Effect of renal ischemia on renal tubular function in the rat as measured by PAH uptake in vitro.

S TUDIES on the influence of renal ischemia on kidney function have indicated that following a period of ligation of the renal pedicle (and the subsequent release of the ligature) there is a decrease in clearance of paraaminohippuric acid (C,,,) greater proportionally than the decrease in both renal plasma (RPF) (I) and renal blood flow (RBF) (2). Selkurt (3) has shown that the extraction ratio of PAH decreases to 18 !% of the control following renal ischemia of 20 minutes duration in dogs. Gradual recovery of tubular function ensues if renal ischemia does not persist beyond a certain period. The in situ methods used heretofore for the determination of tubular damage following ischemia do not distinguish between a decrease in active tubular transport of PAH and an increase in permeability of the tubules to PAH thus allowing PAH to diffuse back to the plasma. Iti an attempt to study only one of these factors at a time, the in vitro method of Cross and Taggart (4) for mammalian kidney slices has been used. The assumption has been made by many investigators that this technique is a measure of active renal tubular transport. One of its advantages is that the results are not dependent on an intact blood supply. According to Selkurt, renal ischemia impaired the excretory ability of the tubules. If there were damage to the mechanism for the transport of PAH a decrease in accumulation of PAH by the slices would result. Upon calculation of our data it was clearly shown that the ability of the slices to concentrate PAW: was greater in the ischemic kidney than in the kid-