Pentoxifylline alone versus pentoxifylline combined with superoxide dismutase prolongs survival in a rat hemorrhagic shock model

Direct peritoneal resuscitation from hemorrhagic shock: effect of time delay in therapy initiation

BACKGROUND

After conventional resuscitation from hemorrhagic shock, splanchnic microvessels progressively constrict, leading to impairment of blood flow. This occurs despite restoration and maintenance of central hemodynamics. The authors' recent studies have demonstrated that topical and continuous ex vivo exposure of the gut microvasculature to a glucose-based clinical peritoneal dialysis solution (Delflex), as a technique of direct peritoneal resuscitation (DPR), can prevent these postresuscitation events when initiated simultaneously with conventional resuscitation. This study aimed to determine whether DPR applied after conventional resuscitation reverses the established postresuscitation intestinal vasoconstriction and hypoperfusion.

METHODS

Male Sprague-Dawley rats were bled to 50% of baseline mean arterial pressure and resuscitated intravenously over 30 minutes with the shed blood returned plus two times the shed blood volume of saline. Initiation of ex vivo, topical DPR was delayed to 2 hours (group 1, n = 8), or to 4 hours (group 2, n = 8), respectively, after conventional resuscitation. Intravital microscopy and Doppler velocimetry were used to measure terminal ileal microvascular diameters of inflow A1 and premucosal A3 (proximal pA3, distal dA3) arterioles and blood flow in the A1 arteriole, respectively. Maximum arteriolar dilation capacity was obtained from the topical application, in the tissue bath, of the endothelium-independent nitric oxide-donor sodium nitroprusside (10M).

RESULTS

Hemorrhagic shock caused a selective vasoconstriction of A1 (-24.1% +/- 2.15%) arterioles from baseline, which was not seen in A3 vessels. This caused A1 blood flow to drop by -68.6% of the prehemorrhage value. Conventional resuscitation restored and maintained hemodynamics in all the animals without additional fluid therapy. In contrast, there was a generalized and progressive postresuscitation vasoconstriction of A1 (-21.7%), pA3 (-18.5%), and dA3 (-18.7%) vessels. The average postresuscitation A1 blood flow was -49.5% of the prehemorrhage value, indicating a persistent postresuscitation hypoperfusion. Direct peritoneal resuscitation reversed the postresuscitation vasoconstriction by 40.9% and enhanced A1 blood flow by 112.9% of the respective postresuscitation values.

CONCLUSIONS

Delayed DPR reverses the gut postresuscitation vasoconstriction and hypoperfusion regardless of the initiation time. This occurs without adverse effects on hemodynamics. Direct peritoneal resuscitation-mediated enhancement of tissue perfusion results from the local effects from the vasoactive components of the Delflex solution, which are hyperosmolality, lactate buffer anion, and, to a lesser extent, low pH. The molecular mechanism of this vasodilation effect needs further investigation.

Early treatment with pentoxifylline reduces lung injury induced by acid aspiration in rats

STUDY OBJECTIVES

To evaluate the effect of pentoxifylline treatment on gas exchange and mortality immediately after bilateral instillation of hydrochloric acid.

DESIGN

Randomized, prospective, placebo-controlled trial.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Twenty-four, adult, male Sprague-Dawley rats.

METHODS

Sevoflurane-anesthetized rats (n = 12 in each group) underwent tracheostomy and insertion of a cannula into a hind paw vein and the left carotid artery. All animals received volume-controlled mechanical ventilation (zero positive end-expiratory pressure; fraction of inspired oxygen, 0.21). Acute lung injury was induced by instillation of 0.4 mL/kg 0.1 mol/L hydrochloric acid. The animals were randomized into two groups. The pentoxifylline group (n = 12) received a bolus of 20 mg/kg IV pentoxifylline after aspiration, followed by a continuous infusion of 6 mg/kg/h. The placebo group (n = 12) received an equivalent volume of saline solution. Arterial blood samples were collected for blood gas analysis 15 min and 0 min prior to aspiration and 30, 90, 180, 270, and 360 min after aspiration. Hemodynamic parameters, temperature, and ECG were recorded simultaneously. The primary end point was 6 h after aspiration. All surviving rats were killed by IV administration of pentobarbital. To assess morphologic changes due to lung injury, all animals underwent CT in inspiratory hold at the end of the experiment.

MEASUREMENTS AND RESULTS

No difference in baseline measurements was observed. In pentoxifylline-treated rats, Pao(2) was significantly increased (p < 0.05) at 30, 90, 180, 270, and 360 min. Mortality at 6 h was 17% in the pentoxifylline group vs 67% in the placebo group. Placebo-treated rats showed significant abnormalities in CT lung scans compared with the pentoxifylline group.

