trimethyllysine and Starvation

Free and peptide-linked trimethyllysine were measured in fed and 5-d starved rats. The trimethyllysine content of liver and kidney was significantly increased on d 5 of starvation to two to three times the levels found in fed animals. Skeletal muscle of fed rats contained over six times as much trimethyllysine (19.3 nmol/g) as that found in liver (3.2 nmol/g) or kidney (2.7 nmol/g). Plasma free trimethyllysine significantly increased from 1 nmol/ml in fed rats to 2.2 nmol/ml in 5-d starved rats. During this same period, daily total trimethyllysine excretions averaged approximately 400 nmol/d. Urinary free trimethyllysine was significantly depressed during starvation. Assuming that trimethyllysine in plasma does not exist in a protein-bound form, clearance calculations based on concentrations of plasma and urinary trimethyllysine indicated that this compound is readily reabsorbed by the kidney. As previous studies have indicated that trimethyllysine is not readily absorbed by other tissues, this indicates that the kidney may be the primary regulatory site for the disposition free of free trimethyllysine in plasma and urine. Estimates of the efficiency of entry of trimethyllysine into the carnitine biosynthetic pathway were calculated and ranged from 41% in 3-d starved rats to 80% in fed rats. We conclude that carnitine biosynthesis is limited by the availability of trimethyllysine, which, in the starved rat, is limited by the rate of protein turnover.

Topics: Animals; Carnitine; Kidney; Liver; Lysine; Male; Muscles; Rats; Rats, Inbred Strains; Starvation

Trimethyllysine residues in peptide linkage, precursors of carnitine biosynthesis, were measured in fed and 3-day fasted rats. Whole-body peptide-linked trimethyllysine in fasted rats was significantly less than in fed rats when expressed per initial body weight (17.8 vs 24.8 mumol/100 g initial body weight). Skeletal muscle had the highest peptide-linked trimethyllysine content (2.5 nmol/mg protein), followed by heart (1.9 nmol/mg protein). The content in kidney, liver and small intestine were similar, but less than in heart. Of the eight tissues tested, the brain had the only significant increase with fasting. The hepatic peptide-linked trimethyllysine in fasted rats was significantly decreased when expressed per milligram DNA. The study shows a commensurate loss of peptide-linked trimethyllysine accompanying protein loss during fasting. The study also shows that muscle contains over 65% of the whole-body peptide-linked trimethyllysine, and as such is a major reservoir of precursor for carnitine biosynthesis.

Topics: Animals; Body Weight; Brain; Carnitine; Lysine; Male; Muscles; Peptides; Rats; Rats, Inbred Strains; Starvation; Tissue Distribution