Lepirudin is a safe and effective anticoagulant for patients with heparin-associated antiplatelet antibodies.

OBJECTIVE: The purpose of this study was to determine whether lepirudin, a direct thrombin inhibitor, is a safe and effective anticoagulant for patients with heparin-associated antiplatelet antibodies (HAAbs). METHODS: The charts of HAAb-positive patients who received lepirudin were reviewed. Lepirudin use was analyzed for indication, duration, and effectiveness of anticoagulation, and for adverse events. HAAb presence was determined by platelet aggregation. RESULTS: Eighteen HAAb-positive patients received lepirudin: 9 had previous documentation of HAAb, 6 had thrombocytopenia while receiving heparin; and 3 had HAAb after a thrombotic event. The indications for lepirudin anticoagulation included thromboembolism prophylaxis (5), arterial thromboses (5), pulmonary embolus (3) or deep venous thrombosis (1), and one each for atrial fibrillation, myocardial infarction, artificial heart valves, and hemodialysis access. The average duration of therapy was 4.04 days. Fifteen patients achieved adequate anticoagulation (activated partial thromboplastin time [aPTT] ratio > 2.0) with lepirudin. Seven patients had aPTTs that were sometimes supratherapeutic (aPTT > 100 seconds) but did not bleed. In all patients who had heparin-induced thrombocytopenia, platelet counts were normalized while they received lepirudin. There were two complications: one patient fell and had a calf hematoma (aPTT ratio 3.24), and one patient who received lepirudin during nine separate hospitalizations had epistaxis (aPTT ratio 2.86) during her ninth hospitalization. Another patient received lepirudin during two hospitalizations without an adverse event. CONCLUSION: Lepirudin is a safe and effective anticoagulant for patients with HAAbs. The platelet counts of all patients with heparin-induced thrombocytopenia were normalized while they received lepirudin. Careful monitoring of the aPTT and avoidance of trauma while patients are receiving lepirudin are recommended.

Cholesterol, but not cigarette smoke, decreases rabbit carotid artery relaxation.

The purpose of this study was to determine the physiologic effects of cigarette smoke exposure and dietary cholesterol on the availability of nitric oxide in carotid vascular rings. New Zealand white rabbits were placed in an airflow chamber for 3 hr/day over an 8-week period and were exposed to smoke from 600 cigarettes/per day added to the chamber inflow by a robotic smoke generator. New Zealand white rabbits, made hypercholesterolemic, and one group fed a normal diet, were similarly placed in the chamber without exposure to cigarette smoke. In those exposed groups, serum cotinine and cholesterol levels were consistently elevated. After the 8-week period, the carotid arteries were harvested. The vessels were cut into 3-mm rings which were suspended from pressure transducers. The rings were contracted with potassium chloride (KCl) to determine vessel integrity. One ring from each carotid was maximally contracted with 1 x 10(-3) molar norepinephrine (NE) while the experimental ring was contracted to 50% of maximum. Relaxation of the rings was achieved by adding incremental doses of acetylcholine. Our results showed that endothelial dysfunction, as measured by acetylcholine-mediated vasorelaxation, occurs in the rabbit carotid artery when exposed to high dietary cholesterol. Cigarette exposure alone in this particular vessel did not result in significant alteration in acetylcholine-mediated vasorelaxation.

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

BACKGROUND: 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. METHODS: 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 SIN-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. RESULTS: No significant differences were seen in contraction caused by either potassium chloride or norepinephrine in all 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 x 10(-8) M and 1 x 10(-7) M, 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 x 10(-8) M to 1 x 10(-7) M (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. CONCLUSION: 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.

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

BACKGROUND: 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. METHODS: 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 SIN-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. RESULTS: No significant differences were seen in contraction caused by either potassium chloride or norepinephrine in all 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 x 10(-8) M and 1 x 10(-7) M, 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 x 10(-8) M to 1 x 10(-7) M (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. CONCLUSION: 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.

