Studies of the Effects of an Elevated Glucose Concentration on the Ultrastructure and Composite Metabolism of the Intact Rabbit Aortic Intima-Media Preparation

To assess whether the ultrastructure and composite metabolism of the arterial wall are subject to acute modification by exposure to an elevated glucose concentration, paired samples of the intact rabbit aortic intima-media preparation were incubated with 5 mM or 20 mM glucose for 1 h under conditions in which the ultrastructural and metabolic stability of samples incubated with 5 mM glucose has previously been demonstrated. Incubation with 20 mM glucose did not alter the qualitative electron-microscopic appearance of the tissue, and no significant changes were found on a quantitative morphometric evaluation of the aortic endothelium. A detectable, composite-free intracellular glucose concentration was not demonstrable in samples incubated with 5 mM or 20 mM glucose by a comparison of the ratio of glucose space:inulin space. Samples incubated with 5 mM glucose had significant sorbitol concentrations and unexpectedly high fructose concentrations but did not release fructose into the medium at detectable rates. Incubation with 20 mM glucose resulted in an increase in tissue sorbitol without an increase in tissue fructose or a detectable rate of fructose release. Tissue water content and myoinositol concentration were unaltered by incubation with 20 mM glucose, as were the rates of O₂ uptake and lactate production whether the gas phase was 5% CO₂:95% O₂ or 5% CO₂:95% air. The ultrastructure' of intact aortic intima-media is not acutely altered by exposure to an elevated glucose concentration. Ambient glucose concentration is not the primary determinant of composite-free intracellular glucose concentration in arterial wall, and an increase in medium glucose concentration does not result in a significant increase in glucose utilization via the polyol pathway or induce the concomitants of increased polyol pathway activity demonstrable in a conventionally prepared aortic intima-media preparation.