Pharmacologic interventions in acute mesenteric ischemia: Improved survival with intravenous glucagon, methylprednisolone, and prostacyclin

Prophylactic Treatment of Intestinal Ischemia-Reperfusion Injury Reduces Mucosal Damage and Improves Intestinal Absorption

Purpose

Intestinal ischemia-reperfusion injury (i-IRI) involves a blood flow interruption in an intestinal segment followed by blood flow restoration. When blood flow is restored, oxidative and inflammatory molecules are distributed throughout the bloodstream, triggering both local and systemic damage. Our goal was to evaluate the potential of three antioxidant and/or anti-inflammatory compounds (curcumin, dexmedetomidine and α-tocopherol) to prevent or reverse local and systemic damage induced by i-IRI.

Methods

i-IRI was induced by placing a microvascular clip in the superior mesenteric artery of female WAG/RijHsd rats; the clip was removed after 1h and reperfusion was allowed for 4h. Curcumin (200 mg/kg, orally), α-tocopherol (20 mg/kg, i.p.), and dexmedetomidine (5 or 20 µg/kg, s.c.; DEX5 and DEX20, respectively) were administered. Blood and terminal ileum specimens were collected for biochemical and histological determination. Furthermore, D-xylose absorption test was performed to evaluate intestinal absorption; after completing the 1-hour ischemia and 4-hour reperfusion period, 1 mL of aqueous D-xylose solution (0.615 mg/mL) was administered orally, and one hour later, plasma D-xylose levels were quantified.

Results

The histological injury degree (HID) measured by the Chiu scale was significantly reduced when the treatments were applied (non-treated rats, 2.6 ± 0.75; curcumin, 1.54 ± 0.8; DEX5, 1.47 ± 0.7; DEX20 1.14 ± 0.5; and α-tocopherol, 1.01 ± 0.6); intestinal absorptive capacity also improved in all cases healthy rats (2.06 ± 0.07 µg/mL; non-treated, 1.18 ± 0.07 µg/mL; curcumin 1.76 ± 0.3 µg/mL; DEX5, 2.29 ± 0.2 µg/mL; DEX20, 2.25 ± 0.26 µg/mL; and α-tocopherol 1.66 ± 0.21 µg/mL). However, it failed to reduce liver enzyme levels. Finally, only dexmedetomidine significantly reduced urea and creatinine levels compared to non-treated animals.

Conclusion

All drugs were effective in reducing HID, although α-tocopherol was effective to a greater extent. Only dexmedetomidine reverted intestinal absorption to normal values of healthy animals.

Mesenteric ischemia-reperfusion injury: clearly improved hemodynamics but only minor protection of the rat small intestine by (sub)therapeutic heparin sodium and enoxaparin doses

BACKGROUND

Tissue protection against ischemia (I)/reperfusion (R) injury by heparins can be due to their anticoagulant and/or non-anticoagulant properties. Here we studied the protective potential of the anticoagulant and the non-anticoagulant features of heparin sodium (HepSo) and enoxaparin (Enox) against mesenteric I/R injury in a rat model.

MATERIALS AND METHODS

Mesenteric I/R was induced in rats (n = 6 per group) by superior mesenteric artery occlusion (SMAO; 90 min) and reopening (120 min). Therapeutic/clinical and subtherapeutic/non-anticoagulant doses of HepSo (0.25 mg/kg bolus + 0.25 mg/kg × h; 0.05 mg/kg bolus + 0.1 mg/kg × h) or Enox (0.5 mg/kg bolus + 0.5 mg/kg × h; 0.05 mg/kg bolus + 0.1 mg/kg × h) were administered intravenously starting 30 min before SMAO to the end of reperfusion. Systemic/vital and intestinal microcirculatory parameters were measured during the whole experimental procedure, those of small intestine injury at the end.

