THE PHYSIOLOGICAL ROLE OF GLYCOSYLATED HUMAN PROLACTIN

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Previous investigations from The Whittier Institute have demonstrated that human pituitary glands contain a glycosylated form of prolactin. This newly recognized form of prolactin contains a carbohydrate unit on asparagine 31. We have also shown that glycosylated prolactin is found in human serum and amniotic fluid and that both human pituitary cells and human decidual tissue secrete glycosylated prolactin in vitro. Since preliminary studies have shown that glycosylation of prolactin alters its biological activity, determination of the factors that affect synthesis and secretion of the glycosylated form will provide insight into the physiological role of glycosylated prolactin. The hypothesis to be tested is that the basal secretory form of prolactin is the less biologically active glycosylated form and that the more active, nonglycosylated form is released in response to specific stimuli. Using primary cultures of human pituitary cells as a model system, experiments are now proposed to investigate the effects of thyrotropin releasing hormone, bromocriptine, dopamine, estrogen, cylic AMP, and calcium on the synthesis and secretion of glycosylated prolactin by normal human pituitaries. Studies are also proposed to measure serum levels of glycosylated prolactin from normal individuals in various physiological states including women in the follicular, ovulatory, and luteal phases of their menstrual cycles, post-menopausal women, and pregnant and nursing women with physiologic hyperprolactinemia. The release of glycosylated prolactin will also be studied in normal volunteers after thyrotropin releasing hormone, arginine and L-dopa infusion. In addition, serum glycosylated prolactin will be measured in hyperprolactinemics with and without adenomas. Overall, this proposal will permit the evaluation of the role of newly recognized forms of prolactin in normal physiology and in certain pathologic conditions such as the various forms of hyperprolactinemia.