The effect of Captopril on benign and malignant reactions in irradiated rat skin.

The effect of the angiotensin converting enzyme inhibitor Captopril on the severity of radiation-induced epilation and moist desquamation and the incidence of skin tumours was determined for up to 52 weeks in male rats. The irradiation consisted of a range of single doses (0, 10, 20, 30 Gy) of 60Co gamma rays to a 3.5 cm2 right hemithorax port. Half of each radiation dose group consumed control powdered chow, and half consumed chow containing Captopril (50 mg/kg/day) continuously after irradiation. There were time- and radiation-dose-dependent increases in all three skin reactions. Rats exposed to 10 Gy exhibited a mild and transient epilation, but no moist desquamation or neoplasia in the radiation port. In animals exposed to 30 Gy, however, epilation began at 2 weeks after irradiation, reached a peak at approximately 7 weeks, then persisted essentially unchanged through 52 weeks. Captopril had no significant effect on the epilation reaction. Two waves of moist desquamation were observed after 30 Gy. The first appeared at 3 weeks after irradiation, reached a peak from 6-10 weeks, then subsided partially but significantly from 12-26 weeks. The second wave of moist desquamation began at 26-28 weeks, often was ulcerative, and occasionally was accompanied by the appearance of tumours in the irradiated volume. Captopril significantly (p less than 0.05) reduced the severity of both phases of the moist desquamation reaction after 30 Gy, and reduced the percentage of animals exhibiting the most severe desquamation score (involving 50% of the radiation port). Of particular interest was the observation that Captopril also reduced the incidence of tumours. Of the 14 tumours detected, all were malignant (fibrosarcomas, squamous cell carcinomas), and only three (p less than 0.05) occurred in rats receiving Captopril. Multiple tumours (three cases), tumours induced by 20 Gy (three cases), and tumours appearing before 6 months (one case) were observed only in rats consuming control diet, never in Captopril-treated animals. Animals which developed tumours in the second 6 months post-irradiation exhibited significantly more severe moist desquamation during the first 6 months than did the tumour-free members of their treatment group. Thus Captopril, known to ameliorate acute lung damage in irradiated rats, also reduces chronic benign and malignant skin reactions in the radiation treatment field.