Effect of dietary salt on hemodynamics of established renal hypertension in the rabbit. Implications for the autoregulation theory of hypertension.

Abstract

Two groups of 10 rabbits were subjected to renal cellophane wrapping and sham operation. Their initial mean arterial pressures (MAP) were similar, 92 .+-. 1.5 and 90 .+-. 2.9 mm Hg. Six weeks later 3 experimental periods began, each of 2 wk duration, on low, normal and high salt (1,9 and 50 mmol Na/100 g food) diets. Each group had 2 subgroups: rabbits with both kidneys and rabbit with only 1 kidney and previous nephrectomy. The hemodynamic findings were similar in each group. After sham operation, the range of dietary salt produced no significant circulatory changes. After wrapping, MAP was reduced on low compared with normal and high salt diets (122 vs. 132 and 136 mm Hg; P = 0.01). This was entirely due to lowering of cardiac output (CO) on low salt; on normal and high salt, CO was higher than in sham-operated rabbits. Total peripheral resistance (TPR) in the wrapped animals was unaffected by diet, i.e., 21.4 20.5 and 21.2 U on low, normal and high salt, .apprx. 35% above values of sham-operated rabbits. Volume-related CO changes produce long-term changes in MAP without alteration in TPR, which is not in conformity with the autoregulation theory of hypertension. Evidence of impaired capacity of wrapped compared with sham-operated rabbits to handle salt included diet-related hematocrit changes, lower creatinine clearance and some differences in renin responses to salt. Giving saralasin reduced TPR while the rabbits were on low salt; the fall was twice as great in wrapped compared with sham-operated rabbits.