CONCLUSIONS

Acid aspiration impairs gas exchange and induces hypotension. Pentoxifylline administration shortly after acid instillation results in significant alleviation of impaired oxygenation, stabilization of BP with higher heart rates, and improved survival after 6 h.

Hypertonic saline improves tissue oxygenation and reduces systemic and pulmonary inflammatory response caused by hemorrhagic shock

BACKGROUND

The treatment of hemorrhagic shock (HeS) with large volumes of fluid does not ensure an adequate peripheral perfusion or prevent inflammatory activation despite hemodynamic recovery. The purpose of this study was to compare the effect of hypertonic saline (HTS) and isotonic saline (IS) solutions on oxygenation, perfusion, tumor necrosis factor-alpha and interleukin-6 levels, accumulation of polymorphonuclear neutrophils, and pulmonary perivascular edema in the treatment of controlled HeS in rats.

METHODS

Wistar rats submitted to HeS for 50 minutes (mean arterial pressure, 45-50 mm Hg) were treated with IS at three times the bled volume or with 5 mL/kg HTS.

RESULTS

The animals treated with HTS presented higher oxygenation and perfusion indices (p < 0.0001); lower arterial lactate, tumor necrosis factor-alpha, and interleukin-6 levels (p < 0.0001); less pulmonary perivascular edema and polymorphonuclear neutrophil sequestration (p < 0.0001); and lower mortality (p < 0.01) than those that received IS.

CONCLUSION

HTS improved tissue oxygenation and perfusion and reduced systemic and pulmonary inflammatory responses compared with IS in the treatment of HeS in rats.

Pentoxifylline attenuates ischemia/reperfusion injury to the small intestine in the rat

There is a large body of evidence that neutrophils may play an important role in the mucosal injury that follows ischemia of the intestine. Pentoxifylline (PTF), a methylxanthine derivative, prevents leukocyte adherence to vascular endothelium and restores intestinal blood flow following hemorrhagic shock and sepsis. The purpose of this study was to evaluate the protective properties of PTF in an ischemia-reperfusion model of the intestine and whether its action is mediated through tissue neutrophils as assessed by myeloperoxidase (MPO) determination. Intestinal ischemia of either 1 or 2 h was induced in rats by clamping the superior mesenteric artery, followed by a 17-min reperfusion period. PTF (25 mg/kg) or saline solution was injected IP 10 min prior to ischemia. Multiple bowel samples were harvested at the end of the reperfusion period and evaluated for histology and tissue MPO. PTF significantly changed the resultant histologic damage to the intestinal mucosa exerted by prolonged ischemia of 1 and 2 h duration, although the beneficial effect of PTF in this animal model was independent of the number of tissue neutrophils as assessed by tissue MPO levels. Pretreatment with PTF can thus reduce the histologic damage caused by prolonged ischemia to the intestine.

Pentoxifylline attenuates the depressed endothelial cell function and vascular muscle contractility following trauma and hemorrhagic shock

Although pentoxifylline (PTX) produces various beneficial effects following adverse circulatory conditions, it is not known whether this agent attenuates the depressed vascular endothelial cell function [i.e., the reduced release of endothelium-derived nitric oxide (EDNO)] and smooth muscle contractility after trauma and hemorrhage. To study this, rats underwent a midline laparotomy (i.e., trauma induced) and were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of maximal shed volume was returned in the form of lactated Ringer's solution. The animals were then resuscitated with 4 times the volume of maximal bleedout with lactated Ringer's solution, following which PTX (50 mg/kg body weight), or an equivalent volume of normal saline, was infused intravenously over 95 minutes. At 1.5 hours after resuscitation, the aorta was isolated and studied in vitro. Norepinephrine-induced vascular contraction and dose responses for acetylcholine (ACh), an endothelium-dependent vasodilator, were then determined. The results indicate that the decreased ACh-induced relaxation in hemorrhaged animals was restored with PTX treatment. Moreover, the increased ACh IC50 values (ACh concentration that causes half-maximum relaxation) after hemorrhage were reduced by PTX. In contrast, there was no significant difference in the relaxation induced by an endothelium-independent vasodilator, nitroglycerine, in the tested groups. Thus, PTX restores a hemorrhage-induced decrease in endothelium-derived nitricoxide production. In addition, the depressed smooth muscle contractile function was also attenuated by PTX treatment. Because PTX restored the depressed endothelial cell function and smooth muscle contractility, this agent appears to be a useful adjunct to fluid resuscitation for the management of trauma and hemorrhage.