Renal Tubular Effect of Nisoldipine, A Calcium Channel Blocker, in Rats

Abstract

The renal tubular effect of nisoldipine (10 micrograms/kg/h) was evaluated using clearance and micropuncture techniques in spontaneously hypertensive rats made diuretic by i.v. infusion of 2.5% NaCl. In one group of 11 rats the renal innervation was intact, whereas in a second group of 10 rats the left kidney was denervated. The drug reduced mean blood pressure in both groups of rats without a significant change in heart rate or glomerular filtration rate. Nisoldipine increased urine flow from 22.3 +/- 2.1 to 26.8 +/- 2.5 microliter/min/100 g BW and from 23.8 +/- 1.3 to 31.5 +/- 1.4 microliter/min/100 g BW in the innervated and denervated rats, respectively (p less than 0.05 for both). Fractional excretion of sodium and total solute were significantly higher under nisoldipine action in both groups of rats, indicating reduced reabsorption of water as well as solute by the nephron. Potassium excretion was unaltered in the innervated rats while in the denervated group it was significantly reduced by the drug. Fractional water excretion was enhanced from 3.3 +/- 0.3% to 4.1 +/- 0.4% of the filtrate in the innervated rats and from 3.4 +/- 0.2% to 4.6 +/- 0.3% in the denervated rats. Tubular fluid to plasma inulin concentration ratios at late distal puncture sites were lowered by nisoldipine in both the innervated kidneys (from 10.5 +/- 1.6 to 8.3 +/- 0.8, with p less than 0.05) and denervated kidneys (from 8.8 +/- 0.5 to 6.7 +/- 0.5, with p less than 0.05). The mean percentage of filtrate reabsorbed between late proximal and late distal tubular fluid collection sites was lowered in both groups of rats.(ABSTRACT TRUNCATED AT 250 WORDS)