Graduate Thesis Or Dissertation

 

Influence of controlled strenuous exercise on vitamin B-6 metabolism in man : effects of carbohydrate depletion-repletion diets and vitamin B-6 supplements Public Deposited

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  • Recent studies in men have shown plasma levels of vitamin B-6 and pyridoxal 5'-phosphate (PLP), the active form of vitamin B-6, to increase with exercise. It was hypothesized that muscle glycogen phosphorylase might be the source of these increases as this enzyme has been shown to increase with increasing vitamin B-6 (B6) intake in the rat, seemingly to store PLP. The investigation was designed to study the effects of diet-altered glycogen stores and B6 supplements on B6 metabolism during controlled strenuous exercise. The effect of exercise (EX) on the excretion of 4-pyridoxic acid (4PA), the major B6 urinary metabolite, was also studied. The study consisted of three experimental weeks during which carbohydrate (CHO)-modified diets were fed and six EX tests were administered (one each Wednesday and Saturday). Four trained male cyclists (20-23 years) served as subjects. Week 1 a normal CHO diet was fed (NC diet, 40% of total kilocalories as CHO). During week 2, which began 7 days after week 1, a low CHO diet was fed Sunday through Tuesday (LC diet, 11% CHO) to deplete muscle glycogen. In the same week, the LC diet was followed by a high CHO diet (HC diet, 71% CHO). The HC diet was fed Wednesday through Saturday to replete, or load, glycogen stores. The NC, LC, and HC diets contained 1.64, 1.55, and 1.82 mg of B6, respectively. Week 3, beginning 14 days after week 2, was identical to week 2, but with the daily addition of an 8 mg supplement of pyridoxine. Daily exercise was encouraged Sunday through Tuesday to facilitate glycogen depletion. The EX test consisted of 50 min of continuous bicycle ergometer exercise (30 min at 60% HRmax (maximal heart rate), 15 min at 80% HRmax, and 5 min at 90% HRmax). Blood samples were drawn prior to the exercise test (pre), 2 min prior to the 90% HR max interval (during), immediately post EX (post), 30 min post, and 60 min post EX. Plasma samples were analyzed for PLP, PB6, creatine kinase (a muscle enzyme), and hematocrit and hemoglobin. Urine was collected in 24 hour aliquots and analyzed for 4PA and creatinine. The HC diet was associated with significantly lower pre exercise PB6 and PLP levels than LC diet. This was attributed to the high CHO content of HC. Increased plasma PLP and PB6 levels (pre versus post) were seen for all EX tests. This was significant for PB6 levels of all EX tests. Exercise following LC resulted in smaller pre to post increases in PB6 and PLP than other unsupplemented EX tests, but this was significant only for EX following LC versus NC(Wed). Supplementation resulted in greater pre to post increases in PLP and PB6 than EX following unsupplemented diets, but this was significant only for LC versus LC+B6. Plasma PLP and PB6 levels dropped throughout the 60 min post EX period. The 60 min post PLP levels were significantly below pre for the EX tests following diets NC(Wed), LC, HC+B6. Neither plasma volume percent (%) changes (calculated from hematocrit) nor creatine kinase % changes correlated significantly with % changes in PB6 and PLP. Urinary 4PA was elevated on all EX test days as compared to non-test days, except for EX following LC. Tissue redistribution of B6 appears to be occurring with exercise. With the LC diet, more B6 is needed for increased amino acid catabolism in the liver. In this situation tissue redistribution was not associated with increased conversion of B6 to 4PA. Greater increases in PLP with EX following supplementation suggests increased storage may have occurred. These findings are supportive of the hypothesis that increased PLP levels with exercise may originate from PLP bound to phosphorylase. The need for supplemental B6 for the athlete was not established, as status was adequate with normal intakes.
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