Uric Acid Metabolism and Tubular Sodium Handling. Results from a Population-based Study

Objective: To define the relationship, if any, between uric acid metabolism (serum and urinary levels) and proximal tubular sodium handling in a sample of general male population.

Design: Cross-sectional survey of a sample of the male working population conducted as part of a nationwide survey of the prevalence of cardiovascular risk factors.

Setting: The Olivetti factory in Pozzuoli, a suburb of Naples, Italy.

Participants: Five hundred sixty-eight untreated male workers aged 21 to 68 years (90.8% of those eligible).

Measurements: Anthropometry, blood pressure, blood tests, a detailed questionnaire, and urinary measurements on a fasting timed collection after a 300-mg lithium carbonate capsule was taken the night before the investigation.

Results: Serum uric acid level was inversely and significantly associated with the fractional excretion of lithium (r = -.22, P < .001), ie, the higher the serum uric acid level, the greater the amount of sodium reabsorbed at nephron sites proximal to the distal tubule. The association was graded and independent of possible confounders such as age, body mass, smoking, wine consumption, blood pressure, fractional excretion of sodium, and serum creatinine (R2 = .34, P < .001).

Conclusions: High serum uric acid levels are independently associated with increased proximal tubular sodium reabsorption in men. This relationship suggests an altered tubular sodium handling and uric acid metabolism consistent with hyperinsulinemia, insulin resistance being the possible pathophysiological link.