Cholinergic modulation of contractile responses in caprine urinary bladder smooth muscle: Role of urothelium and atropine sensitivity

The cholinergic system plays a pivotal role in urinary bladder function, primarily facilitating bladder emptying through the activation of muscarinic receptors in smooth muscle. This process can also be modulated by signaling molecules from the urothelium. In this study, we investigated the role of the urothelium in cholinergic-mediated bladder smooth muscle contraction. Bladder smooth muscle contraction was induced using the muscarinic agonist acetylcholine (ACh). Our results demonstrated that ACh elicited a concentration-dependent contractile response in goat urinary bladder smooth muscle. Notably, the removal of the urothelium (detrusor muscle strips) resulted in a leftward shift of the ACh-induced contractile response curve, leading to a stronger and more pronounced contraction. The muscarinic response was significantly enhanced in the absence of the urothelium compared to intact bladder smooth muscle. Furthermore, in the presence of atropine, a muscarinic receptor antagonist, ACh-mediated contractions were abolished. Minimal responses were observed in denuded caprine detrusor muscle strips, while no contraction occurred in detrusor muscle strips with an intact urothelium. Our findings suggest that the caprine urinary bladder exhibits pharmacological properties similar to those of the human bladder, making it a potentially valuable model for evaluating new therapeutic agents for urinary incontinence.