Evidence for damage due to free radicals at reperfusion in porcine liver transplants.
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Animals↗
Biomedical subjects
G B Bulkley
Publications and source records attributed to G B Bulkley.
Functional and structural evaluation of the vasculature of skin flaps after ischemia and reperfusion.
Free radicals and other toxic oxygen species play a role in the pathogenesis of ischemic organ damage. The abdominal skin flap has been used as a model to study the effects of superoxide dismutase on the survival of ischemic skin. We have evaluated the evolution of functional and structural injury to the vasculature after ischemic injury in superoxide dismutase-treated and control skin flaps. Ischemia was induced by creating abdominal skin flaps and occluding either the venous or both the venous and arterial blood supplies. Superoxide dismutase was administered immediately after the occlusion was released. At 1 hour of reflow, erythrocyte stasis, platelet deposition, neutrophil adherence, and injury to the endothelium of the large vessels and of the microvasculature were evident. The blood flow in the ischemic skin was only 3 percent of normal. Superoxide dismutase caused no change in the ultrastructure of the vasculature and a marginal decrease in vascular permeability in the ischemic skin at 1 hour of reflow. Increased fluorescent staining of the skin was evident after 24 hours of reflow in the superoxide dismutase-treated flaps. These findings indicate that injury to vascular endothelium by ischemia and reperfusion plays a role in the evolution of skin necrosis.
Abdominal Muscles↗
Ablation of free radical-mediated reperfusion injury for the salvage of kidneys taken from non-heartbeating donors. A quantitative evaluation of the proportion of injury caused by reperfusion following periods of warm, cold, and combined warm and cold ischemia.
Postischemic renal failure is a severe problem following cadaveric renal transplantation, especially if the kidney has been harvested from a non-heartbeating donor, and thereby subjected to periods of both warm and cold ischemia. It is well established that a substantial component of postischemic injury is produced by oxygen-derived free radicals generated from xanthine oxidase at reperfusion. However, the clinical potential of free radical ablative therapy is dependent upon the proportion of the total injury caused by this reperfusion mechanism, compared with the proportion resulting from ischemic injury per se. Therefore, we quantitatively evaluated these proportions in porcine kidneys subjected to various periods of warm (renal artery occlusion in situ), cold (harvest, cold preservation, and allotransplantation), and combined warm and cold ischemia. Experiments were paired, one kidney treated with either superoxide dismutase (SOD) or allopurinol for free radical ablation, the contralateral kidney serving as a control. Creatinine clearance (Ccr) was measured separately for each kidney 48 hr after reperfusion. After 1 and 2 hr of warm ischemia, Ccr dropped to 50% and 36% of normal, respectively. This was improved to 110% and 55% when SOD was given into the renal artery at reperfusion. Similarly, after 24 and 48 hr of cold ischemia, kidney function was significantly improved from 30% and 18% to 72% and 47% of normal, respectively, when allopurinol was added to the preservation solution. SOD used at harvest and again at reperfusion was particularly effective following combined warm and cold ischemia, in a situation mimicking the harvest of cadaver kidneys from a non-heartbeating donor. These findings suggest that the ablation of free radical-mediated reperfusion injury may improve posttransplant renal function sufficiently to allow expansion of the cadaveric donor pool to include non-heartbeating donors.
Allopurinol↗
Haemodynamic characterization of the isolated (denervated) parabiotically perfused rat jejunum.
The isolated (denervated) parabiotically perfused rat jejunum was characterized for base-line haemodynamics, autoregulation of blood flow and oxygen consumption and long-term (3 h) stability with respect to both haemodynamics and the absence of tissue injury. In short-term experiments, the parabiotically perfused preparation autoregulated oxygen consumption but not blood flow over a wide range of perfusion pressures (25-85 mmHg). When the intestinal segment was subjected to near total ischaemia for I h, followed by I h of reperfusion, mucosal injury was induced which could be prevented by i.v. administration of superoxide dismutase after ischaemia just prior to reperfusion, or allopurinol prior to ischaemia. These findings support the concept of post-ischaemic reperfusion injury in the denervated preparation without hepatic ischaemia. This preparation could thus serve as an improved model for the study of the pathophysiology of post-ischaemic reperfusion injury in the rat intestine.
