The radioprotective effect of indralin in rhesus monkeys was examined over 60 d following gamma irradiation. Male and female rhesus macaques (Macaca mulatta) 2–3-years-old and weighing 2.1–3.5 kg were used. Animals were exposed to total-body gamma irradiation from 60Co at a dose of 6.8 Gy (lethal dose, 100% lethality over 30 days). Indralin (40–120 mg kg–1) was administered intramuscularly 5 min prior to radiation exposure. Indralin taken at a dose of 120 mg kg–1 protected five out of six monkeys (compared with the radiation control group, in which all 10 animals died). The average effective dose of indralin in the monkeys exposed to gamma irradiation for 30 min was equal to 77.3 (63.3–94.3) mg kg–1, and the maximum tolerated dose of indralin administered to monkeys was 800 mg kg–1. Indralin reduced radiation-induced injuries in macaques, thus resulting in a less severe course of acute radiation syndrome. Delayed and less pronounced manifestation of the haemorrhagic syndrome of the disease, and milder forms of both leukopenia and anaemia were also noted. The therapeutic index for indralin, expressed as the ratio of the maximum tolerated dose to the average effective dose, was equal to 10. Therefore, indralin has a significant radioprotective effect against radiation and has a high therapeutic index in rhesus monkeys.

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