Precocious development of granular convoluted tubules in the mouse submandibular gland induced by thyroxine or by thyroxine and testosterone

The effects of the administration of thyroxine (T₄) and/or testosterone (TP) on the early postnatal differentiation of granular convoluted tubule (GCT) cells of the submandibular glands were studied in Swiss-Webster mice. From birth, mice were injected daily with T₄ up to the time of killing at 15 or 20 days of age. In addition, groups of mice were given one injection of TP eight days before killing. Control animals received vehicles (saline and/or sesame oil). Sections of the glands were stained with toluidine blue, or immunocytochemically by the unlabelled antibody enzyme method, for the localization of protease A, epidermal growth factor, or renin. Supernatants of the gland were analyzed for protease activity (pH 8.5, substrate: tosyl-glyclyl-L-prolyl-L-arginine nitroanilide acetate), or by radioimmunoassay for EGF content. At 15 days of age no GCT cells were present in the glands of control or TP-treated mice. In T₄-injected mice many small GCT cells occurred, while larger and more numerous GCT cells were seen in the glands of mice that received both hormones. TP alone had no effect on levels of EGF or protease activity. In T₄-treated mice, protease levels increased 10-fold and EGF content rose 28-fold. TP administration to T₄-treated mice caused a further threefold, increase in both protease activity and EGF content. At 20 days of age the glands of control mice had a few small GCT cells, and both protease activity and EGF content were substantially increased. TP treatment was again without effect. However, daily injections of T₄ caused both protease activity and EGF levels to increase 20- and 11-fold, respectively. Just as in 15-day-old mice, TP administration to T₄-primed mice resulted in further increases in the two polypeptides. Immunocytochemical staining for protease A and EGF confirmed the chemical data. Renin was detectable immunocytochemically at both ages in the glands of mice that had received T₄, but it was seen in the glands of mice that had received TP alone only at 20 days of age. It is concluded that T₄ caused a precocious induction of GCT cells and their specific products. Although TP alone had no effect on their early differentiation, it acted synergistically with T₄ in inducing GCT cells. There were no obvious sex differences in any of these features in control or treated animals.