Temporal expression of nitric oxide synthase isoforms in healing Achilles tendon

We investigated the temporal expressions of the three nitric oxide synthase (NOS) isofolms by semi-quantitative polymerase chain reaction (PCR) assays and by immunoblot analysis, following Achilles tendon transection in rats. Four days after injury, there were increases in the steady-state levels of mRNA for all three NOS isoforms, with peak for the inducible isoform (iNOS ) (seven-fold increase) at day 4, the endothelial isoform (eNOS) (23-fold i ncrease) at day 7 and the neuronal isoform (bNOS) (seven-fold increase) at day 21. The temporal expression of NOS isoforms at a protein level was cons istent with the results at the mRNA level. We have previously shown a five- fold increase in the NOS activity, as detected by: H-3-arginine to H-3-citr ulline conversion, at day 7 postinjury. These findings indicate that all th ree NOS isoforms are expressed during tendon heeling with differential expr ession patterns during the various phases of tendon healing. These findings may prove clinically relevant with respect to strategies for regulating te ndon healing. (C) 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.