MODIFICATION OF THE FRACTIONATED GAMMA-RADIATION-INDUCED ALTERATION IN THE NA+ K+-ATPASE ACTIVITY OF RADIOSENSITIVE TISSUES BY VITAMIN-A/

The effect of pre or post-administration of vitamin A in ameliorating the radiation-induced alteration in intestinal and spleen Na+/K+-ATPas e activity of rats was determined. Rats subjected to multifractionated gamma-radiation (20 x 0.5 Gy) over the whole-body showed a significan t reduction in Na+/K+-ATPase activity being more obvious in spleen tha n in intestine. Administration of vitamin A at a daily i.p. dose of 15 ,000 IU/kg bd. wt. for 7 days prior to fractionated gamma-irradiation and thereafter twice weekly throughout the exposure period (as pretrea tment regimen) or following the end of irradiation for 7 days (as post treatment regimen) afforded a significant protection from radiation-in duced inhibition of spleen and intestinal Na+/K+-ATPase activity. Even though, pretreatment regimen is more efficient against radiation inju ry to this enzyme than posttreatment, so that its activity was nearly normalized in the first regimen. The regeneration of normal enzyme act ivity in the tissues of the vitamin A-pretreated group suggests that t he intestinal and spleen epithelia in presence of vitamin A are render ed relatively radioresistant.