Changes of muscarinic receptors and connexin-43 expression as a mechanism of overactive bladder in ovariectomized rats.

Abstract

After menopause, the bladder is known to become overactive. To investigate the mechanisms involved in these changes, we examined the muscarinic receptors M2, M3 and gap junction protein connexin-43 in an ovariectomized rat bladder. Twenty 10-week-old female SD rats were used. Ten rats were ovariectomized, (Ovx group) and 10 rats received a sham operation (Con group). Four weeks after the operation, urodynamic tests were performed to verify overactive bladder, and the animals were killed. The body, bladder and uterus weights were measured. The bladder specimens were prepared for immunohistochemical staining for muscarinic receptors M2, M3 and connexin-43. Western blotting was also used for the same protein measurement (M2, M3 and connexin-43). A t test with a p value of 0.05 was considered significant, and SPSS 12.0 for Windows was used to analyze the data. The mean body weight of the Ovx group (315.8 ± 18.1 g) was heavier than the Con group (270.0 ± 23.6 g) (p = 0.009). The mean uterus weight of the Ovx group (260.4 ± 186.8 g) was lighter than the Con group, (600.6 ± 175.9 g) (p = 0.028) and the mean bladder weight of the Ovx group (80.2 ± 15.9 g) was lighter than the Con group (97.4 ± 10.6 g) (p = 0.041). The mean bladder contraction of the Ovx group (5.5 ± 2.3/10 min) was more frequent than that of the Con group (3.2 ± 2.8) (p < 0.05). The expressions of M2 and M3 were not different between the Ovx and the Con group, but the expression of connexin-43 in the Ovx group was more intense than in the Con group in immunohistochemical staining. These findings were also confirmed by Western blotting results. Ovariectomized rats showed frequent bladder contraction and increased connexin-43 expression without changes in M2 and M3 receptor expression. These results imply that ovariectomy-induced overactive bladder may be due to an altered gap junction protein function rather than muscarinic receptor modification.