Pilot experiments on the actions of drugs injected into the human corpus cavernosum penis.

Seven drugs that are known to relax smooth muscle (phenoxybenzamine, phentolamine, thymoxamine, imipramine, verapamil, papaverine, naftidrofuryl) caused erection when injected intracavernosally. Salbutamol, hydralazine, lignocaine and bupivacaine caused tumidity but not erection. Metaraminol and guanethidine caused shrinkage followed by tumidity. Neostigmine, atropine, propranolol and idazoxan had no effect in the doses tried. It is argued that the seven drugs that cause erection do so by relaxing vascular and trabecular smooth muscle within the cavernosal space, and that the two that cause shrinkage of the penis do so by constricting vascular and trabecular smooth muscle within the cavernosal space. It is argued that muscarinic and beta-adrenergic transmission play no important part in erectile mechanisms within the corpora cavernosa. Papaverine, phenoxybenzamine and metaraminol, given intracavernosally, are already used therapeutically. Uses are suggested for thymoxamine, phentolamine, verapamil and guanethidine.