Effects of 8-Gy radiation on the microcirculation of muscle flaps in the rat

Combination of radical excision and radiation has been used as a treatment modality for cancer patients. As a result, in reconstructive surgery there is often a need to harvest flaps in the vicinity of previously irradiated tissues. Radiation has been shown to cause progressive injury to the macrocirculation and microcirculation, often jeopardizing flap survival. The purpose of this study was to examine whether radiation significantly affects the sequence of leukocyte-endothelial interactions or the hemodynamics of the muscle flap in both acute and chronic situations. Male Sprague-Dawley rats (n = 42) were divided into seven groups of six rats each. Rats in group I were not irradiated. Groups II through VII received 8-Gy radiation to the right groin and scrotum. Groups II, III, and IV were examined at 4, 24 and 72 hours, respectively, and groups V, VI, and VII were examined at 1, 2 and 12 weeks. For intravital microscopy, the cremaster muscle was dissected on its neurovascular pedicle. Vessel diameters and red blood cell velocities were measured in the central cremasteric branches and branch arterioles. Capillary perfusion was evaluated in 27 visual fields of each flap. Leukocyte-endothelial interactions were evaluated by numbers of rolling, adhering, and transmigrating leukocytes in post-capillary venules. In the same postcapillary venule, we measured the endothelial edema index (constriction index). The hemodynamics of irradiated flaps did not differ significantly from those of controls. Diameter and red blood cell velocity were increased in the first- and second-order arterioles and were highest at 72 hours and 1 week. After irradiation, third-order arterioles were constricted. Radiation reduced capillary perfusion by 4.3, percent. None of the differences were statistically significant. Neither leukocyte behavior nor the constriction indices differed among the groups. In conclusion, low-dose radiation of 8 Gy does not affect hemodynamics or leukocyte-endothelial interactions of muscle flaps in the rat. Muscle tissue with intact microvasculature can be harvested for reconstructive procedures after low-dose radiation.