Acquisition of submandibular gland nerve growth factor (SMG-NGF) responsiveness to thyroxine administration in neonatal mice

The growth of the submandibular gland (SMG) was studied in newborn mice from birth to 15 days of age. Progressive changes in wet weight were observed to accompany changes in biochemical constituents such as RNA, protein, and lipid. Thyroxine (T4) administration from days 0–6 produced changes in SMG growth and SMG accumulation of RNA, protein, and lipid components relative to control pups treated with a similar volume of vehicle. This hormone regimen produced no measurable changes in SMG nerve growth factor (SMG‐NGF) concentration. T4 responsiveness also was studied from days 0–15. Three patterns of T4 injection (from days 0–6, 7–14, and 0–14) were found to elicit a differential response in the three biochemical constituents measured, but treatment from days 7–14 and 0–14 elicited precocious increments in SMG‐NGF concentrations on day 15. The effect of T4 injection from birth was more effective in augmenting SMG‐NGF concentration than hormone treatment initiated from days 7–14. A persistent T4 effect on SMG‐NGF also was observed on day 21 following hormone treatment from days 7–14 or 0–14. In summary, the acquisition of SMG‐NGF responsiveness to T4 appears to develop during the neonatal period. The administration of T4 during this period also precociously stimulates the mechanisms that govern the normal ontogeny of SMG‐NGF at the time of weaning.