Right ventricular performance after monocrotaline-induced pulmonary hypertension.

Chronic pulmonary hypertension leads to a compensatory hypertrophy of the right ventricle (RV). Performance of the hypertrophied heart has been shown to vary depending on the type and severity of the overload, the species, age, and sex of the animal in which the hypertrophy is induced and the ventricle to which the overload is applied (left ventricle vs. right ventricle). In this study we employed two novel approaches to examine the performance of the hypertrophied right ventricle in male Sprague-Dawley rats. First, monocrotaline (MCT), a pyrrolizidine alkaloid isolated from the plant Crotalaria spectabilis, was used to noninvasively induce chronic pulmonary hypertension, RV pressure overload, and RV hypertrophy. After 5 wk the RV-to-(left ventricle + septum) ratio was increased by 94% over control. The volume of isolated right ventricular myocytes from MCT-treated rats was increased due primarily to an increase in cell cross-sectional area. Second, a stable, isolated, working heart preparation, normally used to study left ventricular function, was modified to study right ventricular function. In vitro ventricular performance of severely hypertrophied hearts was elevated compared with control hearts at all preloads. Significant elevations in positive and negative maximum pressure development (dP/dtmax) suggested that both the rate of pressure development and the rate of relaxation were enhanced. Coronary flow and RV-diastolic pressure were similar in the MCT and control group. Thus RV hypertrophy caused by a chronic pressure overload induced by MCT resulted in enhanced ventricular performance with no evidence of failure.