Strain-specific and endocrine control of granular convoluted tubule cells and epidermal growth factor expression in the mouse submandibular gland.

Submandibular glands (SMGs) of 11-week-old mice from four strains, ICR, C57BL/6J, BALB/c, and C3H/HeN were examined by immunohistochemistry for epidermal growth factor (EGF). In addition to sex-related differences in granular convoluted tubules (GCTs), the GCT cells were significantly larger in ICR mice than in other three strains. In males from each of the strains, almost all the GCT cells were strongly positive for EGF. The EGF-positive cells in the females, however, were markedly fewer in number, and were stained weaker in C57BL/6J, BALB/c, and C3H/HeN mice than in ICR mice. The GCT cells and their EGF expression in the F1 progeny from ICR and C3H/HeN strains were approximately intermediate between those of the parent strains of the same sex. T(3) and/or dihydrotestosterone (DHT) enhanced the GCT phenotype in the C3H/HeN mice, and remarkably increased the EGF-positive cells in females. Electron microscopy revealed that gold-labeling of EGF was confined to the secretory granules, and that the GCT cells in females, given T(3) + DHT, had a well-developed Golgi apparatus and net-like RER but few basal infoldings, whereas the equivalent cells in the untreated females had poor RER and prominent basal infoldings. These results suggest that the EGF concentration in SMGs is genetically high in ICR mice and low in other strain mice and that, considering the same response of GCT cells to T(3) and/or DHT between the high and low EGF strains, the low EGF concentrations might be partly caused by a lesser sensitivity of the GCT cells to thyroid hormones.