TRANSPORT OF CARBON-11-METHIONINE IS ENHANCED BY INSULIN

The anabolic effects of insulin are not restricted to carbohydrate and lipid metabolism but also include protein metabolism. However, the ef fects of insulin on protein metabolism have been difficult to demonstr ate in vivo. Amino acid transport is partly regulated by insulin accor ding to the experimental data. PET provides a way to measure fractiona l uptake rates of amino acids. The purpose of this study was to measur e the effect of insulin on amino acid transport from the plasma to the human parotid glands. Methods: We compared the uptake of L-[methyl-C- 11]methionine ([C-11]methionine) into the parotid glands and cerebellu m in seven healthy volunteers during the fasting state and euglycemic insulin clamp technique (1 mU/kg per minute), Results: The fractional uptake rate of [C-11]methionine was increased by 31% for the right par otid gland (p = 0.003) and by 29% for the left parotid gland (p = 0.00 9) during insulin clamp, while the increase was 19% for the cerebellum (p = 0.01). The concentration of amino acids typical for the hormone- sensitive transport system A was 11% lower during insulin infusion tha n in the fasting state, Conclusion: The uptake of methionine into brai n tissue does not seem to be under major control by insulin, while the transport of methionine in the parotid glands is stimulated by insuli n. PET provides a sophisticated method to study the transport system o f amino acids in vivo.