Calcium specifically stimulates prolactin synthesis and messenger RNA sequences in GH3 cells.

Addition of CaCl2 (0.4 mM) to GH3 cells incubated in a serum-free, Ca2+-free medium increased relative prolactin synthesis (prolactin synthesis/total protein synthesis) 7- to 150-fold by 3-4 days, but had no effect on relative growth hormone synthesis. Half-maximal and maximal stimulation of relative prolactin synthesis occurred at about 0.07 and 0.2 mM CaCl2, respectively. Neither MgCl2 (0.4 mM) nor KCl 0.4 mM) affected relative prolactin synthesis. 32P-labeled rat prolactin and growth hormone cDNA plasmids were employed to measure by RNA gel blot hybridization changes in cytoplasmic levels of the corresponding mRNA sequences. Both prolactin mRNA sequence levels and translatable prolactin mRNA increased in parallel with the CaCl2-induced increase in relative prolactin synthesis. CaCl2 increased prolactin mRNA sequences by 7- to 200-fold, without affecting growth hormone mRNA sequence levels. Dexamethasone (100 nM) decreased prolactin mRNA sequences in cells incubated with CaCl2, antagonized the CaCl2-induced increases in prolactin mRNA sequences independently of the CaCl2 concentration.