PHARMACOLOGICAL CHARACTERIZATION OF ADRENOCEPTORS IN HORSE CORPUS CAVERNOSUM PENIS

1 The presence and types of alpha and beta-adrenoceptors in the corpus cavernosum of the horse were studied in vitro by using selected ligan ds of adrenoceptors and isometric tension recording. 2 Noradrenaline a nd phenylephrine induced concentration-dependent contractions in corpu s cavernosum preparations. B-HT 920 had no effect. 3 Phentolamine and prazosin produced a shift to the right of the dose-response curve of n oradrenaline, while the alpha(2)-antagonist, rauwolscine had no effect on the response to noradrenaline. Phenylephrine-evoked contractions o f corporal strips were significantly inhibited by the alpha(1)-adrenoc eptor antagonist, prazosin. 4 Isoprenaline and salbutamol each relaxed precontracted corpus cavernosum preparations in a concentration-depen dent manner; the isoprenaline effect was blocked by propranolol, pract olol and butoxamine. The salbutamol effect was blocked by butoxamine. 5 These results suggest the presence of postjunctional alpha(1)-adreno ceptors in horse corpus cavernosum. There is also a heterogenous popul ation of beta-adrenoceptors in this tissue, belonging to the beta(1) a nd beta(2) subtypes.