[A micropuncture study of several indices of renal function in rats during development].

The function of single superficial nephrons has been studied by means of several micropuncture methods in 22-, 30- and 42-day rats. It was shown that intratubular hydrostatic pressure, transit time of tubular fluid through a proximal tubule and Henle's loop, as well as local reabsorption in the proximal tubules measured by Gertz's split oil droplet method increase between the 22nd and the 30th days. The ration of tubular fluid and plasma (TF/P) inulin concentrations in late proximal and in early distal tubules increases with age. The values of TF/P for Na in early distal tubules are higher in 22- and 30-day rats than in older ones. TF/P for K does not change simultaneously with that for Na. These data are consistent with the assumption that the sodium load in the distal part of the nephron is higher in young rats than in adult ones.