Tissue trimethyllysine biosynthesis and carnitine content in pregnant and lactating rats fed a lysine-limiting diet.

Previous studies have indicated that carnitine biosynthesis is primarily regulated by the availability of trimethyllysine. The present study investigated the rate of trimethyllysine biosynthesis during pregnancy in rats fed a lysine-restricted diet. Pregnant Sprague-Dawley rats were fed ad libitum a crystalline amino acid diet (18% amino acids) containing either 1.44% or 0.36% lysine. Food intakes were not significantly different between the two groups, either during 19 d of gestation or 12 d of lactation (p greater than 0.05). Trimethyllysine content and synthetic rates were not significantly different between the treatment groups for any of the five tissues tested at either of the two time points. Tissue carnitine content was not consistently affected by dietary lysine content. Liver carnitine content was significantly higher in control rat pups at 12 d of lactation than in pups in the lysine-deficient group. Pups in both groups had peptide-linked trimethyllysine levels in skeletal muscle that were 46% of those seen in the control adults. However, previous reports of higher protein turnover in the neonate would indicate that trimethyllysine is not limiting at this age. Under these experimental conditions, carnitine biosynthesis is not impaired because of restricted availability of trimethyllysine.