In a well done study, researchers have shown when athletes are given an intratendinous injection of leukocyte-enriched platelet rich plasma (PRP), they will have elevated levels of growth factors in their blood up to four days after the procedure. (see abstract below)
Vascular-endothelial growth factor (VEGF), a molecule known to enhance angiogenesis (new blood vessel formation), was elevated in all 25 patients after injection. This is very interesting and important data suggesting PRP may trigger a systemic response. It also helps explain why PRP may be a useful treatment for tendon related injuries and disorders. Several controlled studies confirm PRP can be an effective treatment for chronic tennis elbow and this study may reveal one of the mechanisms of action.
Tennis Elbow Study 1, Tennis Elbow Study 2
It would be quite interesting and important to also measure growth factors in athletes who have received a saline injection or dry needling of their tendons to see if the act of introducing a needle into a damaged tendon produces a similar or different systemic response.