Graduate Thesis Or Dissertation
 

The effect of a 50-km ultramarathon on vitamin B-6 metabolism and plasma and urinary urea nitrogen

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  • The purpose of this study was to examine the effect of extreme exercise on vitamin B-6 metabolism and urea nitrogen. Nine men and five women completed two 5-day trials; Trial 1 (T1) included a 50-km ultramarathon on day 4 and during Trial 2 (T2) subjects were "inactive" on day 4. During both trials, subjects consumed a diet providing men 2.0 and women 1.5 mg of vitamin B-6. With the exception of the ultramarathon, T1 activity was replicated during T2. Twenty four-hour urine collections were completed and blood was drawn pre-race (pre), mid-race (mid), post-race (post) and 60 minutes post race (P-60). On the inactive, day blood was drawn at the same intervals. Plasma was analyzed for pyridoxal 5'-phosphate (PLP), pyridoxal, 4-pyridoxic acid (4-PA), urea nitrogen (PUN), creatinine, albumin, glucose, and lactate concentration and alkaline phosphatase activity. Urine was analyzed for 4PA, creatinine, and total urinary nitrogen (TUN). During T1, compared to pre, plasma PLP concentration increased 17% at mid, decreased 5% by post, and 19% by P-60. During T2, plasma PLP concentration decreased 13% pre to P-60. During T1, plasma 4-PA concentration increased 135% and the percent dietary vitamin B-6 that was excreted as urinary 4-PA the day of the ultramarathon was higher than that excreted the day before and the day after. During T1, from pre to post mean PUN concentration increased 36.9%, and the average rate ofincrease from pre to mid, mid to post, and post to P60 was 0.5, 1.75, and 2 mg/dL/hour, respectively. During T1 on days 3, 4, and 5,88%, 100%, and 95% of nitrogen intake was excreted in the urine compared to 86%, 83%, and 84% for the same days during T2. The day of the ultramarathon, 24-hour TUN excretion was 2 g higher than the previous day. Extreme exercise of greater than six hours initially increases the plasma concentration of PLP but ultimately results in a significant decrease in plasma PLP, an increase in plasma 4-PA, and an increase in percent of dietary vitamin B-6 (as 4-PA) excreted in the urine. Additionally, the rate of change in PUN inoeases as duration increases.
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