Does Sustained Epinephrine Release Trigger a Hypoxia-Neovascularization Cascade?

Abstract

Recent data regarding the long-term local administration of epinephrine to soft tissues for the purpose of inducing prolonged vasoconstriction have yielded promising results. These studies postulated that long-term release of epinephrine by a microsphere/drug delivery system caused continuous vasoconstriction and subsequent vascular augmentation. The goal of this study was to test the hypothesis that epinephrine induces a hypoxia-neovascularization cascade and plays a primary role in vascular proliferation within soft tissues. Thirty male New Zealand White rabbits were randomly grouped as follows: group I, control (n = 10); group II, saline-loaded microsphere/drug delivery system injection (n = 10); and group III, epinephrine-loaded microsphere/drug delivery system injection (n = 10). A 2 x 1-cm rectangle was marked on the dorsal surface of the left ear of each rabbit. No solutions were injected in the control group, whereas 1 ml of saline-loaded and epinephrine-loaded microspheres was injected into groups II and III, respectively. A laser Doppler device was used to measure tissue blood volume and tissue blood flow. Laser Doppler monitoring in tissue blood flow yielded a distinct difference between the epinephrine-loaded microsphere-injected group and the other two groups (p < 0.05). The ability of epinephrine-loaded microspheres to augment the vascular network in vivo is the result of sustained vasoconstriction with consequent tissue hypoxia and subsequent neovascularization. Data extracted from the present study, first, might be applied to improve hemostasis for operations typically plagued by serious intraoperative blood loss. Second, the ability to intentionally augment the vascularity of certain flaps before elevation should result in their increased survival. Radiation-injured tissues may also derive great benefit from this treatment.