Role of peritubular capillary forces in the renal action of carbonic anhydrase inhibitor

Abstract

Micropuncture study was performed in Munich-Wistar rats to assess peritubular capillary Starling forces in renal superficial cortex during suppression of proximal fluid reabsorption by carbonic anhydrase inhibitor. Administration of benzolamide (2 mg/kg/hr, i.v., Group 1, N = 7 rats) caused not only reduction in absolute rate of proximal fluid reabsorption (APR, from 26.7 +/- 4.0 nl/min to 17.7 +/- 3.6, P less than 0.001), but also an increase in peritubular transcapillary hydraulic-pressure difference (from 10.0 +/- 0.5 mm Hg to 15.2 +/- 0.5, P less than 0.001). In a separate group of seven rats (Group 2), these parameters did not change significantly without benzolamide treatment. In Group 1 rats, an attempt was made to nullify the benzolamide-induced reduction in the peritubular capillary net reabsorptive forces by infusing hyperoncotic high-hematocrit blood. Following this treatment, while benzolamide administration was continued, values for APR returned to levels (25.6 +/- 4.8 nl/min) nearly identical to those measured prior to benzolamide administration, in association with a rise in peritubular transcapillary oncotic pressure difference. A separate group of six rats treated in a fashion identical to that of Group 1 showed continued suppression of carbonic anhydrase activity following blood infusion as indicated by low levels of whole kidney bicarbonate reabsorption rate. Peritubular capillary reabsorption coefficient was calculated based on the measured values for Starling forces in Group 1 and were unaffected throughout the study. Continued benzolamide administration alone without the treatment of hyperoncotic blood did not change APR significantly (Group 3, N = 7 rats).(ABSTRACT TRUNCATED AT 250 WORDS)