Functional, metabolic, and histological changes of vascular tissues after warm ischemia

We examined functional, metabolic, and histological changes in the aortic tissue of rats after the period of warm ischemia ranging from 0 to 24 hours to determine the window of time in which grafts can be optimally viable for harvest. Sixty aortas from Brown Norway rats obtained after warm ischemia were used and changes in contraction, endothelial-dependent or -independent vasodilatation, cell viability, and histology were examined. Maximal contraction induced by norepinephrine and potassium chloride decreased time-dependently after exposure to warm ischemia. The warm ischemic period when 50% of the maximal contractile response of freshly isolated arteries was preserved, ranged from 6 to 8 hours. Maximal endothelium-dependent relaxation induced by acetylcholine decreased along with the time of warm ischemia. Endothelium-independent relaxation induced by sodium nitroprusside and forskolin was unaltered for up to 9 hours. Cell viability gradually decreased, and a significant negative correlation was found between warm ischemic period (T: hours) and cell viability (V: %) (V=101.9-2.35T; r(2)=0.96; p<0.0001). Cell viability was greater than 70% within 12 hours postmortem. Histologically, after 9-hour-warm ischemia irreversible changes were detected. Results suggest that the period of warm ischemia for up to 6 hours would be acceptable for preservation of tissue viability.