Gastric intramucosal pH and multiple organ injury: impact of ischemia-reperfusion and xanthine oxidase

OBJECTIVES

To determine if gastric intramucosal pH is affected by hepatoneteric ischemia-reperfusion. We additionally proposed to determine if changes in gastric mucosal hydrogen ion concentration are associated with liver and lung injury following hepatoenteric ischemia-reperfusion. Finally, we hypothesized that gastric intramucosal pH is influenced by xanthine oxidase, an oxidant-generating enzyme released after hepatoenteric ischemia-reperfusion.

DESIGN

Randomized, controlled, animal study.

SETTING

University-based animal research facility.

SUBJECTS

Thirty-six New Zealand white male rabbits (2 to 3 kg).

INTERVENTIONS

Anesthetized rabbits were randomly assigned to one of four groups (n = 9 per group): a) sham-operated group; b) sham-operated group pretreated with sodium tungstate (xanthine oxidase inactivator); c) aorta occlusion group; and d) aorta occlusion group pretreated with sodium tungstate. Descending thoracic aorta occlusion was maintained for 40 mins with a 4-Fr Fogarty embolectomy catheter, followed by 2 hrs of reperfusion.

MEASUREMENTS AND MAIN RESULTS

Gastric tonometry was performed after completion of the surgical preparation (30-min equilibration) and at 30, 60, 90, and 120 mins of reperfusion. Plasma alanine aminotransferase activity was determined at 120 mins of reperfusion to assess hepatic injury. Bronchoalveolar lavage of the right lung was performed after 120 mins of reperfusion, and the protein content was determined as a measure of pulmonary alveolar-capillary membrane compromise. Descending thoracic aorta occlusion resulted in a significant decrease in gastric intramucosal pH as compared with sham-operated rabbits (p < .001). The change in gastric mucosal hydrogen ion concentration was significantly associated with plasma alanine aminotransferase activity (r2 = .48, p < .01) and bronchoalveolar protein content (r2 = .51, p < .01). Xanthine oxidase inactivation significantly improved gastric intramucosal pH after aortic occlusion and reperfusion (p < .001), with a concomitant attenuation of the release of plasma alanine aminotransferase (p < .05) and accumulation of bronchoalveolar protein (p < .05) during reperfusion.

CONCLUSIONS

Gastric intramucosal pH was significantly decreased after hepatoenteric ischemia-reperfusion. Furthermore, an increase in gastric intramucosal hydrogen ion concentration was associated with a concomitant increase in tissue injury, a presumed harbinger of multiple organ failure. Gastric intramucosal pH values improved during reperfusion after xanthine oxidase inactivation, concomitant with attenuation of hepatic and pulmonary injury. Gastric tonometry is an important clinical tool that can provide critical insight into the pathogenesis of multiple organ injury after hepatoenteric ischemia-reperfusion. Gastric tonometry may aid in the rapid assessment of pharmacologic interventions designed to attenuate multiple organ injury in similar clinical settings (e.g., trauma, shock, major vascular surgery).

Synthesis of methyl 3-(2-octadecylcyclopropen-1-yl)propanoate and methyl 3-(2-octadecylcyclopropen-1-yl)pentanoate and cyclopropane fatty acids as possible inhibitors of mycolic acid biosynthesis

(Z)-Tetracos-5-enoic acid is a key intermediate in the biosynthesis of myocobacterial mycolic acids. Recently the methyl ester of its cyclopropene analogue, methyl 4-(2-octadecylcyclopropen-1- yl)butanoate, was shown to act as an inhibitor of mycolic acid biosynthesis. The related analogues methyl 5-(2-octadecylcyclopropen-1-yl)pentanoate and methyl 3-(2-octadecylcyclopropen-1-yl)propanoate have been synthesized, as well as the related cyclopropane esters methyl (Z)-4-(2-octadecylcyclopropan-1-yl)butanoate and methyl (Z)-5-(2-octadecylcyclopropan-1-yl)pentanoate. The synthesis of methyl 3-(2-octadecylcyclopropen-1-yl)propanoate involved protection of the cyclopropene ring by iodination to allow oxidation of an alcohol to a carboxylic acid; the diiodocyclopropane was deprotected by a new mild procedure using activated zinc.