Combined exposure to cigarette smoke and hypercholesterolemia decreases vasorelaxation of the aorta.

PURPOSE: The purpose of this study was to determine the physiologic effects of cigarette smoke exposure and dietary cholesterol on the availability of nitric oxide in aortic vascular rings. METHODS: Four groups of New Zealand White rabbits were placed in an air flow chamber for 3 hours per day for 8 weeks. Two of these groups were exposed to smoke from 600 cigarettes per day 5 days a week added to the chamber inflow by a robotic smoke generator. One of these groups was made hypercholesterolemic by being fed a 0.3% cholesterol diet. Two groups of rabbits were similarly placed in the air flow chamber but without smoke exposure, of which one group was also made hypercholesterolemic. After an 8-week period, the rabbits were killed and the infrarenal aortas were excised. The vessels were cut into 3 mm rings and suspended from tension transducers. The rings were contracted with potassium chloride to determine vessel integrity. Then one ring from each aorta was maximally contracted with norepinephrine, and the experimental ring was contracted to 50% of maximum. Relaxation of the rings in response to incremental doses of acetylcholine was measured. RESULTS: No significant differences were seen in contraction to potassium chloride or norepinephrine in any group. A significant decrease in acetylcholine-mediated relaxation was seen only in the smoke-exposed, cholesterol-fed group. CONCLUSIONS: Endothelial damage, as measured by acetylcholine-mediated vasorelaxation, occurs in the infrarenal aorta in rabbits that are exposed to both cigarette smoke and elevated dietary cholesterol. Cigarette smoke exposure alone or hypercholesterolemia alone in this model did not result in significant alteration in acetylcholine-mediated vasorelaxation.

Pentoxifylline prevents endothelial damage due to ischemia and reperfusion injury.

BACKGROUND: Endothelial injury after ischemia and reperfusion is characterized by an increase in permeability, cellular edema, and loss of acetylcholine-mediated vasorelaxation. Three hours of ischemia followed by 2 hr of reperfusion in the New Zealand white rabbit hindlimb has been shown to result in loss of acetylcholine-induced superficial femoral artery vasorelaxation. The purpose of this study was to evaluate the effect of intraarterial pentoxyfylline (PTX) on this endothelial injury. METHODS: New Zealand white rabbits underwent 3 hr of complete hindlimb ischemia followed by 2 hr of reperfusion. Twenty milliliters of either 100 microM PTX or normal saline was infused over 20 min via the circumflex iliac artery at initiation of reperfusion. Superficial femoral artery rings were then evaluated in vitro for endothelial cell-mediated relaxation. Rings were exposed to standardized incremental doses of acetylcholine after norepinephrine-induced contraction and percentage relaxation was measured. Sections of arteries were also sent for hematoxylin and eosin staining. RESULTS: Similar contraction responses following NE stimulation were observed between control and PTX-treated rings. Control rings relaxed a mean of 14.97 +/- 3.64, 23.17 +/- 5.61, and 31.84 +/- 8.43% in response to acetylcholine doses of 6 x 10(-8), 1 x 10(-7), and 1.5 x 10(-7) M, respectively. In contrast, PTX-treated segments relaxed a mean of 47.52 +/- 8.88, 62.32 +/- 6.83, and 76.73 +/- 4.91% to the same doses of acetylcholine. Differences in relaxation between control and PTX-treated vessels were significantly different at each dose (P < 0.05, Student's t test). Histologic examination of the PTX-treated and control arteries revealed an intact endothelium without morphologic differences between the two groups. CONCLUSION: In this model of rabbit hindlimb ischemia, endothelial cell-mediated vasorelaxation was preserved with the administration of intraarterial PTX during reperfusion compared to controls. The different relaxation responses could not be attributed to altered arterial contractility in response to norepinephrine, or explained by histologic changes in the arterial wall. These studies demonstrate a potential modality for therapeutic intervention to reduce reperfusion injury after acute limb ischemia.