Effects of phentolamine and clonidine on pituitary-adrenocortical axis during stress in conscious rats.

For evaluation of the effect of several drugs on the hypothalamo-pituitary-adrenocortical axis during stress, after testing various tress stimuli (swimming, restrain) the 15 min exposure of rats to novel environment was chosen. Subcutaneous administration of clonidine hydrochloride (BOEHRINGER; Ingelheim, 60 micorgram kg-1), a drug stimulating alpha-adrenergic receptors, did not result in any any changes in plasma corticosterone level either during basal or under stress conditions. In contrast, the administration of alpha-adrenergic blocking agent--phentolamine (RegitineR CIBA; 4 mg kg-1)--produced a significant elevation of resting corticosterone level, but failed to influence the stress-induced corticosterone increase.