The effects of ACTH and cortisone on the adrenal cortex of the rat were studied enzyme-histochemcally. The animals were divided into five groups. 1. control 2. ACTH 2. 0 i. u. /day 3. ACTH 0. 1 i. u. /day 4. cortisone 2. 5 mg/day 5. cortisone 0. 1 mg/day The following enzyme histochemical stainings were performed; lactate dehydrogenase (LD), (glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), isocitrate dehydrogenase (ICD), succinate dehydrogenase (SD), malate

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... ydrogenase (MD) and 3B-hydroxysteroid dehydrogenase (3B-HSD). All these enzyme activities increased after the treatment with ACTH and decreased with cortisone. These changes are especially remarkable in G6PD and 6PGD stainings. After the treatment with ACTH for 21 days, strong activities of these two dehydrogenases remained for the following 7 days, while rapid recovery of enzyme activities were seen in the histochemical stainings of these two dehydrogenases with the cessation of cortisone administration. These findings were observed mainly in zona fasciculata and zona reticularis, and little changes were seen in zona glomerulosao The former two zones showed similar histochemical changes, and might be considered functionally one zone, which consists of clear cells and compact cells.