Functional and biochemical characteristics of urinary bladder muscarinic receptors in long-term alloxan diabetic rats

Objective: To re-examine the function of the urinary bladder in vivo as well as to determine the functional and biochemical characteristics of bladder muscarinic receptors in long-term alloxan-induced diabetes rats. Methods: Two-month-old male Wistar rats were injected with alloxan and the animals showing blood glucose levels >300mg/dL together with age-paired untreated animals were kept for 11 months. Body weight, bladder weight, blood glucose, and urinary volume over a period of 24 hours were determined in both groups of animals. A voiding cystometry in conscious control and diabetic rats was performed to determine maximal micturition pressure, micturition contraction interval and duration as well as voided and post-voiding residual volume. In addition, concentration-response curves for bethanechol in isolated bladder strips, as well as [H-3]-N methyl-scopolamine binding site characteristics in bladder homogenates were determined. Results: Mean bladder weight was 162.5 +/- 21.2mg versus 290 +/- 37.9mg in control and treated animals, respectively (p<0.05). Micturition contraction amplitude (34.6 +/- 4.7mmHg versus 49.6 +/- 2.5mmHg), duration (14.5 +/- 1.7 seconds versus 23.33 +/- 4.6 seconds) and interval (87.5 +/- 17.02 seconds versus 281.11 +/- 20.24 seconds) were significantly greater in alloxan diabetic rats. Voided urine volume per micturition contraction was also significantly higher in diabetic animals. However the post-voiding residual volume was not statistically different. Bethanechol potency (EC50 3 mu M versus 5 mu M) and maximal effect (31.2 +/- 5.9g/g versus 36.1 +/- 6.8g/g) in isolated bladder strips as well as number (169 +/- 4fmol/mg versus 176 +/- 3fmol/mg protein) and affinity (0.69 +/- 0.1nM versus 0.57 +/- 0.1nM) of bladder muscarinic receptors were also not statistically different. Conclusion: Bladder function in vivo is altered in chronic alloxan-induced diabetes rats without changes in functional and biochemical characteristics of bladder muscarinic receptors.