Flow cytometric analysis of functional anterior pituitary cells from female rats

Laser-light scatter signals generated from living cells provide useful information with regard to both cell size (forward-angle light scatter) and granularity (ninety-degree or perpendicular light scatter). By measuring angles of light scatter and fluorescence, a fluorescence-activated cell sorter is capable of analysing and sorting cells on the basis of their size, granularity and cell-surface fluorescence. Using an electronically programmable individual cell sorter we were able to analyse single, viable, dispersed anterior pituitary cells of the female rat on the basis of their laser light scatter characteristics. Two distinct populations of differing granularity were defined: 26 +/- 2.2% (mean +/- S.E.M.) were more granular and 74 +/- 3.5% less granular. Acutely dispersed anterior pituitary cells were labelled with antibodies against four of the anterior pituitary hormones, and cell size and granularity were compared amongst the different hormonal cell types. Somatotrophs were the most granular cell type, gonadotrophs were the largest and corticotrophs the smallest, whilst lactotrophs were of intermediate size. Labelling was demonstrated to be dependent upon the secretory state of the cell. Hypothalamic stimulating factors increased cell-surface labelling, whilst dopamine and somatostatin decreased labelling. These changes compare favourably with published data obtained by immunocytochemistry. Using dual-colour fluorescence cell surface labelling we were unable to define a population of cells secreting both prolactin and growth hormone (mammosomatotrophs).