Animals↗
Vasoactive humoral mediators and the splanchnic circulation in shock.
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Hemodynamics↗
Protection of the small intestine from nonocclusive mesenteric ischemic injury due to cardiogenic shock.
In a pericardial tamponade model of cardiogenic shock in pigs, we had previously shown that acute reductions in cardiac output produce severe mesenteric ischemia due to disproportionate splanchnic vasoconstriction. In this study, we extended the period of cardiogenic shock in order to investigate the pathogenesis of ischemic injury to the small intestinal wall. Four hours of tamponade produced sustained changes in splanchnic hemodynamics, similar to those observed in the prior short-term experiments. The resultant mesenteric ischemia caused necrotic lesions of the small intestine which were characteristic of those seen in nonocclusive mesenteric ischemia in human subjects. Prior alpha-adrenergic blockade failed to prevent either sustained mesenteric vasospasm or ischemic injury. In contrast, prior blockade of the renin-angiotensin axis, whether by nephrectomy or angiotensin-converting enzyme inhibition, blocked the splanchnic vasoconstriction, and thereby protected the small intestine from ischemic injury. The primary hemodynamic and pathologic features of this model of nonocclusive mesenteric ischemia appear to be mediated by the renin-angiotensin axis.
Animals↗
Current management of patients with lower gastrointestinal bleeding.
Other than gastrointestinal bleeding, there are few clinical emergencies the successful management of which is so dependent on the setting of priorities. Sequential attention to resuscitation, localization, specific diagnosis, and definitive therapy at a pace proportional to the rate of blood loss results in a satisfactory outcome in most patients who present with lower gastrointestinal bleeding.
Angiography↗
The fundamental hemodynamic mechanism underlying gastric "stress ulceration" in cardiogenic shock.
Acute hemorrhagic ulceration of the gastric mucosa is seen frequently in patients with hypovolemic or cardiogenic shock. Although such lesions clearly are related to regional gastric ischemia, little attention has been directed at the underlying mechanism(s) mediating the ischemia itself. To this end, anesthetized pigs were subjected to sustained cardiogenic shock (mild hemorrhage and pericardial tamponade) such that cardiac output was reduced to 38 +/- 1% of the baseline level for 4 hours, followed by release of the tamponade, reinfusion of the shed blood, and resuscitation for 2 hours. During the period of shock, there was profound regional gastric ischemia, resulting from severe and disproportionate gastric vasoconstriction. "Blinded" gross and microscopic evaluation of the stomachs removed after the experiment revealed severe mucosal ischemic necrosis, hemorrhage, and ulceration, whereas sham-operated pigs showed no lesions. The characteristics of this model therefore mimic the essential features of the gastric "stress ulceration" syndrome. Prior confirmed total alpha-adrenergic blockade with phenoxybenzamine failed to alter these features significantly. In contrast, prior ablation of the renin-angiotensin axis, whether by angiotensin-converting enzyme inhibition with teprotide or by bilateral nephrectomy, significantly and substantially ameliorated the ischemia, vasospasm, and mucosal injury. In this model of cardiogenic shock, acute gastric mucosal "stress ulceration" is caused by a disproportionately severe regional gastric ischemia resulting from selective splanchnic vasospasm that is unaffected by sympathetic blockade but abolished by prior ablation of the renin-angiotensin axis. Like nonocclusive small bowel ischemia, ischemic colitis, and the "shock liver" syndrome, gastric "stress ulceration" is yet another component of the multiple splanchnic organ failure syndrome that appears to be mediated primarily by the remarkable sensitivity of the splanchnic vascular bed to the renin-angiotensin axis.
Animals↗
The primary localization of free radical generation after anoxia/reoxygenation in isolated endothelial cells.
