Urethral responses to autonomic nerve stimulation

Urethral contraction in response to cholinergic stimulation has been repeatedly proved and is a universally accepted fact. The adrenergic response is still disputed: (1) Is it a contraction or a relaxation, or a combination of both? (2) Where are the adrenergic receptors? Are they on the intrinsic urethral smooth muscles (with a biphasic response); in two different structures of the same organ (urethral and vascular smooth muscles); or on two anatomically different urethral smooth muscular units? Sympathomimetic and hypogastric nerve stimulation alone, as well as with pharmacologic blockade, showed that the contraction response to adrenergics is independent of the pelvic nerve and does persist even after urethral smooth muscle blockade by atropine, but is abolished after alpha blockade by phentolamine. The same contraction response, manifested in rise in intraurethral pressure, can be induced by pure vasoconstrictors. The relaxation response is reduced by beta blockade. Whether it is the direct response of a specific urethral group of musculature to sympathetic stimulation or an indirect urethral response to trigonal activity in answer to the same stimulus is discussed.