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

1. Physical activity is known to increase type I collagen synthesis measure d 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 aime d to determine local type I collagen synthesis and degradation in the perit endinous region by measuring interstitial concentrations of a collagen prop eptide (PICP; 100 kDa) and a collagen degradation product (ICTP; 9 kDa) as well as an inflammatory mediator (PGE(2)). 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 perit endinous space ventral to the Achilles' tendon under ultrasound guidance an d perfused with a Ringer-acetate solution containing H-3-labelled human typ e IV collagen and [15-H-3(N)]PGE(2) for in vivo recovery determination. Rel ative recovery was 37-59% (range of the S.E.M. values) for both radioactive ly labelled substances. 3. PICP concentration decreased in both interstitial peritendinous tissue a nd arterial blood immediately after exercise, but rose 3-fold from basal 72 h after exercise in the peritendinous tissue (55 +/- 10 mu g l(-1), mean /- S.E.M. (rest) to 165 +/- 40 mu g l(-1) (72 h), P < 0.05) and by 25% in c irculating blood (160 +/- 10 mu g l(-1) (rest) to 200 +/- 12 mu g l(-1) (72 h), P < 0.05). ICTP concentration did not change in blood, but decreased t ransiently in tendon-related tissue during early recovery after exercise on ly. PGE(2) concentration increased in blood during; running, and returned t o baseline in the recovery period, whereas interstitial PGE(2) concentratio n was elevated in the early recovery phase. 4. The findings of the present study indicate that acute exercise induces i ncreased formation of type I collagen in peritendinous tissue as determined with microdialysis and using dialysate fibre with a very high molecular ma ss cut-off. This suggests an adaptation to acute physical loading also in n on-bone-related collagen in humans.