Three types of growth hormone cells of the rat anterior pituitary as revealed by immunoelectron microscopy using a colloidal gold-antibody method.

Immunoelectron microscopy using a colloidal gold-antibody method with anti-rat GH serum demonstrated three morphologically different types of GH cells in the rat anterior pituitary. They were distinguished as Types I, II and III GH cells, containing only large secretory granules about 350 nm in diameter, mixed large and small granules, and only small granules about 150 nm in diameter, respectively. Double gold labeling with large gold particles for GH and small particles for PRL or ACTH indicated that neither GH and PRL nor GH and ACTH were contained in the same cell. In adult male rats, Type I cells (68%) predominated over Type II (22%), while Type III cells were rare (9.7%). On the contrary, in the adult female rats, Type II cells (47%) slightly dominated over Type I (44%) though the rate of Type III cells was the same as in the male. In neonatal infants, the frequency of occurrence of Type III cells was as high as about 20%; sex differences between Types I and II were indistinct. The Type III cells were therefore thought to represent an immature type.