Type I collagen synthesis and degradation in peritendinous tissue after exercise determined by microdialysis in humans

Abstract

1. Physical activity is known to increase type I collagen synthesis measured as the concentration of biomarkers in plasma. By the use of microdialysis catheters with a very high molecular mass cut-off value (3000 kDa) we aimed to determine local type I collagen synthesis and degradation in the peritendinous region by measuring interstitial concentrations of a collagen propeptide (PICP; 100 kDa) and a collagen degradation product (ICTP; 9 kDa) as well as an inflammatory mediator (PGE2). 2. Seven trained human runners were studied before and after (2 and 72 h) 3 h of running (36 km). Two microdialysis catheters were placed in the peritendinous space ventral to the Achilles' tendon under ultrasound guidance and perfused with a Ringer-acetate solution containing 3H-labelled human type IV collagen and [15-3H(N)]PGE2 for in vivo recovery determination. Relative recovery was 37-59 % (range of the s.e.m. values) for both radioactively labelled substances. 3. PICP concentration decreased in both interstitial peritendinous tissue and arterial blood immediately after exercise, but rose 3-fold from basal 72 h after exercise in the peritendinous tissue (55 +/- 10 microg l-1, mean +/- s.e.m. (rest) to 165 +/- 40 microg l-1 (72 h), P < 0.05) and by 25 % in circulating blood (160 +/- 10 microg l-1 (rest) to 200 +/- 12 microg l-1 (72 h), P < 0.05). ICTP concentration did not change in blood, but decreased transiently in tendon-related tissue during early recovery after exercise only. PGE2 concentration increased in blood during running, and returned to baseline in the recovery period, whereas interstitial PGE2 concentration was elevated in the early recovery phase. 4. The findings of the present study indicate that acute exercise induces increased formation of type I collagen in peritendinous tissue as determined with microdialysis and using dialysate fibre with a very high molecular mass cut-off. This suggests an adaptation to acute physical loading also in non-bone-related collagen in humans.

Figure 1. The experimental design and sampling

The experiment consisted of a rest period (60 min), an exercise period (180 min) during which the subjects ran 36 km (12 km h⁻¹), a recovery period (120 min) following the acute exercise, and an additional rest period 72 h after the exercise bout (120 min). Microdialysis was performed during rest, recovery immediately after exercise and recovery 72 h following exercise. Sampling was not done till 90 min after insertion of the microdialysis catheters into the tissue in order to minimise the risk of the insertion trauma influencing the results. Blood samples were drawn (arrows) every 30 min during rest, early and late (72 h) recovery, and every 60 min during running.

Figure 2. Carboxy-terminal propeptide of type I collagen (PICP) measured as a marker for collagen synthesis

PICP concentration was determined in the tissue around the Achilles' tendon and in plasma during rest, after 36 km of running (Recovery), as well as 72 h after termination of the exercise (means and s.e.m.). * P < 0·05 vs. Rest.

Figure 3. Carboxy-terminal telopeptide region of type I collagen (ICTP) measured as an indicator of collagen breakdown

ICTP concentration was determined in the tissue around the Achilles' tendon and in plasma at the indicated times (means and s.e.m.). * P < 0·05 vs. Rest.

Figure 4. Effect of exercise on the concentration of PGE₂

PGE₂ concentration was measured in the tissue around the Achilles' tendon and in plasma at the indicated times (means and s.e.m.). * P < 0·05 vs. Rest. As microdialysis was not performed during exercise no value for PGE₂ was obtained in the tissue during Running.