Neonatal Hyperthyroidism in Mice Has Different Effects on Epidermal Growth Factor Levels in Submandibular Gland, Urine, and Blood

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Abstract
We examined long-term effects of neonatal hyperthryoidism in female mice by measuring the epidermal growth factor levels in the submandibular gland, urine, and serum at the age of 31 days. Hyperthyroxinemia was induced by thyroxine injections (0.4 μg/g/day) on days 0–6. Littermate controls received the alkaline saline vehicle. The treatment accelerated incisor eruption and eyelid opening. It also retarded growth. The elevation of plasma thyroxine concentration which normally occurs during wk 2 to reach a peak around day 15 was abolished. Submandibular gland epidermal growth factor levels on day 31 were markedly subnormal, indicating maturational delay. In contrast, epidermal growth factor levels were unaffected in urine and supranormal in serum. These differences in response suggest that the regulatory mechanisms governing epidermal growth factor levels in tissues and fluids may acquire thyroid hormone dependence at different stages.