Altered renal sodium handling in men with abdominal adiposity: a link to hypertension

OBJECTIVES: Central adiposity, insulin resistance and hypertension are clearly interrelated but the mechanisms underlying this association have not been thoroughly elucidated. As renal sodium handling plays a central role in salt-sensitive forms of hypertension, we investigated the relation of renal tubular sodium handling to abdominal adiposity, blood pressure and insulin sensitivity. DESIGN: Population-based study. PARTICIPANTS: Five hundred and fifty-five untreated Olivetti male workers, aged 25-75 years. SETTING: Olivetti factory medical centers in Pozzuoli and Marcianise (Naples, Italy) MAIN OUTCOME MEASURES: Anthropometric indices, serum insulin, homeostatic model assessment index of insulin sensitivity, blood pressure, fractional excretions of uric acid and exogenous lithium (as markers of renal tubular sodium handling). RESULTS: In univariate analysis, measures of central adiposity (i.e. sagittal abdominal diameter and umbilical circumference) were directly correlated with serum insulin (P < 0.001) and blood pressure levels (P < 0.001) and inversely associated with the fractional excretions of uric acid and lithium (P = 0.01-0.001). In multiple linear regression analysis, the same anthropometric indices but not the measures of peripheral adiposity (arm circumference and tricipital skinfold thickness), were significant predictors of the fractional excretion of uric acid and lithium, independently of age, blood pressure and serum insulin levels (P = 0.01-0.001). CONCLUSIONS: Abdominal adiposity was associated with altered renal tubular sodium handling apart from insulin resistance and high blood pressure. The data indicate that men with prevalent abdominal adiposity have an enhanced rate of tubular sodium reabsorption, mainly at proximal sites. These findings provide a possible mechanistic link between central adiposity and salt-dependent hypertension.