Biomedical subjects
D MacLaren
Publications and source records attributed to D MacLaren.
Exogenous carbohydrate utilisation: effects on metabolism and exercise performance.
It is generally recognized that a decrease in carbohydrate availability can lead to the development of fatigue during prolonged exercise in humans. Administration of glucose or other carbohydrates before or during exercise has been shown to postpone fatigue, conserve muscle glycogen and improve performance. Carbohydrates can be categorised according to their ability to increase blood glucose concentration (known as glycaemic index) and by the extent they stimulate the release of insulin. The glycaemic index is reflected in the rate at which consumed carbohydrate is made available in the blood. Glucose is the only type of carbohydrate that can readily be oxidised by skeletal muscle for energy production. Gastric emptying is the primary factor limiting the rate of carbohydrate delivery to the blood and therefore influences the utilisation of exogenous carbohydrate ingested before or during exercise. Various methods have been used to assess the oxidation of exogenous carbohydrates during exercise. Peak rates of CHO oxidation during exercise have been reported between 0.4 and 1.0 g/min, and the rates of oxidation do not appear to be influenced to a major extent by the use of multiple drinking schedule in comparison with a single bolus schedule. Previous studies also suggest that the ingestion of fructose during exercise does not offer any additional benefits over ingestion of glucose or glucose polymer solutions of similar concentration. The hormones insulin, glucagon and adrenaline together with cortisol and growth hormone play key roles in the regulation of carbohydrate metabolism during exercise. Ingestion of moderately concentrated carbohydrate solutions (4-8%) enhances prolonged exercise performance and is appropriate for optimising energy and fluid delivery without causing adverse effects. The ergogenic effects of carbohydrate ingestion on performance during intermittent exercise such as competitive sports are less well established, although the evidence to date suggests diminished performance when carbohydrate are limiting.
Use of radionuclide imaging to determine gastric emptying of carbohydrate solutions during exercise.
OBJECTIVE: To investigate the repeatability of continual assessment of the gastric emptying rates of carbohydrate solutions in exercising subjects using 99mtechnetium labelling. METHODS: Gastric emptying of a 5% glucose solution and an iso-osmotic maltodextrin solution was measured using 3 MBq of 99mtechnetium labelled diethylene triamine penta-acetic acid (DTPA) and continuous gamma camera imaging in five male subjects. The subjects performed four 1 h trials at 70% VO2 peak on a cycle ergometer. After 15 min, 200 ml of a radiolabelled solution of glucose or maltodextrin were ingested in a blind crossover protocol. The two solutions were each ingested on separate occasions (trial 1 and trial 2) to establish repeatability. RESULTS: Statistical analysis showed no differences between trial 1 and trial 2 for both solutions. There were no significant differences for the emptying rates between the two test solutions. CONCLUSIONS: Posterior imaging using a computer linked gamma camera following the ingestion of 99mtechnetium labelled DTPA mixed with carbohydrate solutions provides a repeatable method of assessing gastric emptying characteristics in exercising subjects. This technique showed no significant differences between the emptying rates of a single dose of iso-osmotic glucose or maltodextrin solution.
Iron, copper and zinc concentrations in human sweat and plasma; the effect of exercise.
The effect of 30 or 40 min hard exercise on a cycle ergometer upon plasma concentrations of zinc, iron and copper in twelve healthy male athletes was studied. Sweat samples were also collected from different body sites and analyzed for these metals. The metal content of sweat from different body sites varied, as did the sweating rates of different subjects. Pre-exercise plasma iron concentrations in 10 of the 12 subjects were within the normal range, but at least 4 subjects had sub-normal plasma zinc whereas six had plasma copper levels above normal. The effects of exercise on plasma metal concentrations varied from subject to subject; no general conclusions could be drawn about the biological significance of loss of metals in sweat in relation to whole body metal metabolism. It is suggested that a mild acute phase response may account for lowered zinc and raised copper in the plasma of athletes.
Production, characterization and biological effects of monoclonal antibodies to different parts of the gram-negative lipopolysaccharide core region.
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Measurement in human sera of antibodies to lipopolysaccharide of Escherichia coli J5.
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