Abstract
Abstract
This study was designed to assess the contribution of the proximal convoluted tubule to the blunted natriuretic response of the newborn to volume expansion. Guinea pigs (n = 17) ranging in age between 1 and 56 days were subjected to similar degrees of vascular volume expansion by infusion of an isoncotic albumin solution. Measurements of TF/P inulin in proximal tubular fluid were made by the recollection technique prior to and following the expansion. A decrease in proximal fractional reabsorption of fluid (P < 0.01) was observed at all ages, but there were no significant differences in TF/P inulin between various age groups under both control and experimental conditions. Whole kidney fractional reabsorption of sodium, which was similar in all groups during control conditions, was significantly lower (P < .001) in the oldest than in the two younger groups of animals during volume expansion. These results demonstrate that the proximal convoluted tubule is not the site responsible for the age related differences in sodium reabsorption. The tendency to retain a sodium load observed during maturation appears therefore to be due solely to enhanced reabsorption in segments of the nephron located beyond the proximal convoluted tubule.
Get full access to this article
View all access options for this article.