Sexual dimorphism of pituitary gonadotropes during postnatal development in the rat

In the present study both the reverse hemolytic plaque assay for detecting luteinizing hormone (LH) secretion from single cells and LH immunocytochemistry (ICC) were applied to conduct quantitative studies on sexual differences in the gonadotrope population during postnatal development. Pituitary glands from both sexes at different ages were monodispersed with 0.1% trypsin. Freshly dispersed cells were incubated in Cunningham chambers in the presence of 10(-7) M gonadotropin-releasing hormone (GnRH) for measurement of the fraction of plaque-forming cells and the mean size of plaque formed, or attached to glass slides for measurement of the fraction of cells staining for LH by ICC. The percentage of immunostained LH cells increased with age in both sexes from about 5% of the total pituitary cell population at 5 days of age to a plateau of about 10% by 15 days and then fell to the adult level of about 5%. There were no significant sexual differences except at 30 and 40 days of age. In female rats the fraction of LH-secreting cells detected by plaque assay matched closely with that of LH-containing cells detected by ICC. However, there were significant sexual differences in the percentage of LH-secreting cells at day 15 through day 40. The mean LH output from individual cells of both sexes as indicated by the mean size of plaques also increased with age and reached a peak around 50 days. The sexual differences were first seen around 30 days of age with greater amounts in the female than in the male.(ABSTRACT TRUNCATED AT 250 WORDS)