REGULATION OF (NA++K+)-ACTIVATED ATP HYDROLYZING ENZYME SYSTEM IN RAT KIDNEY .2. EFFECT OF ALDOSTERONE ON ACTIVITY IN KIDNEYS OF ADRENALECTOMIZED RATS

1. 1. The aim of the study has been to examined the effect of aldosterone in vivo on the activity of (Na+ + K+)-ATPase (ouabain sensitive; ATP phosphshydrolase, EC 3.6.1.3) in kidneys of adrenalectomized rats. 2. 2. Repeated injections of aldosterone increased the activity of (Na+ + K+-ATPase in the microsomal fraction from whole kidneys after 14 and 24 h. In this period corticosterone had no effect on activity of the enzyme, while combinations of aldosterone and corticosterone caused a significant increase in activity. After 48 h, corticosterone restored the activity to normal levels, while aldosterone at best increased the activity to a level midway between the activity of adrenalectomized and of normal rats. 3. 3. In an attempt to localize an effect of aldosterone, the activity of (Na+ + K+-ATPase was measured in preparations from subdivisions of the kidneys. Aldosterone in physiological doses (0.25 μg, 2.5 μg, and 5.0 μg per 100 g rat 4. every 4.5 h for 24 h produced a significant increase in activity in the outer medulla where the ascending limbs of Henle predominate. In the inner cortex an increase in activity was observed after treatment with the two higher doses of aldosterone, while only insignificant changes were found in the outer cortex. The rise in activity was gradual and first detectable after more than 6 h of treatment. 4. 4. The results are compatible with an adaptation of the level of (Na+ + K+-ATPase to the sustained increase in reabsorption of sodium following repeated injections of aldosterone to adrenalectomized rats. © 1969.