Search

Objective— Hypoglycemia is associated with increased mortality. The reasons for this remain unclear, and the effects of low glucose exposure on vascular endothelial function remain largely unknown. We endeavored to determine the effects of low glucose on endothelial cells and intact human arterioles. Methods and Results— We exposed human umbilical vein endothelial cells to low glucose conditions in a clinically relevant range (40–70 mg/dL) and found rapid and marked reductions in nitric oxide (NO) bioavailability ( P P P l -N G -Nitroarginine methyl ester. Intact human arterioles exposed to low glucose demonstrated marked endothelial dysfunction, which was prevented by either metformin or TEMPOL. Conclusion— Our data suggest that moderate low glucose exposure rapidly impairs NO bioavailability and endothelial function in the human endothelium and that pharmacological AMP kinase activation inhibit this effect in an NO-dependent manner.

Background: The authors investigated the hypothesis that isoflurane modulates nitric oxide (NO) synthesis and protection against myocardial infarction through time-dependent changes in expression of key NO regulatory proteins, guanosine triphosphate cyclohydrolase (GTPCH)-1, the rate-limiting enzyme involved in the biosynthesis of tetrahydrobiopterin and endothelial nitric oxide synthase (eNOS). Methods: Myocardial infarct size, NO production (ozone-mediated chemiluminescence), GTPCH-1, and eNOS expression (real-time reverse transcriptase polymerase chain reaction and western blotting) were measured in male Wistar rats with or without anesthetic preconditioning (APC; 1.0 minimum alveolar concentration isoflurane for 30 min) and in the presence or absence of an inhibitor of GTPCH-1, 2,4-diamino-6-hydroxypyrimidine. Results: NO−2 production (158 ± 16 and 150 ± 13 pmol/mg protein at baseline in control and APC groups, respectively) was significantly (P < 0.05) increased 1.5 ± 0.1 and 1.4 ± 0.1 fold by APC (n = 4) at 60 and 90 min of reperfusion, respectively, concomitantly, with increased expression of GTPCH-1 (1.3 ± 0.3 fold; n = 5) and eNOS (1.3 ± 0.2 fold; n = 5). In contrast, total NO (NO−2 and NO−3) was decreased after reperfusion in control experiments. Myocardial infarct size was decreased (43 ± 2% of the area at risk for infarction; n = 6) by APC compared with control experiments (57 ± 1%; n = 6). 2, 4-Diamino-6-hydroxypyrimidine decreased total NO production at baseline (221 ± 25 and 175 ± 31 pmol/mg protein at baseline in control and APC groups, respectively), abolished isoflurane-induced increases in NO at reperfusion, and prevented reductions of myocardial infarct size by APC (60 ± 2%; n = 6). Conclusion: APC favorably modulated a NO biosynthetic pathway by up-regulating GTPCH-1 and eNOS, and this action contributed to protection of myocardium against ischemia and reperfusion injury.

Adriamycin (ADR) is a commonly used chemotherapeutic agent that is believed to exert its effects through the generation of oxygen free radicals. We hypothesized that administration of a single dose of ADR results in endothelial nitric oxide synthase (eNOS)-dependent generation of superoxide (O2·-) and acute endothelial dysfunction. A single dose of ADR (10 mg/kg i.v.) administered to rabbits resulted in rapid attenuation of agonist-dependent responses to acetylcholine and calcium ionophore (A23187). In vitro exposure of ring segments to ADR for 2·- generation measured by electron spin resonance (ESR) with the spin trap segments 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) that was abolished by endothelial denudation and incubation with diphenyliodonium (DPI) (10 mM) but not L-NMMA (10 mM). Brachial artery flow-mediated dilation (FMD) in patients undergoing chemotherapy with ADR was markedly attenuated after a single dose of ADR (6.5 6 1.0 to 2.5 6 1.1% (p = 0.0004, time to end of infusion 27 6 8 min) while endothelial-independent dilatation with nitroglycerin was unchanged (16.3 6 3.1 and 14.33 6 2.1% respectively, p = 0.36). Serum nitrite and nitrate concentrations fell from 50 6 6 mmol/l pre-ADR to 33 6 6 mmol/l post-ADR infusion (p = 0.0005) while serum concentrations of CD141 thrombomodulin and von Wille-brand factor (vWF) activity remained unchanged after ADR infusion (36 6 13 to 52 6 22% ng/ml versus 3.25 6 0.98 to 3.01 6 0.91%, respectively, p = NS for pre versus post for both). Doppler indices of diastolic function (IVRT, DT and E/A ratios) were not altered in response to ADR. In conclusion, ADR administration results in rapid depletion of systemic NO· levels and attenuation of agonist-dependent responses in rabbits and flow-mediated dilation in the brachial artery of humans. ESR measurements in rabbit ring suggest an endothelial origin for radical production via flavin-containing oxido-reductases such as eNOS or NADPH cytochrome P450 reductase. These fi ndings may have implications for cardiovascular complications noted with ADR.