The postulate that the hemodynamic changes produced by isoflurane (1.5%) involve release of nitric oxide (NO) was examined. Fifteen dogs were anesthetized with thiamylal (15 mg/kg) and ventilated with isoflurane and oxygen. Catheters were inserted for measurement of aortic pressure, pulmonary artery pressures, and determination of cardiac output. Left thoracotomy was performed and complete heart block was induced by injection of 37% formaldehyde (0.3 mL) into the atrioventricular node; ventricular rate was fixed at 100 beats/min by external pacing. An apical microtransducer was inserted into the left ventricle (LV) via the apex for measurement of left ventricular pressure (LVP) and its first derivative (dP/dt). Flow probes were mounted on the left circumflex (Cx) and anterior descending (AD) coronary arteries. Measurements were obtained before (control period) and during NO inhibition using IV NG-nitro-L-arginine methyl ester (L-NAME) by a 50 mg/kg bolus plus 1 mg/kg/min. Infusion of L-NAME caused immediate and sustained increases in mean arterial pressure to 145 +/- 3% (P < 0.001), mean pulmonary arterial pressure to 128 +/- 5% (P < 0.001), pulmonary capillary wedge pressure to 144 +/- 8% (P < 0.001), coronary perfusion pressure to 163 +/- 4% (P < 0.001), systemic vascular resistance to 209 +/- 9% (P < 0.001), pulmonary vascular resistance to 142 +/- 12% (P < 0.005), anterior descending flow to 115 +/- 4% (P < 0.005), and circumflex flow to 113 +/- 3% (P < 0.01) of control levels.(ABSTRACT TRUNCATED AT 250 WORDS)