Microperfusion study of fluid reabsorption in proximal tubules of rat kidneys

Publisher Website
Google Scholar
Abstract
Single proximal tubules were pump-perfused with Ringer solution containing inulin-''14C at different flow rates and perfusate collected at known distances from the site of infusion. Fluid samples were analyzed for inulin-14C and osmolality. Tubular diameter was measured from photomicrographs of the kidney cortex in vivo. Hence, fractional reabsorption of Na and of fluid could be evaluated as a function of tubular diameter, flow rate, and distance along the nephron segment. Results were independent of the presence of a distal oil block and indicate: Collected perfusate-to-injected perfusion fluid (CP/IP) inulin ratios increase as a function of distance at all perfusion rates and remain unchanged over a range from 10-24 m[mu]l/min. Tubular diameter was increased with elevation of perfusion rates. CP/IP inulin ratios were relatively depressed at perfusion rates of 44 m[mu]l/min. No further increase in tubular diameter duplication was observed. CP/IP inulin ratios at these highest perfusion rates could be elevated into the range observed at lower perfusion rates when further tubular dilatation was achieved by ureteral clamping. These findings are consistent with the view that proximal tubular reabsorption of Na is directly proportional to tubular cross section.