Acquisition of urine, kidney and submandibular gland epidermal growth factor responsiveness to thyroxine administration in neonatal mice

Thyroxine (T4) administration to newborn mice on days 0-6 produced no measurable changes of submandibular gland (SMG) or kidney epidermal growth factor (EGF) concentrations on day 7, compared with vehicle-treated control pups. By contrast, this regimen caused a large increase in urine EGF levels. The effects of three T4 injection regimens (on days 0-6, 7-14 and 0-14) were then studied on day 15. The 0-14 and 7-14 day-regimens elicited large increments in urine, SMG and kidney EGF concentration, the 0-14 day-regimen having the greatest effect. The 0-6 day-regimen had no effect on SMG and kidney EGF concentrations on day 15 but did increase urine EGF. In summary, urine EGF responsiveness to T4 is present during the first week of life, but SMG and kidney EGF responsiveness develops only in the second week. Administration of T4 appears to accelerate the normal ontogeny of urine, kidney and SMG EGF.