Regulation of the rate of synthesis of messenger ribonucleic acid by growth hormone

Abstract

The ability of rat-liver ribosomes to incorporate amino acid into protein in vitro depends on the concentration of circulating growth hormone in the rat, yet little change was observed in the incorporating ability of polysome preparations from liver of normal, hypophysectomized and growth-hormone-treated rats. The yield of polysomes was, however, shown to vary with the amount of circulating growth hormone. Poly-uridylic acid stimulation of phenylalanine incorporation was as great, or greater, with ribosomes from liver of hypophysectomized rats than with normal ribosomes. Growth hormone was able to exert its stimulatory effects on the protein-synthetic ability of ribosomes, and on the number of polysomes, when injected into actinomycin-treated rats. Growth hormone treatment stimulated orotic acid incorporation into nuclear and microsomal RNA of hypophysectomized and normal rats and in actinomycin-treated rats. At least part of the RNA synthesized as a result of growth hormone treatment is messenger RNA. It was concluded that the rate of synthesis of rat-liver RNA, including messenger RNA, is regulated by growth hormone, and that the effects of growth hormone on protein synthesis and growth can be explained in terms of its control of messenger RNA synthesis.