Compensated function in hypertrophied ventricles of Wistar Kyoto and spontaneously hypertensive rats

The aim of the study was to compare the compensatory nature of left ventricular hypertrophy in models of normal and increased peripheral resistance.

Peak left ventricular performance was compared in normotensive Wistar Kyoto (WKY) rats, in a subset of this strain with biventricular hypertrophy associated with volume overload (WKY-CH), and in spontaneously hypertensive rats (SHR), all studied at one year of age (ie, long term hypertrophy).

8 WKY-CH rats with biventricular hypertrophy were compared with 8 WKY (normal right and left ventricular weights). These groups were then compared with 9 SHR rats. All were maintained under identical conditions.

Left ventricular to body weight ratios (mg:g) were as follows: WKY-CH 2.78(SEM 0.09); SHR 2.90(0.09); WKY 2.10(0.09). Systolic blood pressures (mm Hg) were normal in WKY-CH [104(9)] and WKY [111(9)], but raised in SHR [163(8)]. Left ventricles from WKY and WKY-CH had normal histology and no fibre disorientation, fibrosis, or other morphological abnormalities. Peak cardiac index (ml.min-1.body weight-1) measured during rapid volume expansion with Tyrode's solution was higher in WKY-CH [427(33)] than in WKY [315(33)] and SHR [349(31)] (p less than 0.05). When peak stroke volume was expressed per mg left ventricular weight there were no significant differences between the groups. Peripheral resistance (mean arterial pressure divided by cardiac output) at peak cardiac output was higher in SHR [1.20(0.12)] than in either WKY-CH [0.57(0.08)] or WKY [0.74(0.08)].

These data show that both types of hypertrophy enhance peak left ventricular performance. In WKY-CH, which have normal peripheral resistance, the larger ventricle allows a higher peak cardiac index compared to WKY with no left ventricular hypertrophy. In SHR, the higher left ventricular mass is used to overcome an increased peripheral resistance and thereby provide a normal peak cardiac index.