title: A model of xenograft hyperacute rejection attenuates endothelial nitric oxide production: a mechanism for graft vasospasm?
abstract: BACKGROUND
  The deposition of complement components within grafts, complement consumption, and prolongation of graft function by complement inactivation imply a pivotal role for complement in xenograft hyperacute rejection. The current investigations examined the endothelial production of vasoactive substances in pulmonary arteries during simulated hyperacute rejection.
  
  
  RESULTS
  Canine pulmonary arteries were suspended in organ chambers and exposed to either autologous canine serum for 90 minutes or heterologous porcine serum for 30, 60, or 90 minutes. Following serum exposure, the vessels were allowed a one-hour equilibration in buffered crystalloid solution. Dose-response curves were obtained with acetylcholine, sodium nitroprusside, and calcium ionophore A23187 following contraction with phenylephrine (10(-6) M) in the presence of indomethacin (10(-5) M). Receptor-dependent, endothelial-dependent relaxations to acetylcholine (10(-9)-10(-4) M) were impaired with 30-, 60-, or 90-minute porcine serum exposure when compared to vessels exposed to autologous canine serum (n = 10, 7, 9, respectively; p < .05; 2-way ANOVA). Receptor-independent, endothelial-dependent relaxations to calcium inophore (10(-9)-10(-6) M) were significantly impaired at 60- and 90-minute porcine exposures only (n = 7, 8; p < .05). Endothelial-independent relaxations to sodium nitroprusside (10(-9)-10(-4) M) were not impaired with either canine or porcine serum exposure. Oxyhemoglobin (10(-6) M) abolished acetylcholine-mediated relaxations, indicating that nitric oxide was the predominant mediator.
  
  
  CONCLUSIONS
  Simulated hyperacute xenograft rejection impairs endothelium-dependent relaxation of canine pulmonary arteries. Both basal and stimulated production of nitric oxide is impaired by heterologous serum exposure and, subsequently, complement activation. Reduced production of nitric oxide may explain, in part, the vasospasm and thrombosis of xenografts during hyperacute rejection.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000208:Acute Disease; D000818:Animals; D001769:Blood; D000001:Calcimycin / Q000494:pharmacology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000502:physiology; D006084:Graft Rejection / Q000503:physiopathology*; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011651:Pulmonary Artery / Q000378:metabolism; D013552:Swine; D014183:Transplantation, Heterologous; D014661:Vasoconstriction / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology