Thyroid and glucocorticoid hormones synergistically control growth hormone mRNA in cultured GH1 cells

We have previously demonstrated that thyroid hormone controls growth hormone synthesis in GH1 cells and that the induction of the growth hormone response by glucocorticoid appears to be highly dependent on thyroid hormone action. Thyroid hormone induces growth hormone synthesis approximately 5- to 20-fold and cortisol increases this response 2- to 6-fold further. Long-term kinetics of the growth hormone response show that, without added thyroid hormone, cortisol can induce a small-growth hormone response after 48 hr of incubation. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of proteins synthesized in intact cells demonstrates that the cortisol enhancement of growth hormone synthesis in cells incubated with thyroid hormone is a relatively selective process. Quantitation of growth hormone mRNA levels by cell-free protein synthesis demonstrates that the regulation of growth hormone synthesis by thyroid and glucocorticoid hormones is explained by a synergistic pretranslational control mechanism, presumably at the level of the growth hormone gene.