RESULTS

During intestinal reperfusion, mean arterial blood pressure and heart rates were significantly increased by HepSo and, less effectively, by Enox, in a dose-dependent manner. Intestinal microcirculation was only affected by the therapeutic HepSo dose, which decreased the microvascular flow and S(O2) during reperfusion. The subtherapeutic Enox treatment, as opposed to any HepSo dose, most effectively diminished I/R-induced intestinal hemorrhages, myeloperoxidase activity (as a measure of neutrophil invasion), and histopathological changes.

CONCLUSION

Therapeutic but, to a lesser extent, also the subtherapeutic doses of both HepSo and Enox clearly improve hemodynamics during mesenteric reperfusion, while intestinal protection is exclusively provided by Enox, especially at its subtherapeutic dose. Alterations in intestinal microcirculation are not responsible for these effects. Thus, non-anticoagulant Enox doses and, preferably, heparin(oid)s unable to affect coagulation, could diminish clinical risks of I/R-induced gastrointestinal complications.

Acute mesenteric ischemia: diagnostic approach and surgical treatment

Mortality related to acute mesenteric arterial occlusion remains very high. Patient survival is dependent on prompt recognition and revascularization before ischemia progresses to intestinal gangrene. Biphasic computed tomography angiography has surpassed angiography as the diagnostic test of choice due to its ability to define the arterial anatomy and to evaluate secondary signs of mesenteric ischemia. Unlike chronic mesenteric ischemia, the treatment of acute arterial mesenteric ischemia, either embolic or thrombotic, remains largely surgical. This is due to the emergent need for revascularization combined with a careful evaluation of the intestines. Endovascular techniques remain useful, however, and can save precious time in the treatment of these challenging patients if integrated into a treatment pathway combined with definitive surgical treatment. A new hybrid endovascular-surgical treatment for the treatment of acute mesenteric thrombosis is described.

Intravenous iloprost increases mesenteric blood flow in experimental acute nonocclusive mesenteric ischemia

OBJECTIVE

To evaluate the effect of an intravenously administered synthetic epoprostenol analog, iloprost, in nonocclusive acute mesenteric ischemia induced by cardiac tamponade.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

Animal research laboratory at a university medical center.

SUBJECTS

Ten Yorkshire pigs (weight range, 20-25 kg).

INTERVENTIONS

Nonocclusive acute mesenteric ischemia was induced by pericardial tamponade. Pigs were randomized to receive either a low-dose, continuous intravenous infusion of iloprost (0.075 microg/kg/min) or an equivalent volume of normal saline to serve as the control. Infusion of iloprost or saline was continued after pericardial tamponade was reversed.

METHODS

Ten anesthetized and ventilated pigs underwent laparotomy and thoracotomy. A pulmonary artery catheter was inserted, a magnetic flow probe was positioned around the superior mesenteric artery (SMA), and cannulation of the pericardial space was performed. Pericardial tamponade was induced by injecting 5% dextrose in water into the pericardial space until blood flow in the superior mesenteric artery decreased to half of baseline. After 60 mins, animals received either a continuous intravenous infusion of iloprost at 0.075 microg/kg/min (n = 6) or an equal volume of normal saline (n = 4) for 60 mins. Pericardial fluid was then removed, and iloprost or normal saline infusion was continued for another 60 mins.

MEASUREMENTS

Heart rate, blood pressure, cardiac output, oxygen delivery, oxygen consumption, SMA blood flow, ileal Pco2, ileal intramucosal pH, and serum lactate levels of mixed venous blood and mesenteric venous blood were recorded at baseline, after pericardial tamponade was induced, during the iloprost or normal saline infusion with pericardial tamponade, and after removal of pericardial fluid (reperfusion period).

RESULTS

Iloprost infusion increased SMA blood flow by 60% in this model of nonocclusive mesenteric ischemia (from 168 +/- 41 to 269 +/- 76 mL/min; p <.05). The effect of iloprost infusion was more prominent after the tamponade (422 +/- 87 mL/min in the iloprost group vs. 232 +/- 111 mL/min in the control group; p <.05). Increased mesenteric perfusion decreased intestinal mucosal hypercarbia, leading to improvement of intramucosal pH.

