Stereological and biochemical analysis of prolactin and growth hormone secreting rat pituitary cells in culture. Stereology combined with non-parametrical statistics.

The secretion of prolactin is increased by treatment of prolactin producing rat pituitary cells with the hypothalamic tripeptide thyroliberin. To investigate the underlying mechanisms we used three closely related rat pituitary tumor cell strains (GH1 2C1, GH3 and GH4C1), which synthesize and spontaneously secrete prolactin and/or growth hormone. Growth hormone and prolactin released into the culture medium over a period of 24 h were measured by radioimmunoassay. Initial rates of synthesis were measured by immunoprecipitation of intracellular growth hormone and prolactin after incubation of cell cultures with 3H-leucine. The observed increase in prolactin synthesis and release was correlated with morphological effects of thyroliberin treatment. The volume density of Golgi complexes and the volume and surface densities of rough endoplasmic reticulum were compared in untreated cells and thyroliberin treated cells. As normal distribution could not be assumed the non-parametric rank test of Wilcoxon was used whereby the densities calculated for each cell section were ranked. All three morphological parameters increased after thyroliberin treatment in cells secreting prolactin only (GH4C1), implying that the increase of prolactin secretion, at least in part, is due to increased prolactin synthesis.