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 si x weeks before investigation. Detrusor and urethral strips (longitudin al and circular urethral muscle fibers were studied separately) were p repared and length-tension relations studied in organ baths experiment s. In addition, the specimens were examined for collagen content. Maxi mal 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. Ovarie ctomy did not alter the length for development of maximal active tensi on. In detrusor strips, ovariectomy caused a significant increase in m aximal active tension from 39 +/- 7 mN (sham-operated rabbits) to 79 /- 11 mN (p < 0.01), despite an unchanged relative amount of smooth mu scle. The maximal active tension produced in the urethra was lower (15 -25 mN) than in the detrusor, and not significantly affected by ovarie ctomy. Approximately 40% of the dry defatted tissue weight of the detr usor consisted of collagen, whereas corresponding value in the urethra was 50-60%. Ovariectomy had no effect on tissue collagen concentratio ns. In conclusion, ovariectomy for six weeks did not affect the passiv e mechanical Properties or the collagen concentration in rabbit lower urinary tract smooth muscle, but increased the responsiveness of the d etrusor muscle to K+ (124 mM).