This thesis describes the development of an assay for free radical scavenging (antioxidant) activity in biological fluids based on an enhanced chemiluminescent reaction. Light emission from the reaction depends on the constant production of free radical intermediates and is therefore sensitive to interference by antioxidant compounds. The time period of light suppression is directly related to the amount of antioxidant added to the reaction. In this way the antioxidant activity of biological samples can be related to a standard antioxidant solution of the vitamin E analogue, trolox. The effect of a variety of pure compounds upon light emiSSion are described. Based on these observations a mathematical model for the reaction kinetics in response to the addition of antioxidants and other compounds is developed. The impact of more complex biological fluids on the reaction is described with particular reference to serum. An assessment of the contribution of individual antioxidants to serum total antioxidant activity suggests that urate accounts for 70% while ascorbate and vitamin E each account for a further 10%. The use of the assay is extended to the measurement of antioxidant activity in solutions of plasma lipoproteins isolated by density gradient ultracentrifugation. These studies suggest that vitamin E is the major (but not exclusive) contributor to lipoprotein antioxidant activity. The distribution of antioxidant activity across different lipoprotein fractions and co-operative interaction of antioxidant activity in lipoproteins are described.

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Hypohydration can impair the performance of exercise, and fluid balance is therefore of importance to athletes. This thesis aimed to investigate factors regarding fluid losses and gains, with a view to the performance of exercise. Chapter 3 investigated the effect of ingesting 600ml of hypotonic and hypertonic glucose solutions on blood, plasma and red cell volume in resting individuals. Ingestion of 6% and 12% hypertonic glucose solutions showed evidence of a transient decrease in blood and plasma volume possibly due to fluid movement into the intestinal lumen from the body. There was also a suggestion that ingestion of a 2% glucose solution increases blood and plasma volume in comparison to a 0% glucose solution.

The consequences of ingesting different carbohydrate solutions on fluid movement and availability have not been systematically examined. In addition, the role of carbohydrate in the post-exercise rehydration period has received little attention despite the need for substrate replenishment following exercise and the role of carbohydrates in stimulating water absorption in the intestine. The aims of this thesis were to assess fluid absorption characteristics and availability of solutions containing increasing concentrations of glucose and to evaluate their role in the restoration and maintenance of fluid balance following a period of exercise-induced dehydration. The ingestion of a single bolus of a commercially available hypertonic 18% carbohydrate solution (chapter 3) and a hypertonic 10% glucose solution (chapter 4) resulted in reductions in plasma volume that are most likely due to acute net secretion of water into the intestinal lumen. When investigating recovery of whole body hydration status after sweat loss, a hypertonic 10% glucose-electrolyte solution maintained whole body fluid balance for a longer period than a hypotonic 2% glucose-electrolyte solution and an electrolyte only solution when a fixed volume of fluid was consumed during a rehydration period of one hour following cycle exercise in the heat (chapter 5). When fluid was consumed ad libitum over a two hour period following similar cycle exercise in the heat, a hypertonic 10% glucose-electrolyte solution was as effective in restoring and maintaining fluid balance as a 2% hypotonic glucose-electrolyte solution and an electrolyte only solution (chapter 6). The reduced rate of gastric emptying that accompanies the ingestion of high carbohydrate solutions was likely to be the primary cause for the difference in urine production reported between thetrials during this study (chapter 7). In conclusion, ingestion of hypertonic carbohydrate solutions results in a reduction in extracellular fluid volume that is most likely due to secretion of water into the intestinal lumen and the carbohydrate content of an ingested solution is of importance in the post-exercise rehydration period.