MOLECULAR-FORMS OF HUMAN GROWTH-HORMONE AND PROLACTIN SECRETED BY PITUITARY-TUMOR CELL-CULTURES

Functionally active cell cultures were obtained from human pituitary a denomas producing vast amounts of growth hormone (somatotropinomas), p rolactin (prolactinomas), or both hormones (mixed tumors). The molecul ar forms of hormones secreted by these tumors were studied. Electropho resis in polyacrylamide gels in the presence of sodium dodecyl sulfate and immunoblotting with poly- and monoclonal antibodies showed that t he tumor cells release several forms of growth hormone and prolactin, most of which were characteristic of normal human pituitary gland. The 22K form was the major secreted form of growth hormone; in addition, the 20K (a product of alternative splicing of pre-mRNA) and the cleave d double-chain (25K) forms were detected. Prolactin was mainly secrete d in the 23K form; in addition, the glycosylated (25K) form was detect ed. There were no substantial differences in the ratios between indivi dual molecular forms of the hormones released from cells under basal c onditions and upon stimulation with hypothalamic regulators of pituita ry function (somatostatin and thyroliberin). The data suggest that pit uitary adenoma cells can release some amount of anomalous forms of hor mones, such as immature products of postribosomal processing or large immunoreactive fragments. In conclusion, cell cultures derived from pi tuitary adenoma may serve as an effective model system for further bio chemical and physiological studies of the molecular forms and mechanis ms of secretion of human growth hormone and prolactin.