Protective Action of Potassium Iodide on Thiourea Poisoning in Rats

Abstract

KENNEDY1, in reporting the goitrogenic action of the thioureas in rats, mentioned that doses of 200 mgm. of thiourea had no toxic action. This accords with the experience of Astwood2. On the other hand, MacKenzie and MacKenzie3 found thiourea to be highly toxic to adult rats. During 1943 thiourea was administered to large numbers of rats in our laboratory with only infrequent deaths. Such deaths as did take place occurred on the first day of thiourea administration, and autopsy disclosed a condition of pulmonary œdema and pleural effusion, as described by MacKenzie and MacKenzie. From the beginning of 1944 we have, however, experienced a heavy mortality in rats receiving thiourea. Up to 66 per cent of rats have died arid the remainder have recovered only after a period of severe respiratory distress. The severity of the symptoms does not seem to be proportional to the dose of thiourea administered, and in susceptible groups of rats the provision of drinking water containing 0·025 per cent of thiourea has resulted in the death of 50 per cent of the animals. Plainly the response of our rats to thiourea administration has undergone an abrupt change. The same change in response was observed in two separate strains of rats, while no variation of composition of diet or environment had been consciously introduced. We are unable to account for this change but our investigations have confirmed the reported immunity3 of young rats, and also of adult rats which have survived the first dose of thiourea.