STEROIDOGENIC ADRENOCORTICAL-CELLS SYNTHESIZE ALPHA(2)-MACROGLOBULIN IN-VITRO, NOT IN-VIVO

We previously identified alpha(2)-macroglobulin as the major protein secreted by primary cultures of adrenocortical cells. We report here that in the adrenal gland, the distribution of alpha(2)-macroglobulin in the adrenocortical tissue is restricted to the endothelium of blood vessels and that no immunoreactivity is found in steroidogenic cells. A time course study revealed that freshly dissociated bovine adrenocortical cells were void of alpha(2)-macroglobulin immunoreactivity whereas the proportion of alpha(2)-macroglobulin-positive cells reached more than two-thirds of the population between day 4 and day 7 of culture. Double immunoenzymatic labeling of 6-day-old cultures revealed a co-localization of alpha(2)-macroglobulin and the steroidogenic enzyme P-450(scc). Treatment of 5-day-old cultures (expressing alpha(2)-macroglobulin) for 24 h by either ACTH (10(-9)-10(-6) M) or alpha(2)-macroglobulin (2.5 mg/ml) resulted in a marked decrease of the expression of alpha(2)-macroglobulin. These data indicate that ACTH and plasmatic alpha(2)-macroglobulin could physiologically repress alpha(2)-macroglobulin expression in the adrenal cortex in vivo.