Postnatal development of growth hormone and prolactin cells in male and female rat pituitary. An immunocytochemical light and electron microscopic study.

Localization and ultrastructural maturation of prolactin (PRL) and growth hormone (GH) cells were studied in pituitaries from neonatal, immature (4-6 weeks old), and adult rats (2-3 months old) by light and electron microscopic immunocytochemistry. The distribution pattern of these cells did not change with age. Both cell types were concentrated laterodorsally, with PRL cells adjacent to the intermediate lobe and GH cells nearer the center of the pars distalis. Labeling density of the immunogold reaction was highest for both hormones in immature rats. In neonatal and immature rats, one PRL cell type with granules 200 nm in diameter was present. In adult rats, two types of PRL cells were present: one containing polymorphous granules measuring about 500 nm (prevalent in female rats), the other with spherical granules about 200 nm (prevalent in male rats). No changes were detected in GH cells during maturation.