Influence of Radioprotectors on Regeneration of the Mucosa of the Small Intestine of the Mouse after X-Irradiation

Intestinal death occurs in mice from the third to the fifth day after doses of 1 to 10 krad and is preceded by inhibition of cell division, destruction of the crypts, shortening of the villi and denudation of the intestinal epithelium, BALB/c mice, some of which were protected with 2-β-aminoethylisothiourea (AET) or with one of the following mixtures of chemical protectors: AET+ 5-hydroxytryptamine (5-HT), AET + 5-HT + glutathione (GSH), and AET + 5- HT + GSH + cysteine, were irradiated with doses of 1350 or 2000 R of X-rays (300 kV, 20 m A , dose rate 100 R/min). Mitotic activity, abnormal anaphases, size of nuclei, pyknosis and number of nuclei, migration of nuclei along the villi and incorporation of thymidine were investigated. In all experiments, lesions appeared later and were less pronounced in the protected than in the non-protected mice. Furthermore, AET and the associations of radioprotectors appear to protect the crypt cells of the small intestine during all phases of the mitotic cycle. The best results were obtained with a mixture of AET + 5-HT + GSH + cysteine. After such treatment and a dose of 2000 R of X-rays, a delay of 30 days is nevertheless needed to allow complete recovery of the duodenal mucosa. The diminution of incorporation of thymidine and the prolongation of the regeneration time are symptoms of a 'biochemical shock', and the importance of this in the mechanism of action of sulphydryl compounds and of mixtures of protective drugs is discussed. (author)