The Interaction Between Cholinergic and Adrenergic Receptor Functions in the Outlet Region of the Urinary Bladder: An in Vitro Study in the Cat

Abstract

The interaction between cholinergic and adrenergic receptor functions in the outlet region has been studied in vitro on preparations from cat bladder. Variations in resistance to perfusion were recorded, together with changes in the tension in longitudinal musculature. If the outlet region was contracted by continuous perfusion with alphn-adrenergic drugs it could be relaxed completely by intermittent beta-adrenergic stimulation. Cholinergic stimulation with acetylcholine also had a relaxing effect in this situation. On the other hand, if the outlet region was continuously relaxed with a beta-adrenergic stimulating drug, the flow resistance could be increased by alpha-adrenergic induced muscle activity and also by acelylcholine. Thus the adrenergic receptor functions appear to antagonize each other in the internal sphincter region, which is particularly sensitive to beta stimulation. The dual action of acetylcholine on flow resistance is probably due to its effect on the circular musculalure is mediated by adrenergic receptors. It could give rise to both alpha- and beta-effects, depending on which odrenergic muscle receptor was unoccupied in a certain situation. In low concentrations, adrennlin and noradrenalin produced a dose-dependent reduction in flow resistancc: in higher concentrations these catecholamines produced a dose related increase. The beta adrenergic relaxing action on the internal sphincter mechanism, which could be demonstrated with spacific adrenergic receptor stimulating drugs and with the physiological transmitter noradrenalin. was the most sensitive regulator of tension in the sphincter. It can probably be activated by amounts of catecholaminer which occur physiologically in blood and urine