Midwall LV mechanics in rats with or without renovascular hypertension: effect of different Na+ intakes

Abstract

Supranormal left ventricular (LV) function has been reported in one-kidney, one-clip (1K,1C) and two-kidney, one-clip (2K,1C) Goldblatt hypertension. However, this finding might be at least partially due to mismatching endocardial rather than midwall fractional shortening to mean end-systolic stress. Accordingly, relations of echocardiographic endocardial and midwall shortening to circumferential end-systolic stress were calculated in 40 Wistar rats on 0.4% NaCl (r = -0.92, SE of estimate = 4.3% and r = -0.62, SE of estimate = 3.2%, both P < 0.0001). Midwall shortening as a percentage of predicted was related to LV chamber diameter in normal animals (r = 0.56, P < 0.0001). Endocardial and midwall shortening were compared as percentage of the normal values predicted from wall stress in 34 2K,1C and 19 1K,1C on 0.4% Na+ 8-9 wk after surgery. Use of midwall shortening reduced the number of these hypertensive rats with supranormal observed-to-predicted shortening ratio from 28 to 7.5% (P < 0.0001). Salt-deprived and high-salt diets (0.0035 and 4% NaCl, respectively) were given to 16 and 18 additional controls, 9 and 7 2K,1C, and 7 and 7 1K,1C. Salt-deprived sham animals had greater endocardial and midwall shortening (106 +/- 7 and 111 +/- 10% of predicted, both P < 0.002) than sham rats on 0.4% NaCl, whereas 4% NaCl had no effect. Five of sixteen salt-deprived sham rats had supranormal observed-to-predicted midwall shortening ratios for LV chamber size, suggesting an enhanced inotropic state. Salt-deprived and high-salt diets had negligible effects on LV performance in Goldblatt rats. Thus use of midwall shortening reduces the number of renovascular hypertensive rats with apparently increased LV function. Salt deprivation stimulates LV myocardial function in normal rats independent of chamber dimension (i.e., an indirect measure of preload) but does not influence LV performance in Goldblatt hypertension 8 wk after renal artery clipping.