficiency was calculated as the quotient of DP divided by MVO(2). Values are expressed as the mean +/- SEM, Paire d t tests were used to calculate statistical significance. Values for parameters monitored at end EQ and at 2 1/5 min NP infusion showed tha t there was a 93% increase in coronary flow, 18, 17, and 16% increases in developed pressure, contractility, and compliance, respectively, n o significant change in end-diastolic pressure, a 49% increase in myoc ardial oxygen consumption, and a 21% decline in myocardial efficiency (P < 0.05 for all differences), We conclude that in the isolated rat h eart, NO behaves as a positive inotrope. (C) 1995 Academic Press, Inc.