Prolactin and luteinizing hormone cells of pregnant and lactating rats as studied by immunohistochemistry and radioimmunoassay.

Abstract

AbstractThe objective was to describe the cytological changes that occur in prolactin and luteinizing hormone (LH) cells of the rat hypophysis during pregnancy and lactation and to correlate these changes with secretory activity of the two cell types. The cells were demonstrated with immunohistochemistry and secretory activity was indicated by pituitary and serum hormone concentrations as measured by radioimmunoassay.During pregnancy, two forms of prolactin cells were observed in the pars distalis. One form (prolactin cell I) was small, polyhedral, and constituted most of the prolactin cell population. A second form (prolactin cell II) was found occasionally in pituitary glands of nonpregnant rats and became prominent during pregnancy. It was polyhedral, many times larger than prolactin cell I, and had a restricted distribution in the pars distalis. During gestation prolactin cells I exhibited little change in size, number and staining capacity. Similarly, pituitary and serum prolactin concentrations indicated that the hypophysis releases little prolactin during pregnancy, except for the first few days after conception and before parturition. During lactation, the staining intensity of prolactin cells I and the pituitary prolactin concentration varied little. Prolactin cells II were lightly stained and rare throughout lactation.The staining capacity of luteinizing hormone (LH‐) cells increased as pregnancy progressed in parallel with a rising pituitary concentration of LH during the first half of pregnancy. However, the immunohistochemical procedure appeared to be too insensitive to reflect the gradual fall in pituitary LH concentration during late pregnancy. During early lactation, the reduced staining capacity of LH‐cells was correlated with a low pituitary concentration.