Ischaemic colitis

The term colonic ischaemia was first coined approximately 40 years ago. Up until that point, the disease was only diagnosed in cases where the colon was completely gangrenous. In the 1960s reversible non-transmural ischaemia of the colon was described and much has been written about the disease since. Ischaemic colitis is usually a disease process that is seen in the elderly. However, the true incidence of the disease remains unknown since many cases are probably never diagnosed. We now know that the disease can occur both with occlusive and non-occlusive vascular disease, the latter being much more common. Although factors that contribute to non-occlusive disease have been identified, often the exact pathophysiology is unclear and this is an area where further research is needed. Known facts about the pathophysiology and aetiology of the disease will be discussed in this chapter. The key to diagnosis is often a high degree of clinical suspicion. Various diagnostic modalities are described, but colonoscopy remains the main instrument of accurate diagnosis. Fortunately the majority of patients will have self-limiting disease and, accordingly, they usually respond to conservative therapy. When the disease progresses to transmural infarction, surgery is required and the prognosis is guarded. Since many of the patients are elderly with other underlying diseases, it is unlikely that major treatment advances will allow us to significantly alter the prognosis in this group of patients with transmural ischaemia.

Ischemic colitis

This article contains a current review of ischemic colitis, including its etiology, pathophysiology, diagnostic modalities, and treatment options. A special emphasis is given to ischemic colitis following aortic reconstruction.

Effect of intravenous glucagon on intestinal viability after segmental mesenteric ischemia

PURPOSE

We have previously shown that intravenous glucagon significantly improves rat survival if given after release of superior mesenteric artery occlusion. The purpose of this study was to isolate the effects of glucagon on the intestine by creating a rat model of segmental mesenteric ischemia that avoids the systemic shock associated with total superior mesenteric artery occlusion and reperfusion.

METHODS

In 18 anesthetized Sprague-Dawley rats, an 8 cm segment of midileum was made totally ischemic for 110 minutes by occluding its vascular arcades and the bowel ends with microvascular clamps. Control animals (n = 8) received normal saline solution (10 ml/kg/hr intravenously) during ischemia and for 2 hours after declamping. Ten animals also received glucagon (1 microgram/kg/min intravenously) during 2 hours after declamping. After a 24-hour recovery, the ischemic bowel segment, plus nonischemic proximal ileum, was examined histologically by computerized planimetry to measure wall thickness (muscularis, mucosa, and transmural), percent epithelial coverage, and villar surface ratio (villar surface length/bowel circumference). All observations were blinded. Comparisons were made by Student's t test.

RESULTS

Compared with nonischemic ileum, the ischemic segment in control animals showed severe mucosal injury with a reduction in mucosal thickness to 25%, epithelial coverage to 23%, and villar surface ratio to 33% of that seen in nonischemic ileum (p < 0.01). Substantial preservation of ileal mucosal viability was seen in glucagon-treated animals. Mucosal thickness and epithelial coverage were twice as well preserved in glucagon-treated rats compared with control rats (p < 0.05), and villar surface ratio was also increased significantly (p < 0.05). The muscularis was not significantly injured in this model.

CONCLUSIONS

By use of quantitative histologic measurements, we found that intravenous glucagon significantly improved ileal mucosal viability when given early during reperfusion after segmental ischemia. The mechanism of this effect and its potential clinical application merit further study.

