(669): Regulation of vascular permeability via Mu receptors

Abstract

Hemorrhage is associated with an increase in permeability resulting in decreased preload and increased tissue edema. Morphine sulfate is frequently administered as an analgesic or anxiolytic in multi-injured patients. Morphine binds to the Mu receptors located on the surface of endothelial cells and could theoretically augment the hyperpermeable state by histamine release. A recent study from our laboratory demonstrated that morphine inhibited the anticipated increase of vascular permeability in endothelial cells following hemorrhagic shock in rats. The aim of this study is to identify the pathway whereby this inhibition occurs. It is hypothesized that adenylate cyclase is upregulated through Mu receptor activation that inhibits the phosphoinositol/MAP kinase hyperpermeability cascade following hemmorhagic shock. Pilot studies were conducted in urethrane anesthetized Sprague Dawley rats. Initial studies determined the ED50 and LD50 for adenylate cyclase inhibitor (ACI) (sq22536). Six urethrane anesthetized Sprague Dawley rats were instrumented and permitted to recover for 15 minutes. Fluorescein isothiocyanate-bovine albumin (FITC-albumin), 50mg/kg, was administered intravenously after which baseline intra- and extralumenal fluorescent light intensity was measured in mesenteric postcapillary venules of transilluminated segments of small intestine. ACI, 100 mcg/kg, was subsequently administered and identical mesenteric postcapillary venules were examined to quantitate changes in permeability. The fluorescent light intensity emitted from the FITC-albumin was recorded at baseline and at 5-minute intervals for four measures and 10-minute intervals for 120 minutes after ACI administration. These images were downloaded to a computerized image analysis program that quantitates changes in light intensity. The ratio of intralumenal: extralumenal light intensity represents changes in vascular permeability. In the absence of shock, ACI administration resulted in significant decrease in light intensity ratio representing profound increase in permeability. Preliminary data suggest that this increase is attenuated by morphine administration supporting the hypothesis that morphine inhibits the phosphoinositol/MAP kinase hyperpermeability via adenylate cyclase activation. Hemorrhage is associated with an increase in permeability resulting in decreased preload and increased tissue edema. Morphine sulfate is frequently administered as an analgesic or anxiolytic in multi-injured patients. Morphine binds to the Mu receptors located on the surface of endothelial cells and could theoretically augment the hyperpermeable state by histamine release. A recent study from our laboratory demonstrated that morphine inhibited the anticipated increase of vascular permeability in endothelial cells following hemorrhagic shock in rats. The aim of this study is to identify the pathway whereby this inhibition occurs. It is hypothesized that adenylate cyclase is upregulated through Mu receptor activation that inhibits the phosphoinositol/MAP kinase hyperpermeability cascade following hemmorhagic shock. Pilot studies were conducted in urethrane anesthetized Sprague Dawley rats. Initial studies determined the ED50 and LD50 for adenylate cyclase inhibitor (ACI) (sq22536). Six urethrane anesthetized Sprague Dawley rats were instrumented and permitted to recover for 15 minutes. Fluorescein isothiocyanate-bovine albumin (FITC-albumin), 50mg/kg, was administered intravenously after which baseline intra- and extralumenal fluorescent light intensity was measured in mesenteric postcapillary venules of transilluminated segments of small intestine. ACI, 100 mcg/kg, was subsequently administered and identical mesenteric postcapillary venules were examined to quantitate changes in permeability. The fluorescent light intensity emitted from the FITC-albumin was recorded at baseline and at 5-minute intervals for four measures and 10-minute intervals for 120 minutes after ACI administration. These images were downloaded to a computerized image analysis program that quantitates changes in light intensity. The ratio of intralumenal: extralumenal light intensity represents changes in vascular permeability. In the absence of shock, ACI administration resulted in significant decrease in light intensity ratio representing profound increase in permeability. Preliminary data suggest that this increase is attenuated by morphine administration supporting the hypothesis that morphine inhibits the phosphoinositol/MAP kinase hyperpermeability via adenylate cyclase activation.