While free radical-mediated reperfusion injury is clearly important in a variety of disparate organs, the particular cellular source of these radicals is unclear. To address this question, we subjected relatively pure (92% +/- 3% by factor VIII immunoassay) cultures of rat pulmonary artery endothelial cells to 0 to 45 minutes of anoxia (95% N2, 5% CO2), followed by reoxygenation (95% air, 5% CO2), to simulate ischemia/reperfusion. Cell injury was assayed after reoxygenation by the release of previously incorporated 51chromium and/or lactate dehydrogenase, and viability was determined by means of trypan blue exclusion. These three end points correlated closely. Without anoxia, the cells remained viable, with minimal evidence of injury for the entire experimental period, while 45 minutes of hypoxia followed by 30 minutes of reoxygenation produced substantial evidence of cell injury in 71% +/- 6% of the cells. This injury was reduced to 21% +/- 2% by treatment with the highly specific free radical scavengers superoxide dismutase and catalase together, either before anoxia or after anoxia, but just before reoxygenation. Similar protection was provided by xanthine oxidase inhibition with allopurinol. The injury was mimicked (without anoxia) by the exogenous generation of superoxide radicals with xanthine and xanthine oxidase. These experiments establish the essential components of free radical generation at reperfusion to be localized within the isolated endothelial cell in the absence of neutrophils or parenchymal cells.
Allopurinol↗
Detection of intra-abdominal hematomas using intraperitoneal xenon 133.
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Animals↗
Free radical-mediated reperfusion injury: a selective review.
Tissue damage as a consequence of ischemia is a major medical problem in an industrialized society. Whereas the conventional view has attributed this injury process to ischemia itself, recent studies have found that a variable, but often substantial proportion of the injury is caused by toxic oxygen metabolites that are generated from xanthine oxidase at the time of reperfusion. This mechanism was first identified and characterized in a model of moderately mild partial vascular occlusion in the feline small intestine. Strikingly similar mechanisms have been subsequently confirmed as the basis for ischemia/reperfusion injury in the stomach, pancreas, liver, skin, skeletal muscle, heart, lung, kidney and central nervous system. The potential for clinical application of this concept is related primarily to that proportion of the total post-ischemic injury that is due to this reperfusion mechanism, set against the proportion due to ischemia itself. Ironically, in clinical cases of intestinal ischemia the reperfusion component appears to be proportionately small, and the potential for treatment of ischemic bowel disease is correspondingly limited. On the other hand, there is reason to expect that the ablation of free radical-mediated reperfusion injury, something that can be readily achieved through non-toxic means, may provide substantial benefit for the treatment of ischemic renal disease, myocardial infarction, stroke, cardiac arrest, and of organs preserved for transplantation.
Animals↗
On the pathophysiology of intestinal ischemic injury. Clinical review.
Intestinal ischemia induces a spectrum of injury from relatively subtle changes in mucosal capillary permeability to gross transmural infarction depending on severity and duration. There is basically two events that can induce intestinal tissue injury in ischemic states, namely hypoxia during the ischemic period and generation of oxygen free radicals following ischemia at reperfusion. In this paper we review data indicating that there is a continuum of injury from the least to the most severe, and by approaching the problem from this perspective we have, in addition, tentatively defined the roles of the two mechanisms in the development of various degrees of intestinal ischemic tissue injury.
Capillary Permeability↗
Pathophysiology of free radical-mediated reperfusion injury.
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Cerebrovascular Circulation↗
Effect of therapy on bleeding rates in gastrointestinal angiodysplasia.
Sixteen patients with gastrointestinal angiodysplasia requiring transfusion were treated with surgical resection, endoscopic electrocautery, or transfusion alone. Pre- and post-therapy transfusion requirements in each group were compared to gauge the efficacy of each therapy. No superiority of any treatment could be shown statistically. The majority of patients had multiple angiodysplastic lesions throughout the gastrointestinal tract, and, accordingly, complete resolution of bleeding after therapy occurred in fewer than one-half of the patients.
