Nonhepatic thioacetamide injury. I. Thymic cortical necrosis.

Normal and adrenalectomized rats were given a single oral dose of thioacetamide (5, 10 or 20 mg/100 g body weight). The size, weight and histology of the thymus were observed for 3 weeks following intoxication. An initial rapid loss of thymic weight and size occurred during the first 3 days of intoxication; there was no significant recovery. This loss was associated with decreased cortical mass without significant change in medullary size or histology. The decrease of the cortex was associated with significant cortical cell death and the formation of a "starry sky" pattern. This response occurred in both adrenalectomized and nonadrenalectomized rats, suggesting that this phenomenon is not the adrenal-mediated stress response. Measurement of circulating mononuclear cells indicated that thymocyte release did not play a significant role in depletion changes. The basis for this prompt, at least temporarily irreversible, chemically induced thymic atrophy is not apparent.