Mesenteric ischemia. Acute arterial syndromes

Acute mesenteric ischemia represents one to two percent of all gastrointestinal illnesses. There are three possible causes of acute arterial mesenteric ischemia: embolism, thrombosis, and nonocclusive mesenteric insufficiency. The key to early diagnosis is a high index of suspicion. The classic clinical picture of obvious cardiac disease, sudden onset of severe abdominal pain and gastrointestinal emptying, is not always present. Serum markers and plain films are often nondiagnostic but may suggest acute arterial mesenteric ischemia. Angiography establishes the diagnosis and allows for planning of aortomesenteric bypass, if indicated. Papaverine is immediately instilled to decrease splanchnic vasoconstriction. Embolic and thrombotic disease is treated by laparotomy with re-establishment of visceral perfusion. Only after blood flow is restored is nonviable bowel resected. Clinical methods of assessing intestinal viability include Doppler scanning, intravascular dyes, and tissue oximetry. The decision to perform a second-look laparotomy is made prior to closure of the abdomen. Pharmacologic treatment is the mainstay of nonocclusive ischemia. Surgery is reserved for clinical deterioration. Survival is dependent on the cause and extent of occlusion as well as the rapidity of diagnosis and therapy. Bowel necrosis results in mortality rates between 80 percent and 95 percent.

Adjunctive vasodilator therapy in the treatment of murine ischemia

Potent vasoconstrictors such as angiotensin II and vasopressin have been implicated as mediators of persistent vasoconstriction after reversible superior mesenteric artery (SMA) occlusion. Neither captopril (CAP), an angiotensin-converting enzyme (ACE) inhibitor, nor papaverine (PAP), a vasodilator, has proven effective in reversing this vasoconstriction when employed singly. The present study examined the combined effect of these agents in reducing mortality in a murine model of acute mesenteric ischemia. The SMAs of 106 adult male Sprague-Dawley rats were totally occluded for 85 minutes. Test agents were given intravenously at reperfusion over a 90-minute period. Survival rates were assessed at 48 hours. CAP was given as a single bolus (0.3 mg/kg) and PAP (0.5 mg/kg/h) as an infusion. Aortic and SMA blood flows were measured pretreatment and posttreatment in a separate group of 19 animals treated with CAP and PAP as single agents. chi 2 analysis and analysis of variance were used to test differences with p < or = 0.05 accepted as significant. PAP alone as an adjunct resulted in a significant increase in 48-hour survival (57% versus 19%, p < or = 0.005). PAP in combination with CAP produced the best outcome in this model (87% versus 19%, p < or = 0.005). Aortic blood flow decreased, whereas SMA blood flow increased after treatment both with CAP and with PAP, but not significantly. The combination of an intravenously administered vasodilator with either glucagon or an ACE inhibitor was the most effective adjunctive therapy in this mesenteric ischemia model. There was no evidence that an inotropic effect, rather than SMA vasodilation, was the responsible mechanism of action.

Utility of glucagon in the emergency department

Glucagon is a pancreatic polypeptide hormone that has diverse utility as both a therapeutic and diagnostic agent. Many of its pharmacologic actions are pertinent to the practice of emergency medicine. The author reviews the literature supporting each potential use of the drug and the purported physiologic mechanisms by which glucagon exerts these actions. The indications and proper dosages for glucagon in the acute care setting are summarized.

Does glucagon improve the viability of ischemic intestine?

The effects of glucagon, heparin, urokinase, thromboxane synthetase inhibitor (OKY-046), and the free radical scavengers, superoxide dismutase and catalase (SOD + CAT), on the viability of ischemic intestine were evaluated based on various parameters measured. The mucosal blood flow, the fluorescence pattern, and the histopathological findings in a rabbit model with 3.5 hr total vascular occlusion of a short small intestine indicated that glucagon improved the ischemic intestine. Glucagon increased, tremendously, the mucosal blood flow by 112% in the ischemic intestine compared with that of 25% in the nonischemic intestine. This indicated that vascular spasm, not reperfusion injury or thrombosis, played the initial role in the progression of transmural bowel necrosis. In addition, the outcome in the viability of the ischemic intestine was not detected by the fluorescence technique but was able to be detected through the mitochondrial morphology under the electron microscope.

