We compared the effects produced by acute and chronic administration of captopril in sinoaortic denervated rats. In conscious undisturbed rats acute administration of captopril (10 mg/kg intravenously) produced acute transient reductions in mean arterial pressure of 16 and 26%, 6 h (mean arterial pressure 148 +/- 4 mmHg) and 24 h (133 +/- 3 mmHg) after the sinoaortic denervation, respectively. Chronic captopril treatment (30 mg/day orally) produced a permanent attenuation of the hypertension induced by sino-aortic denervation, as shown by a beat-to-beat analysis of arterial pressure for 80 min. The attenuation was 11% (131 +/- 7 versus 148 +/- 4 mmHg) and 24% (103 +/- 9 versus 133 +/- 3 mmHg) in rats studied 6 and 24 h after the sinoaortic denervation, respectively. Chronic captopril administration produced no alteration in the tachycardia, nor in the heart rate variability of the sinoaortic denervated rats; the latter was lower than that of normotensive rats. These data show that while acute administration of captopril in sinoaortic denervated rats produced a rapid hypotensive response, chronic administration produced a long-lasting attenuation of hypertension, presumably by interference with sympathetic cardiovascular control.