Fatty acids augment endothelium-dependent dilation in hand veins by a cyclooxygenase-dependent mechanism.

Evidence supports the hypothesis that elevated nonesterified fatty acids (NEFAs) in patients with insulin resistance, eg, obese hypertensive subjects, contribute to increased vascular alpha-adrenergic reactivity and tone by impairing endothelium-dependent vasodilation. To generate further support for this notion, we studied responses to endothelium-dependent and independent dilators under control (0.9% NaCl/heparin) conditions in one hand and with elevated NEFAs in the contralateral hand (10% intralipid/heparin). To observe venodilator responses, the dorsal hand vein diameter was first reduced by approximately 60% with phenylephrine. Studies were repeated with indomethacin to block the generation of cyclooxygenase products. In contrast to previous in vitro data, elevating NEFAs locally in vivo augmented rather than suppressed venodilator responses to the two endothelium-dependent dilators acetylcholine and methacholine (P<.05). Responses to the endothelium-independent dilator nitroglycerin were unaffected. Indomethacin attenuated the capacity of intralipid/heparin to enhance endothelium-dependent dilator responses to acetylcholine and methacholine. Indomethacin did not affect venodilator responses to nitroglycerin. The effect of intralipid/heparin to significantly reduce the phenylephrine infusion rate required to reduce hand vein diameter by approximately 60% was reversed by indomethacin. These data indicate that raising fatty acids locally augments endothelium-dependent dilation by a cyclooxygenase-dependent mechanism. The findings also suggest that NEFAs augment alpha-adrenoceptor-mediated constriction in hand veins by a cyclooxygenase-dependent mechanism. These hand vein studies do not support the notion that the elevated NEFAs in obese hypertensive patients augment alpha1-adrenoceptor-mediated reactivity by reducing nitric oxide synthesis.

Carbenoxolone damages endothelium and enhances vasoconstrictor action in aortic rings.

Carbenoxolone causes hypertension indirectly by inhibition of 11beta-hydroxysteroid dehydrogenase and consequent elevation of intracellular glucocorticoid levels and enhancement of vasoconstrictor action. We performed the present study to determine whether carbenoxolone also enhances vascular tone directly by mechanisms independent of glucocorticoids and other systemic influences. Exposure of rat aortic rings to 10 to 100 micromol/L carbenoxolone in aerated Krebs-Henseleit buffer for 24 hours resulted in concentration-dependent increases in angiotensin II (Ang II) (100 nmol/L)-stimulated contractions and significant shifting of the phenylephrine cumulative contraction curve to the left but not increases in KCI (120 mmol/L)-stimulated contractions. Maximal enhancement of Ang II contraction was 39 percent. In contrast, brief (15-minute) exposure to 100 micromol/L carbenoxolone did not alter Ang II contractions. Mechanical denudation of the endothelium obviated enhancement of Ang II contractions by carbenoxolone, suggesting interaction of carbenoxolone with the endothelium. Endothelium-dependent relaxation of precontracted rings to acetylcholine or ATP was reduced by more than 90 percent by 24-hour pretreatment with 100 micromol/L carbenoxolone but not with 100 micromol/L deoxycorticosterone acetate (a mineralocorticoid) or 100 mu mol/L glycyrrhizic acid (a natural 11beta-hydroxysteroid dehydrogenase inhibitor). Vascular smooth muscle relaxation with sodium nitroprusside was not inhibited by carbenoxolone. Incubation of cultured endothelial cells with 100 mu mol/L carbenoxolone for 24 hours did not inhibit nitric oxide synthase activity, as measured by conversion of [3H]L-arginine to [3H]L-citrulline. Electron micrography demonstrated that endothelial cell ultrastructure but not vascular smooth muscle cell ultrastructure was abnormal after incubation of rings for 24 hours with 100 micromol/L carbenoxolone. These studies suggest that carbenoxolone concentrations higher than 10 micromol/L enhance vasoconstrictor action via selective toxicity to the endothelium and elimination of endothelium-dependent relaxation.

Oleic acid inhibits endothelial nitric oxide synthase by a protein kinase C-independent mechanism.

