Calcium Ion as “Second Messenger” in Corticoidogenic Action of ACTH

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The correlation between corticoidogenesis and Ca²⁺-influx in the cell was investigated using isolated rat or bovine adrenocortical cells.
1) ACTH-induced corticoidogenesis in both rat and bovine adrenocortical cells was enhanced in parallel with increasing concentrations of external Ca²⁺. In the bovine cells but not in the rat cells, moreover, the marked stimulatory effect of external Ca²⁺ on the corticoidogenesis was observed despite the absence of ACTH. 2) Ca²⁺-influx and corticoidogenesis always occurred unitedly. 3) Verapamil markedly inhibited either corticoidogenesis or Ca²⁺-influx in response to ACTH. 4) The stimulatory effect of Ca²⁺ on corticoidogenesis was completely blocked by cycloheximide.
It was therefore suggested that Ca²⁺ could regulate corticoidogenesis as a primary “second messenger” of ACTH through biosynthesis of so-called steroidogenic protein.