Immunoelectron microscopic study of the GH cell in the anterior pituitary gland of normal human fetus.

Abstract

Ultrastructural studies of growth hormone-producing cells (GH cells) in the anterior pituitary gland have been reported using several experimental animals. However, no attempt has yet been made to identify the ultrastructural heterogeneity of the GH cells within the human anterior pituitary gland. To this end, we employed immunogold electron microscopy to investigate the ultrastructural characteristics of GH cells in relation to gestational age in normal human fetuses. Based on ultrastructural characteristics, three distinct types of GH cells were identified by immunogold electron microscopy in the anterior pituitary glands of 34 normal human fetal pituitary glands. The age of the tissue samples ranged from 8 to 34 weeks. The Type-I GH cell is a small, round cell with a narrow cytoplasm containing a few small secretory granules (268 nm in mean diameter). The GH cells designated Type-II are polygonal and contain medium-sized secretory granules (347 nm), profiles of rough endoplasmic reticulum (RER) arranged in parallel lamellae, and a Golgi complex which is frequently encountered but only in this cell type. The Type-III GH cell is polygonal, large, and contains numerous large spherical-shaped secretory granules (404 nm). The Type-I was the predominant cell type until about 20 weeks of gestation; its incidence decreased thereafter. In contrast, the Type-II and Type-III cells increased in number starting at 20 weeks of gestational age. From these results, we suggest that Type-I is the most immature type of GH cell, Type-III the most mature, and the Type-II is intermediate in development. The marked difference in the incidence of each GH cell type between the first and second half of gestation appears to be a reflection of the development of the hypothalamic regulation of the anterior pituitary gland, which is reported to be established at around 20 weeks of gestation.