Direct revascularization is superior for rat parathyroid allotransplantation with FK506

Parathyroid gland allotransplantation has been a challenging goal for decades. Our objective was to optimize a parathyroid allotransplantation model for analysis of short-term or low-dose immunosuppressive regimens. Rats that had undergone parathyroidectomy received parathyroid allografts either by direct microvascular anastomoses as part of a composite laryngotracheal graft or by direct implantation into hind limb muscle. All rats were maintained on daily low-dose FK506 (tacrolimus). Intact serum parathyroid hormone (PTH) levels for both groups were recorded over a period of at least 45 days and compared with a repeated-measures mixed model. We found that microvascular anastomosis was superior to implantation for parathyroid gland survival, as all revascularized grafts immediately produced normal levels of PTH, whereas implanted grafts had a significantly slower recovery of function (p < .001). Four of the 11 implanted grafts (36%) never produced detectable PTH levels. Using this model, we are developing innovative strategies that will lead to successful parathyroid allotransplantation without the need for chronic immunosuppression.