Many obese hypertensive individuals have a cluster of cardiovascular risk factors. This cluster includes plasma nonesterified fatty acid concentrations and turnover rates that are higher and more resistant to suppression by insulin than in lean and obese normotensive individuals. The higher fatty acids may contribute to cardiovascular risk in these patients by inhibiting endothelial cell nitric oxide synthase activity. To test this hypothesis, we quantified the effects of oleic (18:1[cis]) and other 18-carbon fatty acids on nitric oxide synthase activity in cultured bovine pulmonary artery endothelial cells by measuring the conversion of [3H]L-arginine to [3H]L-citrulline. Oleic acid (from 10 to 100 mumol/L) caused a concentration-dependent decrease in nitric oxide synthase activity at baseline and during ATP and ionomycin (Ca2+ ionophore) stimulation. At 100 mumol/L, linoleic (18:2[cis]) and oleic acids caused similar reductions of nitric oxide synthase activity, whereas elaidic (18:1[trans]) and stearic (18:0) acids had no effect. Oleic acid also inhibited the endothelium-dependent vasodilator response to acetylcholine in rabbit femoral artery rings preconstricted with phenylephrine (P < .05) but had no effect on the response to nitroprusside. The pattern of 18-carbon fatty acid effects on nitric oxide synthase activity in endothelial cells is consistent with activation of protein kinase C. Although oleic acid increased protein kinase C activity in endothelial cells, neither depletion of protein kinase C by 24-hour pretreatment with phorbol 12-myristate 13-acetate nor its inhibition with staurosporine eliminated the inhibitory effect of oleic acid on nitric oxide synthase.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute renal failure. Prompt diagnosis is key to effective management.

An abrupt decrease in the kidneys' ability to excrete waste products is a common cause of severe morbidity and death in critically ill patients. This complication may result from prerenal, renal parenchymal, or postrenal causes. The authors describe the clinical and laboratory evaluation of acute renal failure and offer an approach to prevention and appropriate management.

Case report: fatal Staphylococcus aureus sepsis from single-donor platelet transfusion.

Bacterial sepsis is a rare and potentially fatal complication of platelet transfusions. Bacterial contamination is estimated to occur in 2% to 6% of platelet concentrates, but clinically apparent septicemia occurs in less than 1% of multi-donor platelet transfusions. The incidence of bacterial sepsis from single-donor platelet transfusions is significantly lower, possibly because of shorter storage time of apheresis platelets. The authors report a case of fatal Staphylococcus aureus sepsis from a single-donor platelet transfusion obtained through a closed system. They conclude that as the demand for platelet transfusion increases, recognition of bacterial sepsis from transfusions and continued reassessment of procedures for collection and storage of platelet concentrates is warranted.

Protein kinase C modulates receptor-independent activation of endothelial nitric oxide synthase.

The intracellular regulation of nitric oxide synthase has been the focus of intense investigation. Bioassay studies using vascular rings have suggested that protein kinase C inhibits endothelium-dependent vascular relaxation. However, information regarding the effects of protein kinase C on the synthesis of nitric oxide in endothelial cells is not available. Therefore, we investigated the effects of protein kinase C to regulate receptor-independent activation of nitric oxide synthase activity in cultured bovine pulmonary artery endothelial cells. Activation of protein kinase C by phorbol 12-myristate 13-acetate or 1,2-dioctanoyl-sn-glycerol inhibited receptor-dependent and receptor-independent nitric oxide synthase activity. The inhibition of nitric oxide synthase by protein kinase C was concentration dependent and markedly blunted by staurosporine. The inhibition of protein kinase C by staurosporine alone enhanced basal nitric oxide synthase activity. Furthermore, depletion of protein kinase C enhanced both basal and agonist-stimulated nitric oxide synthase activity. These studies indicate that protein kinase C modulates the activity of the constitutive Ca2+/calmodulin-dependent endothelial nitric oxide synthase in the basal state and following agonist stimulation through direct inhibition of the enzyme as well as receptor desensitization. These direct regulatory effects of protein kinase C on endothelial nitric oxide synthase activity may have important implications in the physiologic regulation of vascular tone.

Ethanol enhances the endothelial nitric oxide synthase response to agonists.

Chronic ethanol consumption is associated with an increased prevalence of hypertension. The mechanisms of this form of hypertension are unknown. Rats fed ethanol for 2 days develop a tolerance to the acute vasoconstrictive effects of ethanol that is believed to be endothelium dependent. We investigated the effects of acute and chronic ethanol exposure on agonist-stimulated nitric oxide synthase activity in bovine pulmonary artery endothelial cells. Exposure of bovine pulmonary artery endothelial cells to ethanol (100 mmol/L) for 20-120 minutes did not change either basal or agonist-stimulated nitric oxide synthase activity measured as the rate of conversion of [3H]L-arginine to [3H]L-citrulline. Chronic exposure of endothelial cells to ethanol (100 mmol/L) for 96 hours significantly increased bradykinin-, adenosine 5'-triphosphate-, and ionomycin-stimulated nitric oxide synthase activity without affecting basal enzyme activity. The ethanol-induced increase in nitric oxide synthase response to agonists was dependent on the duration of ethanol exposure as well as the concentration of ethanol. Moreover, the effect of ethanol was characterized by an increase in the maximal nitric oxide synthase response to adenosine 5'-triphosphate without changes in the EC50. Removal of calcium or addition of N omega-nitro-L-arginine completely abolished agonist-stimulated nitric oxide synthase activity in both control and ethanol-treated cells. Our observations support the hypothesis that ethanol enhances nitric oxide synthase response to agonists during early ethanol exposure and may serve in a protective role against its hypertensive effect.