Addition of hydrocortisone to the medium of a clonal strain of rat pituitary cells (GH3) stimulated the rate of production of growth hormone. The stimulation had a lag period of about 24 hr, reached a maximum at 70–100 hr, and was observed at a hydrocortisone concentration as low as 5 x 10-8 M. Cells maximally stimulated with 3 x 10-6 M hydrocortisone produced 50–160 µg growth hormone/mg cell protein/24 hr. These rates were four to eight times those observed in control cells. At maximum stimulation, intracellular levels of growth hormone in both stimulated and control cells were equal to the amount secreted into the medium in about 15 min. Removal of hydrocortisone from the medium of GH3 cells caused a return of the rate of growth hormone production to that in control cells. Addition of hydrocortisone to the medium of cells growing exponentially with a population-doubling time of 60 hr caused both an increase in the doubling time to 90 hr and a stimulation of growth hormone production. Cycloheximide (3.6 x 10-5 M) and puromycin (3.7 x 10-4 M) suppressed incorporation of labeled amino acids into protein by 93 and 98%, respectively, and suppressed growth hormone production by stimulated and control cells by at least 94%.

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