Relationship between glutamine concentration and protein synthesis in rat skeletal muscle

Abstract

Muscle glutamine concentration ([GLN]) and protein synthesis rate (Ks) have been examined in vivo in well-fed, protein-deficient, starved, and endotoxemic rats. With protein deficiency (8 or 5% casein diet), [GLN] fell from 7.70 to 5.58 and 3.56 mmol/kg in the 8 and 5% diet groups, with Ks falling from 15.42 to 9.1 and 6.84%/day. Three-day starvation reduced [GLN] and Ks to 2.38 mmol/kg and 5.6%/day, respectively. In all these groups food intakes and insulin were generally well maintained (except in the starved group), whereas free 3,5,3'-triiodothyronine (T3) was depressed in the starved and 5% protein group. The E. coli lipopolysaccharide endotoxin (3 mg/kg) reduced [GLN] to 5.85 and 4.72 mmol/kg and Ks to 10.5 and 9.10%/day in two well-fed groups. Insulin levels were increased, and free T3 levels fell. Combined protein deficiency and endotoxemia further reduced [GLN] and Ks to 1.88 mmol/kg and 4.01%/day, respectively, in the 5% protein rats. Changes in both ribosomal activity (KRNA) and concentration (RNA/protein) contributed to the fall in Ks in malnutrition and endotoxemia, although reductions in the RNA concentration were most marked with protein deficiency and reductions in the KRNA dominated the response to the endotoxin. The changes in [GLN] and Ks were highly correlated as were [GLN] and both KRNA and the RNA concentration, and these relationships were unique to glutamine. These relationships could reflect sensitivity of glutamine transport and protein synthesis to the same regulatory influences, and the particular roles of insulin and T3 are discussed, as well as any direct influence of glutamine on protein synthesis.

Glutamine kinetics and protein turnover in end-stage renal disease

“…Similarly, the alanine and glutamine concentration in the artery (29.8 vs.28.8%) declined more than that in the vein (12.3 vs. 19.1%) and muscle compartments (4.1 vs. 4.7%). Human and animal studies have suggested that the muscle glutamine pool positively influences protein synthesis (24,27). Furthermore, it is claimed that this correlation is specific for glutamine and has not been observed with any other amino acid (32).…”

Duchenne muscular dystrophy: a model for studying the contribution of muscle to energy and protein metabolism

“…It is a major gluconeogenic precursor [14,23], and a major 'fuel' for tissues with a high cell turnover rate (gut, immune system) [6]. It also plays a central role in the regulation of protein turnover [19]. In fact, we have previously shown that a doubling of the plasma glutamine concentration was associated with a significant increase in protein synthesis estimates [ 10,12].…”

Calcium and protein kinetics in prepubertal boys. Positive effects of testosterone.

“…Since these studies have been performed in the postpubertal male after years of exposure to their endogenous sex hormones, it is difficult to extend their physiological implications to the events at pu- berty, when the body is exposed to androgenic hormones after more than a decade ofvery low exposure. Recent animal experiments have revealed a strong correlation between the size of the muscle free glutamine pool (the most abundant amino acid in the body) and the rate of protein synthesis in vivo ( 18,19). Other studies suggest that glutamine per se may stimulate protein synthesis, and that the size of the available free glutamine pool in muscle may be an index of protein accretion (20)(21)(22).…”