Effect of thyroid hormones on epidermal growth factor concentration in neonatal mouse skin

T4 and epidermal growth factor (EGF), given exogenously, both promote similar maturational events in the skin of newborn mice, i.e. precocious incisor eruption and eyelid opening. Moreover, T4 markedly increases the concentration of EGF in developing mouse submandibular glands. To examine the effect(s) of thyroid hormones on local cutaneous levels of EGF, a rapid and sensitive double antibody RIA was developed and standardized for newborn mouse skin. After fixed daily injections of T4, immunoreactive EGF concentrations in whole skin homogenates showed a dose-dependent increase when measured on postnatal days 4, 6, and 17. A similar increase was seen after T3 treatment, but administration of the structurally similar, metabolically inactive analog rT3 produced no significant effect on EGF concentrations. Induction of experimental hypothyroidism with propylthiouracil (PTU) and methimazole produced a relative decrease in skin EGF levels on postnatal day 8. Maternal sialoadenectomy did not result in a significant decrease in neonatal skin EGF, suggesting the presence of an extrasalivary source(s). These studies suggest that the epidermal maturation that follows thyroid hormone administration is mediated by local tissue levels of EGF. Moreover, the results admit of a possible physiological relation between thyroid hormones and EGF during postnatal cutaneous development.