Differential effects of acute thermal injury on rat splanchnic and renal blood flow and prostanoid release

Suprarenal aortic clamping and reperfusion decreases medullary and cortical blood flow by decreased endogenous renal nitric oxide and PGE2 synthesis

OBJECTIVE

This study examined the hypothesis that clamping the aorta above the superior mesenteric artery (SMA) followed by suprarenal aortic clamping and reperfusion (SRACR) decreases microvascular blood flow by loss of endogenous medullary and cortical nitric oxide (NO) and prostaglandin (PG) E(2) synthesis.

STUDY DESIGN

Anesthetized male Sprague-Dawley rats (350 g) had either microdialysis probes or laser Doppler fibers inserted into the renal cortex to a depth of 2 mm and into the renal medulla at 4 mm. Laser Doppler blood flow was continuously monitored (data reported as percentage of change compared to basal), and the microdialysis probes were connected to a syringe pump and perfused in vivo at 3 microL/min with lactated Ringer solution. Dialysate fluid was collected at basal time zero, following 30 minutes of suprarenal aortic clamping (ischemia) followed by 60 minutes of reperfusion and compared to a sham operation. Both groups were treated with saline carrier, indomethacin (INDO) (10 mg/kg, a cyclooxygenase [COX] inhibitor), N(G)-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg, a NO synthase [NOS] inhibitor), or L-arginine (200 mg/kg, an NO precursor). Dialysate was analyzed for total NO (muM) and PGE(2) (pg/mL) synthesis. The renal cortex and medulla were analyzed for inducible NOS (iNOS) and COX-2 content by Western blot. All data are reported as mean +/- SEM, N > 5 and analyzed by analysis of variance.

RESULTS

SRACR caused a marked decrease in medullary and cortical blood flow with a concomitant decrease in endogenous medullary and cortical NO synthesis. Treatment with L-NAME further decreased blood flow and NO synthesis in the medulla and cortex. L-Arginine restored medullary and cortical NO synthesis and blood flow in the cortex but not the medulla. SRACR did not alter renal medullary or cortical PGE(2); however, addition of INDO, COX inhibitor, caused a concomitant decrease in medullary and cortical PGE(2) synthesis and blood flow.

CONCLUSIONS

NO is an important endogenous renal vasodilator that, when maintained can help preserve cortical blood flow following SRACR. These data also suggest that avoidance of COX-2 inhibitors can help maintain endogenous renal cortical and medullary PGE(2) synthesis and thus contribute to maintaining normal blood flow.

CLINICAL RELEVANCE

This study is the first to combine in vivo physiologic assays to simultaneously identify clinically relevant intrarenal vasodilators (cortical and medullary) that are required to maintain microvascular blood flow. Identification of endogenous renal cortical and medullary vasodilators responsible for maintaining renal microvascular blood flow will allow development of treatment strategies to preserve these vasodilators following SRACR. Successful preservation of endogenous intrarenal vasodilators will help maintain renal microvascular blood flow and renal function in the treatment of complex aortic pathology that requires SRACR.

Opposite effects of prostacyclin on hepatic blood flow and oxygen consumption after burn and sepsis

BACKGROUND

Burn and sepsis are associated with hepatic ischemia and reperfusion injury. This study examines the hypothesis that postburn treatment with the vasodilator prostacyclin would be beneficial for hepatic perfusion and oxygenation.

METHODS

Female pigs (n = 18, 20-25 kg) underwent laparotomy, during which ultrasonic flow probes were placed on the portal vein and the common hepatic artery. Catheters were inserted in the superior mesenteric and left hepatic veins. After 5 days, all animals were anesthetized and 12 of them received 40% total body surface area third-degree burn; 100 microg/kg Escherichia coli lipopolysaccharide (LPS) was intravenously administered 18 hours postburn. Burned animals were randomized to receive a constant infusion of iloprost (20 ng/kg per minute) or an equivalent amount of carrier solution (normal saline). All animals were studied for 42 hours.

