The effect of vitamin E on the response of rabbit bladder smooth muscle to hydrogen peroxide

Abstract

There is increasing evidence that ischemia, reperfusion, and the generation of free radicals are major etiological factors in the progression of bladder dysfunction after partial outlet obstruction. In vitro studies demonstrated that the magnitude of contractile dysfunction following exposure of bladder smooth muscle to hypoxia followed by re-oxygenation was related to the level of lipid peroxidation indicating that membrane lipid peroxidation participated in the contractile failure induced. Recent studies demonstrated that incubation of isolated strips of bladder smooth muscle with hydrogen peroxide (H₂O₂) result in progressive contractile dysfunctions and is associated with progressive increases in MDA (peroxidation product). The current study investigates if feeding rabbits a diet high in vitamin E protects the bladder from the effects of in vitro H₂O₂. Sixty-four male New Zealand White rabbits were separated into two groups: The rabbits in group 1 were fed a normal diet (28 rabbits) whereas the rabbits in group 2 were placed on a diet enriched with α-tocopherol (36 rabbits). After 3 weeks on the normal or high E diet, each rabbit was anesthetized and the bladder excised and cut into 6 isolated strips of bladder detrusor. Each strip was mounted in individual 15 ml baths containing oxygenated Tyrode's solution. The contractile responses to field stimulation (FS), carbachol, and KCl were determined. The strips were washed and exposed to one of the following concentrations of hydrogen peroxide (H₂O₂): 0% (control), 0.0625, 0.125, 0.25, 0.5, 1.0 and 3.0% for a period of 1 h. At the end of the hour each strip was washed free of H₂O₂ and a second set of contractile responses were performed and compared to the first set. At the end of the experiment, each strip was frozen and stored at –70°C for analysis of malondialdehyde (MDA) as a measure of peroxidation. In both groups, H₂O₂ produced similar dose dependent decreases in the contractile responses to all forms of stimulation. In the normal-diet group H₂O₂ produced a dose dependent increase in MDA formation, whereas in the high E group there were no increases in MDA at any concentration of H₂O₂. Feeding rabbits a diet high in vitamin E protected the bladder smooth muscle from peroxidation, but had no significant effect on the contractile dysfunctions mediated by direct incubation with H₂O₂.