Hemodynamic effects of glucagon after acute mesenteric ischemia in rats

We have previously shown that iv glucagon improved survival in rats from 33 to 83% when given after, but not during, superior mesenteric artery (SMA) occlusion. This study investigated potential hemodynamic mechanisms of this effect. In Part 1, cardiac output (CO) was measured in 12 male Sprague-Dawley rats with an electromagnetic flow-probe that had been placed around the ascending aorta 5 days previously. Under pentobarbital anesthesia, the SMA was occluded for 85 min. All rats received normal saline (NS, 15 ml/kg/hr) for 1 hr before and after SMA declamping. Control rats (n = 6) received only NS. Treated rats (n = 6) received NS plus glucagon (1.6 micrograms/kg/min iv) for 1 hr postocclusion. CO decreased 50% during the first hour after SMA declamping in control rats, but only 11% in glucagon-treated rats (P less than 0.02). Systemic vascular resistance (SVR) increased by 90% in control rats by 1 hr after declamp, but only 9% in glucagon rats (P less than 0.04). Systemic blood pressure and heart rate were not different in the two groups. In Part 2, relative distribution of visceral blood flow was measured with radiolabeled microspheres injected in the aortic root before clamping, before declamping, and 1 hr postdeclamping in 10 rats (5 glucagon, 5 control) using the above protocol. After SMA clamping, the proportion of visceral blood flow distributed to the intestine fell from 45 to 20% (P less than 0.05). During reperfusion, the proportion of intestinal flow exceeded baseline (P less than 0.05), but was not different in control (64%) and glucagon-treated rats (56%).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of glucose infusion on survival after acute mesenteric ischemia/reperfusion

Perfusion of ischemic tissue with glucose has been shown to be deleterious to heart, spinal cord, and kidney. Observations that glucagon improves survival after acute mesenteric ischemia, however, suggest that hyperglycemia may not be deleterious during bowel ischemia. This experiment examined the effect of glucose infusion on survival in an established rat model of acute mesenteric ischemia. The superior (cranial) mesenteric artery (SMA) was occluded for 85 min in 36 anesthetized Sprague-Dawley rats. Animals were randomized to receive 5% glucose in normal saline (n = 15; 16.5 mL/kg.min iv), normal saline alone (n = 13; 16.4 mL/kg.min iv), or no intravenous fluid (n = 8). Ninety-minute intravenous infusions were initiated 10 min after SMA occlusion. Survival to 48 h was 47% in glucose-saline-treated rats, 31% in saline-only-treated rats, and 12.5% in control rats. These results demonstrate no deleterious effect of glucose infusion on mortality after acute mesenteric ischemia in this model.

Pharmacologic treatment of occlusive mesenteric ischemia in rats

This study assessed the contribution of angiotensin II, oxygen-free radicals, and vasopressin to the mortality of acute mesenteric ischemia in rats. Rats received saline replacement (16 ml/kg/hr) for 3 hr during and after 85 min of superior mesenteric artery (SMA) occlusion. Only 21% of rats that received saline alone (n = 14, control) survived 48 hr, significantly less than the 100% survival of sham-operated rats (no SMA occlusion, n = 5, P less than 0.01). Neither teprotide (an angiotensin converting-enzyme inhibitor), allopurinol (to reduce oxygen-free radical formation), nor a specific vasopressin antagonist [1-(beta-mercapto-beta,beta-cyclopentamethyleneproprionic acid), 2-(O-methyl) tyrosine arginine-vasopressin] improved 48-hr survival, which was 17% in each group (n = 6, each). Survival improved significantly to 86% (n = 7, P less than 0.001) when intravenous glucagon (1.6 micrograms/kg/min) was given for 2 hr after SMA reperfusion. Survival after dopamine infusion (12 micrograms/kg/min iv) was 67% at 48 hr, a nearly significant improvement (n = 9, P less than 0.06). These results suggest that angiotensin II, oxygen-free radicals, and vasopressin do not contribute significantly to the high mortality observed after acute intestinal ischemia in this rat model, but that glucagon, and to a lesser extent, dopamine, are potentially therapeutic.

