Effect of partial obstruction of the rabbit urinary bladder on malate dehydrogenase and citrate synthase activity.

Previous studies have demonstrated that partial outlet obstruction in rabbits induced a significant decrease in oxidative metabolism in urinary bladder smooth muscle. The current experiments were designed to determine whether the decreased oxidative metabolism of obstructed bladder tissue is associated with alterations in the activities of specific mitochondrial enzymes. The activities of two important enzymes in the tricarboxylic acid cycle, malate dehydrogenase and citrate synthase, were measured in samples of bladder body and base from normal bladders and in bladders from rabbits in which partial outlet obstruction had been produced seven days prior to the experiments. The results can be summarized as follows: malate dehydrogenase activity was similar in bladder body and base isolated from control rabbits; and decreased by approximately 40% in both segments of the bladder isolated from obstructed rabbits. In contrast to malate dehydrogenase, citrate synthase activity was significantly higher in the bladder body than in the base of normal rabbits. Outlet obstruction caused about a 50% decrease in activity of this enzyme in the bladder body, but had no significant effect on citrate synthase activity of the bladder base. These findings demonstrate that the deficiency in bladder function following partial outlet obstruction is associated with a marked decrease in the activities of two essential enzymes in oxidative metabolism: malate dehydrogenase and citrate synthase. This decrease in enzyme activity is consistent with the previously observed decrease in oxidative metabolism and would be expected to lead to an inability of the tissue to supply sufficient metabolic energy for proper contractile function.