Objective: To assess distribution, uptake, and persistence of radiolabeled mesenchymal stem cells (MSC) using scintigraphy after intravenous regional limb perfusion (RLP) and subcutaneous injections in standing, sedated horses. Study Design: Experimental study. Animals: Horses (n=12). Methods: Six horses had RLP performed through the cephalic vein on 1 limb and subcutaneous injection in the metacarpal area in the opposite limb. The other 6 horses had RLP performed through the lateral palmar digital vein and subcutaneous injection in the coronary band. A pneumatic tourniquet was used for the RLP. MSC were labeled with technetium-HMPAO. Scintigraphic images were obtained at the time of injection, 1, 6, and 24hours later. Results of RLP were compared with results from previous studies where similar injections were performed in anesthetized horses. Results: Both RLP techniques led to greater variability, lower uptake, lower persistence, and poorer distribution when compared to results previously reported for horses under general anesthesia. The subcutaneous injections in the metacarpal area and coronary band resulted in MSC loss to the general circulation but no evidence of local migration. Conclusion: Due to partial or complete failure of the tourniquet, RLP performed in the standing horse as described is less efficient than performed under general anesthesia. Further work is needed to optimize the use of tourniquets to perform RLP for MSC administration in standing patients. The subcutaneous injections did not result in local migration in these normal horses.
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