INCREASED PROXIMAL SODIUM-REABSORPTION IS ASSOCIATED WITH INCREASED CARDIOVASCULAR RISK IN MEN

Objective To explore the relationship between fractional lithium excre tion (taken as an index of proximal sodium excretion), blood pressure and metabolic risk factors for coronary heart disease in a sample of a general white male population. Design A cross-sectional survey of a s ample of a white male working population carried out as part of the Ol ivetti Heart Study. Setting The Olivetti factory in Pozzuoli, a suburb of Naples, Italy. Participants Five hundred and sixty-seven untreated white male workers aged 21-68 years. Measurements Anthropometry, bloo d pressure, a blood test to determine the lipid profile, electrolytes, glucose and uric acid levels, a detailed questionnaire and urinary me asurements on a fasting timed urine sample after a 300 mg lithium carb onate capsule taken the night before the investigation. Results The fr actional excretion of lithium was inversely associated with body weigh t, body mass index, diastolic blood pressure, serum triglycerides leve l and serum uric acid level whereas it was positively associated with serum high-density lipoprotein cholesterol level, The greater the perc entage of filtered sodium reabsorbed at the proximal tubule the greate r the overall metabolic cardiovascular risk, The association was consi stent across tertiles of fractional excretion of lithium, was independ ent of age, smoking, alcohol consumption and sodium excretion (taken a s an index of sodium intake) and persisted in multiple regression anal ysis, Men with high serum triglycerides, high serum uric acid and low serum high-density lipoprotein cholesterol levels and higher blood pre ssure had significantly lower fractional excretion of lithium (and thu s enhanced proximal sodium reabsorption) than did men with a normal me tabolic profile (21.8 +/- 5.6 versus 26.5 +/- 5.1%, P = 0.002). Conclu sions The independent association between a cluster of risk factors fo r cardiovascular disease suggestive of insulin resistance and increase d proximal sodium reabsorption at the renal tubule indicates a new fea ture of the metabolic syndrome that, if causal, could be amenable to i ntervention.