Prospective Analysis of Traits Related to 6-Year Change in Sodium-Lithium Countertransport

Abstract

Abstract-Sodium-lithium countertransport (Na-Li CT) activity in red blood cells relates cross-sectionally and longitudinally to blood pressure and hypertension. Lifestyle and metabolic factors relate cross-sectionally to this sodium transporter. The aim of this study was to conduct a prospective analysis of 6-year Na-Li CT change and of traits related to Na-Li CT change. In 2183 participants in the Gubbio Population Study (972 men and 1211 women; baseline ages, 18 to 74 years), the following data collected at baseline and 6-year follow-up were analyzed: Na-Li CT; gender; age; body mass index (BMI); blood pressure; antihypertensive treatment; alcohol intake; smoking habits; urinary sodium-to-potassium ratio; and plasma cholesterol, glucose, uric acid, sodium, potassium, and triglycerides (measured only at follow-up). Six-year changes were defined as follow-up minus baseline values. Na-Li CT was higher at follow-up than at baseline in both genders (PϽ0.001). Baseline Na-Li CT; baseline and change values of BMI; and change values of alcohol intake, plasma potassium, and plasma glucose related to Na-Li CT change significantly and independently with control for other variables. Follow-up plasma triglyceride levels also related independently to Na-Li CT change. Coefficients were positive for BMI, alcohol intake, and plasma glucose and triglyceride levels and were negative for baseline Na-Li CT and plasma potassium levels. Baseline and change values of other variables did not relate significantly to Na-Li CT change. In conclusion, in prospective analyses, BMI, alcohol intake, plasma glucose, and lipids were directly related to Na-Li CT change; baseline Na-Li CT and plasma potassium levels were inversely related. The data support the concept that lifestyle and related metabolic factors influence Na-Li CT. (Hypertension. 1999;33:887-893.)Key Words: sodium-lithium countertransport Ⅲ body mass index Ⅲ alcohol Ⅲ plasma glucose Ⅲ plasma lipids Ⅲ plasma potassium Ⅲ Gubbio Population Study S odium-lithium countertransport (Na-Li CT) is a membrane transport system involving a one-to-one exchange of sodium for lithium, usually measured as sodium-dependent lithium efflux in lithium-loaded red blood cells (RBCs). Na-Li CT is considered a marker of hypertension proneness because its activity relates to blood pressure (BP), 1,2 BP change over time, 3 and the prevalence and incidence of hypertension. 2,4,5 Na-Li CT relates also to diabetic nephropathy in insulin-dependent diabetes mellitus, possibly through its association with high BP. 6 The physiological role of Na-Li CT is not defined. There is circumstantial evidence that Na-Li CT activity relates to sodium proton exchange. 7,8 Conflicting data are reported on the relation of Na-Li CT to sodium reabsorption at the renal tubular level. 9,10 Na-Li CT activity is influenced by genetic, 11-14 environmental, and metabolic factors. 14 -17 Cross-sectional population-based data suggest that Na-Li CT activity increases over time because the means of Na-Li CT in adults are progressively h...

Relation of urinary urea to blood pressure: interaction with urinary sodium

“…Descriptive statistics for Na/Li-CT, plasma lipids, and glucose were similar to reported data. 20 Prevalence of previous diagnosis of diabetes mellitus was 5.4%. Prevalence of vitamin or mineral supplementation was Ͻ1%, hence not used in analysis.…”

“…[16][17][18][19][20][21] The analysis is based on data collected in the second examination of the Gubbio Population Study. The target cohort was participants aged 25-74 years (1731 men and 2042 women).…”

“…[16][17][18][19][20] Sodium-lithium countertransport in red blood cells (Na/Li-CT) was measured as reported. 16 Coefficient of variation was measured in 10% of blind duplicate samples; for urinary and plasma variables, the coefficient was Ͻ5% of the average in duplicates.…”

“…Creatinine clearance was calculated as urinary creatinine excretion rate/plasma creatinine; it was expressed per 1.73 m 2 of body surface area (BSA) and used as control for differences in glomerular filtration rate. 20 [17][18][19][20] Previous studies show that urea in partial urine collections is a reliable index of 24-h urinary urea. [23][24][25][26][27][28] For urinary urea, special analyses were done on correlation with urinary total nitrogen and daily variability (see Appendix).…”

Lipid lowering: another method of reducing blood pressure?

“…14,15 It has been shown to be a prospective marker for hypertension in the Gubbio study. 16 The kinetics of SLC activity show similar correlations with ethnicity, hypertension, and cardiovascular risk.…”