Sodium-lithium countertransport and triglycerides in diabetic nephropathy

Elevated erythrocyte sodium-lithium countertransport (SLC) activity is an intermediate phenotype of essential hypertension among Caucasians, and is controversially associated with nephropathy in Type 1 (insulin-dependent) diabetes. Hypertriglyceridemia is a frequent concomitant of elevated SLC in the general population, and may be found in diabetic nephropathy. The present study was designed to investigate the influence of kidney disease, serum triglycerides and blood pressure on the interindividual variability of SLC in Type 1 diabetes. SLC and fasting major serum lipids were studied in 35 Type 1 diabetic patients with persistently elevated urinary albumin excretion and in a group of patients matched for age, sex and duration of diabetes, but with normoalbuminuria. SLC was elevated in patients with clinical nephropathy (N = 10; median: 420 mumol.1RBC-1.hr-1) and in patients with microalbuminuria (N = 25; median: 405 mumol.1RBC-1.hr-1) compared with normoalbuminuric patients (median: 296 mumol.1RBC-1.hr-1; P < 0.01 vs. both groups). Hypertriglyceridemia and hypercholesterolemia were found only among patients with macroalbuminuria. Analysis of covariance indicated that the association of elevated SLC with kidney disease (P < 0.006 in all models) was largely independent of serum triglycerides, but also of total cholesterol, insulin dose and measures of glycemic control. Only diastolic blood pressure was positively associated with SLC (P < 0.02) independently from nephropathy (P < 0.005) also after restricting analysis to the normoalbuminuric patients. Kidney disease and raised blood pressure remain major concomitants of elevated SLC in Type 1 diabetics.