RESULTS

Burn caused a 2.5-fold increase in hepatic arterial vascular resistance (HAVR) and a 39% decrease in hepatic arterial blood flow (HABF). Postburn administration of iloprost did not improve the hepatic arterial hemodynamics (1.8-fold increase in HAVR and 38% decrease in HABF). Post-LPS, HABF was significantly reduced to 22% of baseline and HAVR was 15-fold increased (P < 0.05 vs. baseline, ANOVA). In contrast, iloprost-treated animals did not show hepatic arterial vasoconstriction, as both HABF and HAVR remained baseline values during the endotoxic phase (P < 0.05 vs. nontreated group, ANOVA). Postburn iloprost treatment yielded a significant improvement in post-LPS portal venous blood flow (PVBF, 79% of baseline vs. 45% of baseline in nontreated animals, P < 0.05, ANOVA). Portal venous pressure showed 16% and 56% increases after burn and endotoxin, respectively. Portal hypertension did not occur in iloprost-treated animals, as portal venous pressure remained within baseline range (P < 0.05 vs. nontreated group, ANOVA). Burn and endotoxemia resulted in a significant decrease of hepatic oxygen delivery (hDO2, 63% and 12% of baseline, respectively) and hepatic oxygen consumption (hVO2, 61% and 21% of baseline, respectively). Only during the postburn endotoxic phase, iloprost improved hDO2 and hVO2 (140% and 79%, respectively; P < 0.05 vs. nontreated group, ANOVA).

CONCLUSIONS

Postburn prostacyclin treatment appears to have no beneficial effects on hepatic perfusion early postburn. However, during the late postburn endotoxic phase, prostacyclin seems to significantly improve hepatic total blood flow and oxygenation. In addition, prostacyclin treatment attenuated burn- and endotoxin-induced portal hypertension.

Sialyl Lewis X analog attenuates gastric microcirculatory disturbance and gastric mucosal erosion induced by thermal injury in rats

BACKGROUND AND AIM

We hypothesize that selectins, which are adhesion molecules, are involved in the pathogenesis of stress-induced gastropathy. We therefore investigated whether the novel Sialyl Lewis X (SLex) analog, which is a clinically available antagonist of selectins, attenuate gastric mucosal lesions induced by thermal injury.

METHODS

Male Wistar rats were anesthetized and a 30% full-skin thickness dorsal burn was inflicted on each rat. The SLex analog was administrated into the jugular vein 30 min before and 2.5 h after the thermal injury. Saline was administered to the vehicle group. The distribution of E-selectin immunoreactivity on the luminal side of the gastric mucosal microvascular network was observed by immunohistochemical methods. Active oxygen species were measured by the chemiluminescence method. Rolling leukocytes and endothelial damage, investigated by using Monastral Blue B (MBB), of the gastric mucosal microvascular network were observed through an intravital microscope.

RESULTS

A high intensity of E-selectin fluorescence was observed on the luminal surface of the venular endothelial cells 5 h after thermal injury in the vehicle group. However, E-selectin-associated fluorescence was almost negligible in the non-injury group and in the SLex analog group. The SLex analog also attenuated the rolling of leukocytes in the venules, venular deposits of MBB, luminol-dependent chemiluminescence activities, and gastric mucosal lesion formation.

CONCLUSION

It is suggested that the selectin family is involved in gastric microcirculatory disturbance and the pathogenesis of gastric mucosal lesions after thermal injury. A novel preventive therapy using the SLex analog is considered to effectively protect both gastric microcirculation and the gastric mucosa in rats with thermal injury.

Gut epithelial apoptosis after severe burn: effects of gut hypoperfusion

BACKGROUND

Severe cutaneous burn causes transient mesenteric vasoconstriction and altered gut mucosal integrity. We recently showed that burn also increases gut epithelial cell death by apoptosis. The goal of this study was to determine whether changes in gut perfusion after burn contribute to burn-associated gut apoptosis.

STUDY DESIGN

We first correlated superior mesenteric artery blood flow with measurement of gut perfusion at the tissue level by laser doppler in four nonburned rats before, during, and after arterial clamping to validate our measurements of gut perfusion. We then characterized gut perfusion sequentially over time after burn; gut perfusion was measured 3 cm from the ligament of Treitz before burn and hourly for 6 hours. A group of control rats underwent the exact same protocol without the burn to exclude effects of anesthesia and laparotomy on tissue perfusion (n = 4). We studied a third group of rats with hypoperfusion of the same duration and magnitude induced mechanically without burn (n = 7). Sections of the proximal gut from all three groups (control without burn, burn, and hypoperfusion without burn) were examined for epithelial apoptosis.

RESULTS

Linear regression analysis demonstrated a strong correlation between superior mesenteric artery blood flow and intestinal tissue perfusion measured by laser doppler under both low and high flow conditions (r = 0.85). Laser doppler measurements of gut perfusion after burn showed deceased gut perfusion that was maximal at 2 hours postburn (p < 0.05), and that persisted for 4 hours (p < 0.05). By 6 hours, gut perfusion returned to baseline. Apoptosis increased significantly in the burn group (2.11 +/- 0.17%) compared with control (0.52 +/- 0.2%) and the mechanically decreased perfusion group (0.51 +/- .03) (p < 0.001).

CONCLUSIONS

We conclude that burn-induced gut hypoperfusion is insufficient to cause burn-related increased gut epithelial apoptosis. We speculate that the signal for increased gut epithelial apoptosis is primarily related to proinflammatory mediators induced by the burn wound.

The effect of sequential injuries on splanchnic perfusion and eicosanoid release

BACKGROUND

This study examines the hypothesis that sequential burn injury followed by intraabdominal sepsis induces significantly greater splanchnic hypoperfusion and reduced intestinal PGI2 release than either injury independently.

MATERIALS AND METHODS

Anesthetized Sprague-Dawley rats were randomized to one of four groups: BURN (45% body surface area scald burn) + cecal ligation and puncture (CLP); BURN alone; CLP alone; or uninjured controls (SHAM). Twenty-four hours following injury, superior mesenteric artery (SMA) blood flow was measured with a doppler flow probe. Splanchnic eicosanoid release (6-keto-PGF1alpha, metabolite of PGE2; TxB2, metabolite of TxA2; and PGE2) was measured in mesenteric venous effluent utilizing an isolated, perfused bowel preparation.

RESULTS

SMA blood flow was no different than that of controls 72 h following BURN injury alone; whereas CLP alone resulted in a 80% reduction in splanchnic blood flow when compared with controls (P < 0.001). SMA blood flow in animals sustaining BURN + CLP was only modestly reduced from controls (P = 0.04) and 3.6 times greater than that of animals sustaining CLP alone (P < 0.001). PGI2 was the dominant eicosanoid released by the intestine with levels 10 times greater than TxB2 and nearly 50 times greater than PGE2. CLP either alone or when combined with BURN was associated with a 60% decrease in splanchnic PGI2 release when compared to controls (P < 0.05).

CONCLUSIONS

These data suggest that moderate BURN injury in rats attenuates the severe reduction in splanchnic perfusion associated with intraabdominal sepsis and that this occurs despite profound reductions in the release of the endogenous splanchnic vasodilator PGI2.

A protease inhibitor attenuates gastric erosions and microcirculatory disturbance in the early period after thermal injury in rats

The effects of camostat mesilate, a synthetic serine protease inhibitor on gastric microcirculation and active oxygen species generated by leucocytes from the gastric and jugular veins in the early period after thermal injury were assessed. Male Wistar rats were anaesthetized and a 30% full skin-thickness dorsal burn was inflicted. Camostat mesilate (100 mg/kg) was dissolved in distilled water and administered orally to rats 40 min before thermal injury (the camostat group). The control animals (the vehicle group) were administered distilled water orally. Rolling leucocytes as well as Monastral blue B deposits in venules were observed using in vivo microscopy. Active oxygen species were measured by chemiluminescence. Camostat mesilate decreased the total length of gastric erosion, venular deposits of Monastral blue B, and rolling of leucocytes in venules, and relatively increased luminol-dependent chemiluminescence activity generated by zymosan-stimulated leucocytes 15 min after thermal injury. These results suggest that serine proteases are involved in the formation of gastric erosions and gastric microcirculatory disturbance in the early period after thermal injury.