Enumeration of Lactotropes and Somatotropes among Male and Female Pituitary Cells in Culture: Evidence in Favor of a Mammosomatotrope Subpopulation in the Rat*

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Abstract
The hemolytic plaque assay technique can be used to detect specific hormone release from single pituitary cells. Using antisera raised against murine GH [growth hormone] or rat PRL [prolactin] the active lactotropes and somatotropes from male and female rat pituitary glands were enumerated. These studies reveal sex-related differences in the number of cells exporting GH and PRL among anterior pituitary cells in culture. In the presence of human GH-releasing factor (hGRF), the mean percentage of GH cells was 53% in males and 30% in females (P < 0.005). The mean percentage of PRL cells was 15% in males and 39% in females (P < 0.008). These values were not significantly altered when hGRF was omitted. The sum of GH and PRL cells identified in separate plaque assays significantly exceeds the number obtained when GH and PRL cells were determined concurrently with a simultaneous plaque assay for both hormones. This difference is dependent on the presence of hGRF, since there was no difference when hGRF was omitted. These data identify the mammosomatotrope in numbers lower than previous reports. By this approach, the mammosomatotrope subpopulation numbers .apprx. 5% of all cells in culture. A sex-related difference in the number of cells exporting GH or PRL among pituitary cells in culture was demonstrated. This difference corresponds with and may underly sex-related differences in the responsiveness of GH and PRL secretion from the pituitary gland. A minor subpopulation of normal pituitary cells appears capable of simultaneous secretion of both GH and PRL.