Micropuncture study of isolated perfused rat kidney

Abstract

Fluid was collected by micropuncture techniques from various sites along superficial nephrons of rat kidneys perfused with an artificial cell-poor medium. Samples of tubular fluid and of perfuslon medium were analyzed for Na22 and inulin-C14. Fractional tubular water and Na reabsorption were estimated and compared with urinary excretion rates. The transport capacity of small segments of proximal tubular epithelium was also estimated by the half-time of disappearance of lsoosmotic sodium chloride samples injected into tubules between oil droplets. Rates of renal perfusion, glomerular filtration, and O2 consumption were also measured. Compared to nondluretic rats in vivo, proximal Na and fluid reabsorption was found to be significantly depressed in perfused rat kidneys. This was due to both a diminished tubular Na transfer capacity (split oil-droplet method) and a shortened passage time of fluid along the proximal convolution. The ability of distal nephron segments to lower tubular Na concentration was moderately impaired. Compensatory adjustments of tubular fluid and Na reabsorption along the loop of Henle, the distal tubule, and the collecting duct to the in?creased load are inadequate and lead to the natriuretic and diuretic state of the perfused kidney preparation.