Effects of acetylcholine on isolated urinary bladders of normal and streptozotocin-treated diabetic rats.
This study was prompted by the inconsistent reports and apparent controversies that exist in the biomedical literature on the responses of diabetic bladder strips to cholinergic nerve stimulation or exogenous administration of muscarinic agonists, especially acetylcholine (ACh), in vitro. In the present study, acetylcholine-induced contractions of urinary bladders isolated from normoglycaemic (normal) and streptozotocin-treated, diabetic Wistar rats were examined under physiological conditions. Mechanical contractile changes of the isolated urinary bladders of STZ-treated, diabetic rats in response to bath-applied acetylcholine were compared with those obtained from isolated urinary bladders of normal, age-matched, control rats. Results obtained show that urinary bladders from diabetic rats consistently weighed more, and were always more spontaneously active after mounting, than those of the age-matched normal, control rats. ft A Acetylcholine (ACh, 10" -10" M) provoked concentration-related, atropine-sensitive contractions of the isolated urinary bladders of both diabetic and age-matched normal, control rats. However, acetylcholine always induced more powerful and greater contractions of the diabetic bladders compared with bladders from the age-matched normal, control rats. The enhanced contractile responses of the diabetic bladder strips to bath-applied ACh were detected soon after induction of diabetes, and the magnitude and/or intensity of the enhanced contractile responses to ACh continued to increase as the diabetic state of the animals progressed. Although this preliminary study could not establish the mechanism of the increased contractile responsiveness of the diabetic bladders to the muscarinic agonist (ACh) used, the results tend to suggest that alterations in diabetic urinary bladder synaptosomal, vesicle-bound neurotransmitter (ACh) concentrations and the compensatory increase in the density of muscarinic M3-receptor population in diabetic bladders are two of the most attractive plausible mechanisms of the increased diabetic bladder responsiveness to bath-applied acetylcholine.