Nephron heterogeneity in ischemic acute renal failure.

To uncover the reasons for reported internephron heterogeneity in acute renal failure (ARF) serial micropuncture experiments in norepinephrine-induced ARF and sham-infused control rats were carried out to investigate this phenomenon. Proximal tubular pressures (PT) were scattered at 24, 48, and 72 hr in ARF rats ranging from 4 to 42 mm Hg, but the majority were greater than the mean control values (10 +/- 1 mm Hg). One week ARF PT were less variable than on previous days (5 to 17 mm Hg). The decreased variability was the result of a reduced number of PT values that were greater than controls. When single nephron filtration rates (SNGFR) were measured with spontaneous flow collections without maintaining the existent tubular pressures, results were widely scattered on each day. When SNGFR were measured at the existent PT, individual determinations were tightly clustered on each experimental day, clearly different from controls (all P less than 0.001), and correlated closely with predicted values from whole kidney inulin clearance (all P less than 0.001). Thus, existent internephron SNGFR was uniform in ARF rats and apparent heterogeneity, in large part, was attributable to an artifact of the tubular fluid collection technique. Despite the uniformity of SNGFR, values of PT ranging below as well as above controls, suggested that a mechanism in addition to tubular obstruction was operative in reducing SNGFR. Recoveries of microperfused 14C-inulin were similar to controls excluding significant backleak of tubular fluid.(ABSTRACT TRUNCATED AT 250 WORDS)