The Functional Role of Cholinergic Receptors in the Outlet Region of the Urinary Bladder: Anin VitvoStudy in the Cat

A method for experimental study in vitro of the outlet region (bladder base, bladder neck and proximal urethra) from the cat is described which allows simultaneous recording of resistance to flow through the region and of isometric tension in the longitudinal muscles. The results suggest that acetylcholine (ACh) may influence the smooth muscles in the outlet region by several mechanisms. Contractions in the longitudinal muscles are mediated by atropine sensitive cholinergic receptors. The resistance to flow could be either increased or decreased following ACh stimulation and in neither case could the response be blocked with atropine. If the response was an increase, however, it was blocked by phentolamine and if it was a decrease, it was blocked by propranolol. It is concluded that ACh stimulates the circular musculature in the outflow region through α‐ and β‐adrenergic receptors. It is suggested that the effects of ACh on flow are brought about through short intramural adrenergic neurons. ACh stimulates their ganglion‐cells which results in a release of nor‐adrenaline at the nerve endings and in activation of adrenergic receptors in the circular muscle layer.