Aspects of creatine and arginine supplementation on metabolism in humans
This thesis investigated the effects of dietary supplementation with the guanidino compounds creatine (Cr) and arginine on metabolism in humans. Experiments studied the influence of exercise and Cr + carbohydrate (CHO) ingestion upon muscle glycogen and Cr accumulation, the effects of arginine ingestion upon the fate of ingested CHO, the influence of Cr + CHO supplementation upon muscle glycogen accumulation and endurance exercise performance, and the effects of Cr supplementation upon various indices of health. Biochemical analysis was performed on venous blood samples and on muscle biopsy samples from vastus lateralis obtained from subjects during the experiments. Blood samples were analysed for glucose, insulin and lactate concentrations and muscle samples for adenosine triphosphate, Cr, phosphocreatine and glycogen concentrations. Exhaustive exercise, performed prior to Cr + CHO supplementation, augmented muscle Cr accumulation, but Cr accumulation was diminished in non-exercised muscle. This was possibly due to a blunted CHO-stimulated insulin response after exercise, which would diminish insulin-mediated Cr transport. Creatine + CHO supplementation augmented glycogen resynthesis in exercised muscle to a greater extent than CHO supplementation alone. A tendency for greater glycogen synthesis was observed following Cr + CHO supplementation without prior exercise, and was paralleled by a tendency for subsequent submaximal exercise to be prolonged. Ingestion of 10 g arginine with a CHO drink was found not to have any influence upon the fate of the ingested glucose. This was probably due to the resulting plasma arginine concentration being insufficient to influence CHO disposal. Finally, acute (5 day) and prolonged (8 week) Cr supplementation produced no adverse effect upon health, as indicated by markers of haematological, hepatological, muscle and renal function.