The effect of S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721) was tested in the intestine for its ability to protect against fission neutron irradiation. The parameters tested were lethality, intestinal crypt survival, and DNA synthesizing cellularity. The results showed a dose modification factor (DMF) of 1.6 for lethality in mice treated with WR-2721 prior to fission neutron irradiation. This resulted in the shifting of the dose-mortality probit curve to the right by 149 rad. The crypt survival curve in protected mice was found to have a slope which was significantly different from unprotected controls. The DMF calculated at 50% crypt survival was found to be 1.3. The dose-dependent DNA synthesizing cellularity in the intestine 3 days after irradiation was tested in protected and unprotected animals. WR-2721 was shown to protect the intestine from about 120-140 rad of fission neutrons. This resulted in a DMF between 1.4 and 1.5.

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