Regulation of hepatic transthyretin messenger RNA levels during moderate protein and food restriction in rats.

This study was designed to determine whether the decrease in serum transthyretin that occurs during food restriction results from gross energy reduction or from depressed protein or lipid intake and to examine the relationship between serum transthyretin and hepatic transthyretin mRNA during moderate protein or food deficiency. Groups of young rats were allowed free access to either a 18% (control) or a 6% protein diet (protein-restricted), or reduced intakes. The food-restricted groups received 60% of control intake from the control diet, a 40% protein-enriched diet, or a 40% lipid-enriched diet, for 28 d. Serum transthyretin concentrations were lower in all experimental groups on d 7 relative to the control group. Control values were reached only in the protein-restricted group by d 14. The low serum transthyretin levels, which were similar in the food-restricted groups, likely resulted from gross energy restriction. Hepatic transthyretin mRNA levels were determined in the control, protein-restricted and food-restricted groups. They were unchanged relative to controls in the protein-restricted group but declined moderately in the food-restricted group on d 7 and 14, before returning to control values by d 28. Thus, the changes in liver transthyretin mRNA levels could partially explain the changes in serum transthyretin in food-restricted rats.