Thyroid hormone stimulates de novo growth hormone synthesis in cultured GH1 cells: evidence for the accumulation of a rate limiting RNA species in the induction process.

Abstract

With radioimmunoassay techniques it was shown that physiologic concentrations of thyroid hormone stimulate an increase in growth hormone [GH] production in rat GH1 cells in culture. With radiolabel techniques and selective immunoprecipitation, it is demonstrated that L-triiodothyronine stimulates GH production solely by inducing an increase in the de novo synthesis of the polypeptide hormone. L-Triiodothyronine stimulated synthetic rates of GH by 1.5-fold in 1.25 h, 2-fold in 2.5 h, to a maximal of 3- to 4-fold after 8.5 h of incubation. The time interval between significant L-triiodothyronine binding to putative nuclear receptors and a detectable increase in GH synthesis was 45-60 min. Studies on the effect of actinomycin D, 3''-deoxyadenosine and cycloheximide support the thesis that L-triiodothyronine induces the accumulation of an RNA species which is rate limiting for GH synthesis and lends further support for a primary action of thyroid hormone at the nuclear level.