Acute Effects of Growth Hormone on the Function of Ribosomes of Rat Skeletal Muscle

Summary

The effect of the acute intravenous administration of bovine growth hormone (bGH) to female hypophysectomized rats on the ability of ribosomes isolated from their thigh muscles to incorporate ³H-leucine and ³H-puromycin into protein in vitro was studied. Ribosomes prepared from the muscles of animals that had received bGH (200 μg) 30 min before sacrifice were more active in incorporating leucine and puromycin into protein than the controls. However, no effect of the hormone on leucine incorporation was seen 15 min after its injection, suggesting some lag period in its course of action on ribosome function. In experiments dealing with the ability of the ribosome preparations to incorporate puromycin into protein, it was found that at the completion of the reaction, ribosomes made from the muscles of bGH-treated rats had incorporated 22 % more tracer into protein than the controls, suggesting that these preparations contained a larger population of ribosomes actively engaged in protein synthesis. This conclusion was also supported by the finding that sucrose densitiy gradient profiles of ribosome preparations from the hormone-treated rats had a greater proportion of ribosomes in the polyribosome fraction than those of the controls. From these and other observations made in this study, it would appear that the acute effect of growth hormone on the function of rat skeletal muscle ribosomes is to increase the fraction of ribosomes active in peptide synthesis.

Key-Words

Growth Hormone - Muscle Ribosomes - Protein Synthesis - Peptidyl-Puromycin Formation