Effect of X-radiation on the Absorption of Naturally-occurring Folates

Abstract

Folate absorption was studied in vivo and in vitro in rats before and after 700 R whole-body x-irradiation. Absorption in vivo of conjugated folates was completely impaired in irradiated rats, as judged by the absence of the expected rise in blood folate levels after folate ingestion. While the folyl conjugase activity, which converts the dietary conjugated folates to a level suitable for absorption, was not adversely affected by irradiation, there was an increased accumulation of simple folates in intestinal tissue and the luminal washings, suggesting a defect in the folate-absorption mechanism. It is suggested that folate transport across the everted intestinal segments is an active process, inhibited at higher folate concentrations and sensitive to 2,4-dinitrophenol. It was reduced by about 43 per cent in the irradiated rat. Addition of ATP to the incubation medium restored the overall folate transport in vitro, suggesting that irradiation had adversely affected the metabolic pathway, providing ATP required directly or indirectly for folate transport. Significant decrease in the oxygen-uptake and especially the coupled phosphorylation were observed in the small intestine after 700 R whole-body irradiation, possibly explaining the restoration of folate transport observed in vitro on addition of ATP.