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 ligands of adrenoceptors and isometric tension recording. 2. Noradrenaline and phenylephrine induced concentration-dependent contractions in corpus cavernosum preparations. B-HT 920 had no effect. 3. Phentolamine and prazosin produced a shift to the right of the dose-response curve of noradrenaline, while the alpha(2)-antagonist, rauwolscine had no effect on the response to noradrenaline. Phenylephrine-evoked contractions of corporal strips were significantly inhibited by the alpha(1)-adrenoceptor antagonist, prazosin. 4. Isoprenaline and salbutamol each relaxed precontracted corpus cavernosum preparations in a concentration-dependent manner; the isoprenaline effect was blocked by propranolol, practolol and butoxamine. The salbutamol effect was blocked by butoxamine. 5. These results suggest that presence of postjunctional alpha(1)-adrenoceptors in horse corpus cavernosum. There is also a heterogenous population of beta-adrenoceptors in this tissue, belonging to the beta(1) and beta(2) subtypes.