Aged↗
The role of leukocytes in the production of oxygen-derived free radicals in acute experimental pancreatitis.
Oxygen-derived free radicals mediate an important step in the initiation of experimental acute pancreatitis in the ex vivo perfused canine pancreas model. In other organ systems, circulating leukocytes may serve as one source of oxygen-derived free radical production. The current experiments were designed to evaluate the role of circulating leukocytes in the generation of injury in this model. Four experimental groups of animals were studied: group I consisted of controls (n = 6); group II had white blood cell (WBC) depletion (n = 4) in which the recirculating whole blood perfusate was depleted of 98% of its circulating leukocytes; group III had oleic acid infusion (FFA) alone (n = 9), which induced pancreatitis; group IV had WBC depletion and FFA (n = 6), in which oleic acid was infused after depletion of the circulating leukocytes in the perfusate. During the 4-hour perfusion period, the pancreatic preparations were monitored hourly for the development of edema, weight gain, and release of alpha-amylase into the perfusate. Animals in groups I and group II manifested no gross edema, gained minimal weight, and did not manifest hyperamylasemia. Leukocyte depletion alone had no effect. In group IV animals marked edema, significant weight gain, and hyperamylasemia developed to the same extent as in group III animals. These results demonstrate that circulating leukocytes are not essential to the development of pancreatitis in this model and suggest that another source of oxygen-derived free radicals mediates this injury.
Acute Disease↗
Temporal efficacy of allopurinol during the induction of pancreatitis in the ex vivo perfused canine pancreas.
Oxygen-derived free radicals play an important role in the pathogenesis of experimental acute pancreatitis in the isolated perfused canine pancreas. We have previously found that pretreatment with allopurinol inhibits xanthine oxidase--apparently the primary source of free radical generation in this model--and prevents the initial development of pancreatitis. In these experiments, we evaluated whether allopurinol administered after the onset of pancreatitis would arrest the progression of the disease process. Edema formation, weight gain, and the release of amylase activity into the perfusate in the ex vivo perfused canine pancreas model were monitored during a 4-hour perfusion period. There were six experimental groups: Group I (control) received no treatment, group II (allopurinol alone) received only allopurinol (100 mg) at the start of perfusion, and groups III through VI were each given an infusion of 0.3 ml of oleic acid (FFA) over a 1-hour period to initiate acute pancreatitis. Group III (FFA alone) received no other treatment. In group IV (pretreatment with allopurinol), group V (concurrent treatment with allopurinol), and group VI (posttreatment with allopurinol), allopurinol (100 mg) was administered 1 hour before, concurrent with, or at the end of the FFA infusion, respectively. Pretreatment with allopurinol prevented edema formation, markedly attenuated weight gain, and the release of amylase caused by the FFA infusion. Administration of allopurinol concurrent with the FFA infusion provided only partial protection, whereas posttreatment with allopurinol failed to arrest the progression of the injury process. Therefore, the use of allopurinol to inhibit oxygen-derived free radical production from xanthine oxidase prevented the development of acute pancreatitis in this model; however, treatment with allopurinol after initiation of the disease process failed to arrest the progression of acute pancreatitis.
Allopurinol↗
Pathophysiology of hepatic ischemia in cardiogenic shock.
The hepatic hemodynamic response to cardiogenic shock was investigated in a porcine model produced by pericardial tamponade to better understand the pathophysiology of postshock hepatic insufficiency. Reductions of cardiac output to 50 percent of baseline levels produced marked hepatic ischemia by causing disproportionate reductions in blood flow through the celiac and hepatic arteries and portal vein. These were due to selective vasoconstriction of the splanchnic resistance vessels that was mimicked without tamponade by the infusion of angiotensin II, ablated by angiotensin-converting enzyme blockade, unaffected by alpha-adrenergic ablation, and correlated closely with levels of plasma renin activity. The ischemic liver injury of cardiogenic shock appears to be largely due to an exquisite responsiveness of the splanchnic vascular smooth muscle to endogenously released angiotensin II.
Angiotensin II↗