Background
Administration of the acute-phase protein alpha2-macroglobulin (MG) prior to total-body irradiation of rats with a 6.7 Gy (LD50) dose of X-rays exerts a radioprotective effect.
Material and Method
MG was administered 30 min before irradiation with a 6.7 Gy (LD50) dose of X-rays. Its radioprotective efficacy was compared with that of the synthetic agent amifostine (WR-2721), a sulfhydryl compound which is currently the most effective radioprotector in clinical use. After administration of either MG or amifostine, changes in body and liver weight were recorded and histological liver sections were examined during a four-week follow-up period.
Results
As observed in the experimental group administered amifostine, rats that received MG prior to irradiation exhibited 100% survival and restoration of the body and liver weight to the control values. The morphological damage seen in the liver after irradiation of untreated rats was absent in both the MG- and amifostine-pretreated rats. Also, hepatocytes and granulated cells had prominent nuclei and did not exhibit major changes in volume. Dilation of the central vein was not observed.
Conclusions
Administration of MG before irradiation, similar to pretreatment with amifostine, provided complete survival of experimental rats and recovery of liver weight and preserved major histological parameters of the liver.

Keywords: alpha-Macroglobulins - pharmacology, Radiation-Protective Agents - pharmacology, Organ Size - drug effects, Liver - pathology, Body Weight - drug effects, Amifostine - pharmacology