Thyroid hormone regulation of granular intercalated duct cells in the submandibular glands of female mice.

Intercalated ducts (IDs) in the submandibular glands (SMGs) of mice exhibit a sexual dimorphism, in which a few cells in the IDs of females, but not of males, possess secretory granules. The effects of a hypophysectomy (Hypox) followed by the administration of triiodo- l-thyronine (T3) on such granular intercalated duct (GID) cells in the female gland were histologically examined. Semithin sections stained with Heidenhain's iron hematoxylin revealed that Hypox resulted in the complete disappearance of the GID cells. In Hypox females, electron-microscopy examination of the ID cells whose localization corresponded to that of the GID cells in normal females showed that these cells had a pale, centric nucleus, poorly developed rough-surfaced endoplasmic reticulum (RER) and Golgi apparatus, and no secretory granules. When T3 (1 mg/kg body weight) was given to Hypox female mice every other day for 2 weeks, the GID cells reappeared in most of the ID segments. Electron microscopy revealed that these cells had abundant secretory granules in their apical cytoplasm, a nucleus located near the base of the cell, and layered cisterna of RER and segments of Golgi apparatus in the perinuclear cytoplasm. The localization and distribution of the GID cells in the T3-treated Hypox females were almost the same as those in normal females. Taken together, these results suggest that thyroid hormones upregulate the GID phenotype, and that thyroid hormones are essential for the exocrine activities of GID cells.