Ontogeny of Na-K-ATPase activity in thick ascending limb and of concentrating capacity.

Na-K-ATPase activity in the thick ascending limb of Henle (TAL) and the capacity to concentrate urine was determined in 12-, 16-, 20-, 30-, and 40-day-old rats. The most pronounced increase in enzyme activity occurred between 16 and 20 days of age. The relation between enzyme activity in the cortical and medullary TAL was found to be the same in 16-, 20-, and 40-day-old rats, and most enzyme determinations were made in the medullary TAL. The development of Na-K-ATPase activity in TAL and urinary concentrating capacity followed the same pattern. The developmental increase in Na-K-ATPase activity and concentrating capacity between 16 and 20 days of age was accompanied by an increase in serum corticosterone level and was abolished by adrenalectomy. Treatment with glucocorticoid hormones precociously induced Na-K-ATPase activity and concentrating capacity in 13- to 16-day-old rats but had no effect on Na-K-ATPase activity in 17- to 20-day-old rats. The increase in enzyme activity from 20 to 40 days of age was accompanied by an increase in the single nephron glomerular filtration rate. The results suggest that Na-K-ATPase activity in the TAL is an important determinant of the concentrating capacity during development. The developmental surge in Na-K-ATPase activity and concentrating capacity between 16 and 20 days of age is probably set off by the rise in the serum corticosterone level.