Endothelial damage due to ischemia and reperfusion is prevented with SIN-1

Acute ischemia followed by reperfusion results in direct endothelial damage characterized by cell swelling, increased permeability and loss of acetylcholine-mediated vasorelaxation. Ischemia followed by reperfusion in a New Zealand white rabbit hindlimb has been shown to result in loss of acetylcholine-induced relaxation of superficial femoral arteries. This loss of relaxation in response to acetylcholine is a reflection of the decreased nitric oxide availability that occurs with reperfusion injury. The purpose of this investigation was to evaluate the effect of SIN-1. a direct nitric oxide donor, on this endothelial injury. New Zealand white rabbits underwent complete ischemia of the right hindlimb for 3 h followed by 2 h of reperfusion. Aliquots of 20 ml of either 0.88-mM S1N-1 or normal saline was infused via a lateral branch of the right common iliac artery during the first 20 min of reperfusion. Sham vessels were subjected to the 5-h operative intervention to control for anesthetic effect. Control vessels were harvested from rabbits not exposed to ischemia or reperfusion. Superficial femoral artery rings were evaluated in vitro for endothelial cell-mediated relaxation. Rings were contracted with potassium chloride and norepinephrine and then exposed to standardized incremental doses of acetylcholine to measure percent relaxation. Artery sections were sent for hematoxylin and eosin staining. No significant differences were seen in contraction caused by either potassium chloride or norepinephrine in ail four experimental groups. Saline infused vessel rings relaxed a mean of 8.42 ± 2.39% and 49.57 ± 8.65% in response to acetylcholine doses of 3 × 10₋₈ M and 1 × 10₋₇M, respectively. In contrast, SIN-1 infused vessels relaxed a mean of 57.82 ± 2.65% and 100.23 ± 1.53% to the same doses of acetylcholine. Control and sham arteries showed a similar relaxation response as compared with SIN-1 infused vessels. Differences in relaxation when comparing saline infused vessels with SIN-1 infused, sham and control arteries, were significantly different at each dose of acetylcholine from 3 × 10₋₈M to 1 × 10₋₇M (P < 0.05, ANOVA). Histologic examination of the vessels revealed no morphologic differences among the experimental groups. All vessels were structurally normal with an intact endothelium. In this model of rabbit hindlimb ischemia, preservation of endothelial cell-mediated vasorelaxation occurs with administration of intra-arterial SIN-1 during reperfusion. This preservation of endothelial function cannot be explained by histologic changes in the arterial wall or attributed to altered arterial contractility in response to potassium chloride or norepinephrine.