alpha(2)-adrenoreceptor subtypes regulate ACTH and beta-endorphin secretions during stress in the rat

The effect of different alpha(2)-adrenoreceptor subtype agonists and antago nists on adrenocorticotrop hormone (ACTH) and beta-endorphin release induce d by ether stress was examined. Ether inhalation-induced ACTH and beta-endo rphin increase was inhibited by ICV administration of 30 mu g but not 1 and 10 mu g clonidine (alpha(2)-adrenoreceptor agonist). ICV oxymetazoline (al pha(2A)-adrenoreceptor agonist; 1-10-30 mu g) or the alpha(1)-agonist metho xamine (100 mu g/rat) failed to inhibit the stress-induced rise. Pretreatme nt with the alpha(1)/alpha(2B,C)-antagonist prazosin (0.5 mg/kg, IP) preven ted the effect of clonidine on the ether stress, while the alpha(1)/alpha(2 A)-antagonist WB-4101 (0.5 mg/kg, IP) was unable to counteract the inhibito ry effect of clonidine. Prazosin alone had no effect on the ether-induced p lasma ACTH and beta-endorphin elevation. These results suggest that noradre naline in the central nervous system may inhibit the stress-induced hypotha lamo-pituitary-axis and pituitary beta-endorphin activation via alpha(2B,C) -adrenoceptor subtypes and prazosin may antagonize its effect on these rece ptors. (C) 1999 Elsevier Science Ltd. All rights reserved.