EFFECTS OF GENDER AND OESTROGEN ON INTRACELLULAR CALCIUM AND CONTRACTILITY OF RAT URINARY BLADDER SMOOTH MUSCLE

Igor R. Wendt, Hamdia Solaiman, Department of Physiology, Monash University, Vic. 3800.

Oestrogen deficiency has been suggested to be one of the factors involved in the increased incidence of incontinence in post-menopausal women and oestrogens have been used clinically in the treatment of urinary disorders during and after menopause. This suggests that oestrogen may modulate urinary bladder contractility. The present study investigated possible effects of gender on contractile responsiveness and intracellular calcium in rat urinary bladder smooth muscle. In addition, the ability of estrogen to acutely to inhibit contraction of bladder smooth muscle was investigated. Smooth muscle strips were isolated from bladders of young adult male and female Wistar rats, and force and [Ca²⁺]_i monitored during contractile stimulation. Acute effects of estradiol were examined by stimulating the muscles with high K⁺ solution in the presence of varying concentrations of 17ß-estradiol. There were no differences in the maximum force responses of muscle strips from males and females to carbachol or electrical field stimulation. However, muscle strips from males were less sensitive at submaximal levels of stimulation. No differences were found in either the absolute or relative contractile force responses between male and female bladder muscle strips stimulated with high K⁺ solutions. [Ca²⁺]_i was similar in muscle strips from males and females, both under resting conditions and during stimulation with high K⁺. 17ß-estradiol acutely inhibited high K⁺ contractions in a concentration-dependent manner in both male and female muscle strips, however, muscle strips from males were more sensitive to estrogen than those from females. The inhibition of contraction by 17ß-estradiol was associated with a reduction in the magnitude of the high K⁺ induced increase in [Ca²⁺]_i. This study found little evidence for gender related differences in the contractile responsiveness of urinary bladder smooth muscle, with the exception of an apparent slight difference in the relative sensitivity to muscarinic receptor activation. Oestradiol at high concentrations acutely inhibited Ca²⁺ entry and force in urinary bladder smooth muscle and was more effective in this regard in male bladder than in female bladder.