Adrenoreceptors in the Human Penis

Abstract

1. Adrenaline, noradrenaline and phenylephrine caused contraction of the corpus cavernosum muscle of the human penis. These sympathomimetic amines did not product inhibitory effects even in the presence of the alpha-adrenoreceptor blocker, phentolamine. The effect of dopamine was similar to that produced by these three sympathomimetic amines. Higher doses of isoprenaline and salbutamol also contracted this preparation. 2. Cocaine and guanethidine enhanced the motor response to adrenaline, noradrenaline and phenylephrine while the action of dopamine was blocked by these two drugs. 3. The motor response to adrenaline, noradrenaline and phenylephrine was antagonized by phentolamine and often potentiated by the beta-adrenoreceptors blocking drug, propranolol. The contractions produced by high doses of salbutamol and isoprenaline were also abolished by phentolamine. These findings indicate that the motor response to sympathomimetic amines is the result of activation of alpha-adrenoreceptors in the corpus cavernosum muscle. 4. At low doses, isoprenaline and salbutamol relaxed the corpus cavernosum muscle strip. The inhibitory action was blocked by low concentrations of the beta-adrenoreceptor antagonist, propranolol but not by practolol (beta 1-adrenoreceptor antagonist) and butoxamine (beta 2-adrenoreceptor antagonist). beta-adrenoreceptors are present in the corpus cavernosum muscle but these are unlikely to be either of the beta 1 or beta 2 type. The possible existence of a third type of beta-adrenoreceptor is suggested.

Involvement of β 3 -adrenergic receptor activation via cyclic GMP- but not NO-dependent mechanisms in human corpus cavernosum function

“…To rule out any involvement of ␤ 1 -and ␤ 2 -adrenergic receptors in the relaxant responses to BRL 37344, propranolol (nonselective antagonist of ␤ 1 -and ␤ 2 -receptors) and butoxamine (selective antagonist of ␤ 2 -receptors) were tested and found to have no effects (data not shown). The latter observations are in agreement with those from a report in which analysis of the effects of selective ␤ 1 -and ␤ 2 -adrenergic receptor antagonists on relaxant responses in HCC suggested the existence of a third receptor type (14). To determine any role for prostanoids or nonadrenergic͞noncholinergic neurons in the relaxant responses to BRL 37344, indomethacin or atropine in the presence or absence of guanethidine, respectively, was tested and found to exert no appreciable influence (data not shown).…”

Effect of Korean red ginseng on the rabbit corpus cavernosal smooth muscle

“…Norepinephrine or PHE induces concentration-dependent contraction of isolated strip preparations of corpus cavernosum and this contraction is attenuated or blocked by a-adrenoreceptor blockers. 30,31 In our studies with isolated corpus cavernosal strips, PHE induced contraction was inhibited by EKG. The mechanism of this response is not understood at present.…”

Pharmacological studies of human erectile tissue: characteristics of spontaneous contractions and alterations in α‐adrenoceptor responsiveness with age and disease in isolated tissues

“…Previous studies concerning the classification of the aadrenoceptor subtype mediating contraction in HET have relied primarily on the rank order of agonist potency, displacement of agonist concentration-response curves by a single concentration of antagonist (without calculation of antagonist affinity) and the relaxation of precontracted HET by selective a-adrenoceptor antagonists (Adaikan & Karim, 1981;Hedlund & Andersson, 1985a Pharmacological studies on human isolated vascular smooth muscle tissues represent an initial step toward understanding mechanisms of contraction and relaxation in vivo and, ultimately, toward characterization of alterations in vascular smooth muscle function related to age and pathology. At present, we are using the steady-state logistic parameters as an index for detecting fundamental alterations in the pharmacology of vascular smooth muscle with age or disease.…”

“…The current preponderance of evidence, both in vitro and in vivo, indicates that maintenance of the flaccid penile state is, at least in part, related to release of noradrenaline from sympathetic nerves and contraction of corporal smooth muscle subsequent to activation of a homogeneous postsynaptic a-adrenoceptor population (Adaikan & Karim, 1981;Hedlund & Andersson, 1985a;Saenz de Tejada et al, 1989a,b). Although binding studies in membrane preparations of HET also suggest the presence of a single population of aadrenoceptors (Levin & Wein, 1980), a conclusive pharmacological classification of the receptor that mediates .el MacmiHan Press Ltd, 1990 phenylephrine-and noradrenaline-induced contractions at the intact tissue level, as either the al-or a2-adrenoceptor subtype, is still lacking.…”

“…The human erectile tissue (HET) preparation has been used by several laboratories to study the pharmacology of human vascular smooth muscle (Adaikan & Karim, 1981;Fovaeus et al, 1987;Heaton, 1989;Saenz de Tejada et al, 1989a,b;Christ et al, 1989). HET is a readily available smooth muscle 1 Author for correspondence.…”