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

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Abstract
Adrenal corticoid hormones (ACH) induce NaK-ATPase activity in immature proximal tubular (PT) cells in rats. 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 NaK-ATPase activity was determined 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 NaK-ATPase activity in young than in adult rats. BLM surface area (.mu.m2/.mu.m-3 cell volume), J v (a) and NaK-ATPase were significantly lower in young than in adult rats. Three-day treatment with high doses of beta (60 .mu.g/100 g) or aldo (40 .mu.g/100 g) 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 h) with high doses of ACH did not significantly increase NaKATPase activity and J v (a) in young rats.