Influence of nifedipine on ventricular function and myocardial hypertrophy in spontaneously hypertensive rats.

We compared left ventricular (LV) hemodynamics, LV muscle mass (LVMM), and LV geometry of 13 spontaneously hypertensive rats (SHRs) treated for 20 weeks with nifedipine (30 mg/kg/day) with those of 11 age-matched untreated SHRs. LVMM, LVMM related to end-diastolic volume (LVMM/EDV), LV pressure (PLV), systolic wall stress (Tsyst), ejection fraction (EF), cardiac index (CI), and isovolumetric contractility indices (dP/dtmax, IP, t-dP/dtmax, and VCE) were determined. Nifedipine treatment lowered PLV from 170 to 136 mm Hg and Tsyst from 222 to 194 10(3) dyn/cm2. LVMM and LVMM/EDV decreased moderately from 800 to 744 mg and from 2.56 to 2.29 mg/microliter, respectively. Left ventricular ejection was markedly increased (EF from 52 to 64%; CI from 154 to 178 ml/min X kg), whereas isovolumic contractility indices remained unchanged. Thus, nifedipine reduced but did not totally prevent myocardial hypertrophy and enhanced LV function. These effects seem to result from reduction in LV afterload and not from altered myocardial contractility.