Single lactotroph responses to dopamine, angiotensin II, and culture duration

Prolactin cells were isolated from male rat pituitaries and studied individually with the reverse hemolytic plaque assay. Plaque area, linearly correlated with radioimmunoassayable prolactin in the culture medium, and percent lactotrophs were measured. A 20-h incubation period markedly enhanced the potency and efficacy of dopamine to inhibit prolactin release compared with an assay conducted on the day of enzymatic dispersion. Frequency histograms of plaque areas showed unimodal distributions after angiotensin II (ANG II)-stimulated prolactin release, with the mode shifting to the right. In contrast, the addition of dopamine to either basal or ANG II-stimulated lactotrophs shifted the mode to the left and decreased the overall range of plaque areas. No clear evidence for discrete subpopulations was generated with this approach; rather, an extensive range of secretory behavior was defined as a continuum, indicating a diverse repertoire of secretory potential in different lactotrophs. Furthermore, comparing lactotrophs from the lateral wings with the central region of the pituitary suggested that lateral cells were less inhibited by dopamine treatment. We conclude that this improved assay allows more precise assessment of the contribution that single lactotrophs make to the population response to dopamine and ANG II.