Effects of outlet obstruction and its reversal on mitochondrial enzyme activity in rabbit urinary bladders

This study investigated the effects of outlet obstruction and its reversal on mitochondrial enzyme activity in the rabbit urinary bladder.

We induced mild bladder outlet obstruction in male New Zealand White rabbits. Following two weeks of obstruction, one group of animals (n = 6) was sacrificed, while outlet obstruction was relieved in three additional groups of animals, which were sacrificed one (n = 5), two (n = 5) and four (n = 5) weeks after relieving the obstruction. Seven sham operated rabbits served as controls. We extracted mitochondria from fresh detrusor and assayed activities of key mitochondrial enzymes in the citric acid cycle, citrate synthase and malate dehydrogenase, as well as those in the electron transport chain, succinate cytochrome c reductase, NADH-cytochrome c reductase and cytochrome c oxidase. With high performance liquid chromatography (HPLC) we determined the tissue content of phosphocreatine and the adenine nucleotides (ATP, ADP and AMP), which was used for calculating energy charge. Responses of detrusor strips to 500 microM bethanechol and 120 mM KCl provided the assessment of detrusor contractility.

Contractile response of the detrusor strips to bethanechol stimulation was significantly reduced by outlet obstruction, nevertheless, it recovered gradually toward the control level after the relief of outlet obstruction. Outlet obstruction reduced the detrusor content of phosphocreatine, ATP and energy charge. After relieving the obstruction, however, these recovered gradually, reaching control levels 4 weeks later. The activities of all assayed enzymes were reduced by two weeks of outlet obstruction. Relieving the obstruction restored enzyme activity gradually but at different rates for different enzymes. Activities of the citric acid cycle enzymes citrate synthase and malate dehydrogenase recovered and were similar to control levels four weeks after relief of the obstruction. Of the enzymes in the electron transport chain, NADH cytochrome reductase activity recovered most quickly by one week after relief of the obstruction. The activity of cytochrome c oxidase improved more slowly, but 4 weeks after relieving the obstruction it, also, was restored and was similar to the control level. Succinate cytochrome reductase activity remained lower than the control over the entire four weeks of recovery.

The close association between mitochondrial enzyme activity, energy metabolism and contractility of the detrusor indicates the important role of mitochondrial enzyme damage in decreasing energy production and impairing contractile function of the urinary bladders following outlet obstruction. Our findings also show that various mitochondrial enzymes exhibit different susceptibilities and reversibilities to pathological stress.