Restoration by Iodide of Hepatic Reactions to 2-Aminofluorene in Thyroidectomized Rats

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Abstract
Male rats were surgically thyroidectomized at 4 weeks of age, and after an interval of 4 weeks they were treated with 2- aminofluorene (AF) given percutaneously and iodide (as KI) given in the drinking water. The duration of the combined treatment was 30 weeks. For the first 20 weeks the dose of iodide taken was 3.8 mg 1/100 g/day, and it was then raised to 6.1 mg/100 g/day. There was a striking stimulation of growth, which ceased after 20 weeks and was not restored by the higher dose of iodide. The testes and seminal vesicles showed signs of partial repair, but there was no restoration of the hypoplastic adrenals. Invasive hepatocellular carcinomas developed in 12 out of 16 rats with a latency comparable to that in intact controls. The dosage of AF used induced liver tumors in all the intact, but in none of the thyroidectomized, control rats. Extrahepatic tumors occurred with similar frequencies in all 3 groups. The specific restoration of hepatic susceptibility to AF-carcinogenesis in the iodide-treated rats is discussed, and it is suggested that it may be attributable to increased amounts of circulating growth hormone in such animals. (Endocrinology76: 1027, 1965)