Effects of Ovariectomy on Mechanical Properties and Collagen Content in Rabbit Lower Urinary Tract Smooth Muscle

Fourteen female rabbits underwent ovariectomy or were sham-operated six weeks before investigation. Detrusor and urethral strips (longitudinal and circular urethral muscle fibers were studied separately) were prepared and length-tension relations studied in organ baths experiments. In addition, the specimens were examined for collagen content. Maximal active tension in the detrusor, longitudinal and circular urethral preparations, determined as the response to K+ (124 mM), was reached when the length of the strips was 178 ± 8% (n = 7), 153 ± 9% (n = 5), and 127 ± 5% (n = 7) of the resting length, respectively. Ovariectomy did not alter the length for development of maximal active tension. In detrusor strips, ovariectomy caused a significant increase in maximal active tension from 39 ± 7 mN (sham-operated rabbits) to 79 ± 11 mN (p < 0.01), despite an unchanged relative amount of smooth muscle. The maximal active tension produced in the urethra was lower (15-25 mN) than in the detrusor, and not significantly affected by ovariectomy. Approximately 40% of the dry defatted tissue weight of the detrusor consisted of collagen, whereas corresponding value in the urethra was 50-60%. Ovariectomy had no effect on tissue collagen concentrations. In conclusion, ovariectomy for six weeks did not affect the passive mechanical properties or the collagen concentration in rabbit lower urinary tract smooth muscle, but increased the responsiveness of the detrusor muscle to K+ (124 mM).