Na-K-ATPase activity was measured with an ultramicromethod in single portions of the proximal and distal convolution and of the thick ascending limb of Henle from adrenalectomized rats and after treatment with 5 mug aldosterone per 100 g body wt. The activity in all tubular structures returned to normal within 1 h after injection. This rapid activation of Na-K-ATPase induced by hormone was completely prevented by actinomycin D and cycloheximide. It appears that this aldosterone effect on Na-K-ATPase requires an intact protein synthetic process.
