Characteristics of prolactin secretion in normal and estrogen-treated pituitaries of rats at the single cell level: analysis by reverse hemolytic plaque assay.

We studied PRL release from individual pituitary cells in normal and estrogen (E2)-treated female Fischer 344 rats by means of a reverse hemolytic plaque assay. In this assay, the area of the hemolytic plaque around a pituitary cell is proportional to the amount of hormone secreted from the cell. Multimodal distribution of the plaque area was observed in normal pituitary cells, and was unchanged in the course of aging. In E2-treated pituitary cells, bimodal distribution was found. The heterogeneity of the distribution pattern (functional heterogeneity) and PRL secretion from a single pituitary cell decreased in association with the length of E2 treatment. The mean plaque area for the E2-treated pituitary cells was smaller than that for the normal pituitary cells. These results suggest that in E2-treated pituitary cells, the functional heterogeneity and PRL release from a single cell decrease as tumorigenesis progresses.