Effects of Ca ++ and Mg ++ on Secretion and Synthesis of Growth Hormone and Prolactin by Clonal Strains of Pituitary Cells in Culture

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Abstract
Clonal strains of rat pituitary cells synthesize and secrete both growth hormone and prolactin in monolayer and suspension culture. Effects of alterations of [Ca++] and [Mg++] in medium and of the addition of Mn++ were examined using immunological methods to measure both intracellular and extracellular hormone levels. Reduction of medium [Ca++] of 20 and 90% by the addition of NaEGTA lowered the extracellular levels of both hormones by 60 and 90%, respectively, after 24 hr of incubation, and still further after 96 hr. Reductions in extracellular hormone levels were seen after 4 hr, but not earlier. Functional changes induced by low [Ca++] were reversible. Medium [Ca++] of 6 KM caused an increase in the production of growth hormone and prolactin, and this effect was blocked by an equimolar increase in [Mg++]. Increased [Mg++] in medium caused a decrease in the extracellular levels of both hormones. In all experiments the intracellular concentrations of growth hormone and prolactin always paralleled the hormone levels in medium. Alterations in [Ca++] and [Mg++] were not accompanied by changes in total cell protein synthesis, but low [Ca++] did inhibit incorporation of 3H-leucine into newly synthesized prolactin. Low [Ca++] also inhibited the cortisol-stimulated rate of growth hormone production and the thyrotropin releasing hormone-stimulated rate of prolactin production. Manganese increased the extracellular levels of growth hormone and prolactin after 2 hr, but caused a decrease after 36 hr. We conclude that low [Ca++] reversibly reduces the basal synthesis of growth hormone and prolactin in GH3 cells as well as inhibiting the stimulating effects of cortisol and thyrotropin releasing hormone. The changes in growth hormone and prolactin production due to high extracellular [Ca++] and [Mg++] are also probably mediated through an effect primarily on the synthesis of the hormones.(Endocrinology92: 573, 1973)