HIGH PROTEIN-INTAKE ACCELERATES THE MATURATION OF NA,K-ATPASE IN RAT RENAL TUBULES

We have examined the effect of a high protein intake on renal maturation by studying the Na,K-ATPase activity in proximal convoluted tubules (PCT) and medullary thick ascending limb of Henle (TAL) in kidneys from 16- to 24-day-old rats. The rats received an isocaloric diet containing 21% (normal protein, NP) and 50% (high protein, HP) protein from 16 days of age. HP diet significantly increased the nephron filtration rate after 2 days. There was a proprotionate increase in proximal tubular reabsorption. HP diet significantly increased Na,K-ATPase in both PCT and TAL after 4 days, but not after 2 days. Although HP diet caused a similar increase in Na delivery to PCT and TAL, the increase in Na,K-ATPase activity after 8 days was more pronounced in TAL than in PCT. To determine whether stimulation of Na,K-ATPase required the presence of adrenal corticoid hormones, rats adrenalectomized at 16 days of age were studied. HP diet significantly increased Na,K-ATPase in both PCT and TAL from adrenalectomized rats. To determine whether stimulation of Na,K-ATPase in PCT was mediated by increased Na entry via the amiloride-sensitive Na/H exchange, rats were treated with amiloride via an osmotic minipump from 16 to 20 days of age. Amiloride treatment significantly retarded the normal increase in Na,K-ATPase in NP rats but had no effect on ouabain-insensitive ATPase. HP diet significantly increased PCT Na,K-ATPase, in spite of chronic amiloride treatment. Conclusion: HP intake accelerates maturation of Na,K-ATPase in PCT and TAL regardless of the presence of adrenal corticoid hormones. In the PCT, the effect may not be directly related to an increase in Na entry via the Na/H exchanger.