Improved Methods for Transplanting Split-heart Neonatal Cardiac Grafts Into the Ear Pinna of Mice and Rats

The rodent heterotopic ear–heart transplant method is a useful alternative to the more technically demanding vascularized graft technique. We modified the procedure to improve efficiency and used it in mice and rats to determine the survival times of both isologous and allogeneic grafts and compare reference immunosuppressants. Bisected rat and mouse cardiac (split-heart) isografts were uniformly viable up to 4 weeks postimplant; however, by 24 weeks only 90% of Lewis rat or C3H mouse split-heart isografts retained electrocardiographic activity, regressing to 81% by 60 weeks for the Lewis rat and to less than 50% for the C3H mouse by 43 weeks post-implant. The potency of tacrolimus, sirolimus, and cyclosporine for prevention of allograft rejection was comparable whether using split-hearts or whole hearts in the Balb/C to C3H mouse model. The maximally effective doses at 2 weeks postimplant for intraperitoneally administered tacrolimus, sirolimus, cyclosporine, and oral leflunomide with Brown-Norway (BN) to Lewis rat ear-split-heart allografts (0.3, 0.1, 3.0, 10, mg/kg/day, respectively) agreed extremely well with published data for the rat primary vascularized heterotopic heart model. This reproducible and efficient transplantation model was improved by using split-hearts to double available donor tissue, a gonadotropin-enhanced breeding strategy that enables routine use of low-fecundity inbred rats as donors, implantation devices that speed and simplify the procedure, and defined electrocardiographic evaluation criteria to maximize sensitivity and provide an objective endpoint for defining rejection.