Lack of control by adrenal steroids of oxidative enzymes and Na/K-ATPase development in the rat proximal tubule.

The activities of citrate synthase, 3-oxoacid CoA-transferase, and Na/K-ATPase were determined in the proximal convoluted tubules (PCT) of midcortical nephrons from 16-, 21- and 30-day-old and adult rats. Enzyme microassays based on NAD amplification were run on tubule segments microdissected from lyophilized tissue sections, and the activities were expressed per unit of tissue dry weight. The activities of 3-oxoacid CoA-transferase (+ 155%) and citrate synthase (+ 44%) increased between 16 and 30 days, while no significant change in Na/K-ATPase activity occurred during this period. The results obtained in PCT from subcapsular nephrons were similar. It is concluded that active transport of Na+ coupled to mitochondrial ATP production might be mature in the PCT by the time of weaning, consistent with data on the development of Na+ reabsorption. Since adrenalectomy on day 16 induced no changes in the activities of oxidative enzymes or Na/K-ATPase on day 21 in midcortical or subcapsular PCT, the physiological rise in circulating glucocorticoids, characteristic of the weaning period, does not trigger the development of oxidative enzymes and Na/K-ATPase in the PCT of the developing rat kidney.