Hydrolysis of exogenous [3H]phosphatidylcholine by brain membranes and cytosol

Phosphatidylcholine, in addition to the widely studied inositol phospholipids is cleaved to produce second messengers in neuronal signal transduction processes. Because of the difficulty in labelling and measuring the metabolism of endogenous phosphatidylcholine in brain tissue, we investigated the utility of measuring the hydrolysis of exogenous labelled substrate incubated with rat cerebral cortical cytosol and membrane fractions as has been successful in studies of phosphoinositide hydrolysis. In the cytosol [3H]phosphatidylcholine was hydrolyzed at a linear rate for 60 min of incubation and GTP gamma S stimulated hydrolysis by 63%. The products of phospholipase C and phospholipase D, phosphorylcholine and choline, contributed only 44% of the [3H]phosphatidylcholine hydrolytic products in the cytosol, with phospholipase D activity slightly predominating. GTP gamma S stimulated cytosolic phospholipase C and reduced phospholipase D activity. [3H]Phosphatidylcholine was hydrolyzed much more slowly by membranes than by cytosol. In membranes the production of [3H]phosphorylcholine and [3H]choline were approximately equal, contributing 27% of the total [3H]phosphatidylcholine hydrolysis, and GTP gamma S only caused a slight stimulation of phospholipase C activity. Chronic lithium treatment (4 weeks) appeared to slightly reduce [3H]phosphatidylcholine metabolism in the cytosol and in membranes, but no statistically significant reductions were achieved. Cytosol and membrane fractions from postmortem human brain metabolized [3H]phosphatidylcholine slowly, and GTP gamma S had no effects. In summary, exogenous [3H]phosphatidylcholine was hydrolyzed by brain cytosol and membranes, and this was stimulated by GTP gamma S, but the complex contributions of multiple metabolic pathways complicates the application of this method for studying individual pathways, such as phospholipase D which contributes only a fraction of the total processes hydrolyzing exogenous [3H]phosphatidylcholine.

Alterations of choline acetyltransferase, phosphoinositide hydrolysis, and cytoskeletal proteins in rat brain in response to colchicine administration

Colchicine, a microtubule disrupting toxin, was administered intracerebroventricularly to rats, followed by measurements of (i) the activity of choline acetyltransferase, a biochemical marker of cholinergic neurons, (ii) cytoskeletal protein concentrations, including tau, MAP-2, spectrin, and tubulin, and (iii) the activity of the second messenger-generating system, receptor-coupled phosphoinositide hydrolysis. One week after colchicine treatment there was a 60% decrease in choline acetyltransferase activity in the hippocampus, which was followed by a gradual increase in only a 29% deficit after 12 weeks. In the striatum and cerebral cortex, choline acetyltransferase activity was slightly reduced (by 13% and 19%, respectively) 1 week after colchicine treatment followed by increases to control values. The concentrations of tau and tubulin in the hippocampus were unaltered by colchicine treatment, and MAP-2 and spectrin were only slightly reduced 4 weeks after colchicine. Hippocampal phosphoinositide hydrolysis induced by norepinephrine was elevated approximately 28% 1 and 2 weeks after colchicine treatment and that induced by ibotenate was increased by 53% 2 weeks after colchicine. These results demonstrate that colchicine causes a severe depletion of choline acetyltransferase 1 week after administration. There was not a significant reduction of the concentration of any of the cytoskeletal proteins after 1 week, possibly due to the cell-selectivity of the toxic effect of colchicine, but there was a delayed, and temporary, decline of MAP-2 and spectrin concentrations. Associated with the decreased choline acetyltransferase activity after 1 week was an enhanced phosphoinositide hydrolysis in response to norepinephrine, and after 2 weeks there were enhanced responses to norepinephrine and to ibotenate.(ABSTRACT TRUNCATED AT 250 WORDS)