The purpose of this study was to examine the effects of nicardipine and sodium nitroprusside (SNP) on vascular capacitance in the rat. In ten rats anesthetized with pentobarbital, mean arterial pressure was lowered to about 70 mmHg and subsequently 50 mmHg by intravenous infusion of nicardipine or SNP. Vascular capacitance was assessed before and during nicardipine- or SNP-induced hypotension by measuring the mean circulatory filling pressure (MCFP). MCFP was measured during a brief period of circulatory arrest produced by inflating a balloon inserted in the right atrium. MCFP was significantly decreased by SNP from 7.1 ±0.3 mmHg at control to 5.6 ± 0.4 mmHg and 4.4 ± 0.3 mmHg at mean arterial pressures of 70 mmHg and 50 mmHg, respectively. However, MCFP stayed at a similar level to that of the control during nicardipine-induced hypotension. These results suggest that nicardipine has a negligible influence on vascular capacitance during induced hypotension, whereas SNP has a potent vasodilating effect on the venous system as well as the arterial system.
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