Effects of human somatomedin preparations on membrane transport and protein synthesis in the isolated rat diaphragm.

Abstract

Partially purified preparations of human somatomedin stimulated amino acid and sugar transport and protein synthesis in isolated diaphragms of hypophysectomized rats when added in vitro. These metabolic effects cannot be ascribed to the low level of insulin present in the somatomedin preparations. Effects were obtained with amounts of the preparations that contained less insulin than that required to stimulate membrane transport and protein synthesis in the diaphragm. Further, sugar transport was stimulated by one of the preparations in the presence of a large excess of insulin antibodies. The action of the somatomedin preparations on the transport of amino acids into the diaphragm was found to be qualitatively similar to the effect of insulin on this process, i.e., it is very rapid, and not sensitive to puromycin or theophylline. The later finding would suggest that protein synthesis and shifts in intracellular cyclic nucleotide levels are not involved in mediating the effect of these materials on amino acid transport in the diaphragm.