Induced development of proximal tubular NaKATPase, basolateral cell membranes and fluid reabsorption.

We have previously demonstrated that adrenal corticoid hormones (ACH) induce NaK-ATPase activity in immature proximal tubular (PT) cells in rats. We have now determined the effect of betamethasone (beta) and aldosterone (aldo) on the size of PT basal and lateral cell membranes (BLM), PT fluid reabsorption (J v (a] measured in vivo with the split drop technique and PT NaKATPase activity in 20-day-old (young) and 40-day-old (adult) rats. Serum levels of ACH were the same in young and in adult rats, but adrenalectomy caused a significantly larger fall in NaKATPase activity in young than in adult rats. BLM surface area (micron 2/micron -3 cell volume), J v (a) and NaKATPase were significantly lower in young than in adult rats. Three-day treatment with high doses of beta (60 micrograms X 100 g-1 or aldo (40 micrograms X 100 g-1) significantly increased BLM surface area. J v (a) and NaKATPase activity in young but not in adult rats. Three days after adrenalectomy, J v (a) was significantly depressed in adult rats. There was a significant correlation between the ACH-dependent changes in NaKATPase activity and J v (a). Short-term treatment (2-3 hours) with high doses of ACH did not significantly increase NaKATPase activity and J v (a) in young rats.