Pars tuberalis specific cells within the pars distalis of the adenohypophysis. An ontogenetic study

Several types of secretory cells of the pars distalis (pd), especially gonadotrophs, are known to occur in the distal pars tuberalis (pt) of the rat. The distribution of the pt-specific cells, however, within the pd has not been investigated in detail and is the subject of this study. Pt and pd of the rat adenohypophysis were investigated at different stages of the peri- and postnatal development by light and electron microscopy using conventional and immunohistochemical staining. The distribution of pt-specific cells changes from a continuous strand of cells extending on the ventral surface to the centre of the pd perinatally to single clusters in the vicinity of the big portal vessels in adult rats. The secretory activity of pt-specific cells within the pd also varies with age. It is highest perinatally, declines in the young rat, and increases again in the adult animal. Functional implications of our observations are discussed especially in relation to the distribution of melatonin-binding pituitary cells.