Protein turnover in rat skeletal muscle: Effects of hypophysectomy and growth hormone

K. E. Flaim, J. B. Li, Leonard "Jim" Jefferson

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Abstract

The role of growth hormone in regulating protein turnover was examined in a perfused preparation of rat skeletal muscle. The perfused muscle maintained in vivo levels of ATP and creatine phosphate and exhibited constant rates of oxygen consumption and protein synthesis. Hypophysectomy reduced the rate of protein synthesis, the concentration of RNA, and the efficiency of protein synthesis in gastrocnemius muscle to 30, 46, and 66% of normal, respectively. In vivo treatment of hypophysectomized (hypox) rats with bovine growth hormone (250 μg/day for 5 days) resulted in small increases in protein synthesis and RNA, whereas synthesis/RNA was returned to near normal. Elevation of ribosomal subunits in psoas muscle indicated an inhibition of peptide-chain initiation in hypox rats that was reversed by in vivo growth hormone treatment. Thus, hypox rats exhibited both a decreased capacity and a decreased efficiency of protein synthesis. Growth hormone replacement primarily increased efficiency of protein synthesis. The rate of protein degradation and the activity of cathepsin D in gastrocnemius muscle were decreased by hypophysectomy. Growth hormone treatment had no significant effect on degradation.

Original languageEnglish (US)
JournalAmerican Journal of Physiology Endocrinology Metabolism and Gastrointestinal Physiology
Volume3
Issue number1
StatePublished - Jan 1 1978

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Hypophysectomy
Growth Hormone
Skeletal Muscle
Proteins
RNA
Psoas Muscles
Ribosome Subunits
Cathepsin D
Phosphocreatine
Oxygen Consumption
Proteolysis
Adenosine Triphosphate
Muscles
Peptides

All Science Journal Classification (ASJC) codes

  • Medicine(all)

Cite this

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abstract = "The role of growth hormone in regulating protein turnover was examined in a perfused preparation of rat skeletal muscle. The perfused muscle maintained in vivo levels of ATP and creatine phosphate and exhibited constant rates of oxygen consumption and protein synthesis. Hypophysectomy reduced the rate of protein synthesis, the concentration of RNA, and the efficiency of protein synthesis in gastrocnemius muscle to 30, 46, and 66{\%} of normal, respectively. In vivo treatment of hypophysectomized (hypox) rats with bovine growth hormone (250 μg/day for 5 days) resulted in small increases in protein synthesis and RNA, whereas synthesis/RNA was returned to near normal. Elevation of ribosomal subunits in psoas muscle indicated an inhibition of peptide-chain initiation in hypox rats that was reversed by in vivo growth hormone treatment. Thus, hypox rats exhibited both a decreased capacity and a decreased efficiency of protein synthesis. Growth hormone replacement primarily increased efficiency of protein synthesis. The rate of protein degradation and the activity of cathepsin D in gastrocnemius muscle were decreased by hypophysectomy. Growth hormone treatment had no significant effect on degradation.",
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N2 - The role of growth hormone in regulating protein turnover was examined in a perfused preparation of rat skeletal muscle. The perfused muscle maintained in vivo levels of ATP and creatine phosphate and exhibited constant rates of oxygen consumption and protein synthesis. Hypophysectomy reduced the rate of protein synthesis, the concentration of RNA, and the efficiency of protein synthesis in gastrocnemius muscle to 30, 46, and 66% of normal, respectively. In vivo treatment of hypophysectomized (hypox) rats with bovine growth hormone (250 μg/day for 5 days) resulted in small increases in protein synthesis and RNA, whereas synthesis/RNA was returned to near normal. Elevation of ribosomal subunits in psoas muscle indicated an inhibition of peptide-chain initiation in hypox rats that was reversed by in vivo growth hormone treatment. Thus, hypox rats exhibited both a decreased capacity and a decreased efficiency of protein synthesis. Growth hormone replacement primarily increased efficiency of protein synthesis. The rate of protein degradation and the activity of cathepsin D in gastrocnemius muscle were decreased by hypophysectomy. Growth hormone treatment had no significant effect on degradation.

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