WHOLE-BODY AUTOREGULATION IN REDUCED RENAL MASS HYPERTENSION

Whole body autoregulation in conscious rats can be shown in the absence of the rapid acting neural and hormonal controllers of blood pressure. It is hypothesized that this phenomenon is responsible for the gradual rise of vascular resistance observed in volume-dependent forms of hypertension such as reduced renal mass-salt-induced hypertension. To examine the hypothesis, we evaluated the gain of whole body autoregulation at various stages of reduced renal mass hypertension to determine if acute autoregulatory capacity is altered during chronic hypertension. Rats underwent reduced renal mass surgery (nephrectomy plus 70% reduction of remaining kidney) and were studied at 2 (n=8), 4 (n=6), and 6 (n=7) weeks after high salt diet. Control rats (n=6) underwent nephrectomy and sham surgery and were studied after 2 weeks of high salt diet. All reduced renal mass rats showed progressive hypertension (2 weeks, 136+/-5; 4 weeks, 157+/-8; and 6 weeks, 171+/-10 mm Hg) compared with sham rats (113+/-4 mm Hg). We observed an increase in basal level of total peripheral resistance index after neurohumoral blockade in reduced renal mass rats (2 weeks, 1.64+/-0.06; 4 weeks, 1.79+/-0.10; and 6 weeks, 1.89+/-0.09 mm Hg . 100 g-1 . min-1 . ml-1) compared with sham rats (1.56+/-0.10 mm Hg . 100 g-1 . min-1 . ml-1). Blood volume expansion in the four groups during neurohumoral blockade caused significant whole body autoregulation in all rats as indicated by the slopes of the pressure-flow relations: 0.38 in sham, 0.41 in 2-week, 0.45 in 4-week, and 0.43 in 6-week reduced renal mass rats (slope=0, perfect autoregulation; slope=1, rigid vasculature). There were no significant differences in the autoregulatory capacity between the reduced renal mass rats and sham rats. We conclude that chronic reduced renal mass hypertension does not modify whole body autoregulation in response to acute volume expansion.