The effects of phenoxybenzamine on specific binding and function of central alpha-adrenoceptors in the rabbit

Medical management of benign prostatic hyperplasia: a canine model comparing the in vivo efficacy of alpha-1 adrenergic antagonists in the prostate

Medical management of benign prostatic hyperplasia (BPH) is an alternative to surgical treatment of this disease. A major target for pharmacologic therapy is the alpha-1 adrenergic receptor, since activation of this receptor by endogenous catecholamines is thought to contribute to outlet obstruction. In the present study, we compared the potency of various alpha-1 adrenergic antagonists against epinephrine-induced contraction of the canine prostate. The drugs tested were dibenzyline, prazosin, terazosin and YM617. The rank order of potency, comparing inhibitory constants (Ki's), was found to be YM617 >> prazosin > terazosin > dibenzyline. This study is the first to compare all of these drugs directly in the prostate in vivo. The rank order of potency of the drugs is similar to the rank order of potency at other alpha-1 receptors. These results demonstrate that 1) our model is useful in confirming activity of drugs at the alpha-1 receptor and 2) the prostate alpha-1 receptor is similar to other alpha-1 receptors. Whether activity at the alpha-1 adrenergic receptor is a sufficient determinant of clinical efficacy of these drugs remains to be determined.

Effects of receptor blockers on ACTH-induced changes in extinction of active avoidance reflex in rat

The actions of blockers of dopaminergic receptors (haloperidol), alpha-receptors (phenoxybenzamine), beta-receptors (propranolol) and muscarinic cholinergic receptor (atropine) on the ACTH-induced delay of the extinction of active avoidance behavior were studied in rats. In the doses used, none of the receptor blockers modified the extinction of active avoidance behavior. ACTH delayed the extinction. However, the dopamine receptor blocker (haloperidol) and the muscarinic cholinergic receptor blocker (atropine) did prevent the action of ACTH in delaying the extinction of active avoidance behavior, whereas the alpha-(phenoxybenzamine) and beta- (propranolol) receptor blockers were ineffective. The results suggest that mainly dopaminergic and cholinergic mediations are involved in the delaying action of ACTH on the extinction of active avoidance behavior.