Dehydroepiandrosterone-induced thyrotrophin release during heat stress in rats

Six groups each of 12 male albino rats were reared from day 21 of life at temperatures of 23, 34 or 37 degrees C. While the rats survived for unlimited periods at 23 and 34 degrees C, the animals reared at 37 degrees C succumbed within 5 days to heat stress. The latter group, when injected s.c. or i.p. with 50 mg dehydroepiandrosterone (DHA)/kg/day were no longer affected by the heat. During this treatment thyroid epithelial cell height doubled, colloid decreased by 20%, connective tissue did not change, the basic metabolic rate decreased by 10% and rectal temperatures of the treated rats increased with the ambient temperatures. Body weight increased only slightly, pituitary TSH decreased by 25%, serum TSH increased by over 50%, thyroxine and 125I uptake increased by 200%. The survival of the DHA-treated rats was apparently secured by blocking the hypothalamic thermoreceptors.