Comparison of long-term and short-term stretch on rat urinary bladder in vitro.

Distension of the human urinary bladder often causes prolonged impairment of its function. To investigate the effects of the duration of stretch on bladder smooth muscle the active length-tension relation, electrically evoked, was described in rat detrusor strips during a short-term and a long-term stretch. The amplitude of active tension increased at first and then decreased abruptly at greater stretch lengths, the maximum being at muscle lengths 230-250% (100% = resting length) in both types of stretches. When the strips had been at maximum length (300%) for three hours the amplitude was significantly decreased during release as compared to the amplitude found during stretch to the maximum length at comparable lengths. If the strips were released immediately from the maximum length the amplitude responded in an opposite manner. Therefore we conclude that the duration of stretching of bladder smooth muscle significantly affects its mechanical activity.