Mechanism of ACTH Action in Corticosteroidogenesis of Rat Adrenal

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We previously investigated the mechanism of ACTH action in fat mobilization. These investigations appeared to indicate that this hormone stimulated calcium ion uptake into adipose tissue, and the incorporated calcium ion stimulated lypolysis in the tissue through an increase in formation of lipase-fat (enzyme-substrate) complex.<BR>On the other hand, recent investigations on adrenal cortex, another target organ of ACTH, have revealed that the action of ACTH in vitro requires calcium ion in the medium, ACTH stimulates radioactive calcium ion uptake into this organ, and calcium ion stimulates steroidogenesis in adrenal homogenate.<BR>Based on these results, we suggested that ACTH increased calcium ion uptake into this organ, and the incorporated calcium ion stimulated steroidogenesis. In the present investigation, we tried to clarify the mechanism of the stimulatory effect of calcium ion on steroidogenesis. It was demonstrated that sonication of adrenal homogenate did not affect the stimulatory effect of calcium ion on steroidogenesis. It was also clarified that calcium ion stimulated the reaction of 21-hydroxylation as well as 11-hydroxylation.<BR>Stimulation of steroidogenesis was also observed with other metal ions such as alkaline earth metal ions (magnesium, barium, and strontium ions), but not with such ions as transition metal ions (manganese, cobalt, nickel, zinc ions).
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