RENAL EFFECTS OF GLIBENCLAMIDE - A MICROPUNCTURE STUDY

The renal effects of glibenclamide were investigated using free flow m icropuncture techniques in anesthetized Sprague-Dawley rats. Intraveno us infusion of the drug (3 mg/hr) evoked a natriuresis and diuresis; p otassium excretion remained unchanged. Fractional reabsorption in the proximal convoluted tubule in glibenclamide-infused rats did not diffe r significantly from that in control animals, although the late proxim al tubular fluid to plasma concentration ratio for potassium was reduc ed. Fractional sodium delivery to the early distal tubule was elevated , while the fractional deliveries of water and potassium to this nephr on site were unaffected. We conclude that glibenclamide impairs sodium reabsorption in one or more of the nephron segments that comprise the loop of Henle. These results are consistent with the hypothesis that the natriuresis resulting from glibenclamide administration is a conse quence of blockade of potassium channels in the apical membrane of the thick ascending limb of Henle's loop. The data suggest that glibencla mide may additionally inhibit a small secretory potassium flux in the proximal tubule.