Immunocytochemical analysis of prolactin cells in the adult rat adenohypophysis: distribution and quantitation relative to sex and strain.

Prolactin immunocytochemistry was conducted 1) in serial sections of whole fixed pituitaries, for cell distribution analysis; and 2) on preparations of enzymatically dispersed anterior pituitary cells maintained for 1-4 days in vitro, for quantitation of the relative population of prolactin (PRL) cells. Both types of analysis were conducted on glands from young adult rats of both sexes in Long-Evans, Sprague-Dawley, and Fischer 344 strains. Cell quantitation results were compared with serum levels, intracellular content, and in vitro release of prolactin, for individual cell preparations. The results show that both PRL cell distribution and relative population numbers are similar between sexes in all three rat strains. Average percentages ranged from 25.9% to 32.1% in all young males and diestrous females. Prolactin-positive numbers of cells correlated positively with intracellular hormone content but not with serum or medium PRL levels. The prolactin cell population was significantly larger in aged Fischer 344 males but was not correlated with intracellular PRL levels. The prolactin cell population was heterogeneous in staining intensity and distribution in both sexes of all three strains.