Effects of acute reduction in blood pressure on the renal function of rats with diseased kidneys.

We studied the effect of an acute reduction in blood pressure, induced by diltiazem, on the renal hemodynamics of spontaneously hypertensive rats (SHR) with focal glomerular sclerosis, as induced by adriamycin (ADR). Renal plasma flow (RPF) and glomerular filtration rate (GRF) were determined before (first period) and during (second period) intravenous infusion of diltiazem in SHR 4-6 weeks after ADR treatment (group 1), 14-20 weeks after treatment (group 2), and in controls without treatment (group 3). Rats in group 1 had a normal renal function (RPF and GFR) in the first period, which was not significantly different from control rats (group 3). Rats in group 2 showed a reduced renal function, reflected by the lower levels of RPF and GFR, compared with groups 1 and 3. Mean blood pressure decreased equally in the 3 groups by about 50 mm Hg after the infusion of diltiazem. During the second period, 13.4 or 12.4% increase in RPF and a 29.0 or 23.2% elevation of GFR were evident in groups 1 or 3, respectively. In contrast, a 32.0% reduction of RPF was observed in group 2, accompanied by a 25.7% decline of GFR. A reduction in renal function (percent change of RPF or GFR) significantly correlated with the severity of renal dysfunction (RPF or GFR in the first period) in group 2. Thus, the renal function of rats with diseased kidneys is sensitive to an acute reduction in blood pressure by diltiazem, and the sensitivity depends on the degree of renal deterioration.