484 Exchange of Purines in Active and Inactive Skeletal Muscle With High Intensity Exercise

Hellsten, Ylva; Madsen, Kjell; Richter, E. A.; Kiens, Bente; din, B. Sj; Bangsbo, Jens

doi:10.1249/00005768-199405001-00485

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“…7). This is slightly higher than observed in recovery from long term intermittent exercise and after 10 min of exhaustive cycling exercise (Hellsten et al 1994;Hellsten et al 1998). The lost nucleotides have to be resynthesized de novo, a process that can be estimated to take about 18 h using an average rate of 25 ìmol h¢ (kg w.w.)¢ for rat mixed muscle after contraction (Tullson & Terjung, 1991).…”

Section: Figurementioning

confidence: 92%

“…No difference between time-matched and measured blood flow was larger than 0•3 l min¢. Although plasma rather than blood NH×, inosine, hypoxanthine and urate concentrations were measured, it was used in combination with blood flow to estimate blood exchange of these variables because the absolute changes in plasma and whole blood concentrations for these variables are virtually identical (Harris & Dudley, 1989;Hellsten et al 1998).…”

Section: Calculationsmentioning

confidence: 99%

“…A release of hypoxanthine from intensely exercised muscle has been observed, representing a loss of nucleotide precursors from the muscle (Bangsbo et al 1992b;Hellsten-Westing et al 1994). Furthermore, the ATP concentration in muscle has been found to be lowered for more than 90 min in recovery from long-term intense intermittent exercise, in part due to release of purines (Hellsten et al 1998). It is, however, uncertain to what extent the release of purines can account for a loss in adenine nucleotides during and after a single bout of short-term intense exercise.…”

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confidence: 98%

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AMP deamination and purine exchange in human skeletal muscle during and after intense exercise

Hellsten

Richter

Bangsbo

1999

The Journal of Physiology

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146

129

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The present study examined the regulation of human skeletal muscle AMP deamination during intense exercise and quantified muscle accumulation and release of purines during and after intense exercise. Seven healthy males performed knee extensor exercise at 64.3 W (range: 50–70 W) to exhaustion (234 s; 191–259 s). In addition, on two separate days the subjects performed exercise at the same intensity for 30 s and 80 % of exhaustion time (mean, 186 s; range, 153–207 s), respectively. Muscle biopsies were obtained from m.v. lateralis before and after each of the exercise bouts. For the exhaustive bout femoral arterio‐venous concentration differences and blood flow were also determined. During the first 30 s of exercise there was no change in muscle adenosine triphosphate (ATP), inosine monophosphate (IMP) and ammonia (NH3), although estimated free ADP and AMP increased 5‐ and 45‐fold, respectively, during this period. After 186 s and at exhaustion muscle ATP had decreased (P < 0.05) by 15 and 19 %, respectively, muscle IMP was elevated (P < 0.05) from 0.20 to 3.65 and 5.67 mmol (kg dry weight)−1, respectively, and muscle NH3 had increased (P < 0.05) from 0.47 to 2.55 and 2.33 mmol (kg d.w.)−1, respectively. The concentration of H+ did not change during the first 30 s of exercise, but increased (P < 0.05) to 245.9 nmol l−1 (pH 6.61) after 186 s and to 374.5 nmol l−1 (pH 6.43) at exhaustion. Muscle inosine and hypoxanthine did not change during exercise. In the first 10 min after exercise the muscle IMP concentration decreased (P < 0.05) by 2.96 mmol (kg d.w.)−1 of which inosine and hypoxanthine formation could account for 30 %. The total release of inosine and hypoxanthine during exercise and 90 min of recovery amounted to 1.07 mmol corresponding to 46 % of the net ATP decrease during exercise or 9 % of ATP at rest. The present data suggest that AMP deamination is inhibited during the initial phase of intense exercise, probably due to accumulation of orthophosphate, and that lowered pH is an important positive modulator of AMP deaminase in contracting human skeletal muscle in vivo. Furthermore, formation and release of purines occurs mainly after intense exercise and leads to a considerable loss of nucleotides.