When should serum magnesium be measured prior to non-cardiac surgery?

While prospective data is scant, the advisability of magnesium measurement appears to be convincing in selected circumstances. Electrolyte abnormalities, mainly hypokalemia and hypomagnesemia, are associated with an increased risk for developing cardiac arrhythmias, however, conflicting opinions remain. If performed on all patients undergoing non-cardiac surgery, magnesium measurement would add considerably to health care costs; however, if limited to patients identified as high risk by the above parameters, the additional cost per patient is in keeping with other standard tests. Given the low cost of testing and replacement, preoperative magnesium measurement appears reasonable in patients with structural heart disease, diabetes, chronic alcoholism, and chronic (loop) diuretic use. When high risk patients are undergoing high risk operations, the low cost of measurement and replacement appears particularly cost-effective, whether it reduces morbidity and prolonged hospitalization from atrial fibrillation or mortality from sustained ventricular arrhythmias. Until additional data becomes available, use of this simple test in patients likely to manifest hypomagnesemia who are at elevated risk of cardiac tachyarrhythmias and cardiac complications following non-cardiac surgery seems prudent.

Dietary olive oil and menhaden oil mitigate induction of lipogenesis in hyperinsulinemic corpulent JCR:LA-cp rats: microarray analysis of lipid-related gene expression.

In the corpulent James C. Russell corpulent (JCR:LA-cp) rat, hyperinsulinemia leads to induction of lipogenic enzymes via enhanced expression of sterol-regulatory-binding protein (SREBP)-1c. This results in increased hepatic lipid production and hypertriglyceridemia. Information regarding down-regulation of SREBP-1c and lipogenic enzymes by dietary fatty acids in this model is limited. We therefore assessed de novo hepatic lipogenesis and hepatic and plasma lipids in corpulent JCR rats fed diets enriched in olive oil or menhaden oil. Using microarray and Northern analysis, we determined the effect of these diets on expression of mRNA for lipogenic enzymes and other proteins related to lipid metabolism. In corpulent JCR:LA-cp rats, both the olive oil and menhaden oil diets reduced expression of SREBP-1c, with concomitant reductions in hepatic triglyceride content, lipogenesis, and expression of enzymes related to lipid synthesis. Unexpectedly, expression of many peroxisomal proliferator-activated receptor-dependent enzymes mediating fatty acid oxidation was increased in livers of corpulent JCR rats. The menhaden oil diet further increased expression of these enzymes. Induction of SREBP-1c by insulin is dependent on liver x receptor (LXR)alpha. Although hepatic expression of mRNA for LXR itself was not increased in corpulent rats, expression of Cyp7a1, an LXR-responsive gene, was increased, suggesting increased LXR activity. Expression of mRNA encoding fatty acid translocase and ATP-binding cassette subfamily DALD member 3 was also increased in livers of corpulent JCR rats, indicating a potential role for these fatty acid transporters in the pathogenesis of disordered lipid metabolism in obesity. This study clearly demonstrates that substitution of dietary polyunsaturated fatty acid for carbohydrate in the corpulent JCR:LA-cp rat reduces de novo lipogenesis, at least in part, by reducing hepatic expression of SREBP-1c and that strategies directed toward reducing SREBP-1c expression in the liver may mitigate the adverse effects of hyperinsulinemia on hepatic lipid production.