Age-related alterations in prolactin secretion by individual cells as assessed by the reverse hemolytic plaque assay

The objectives of this study were to determine: 1) if lactotropes from old rats, compared to those from young rats, secrete a greater amount of prolactin (PRL) per cell, 2) if the percentage of pituitary cells secreting PRL changes with age; and 3) how estradiol (E2), dopamine (DA), or thyrotropin-releasing hormone (TRH), or the combination of these factors influences both of these parameters in old rats. To meet these objectives we used the reverse hemolytic plaque assay (RHPA), because this method allows us to determine both the percentage of pituitary cells secreting prolactin during the experimental period and the amount of hormone released by each secreting pituitary cell. These parameters were measured in young (2-3 mo old) or old (17-19 mo old) female Sprague-Dawley rats. Animals were ovariectomized (OVX) for 10 days or OVX for 1 wk and then treated with E2 for 3 days. Rats were killed, anterior pituitaries were removed, and cells were enzymatically dispersed and prepared for use in the RHPA. Pituitary cells were treated in vitro with vehicle, DA, or PRL, old OVX and E2-treated rats exhibited a greater percentage of secretory cells than young at both 1 and 2 h of incubation. Administration of E2 increased the percentage of cells secreting PRL in both young and old rats. DA reduced the percentage of cells secreting PRL at the highest dose tested (10(-5) M) regardless of age or E2 status following incubation for 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)