Effects of corticosterone on adrenocorticotrophin-induced mitochondrial differentiation with special reference to 11 beta- and 18-hydroxylation.

The effects of corticosterone in concentrations found in adrenal venous plasma on ACTH-induced changes in cultured cortical cells derived from foetal rat adrenals were studied. Corticosterone at a concentration of 5-7 X 10(-5) mol/l completely inhibited mitochondrial differentiation to fasciculte-like morphology. The same cultures revealed significant inhibition of 11beta- and 18-hydroxylation compared with cultures treated with ACTH only. This was shown by the reduced formation of corticosterone and 18-OH-deoxycorticosterone (48%, P less than 0-001) and simultaneous enhancement of deoxycorticosterone formation (33%, P less than 0-05) from added [4-14C]progesterone. Similar inhibition was observed when dibutyryl cyclic AMP replaced ACTH as an inducer of differentiation. Lower concentrations of corticosterone (1-2 X 10(-5) and 2-4 X 10(-5) mol/l) inhibited ACTH-stimulated formation of corticosterone and 18-OH-deoxycorticosterone from endogenous precursors. The results demonstrate that corticosterone regulates the stage of differentiation in cultured adrenocortical cells. The possible role of corticosterone in the regulation of growth and steroidogenic capacity of the adrenal cortex is discussed.