Alpha-1 adrenergic blockade: a possible mechanism of action of dopaminergic drugs on ACTH secretion.

In some cases of Cushing's syndrome both bromocriptine and lisuride inhibit the secretion of ACTH but it is still unknown if they act at pituitary or at higher levels. In order to evaluate this aspect, we set up an in vitro perfusion system with anterior pituitary cells from rats and from human ACTH-secreting tumors. In both preparations lysine-vasopressin (LVP) and epinephrine (EPI) stimulated ACTH secretion; prazosin (alpha-1 blocker) inhibited the EPI but not the LVP-mediated stimulation. Similarly, the infusion of lisuride blocked ACTH response to EPI but not to LVP. These data may suggest that "dopaminergic" drugs could act by an adrenergic blockade and not necessarily by a dopaminergic inhibition.