Reduced cardiac mass by nitrendipine is dissociated from systemic or regional haemodynamic changes in rats

The effects of prolonged treatment (3 weeks) with nitrendipine (10 mg X kg-1 twice daily) on systemic and regional haemodynamics and cardiac mass were studied in SHR and WKY rats. Nitrendipine markedly decreased mean arterial pressure (26.0 +/- 0.4 vs 19.9 +/- 0.6 kPa, P less than 0.01) and total peripheral resistance (0.090 +/- 0.004 vs 0.066 +/- 0.004 U X kg-1, P less than 0.01) in SHR without significantly affecting cardiac output and heart rate, whereas in the WKY rats no significant systemic haemodynamic changes were noted. Increased splanchnic blood flow and a reduced splanchnic vascular resistance were found in the WKY rats; however, in the SHR rats, blood flows (ml X min-1 X g tissue-1) increased and organ vascular resistances (kPa X ml-1 X min-1 X 100 g tissue-1) decreased significantly (P less than 0.01) in the heart (5.25 +/- 0.28 vs 7.27 +/- 0.31 and 0.04 +/- 0.00 vs 0.02 +/- 0.00; P less than 0.01) and kidneys (6.53 +/- 0.4 vs 7.98 +/- 0.2 and 0.03 +/- 0.00 vs 0.02 +/- 0.00; P less than 0.01), respectively. Nevertheless, in both rat strains, absolute cardiac mass and left ventricular weight were reduced; but in the SHR rats, the relative weight of the heart and left ventricle to body weight was also reduced significantly (3.79 +/- 0.06 vs 3.31 +/- 0.09; P less than 0.01 and 2.85 +/- 0.06 vs 2.70 +/- 0.06; P less than 0.01, respectively). Thus, these studies show that nitrendipine, a slow-entry channel calcium blocker, regressed cardiac mass in rats through mechanisms that may be dissociated from their haemodynamic changes.