Treatment of mesenteric infarction

Eighty-one cases of mesenteric infarction documented by angiography, laparotomy or autopsy were reviewed to assess the cause of the persistently high mortality. Thirty-seven patients (46 per cent) were felt to have inoperable lesions and were treated by supportive care only, while forty-four (54 per cent) underwent bowel resection and/or revascularization. Of these 44 patients 20 (45 per cent) survived, 14 (32 per cent) died of an early recurrence of infarction and 10 (23 per cent) died of an unrelated cause. In view of the high recurrence rate in the early postoperative period, treatment must prevent the causes of persistent or recurrent ischaemia such as vasoconstriction and reperfusion tissue damage. On the basis of recent clinical and experimental research we suggest that treatment should include routine angiography with selective perfusion of vasodilators through the superior mesenteric artery, pharmacological prevention of ischaemic and reperfusion tissue damage before surgery, and postoperative anticoagulation.

Comparative hemodynamic effects of selective superior mesenteric arterial and peripheral intravenous glucagon infusions

This experiment was designed to determine whether any hemodynamic benefits attend administration of equal pharmacologic doses of glucagon (1 micrograms/kg/m) by continuous intravenous infusion (Group I, n = 6) versus selective intraarterial infusion (Group II, n = 6) via the superior mesenteric artery (SMA) in dogs. Cardiac output, heart rate, mean arterial pressure, total peripheral resistance, pulmonary vascular resistance, superior mesenteric artery flow (SMAQ), SMA vascular resistance, and portal venous pressure were measured at baseline (BL) and at 5, 15, 30, and 45 min during glucagon infusion. SMAQ virtually doubled at 5 min from a baseline of 570 +/- 60 ml/min to 1158 +/- 146 ml/min in Group I (P less than 0.001), and from a baseline of 527 +/- 171 to 1018 +/- 331 ml/min in Group II (P less than 0.002). SMAQ was significantly higher in Group I at 30 and 45 min compared to Group II (P less than 0.03) despite similar peripheral plasma glucagon levels. SMA vascular resistance was significantly lowered in both groups, with a greater reduction occurring during intravenous glucagon administration at 45 min (P less than 0.05). Changes in systemic hemodynamic parameters, as well as glucagon and glucose levels were not statistically different between Groups I and II at any time period. Glucagon is a potent mesenteric vasodilator and the resultant profound splanchnic hemodynamic effects are as marked during intravenous administration as during selective SMA infusion.

Effect of intravenous glucagon on the survival of rats after acute occlusive mesenteric ischemia

The purpose of this study was to determine the optimal timing of intravenous glucagon infusion for the treatment of acute occlusive mesenteric ischemia. The superior mesenteric artery (SMA) was occluded for 85 min in 106 Sprague-Dawley anesthetized rats. The animals were divided into 12 treatment groups according to the timing of glucagon and saline administration, and survival was measured to 48 hr. Without treatment, all rats died within 24 hr. Intravenous saline (10 ml/kg/hr) for 2 hr did not significantly improve 48-hr survival (17-33%). Glucagon (1.6 micrograms/kg/min iv) plus saline (10 mg/kg/hr iv) for 2 hr after SMA occlusion significantly improved survival from 33% (saline control) to 83% (P less than 0.02). The same treatment begun 1 hr before SMA release (during ischemia) did not significantly improve survival (33% at 48 hr). Glucagon infusion during occlusive mesenteric ischemia was detrimental when added to effective postischemia treatment, reducing survival from 83 to 33% (P less than 0.02). Adequate saline infusion was required for glucagon efficacy after ischemia, as shown by an intermediate 48-hr survival of 50% when only maintenance saline (1.5 ml/kg/hr) was given. These data suggest that glucagon therapy should be delayed until after operative release of an acute SMA occlusion and should be accompanied by vigorous volume expansion.