The Met-enkephalin analog D-Ala2-Met-enkephalinamide decreases the adrenocortical response to ACTH in dispersed rat adrenal cells.

The effects of the Met-enkephalin analog D-Ala2-Met-enkephalinamide (DALA) on basal and ACTH-stimulated corticosterone secretion from dispersed adrenal cells were investigated. Low doses (10(-10) and 10(-12) M) of DALA resulted in no apparent alteration in the response to ACTH (8 X 10(-9), 3.2 X 10(-8) or 1.6 X 10(-7) M). High doses of DALA (10(-8) and 10(-6) M) produced a decline in the steroidogenic response to ACTH. The opiate receptor antagonist naloxone (10(-4)-10(-10) M) did not influence the basal production of corticosterone or the stimulating action exerted by ACTH. However, the presence of naloxone reversed the blocking action on corticosterone production that was exerted by DALA. These findings indicate that enkephalins may decrease adrenocortical responsiveness to ACTH.