Receptor-specific effects of acute rejection after heart transplantation on endothelium-dependent coronary relaxation in dogs.

To establish the effects of acute rejection on coronary artery endothelial reactivity in a canine model of heart transplantation, we submitted seven mongrel dogs to heterotopic heart transplantation without immunosuppression for a period of 7 days. At harvesting, all transplanted hearts displayed a grade IV histologic rejection. Compared with native heart, the endothelium-dependent relaxation of the coronary arteries from the graft displayed an increased sensitivity to serotonin, a decreased sensitivity to thrombin, and no change in the response to acetylcholine and adenosine diphosphate; endothelium-independent relaxation to sodium nitroprusside was not affected. Therefore, in the canine heterotopic heart transplant model, acute rejection has no effect on endothelium-independent relaxation of coronary arteries but affects endothelium-dependent relaxation in a receptor-specific manner.