Increasing insulin availability does not augment post-prandial muscle protein synthesis rates in healthy young and older men
Bart B.L. Groen The Journal of Clinical Endocrinology & Metabolism First Published Online: July 19, 2016
Skeletal muscle protein synthesis is highly responsive to food intake. It has been suggested that the post-prandial increase in circulating insulin modulates the muscle protein synthetic response to feeding.
Objective: To investigate whether a greater post-prandial rise in circulating insulin level increases amino acid uptake in muscle and augments post-prandial muscle protein synthesis rates.
Participants and design. 48 healthy young (age 22±1 y; BMI 22.0±0.3 kg·m-2) and older males (age 68±1 y; BMI 26.3±0.4 kg·m-2) ingested 20 g intrinsically L-[1-13C]-leucine and L-[1-13C]-phenylalanine labeled casein protein with or without local insulin infusion. Primed continuous infusions of L-[1-13C]-leucine and L-[ring-2H5]-phenylalanine were applied, with arterial and venous blood samples and muscle biopsies being collected during a 5 h post-prandial period.
Results:
Insulin administration did not increase overall leg blood flow (P=0.509), but increased amino acid uptake over the leg in both young and older subjects (P=0.003). The greater amino acid uptake over the leg did not further increase post-prandial muscle protein synthesis rates (0.050±0.006 and 0.037±0.004 %·h-1 versus 0.044±0.004 and 0.037±0.002 %·h-1, in the insulin-stimulated versus control condition in the young and older groups, respectively; P=0.804) and did not affect post-prandial deposition of dietary protein-derived amino acids in de novo muscle protein (P=0.872).
Conclusion:
Greater post-prandial plasma insulin availability stimulates amino acid uptake over the leg but does not further augment post-prandial muscle protein synthesis rates or stimulate the post-prandial deposition of protein derived amino acids into de novo muscle protein in healthy young and older men.
