Insulin Does Not Stimulate Beta-Alanine Transport Into Human Skeletal Muscle

To test whether high circulating insulin concentrations influence the transport of beta-alanine into skeletal muscle at either saturating or subsaturating beta-alanine concentrations, we conducted two experiments whereby beta-alanine and insulin concentrations were controlled. In experiment 1, 12 men received supraphysiological amounts of beta-alanine intravenously (0.11 g.kg(-1).min(-1) for 150 min), with or without insulin infusion. beta-Alanine and carnosine were measured in muscle before and 30 min after infusion. Blood samples were taken throughout the infusion protocol for plasma insulin and beta-alanine analyses. beta-Alanine content in 24-h urine was assessed. In experiment 2, six men ingested typical doses of beta-alanine (10 mg/kg) before insulin infusion or no infusion. beta-Alanine was assessed in muscle before and 120 min following ingestion. In experiment 1, no differences between conditions were shown for plasma beta-alanine, muscle beta-alanine, muscle carnosine and urinary beta-alanine concentrations (all P > 0.05). In experiment 2, no differences between conditions were shown for plasma beta-alanine or muscle beta-alanine concentrations (all P > 0.05). Hyperinsulinemia did not increase beta-alanine uptake by skeletal muscle cells, neither when substrate concentrations exceed the V-max of beta-alanine transporter TauT nor when it was below saturation. These results suggest that increasing insulin concentration is not necessary to maximize beta-alanine transport into muscle following beta-alanine intake.