FOLLICULO-STELLATE CELLS AND INTERCELLULAR COMMUNICATION WITHIN THE RAT ANTERIOR-PITUITARY GLAND

Folliculo-stellate (FS) cell are agranular and arranged around a folli cle. They contain the S-100 protein and beta-adrenergic receptors. It has been suggested that they can act as stem cells, since they show mi totic figures, and could transform into granular or chromophilic cells according to the concept of a ''cell renewal system.'' Cell-to-cell i nteractions among pituitary cells have been described, and recent prog ress with freeze-fracture electron microscopy has provided novel obser vations of the cell surface and gap junctions within the rat or teleos t fish pituitary gland, or in cultured rat pituitary cells. In adult r ats, the anterior pituitary was composed of lobules incompletely separ ated by a basement membrane. Follicles consisted exclusively of FS cel ls. Gap junctions were observed only between adjacent FS cells, in rar e cases on the tips of their cytoplasmic processes. Thus, the FS cells , connected by gap junctions, made up a dense cellular network through out the pituitary. Gap and tight junctions were absent on granular cel ls. Elongated follicles with columnar FS cells were observed in 10-day -old rats and were separated into smaller units. The number of gap jun ctions rapidly increased with age until 40-45 days of age. Few S-100 p rotein positive cells were observed on day 10, along the marginal cell layer and near the so-called postero-lateral wing. The frequency of p ositive cells increased with age and by day 40; numerous cells were ob served throughout the anterior lobe. Gap junction number also varied w ith the stage of the estrous cycle, and frequency; during diestrus, th ey were half of that during proestrus or estrus. The number of gap jun ctions increased in late pregnancy and in lactating rats, probably due to changes in estrogen and progesterone. Hormone (LH-RH and testoster one) treated groups of rats showed accelerated development by almost 1 0 days, compared with controls. In castrated male rats, the ultrastruc ture of the pituitary remained immature even at 40 days of age, when t he number of gap junctions was a quarter or less than the number in in tact rats. Testosterone treatment restored the frequency of gap juncti ons to a normal level. We conclude that the appearance of gap junction s in the pituitary cells and maturation of the gland are dependent to a large degree upon gonadal steroids. (C) 1997 Wiley-Liss, Inc.