Microcirculatory window for early detection of allograft rejection

The purpose of this study is to introduce a technical detail on a transplantation model for in vivo evaluation of microcirculatory changes during the acute phase of allograft rejection. The cremaster muscle is incorporated and transplanted along with the hind limb to detect and study ischemia/reperfusion injury and the acute phase of allograft rejection in rats. Thirty-six animals were studied in three experimental groups of 12 animals each. Each group was divided into subgroups and microcirculatory measurements were taken at two different time periods: 24 and 72 hours. In the ischemic control group (N = 12), cremaster muscles were denervated, prepared as a tube flap, and submitted to the same interval of ischemia as the other groups but without transplantation. In the isograft group (N = 12), rat hind limb-cremaster grafts were transplanted between genetically identical Lewis rats (RT11). In the allograft group (N = 12), 12 transplantations were performed across a major histocompatibility barrier between Lewis Brown-Norway (RT-11+/-n) and Lewis (RT 11) rats. The diameters of first-, second-, and third-order arterioles and venules; red blood cell velocities; and functional capillary density were recorded at 24 and 72 hours after transplantation. Daily follow-up observations were continued until 3 days after the first clinical signs of graft rejection. The mean number of perfused capillaries in the two transplantation groups was significantly lower than in the control group at both 24 hours and 72 hours (p < 0.05). Those results were as follows: 8.2 +/- 2.1 at 24 hours, 7.7 +/- 0.85 at 72 hours in the ischemic control group; 5.4 +/- 0.9 at 24 hours, 6 +/- 0.6 at 72 hours in the isograft group; and 5 +/- 0.9 at 24 hours, 5.5 +/- 0.3 at 72 hours in the allograft group. Red blood cell velocities and vessel diameters in the main arteries were also decreased in transplant groups at 24 hours (p < 0.05) but returned to normal 72 hours after the operation (p > 0.05). The composite rat hind limb-cremaster model presented in this study introduces a reproducible in vivo approach to monitor the differences in microcirculatory hemodynamics of ischemia/reperfusion injury and acute graft rejection. The model allows the study of the timing, sequence, and correlation between clinical and hemodynamic signs during the acute phase of allograft rejection.