1. Na+/Li+ countertransport is not a gold standard, or indeed any other kind of standard. It is a measure of the activity of one particular cation exchanger.
2. There is a large body of literature regarding the effects of oxidized low-density lipoprotein (LDL) in experimental animals and in vitro. Whether abnormal oxidized LDL or one of many other possible mechanisms underlies the inverse relationship that we observed between vascular sensitivity in vivo to nitroprusside or carbachol with erythrocyte Na+/Li+ countertransport in diabetic patients remains to be seen.
3. We caution against post hoc subgroup analysis (smokers versus non-smokers, low versus high plasma lipid levels, etc.) in studies of this size.