Indomethacin increases renal lithium reabsorption in man

Area of Science:

• Nephrology
• Pharmacology
• Human Physiology

Background:

• Nonsteroidal anti-inflammatory drugs (NSAIDs) like indomethacin can affect renal function.
• Fractional lithium reabsorption (FRLi) is often used as a marker for proximal tubule sodium reabsorption.
• The precise renal mechanisms of NSAID action, particularly on tubular handling of electrolytes, require further elucidation.

Purpose of the Study:

• To investigate the impact of semi-acute indomethacin administration on renal function parameters in healthy subjects.
• To assess the effect of indomethacin on fractional lithium reabsorption (FRLi) under varying sodium intake conditions.
• To determine if indomethacin influences renal handling of lithium beyond the proximal tubule.

Main Methods:

• Seven healthy subjects participated in the study.
• Indomethacin (4 x 50 mg orally over 27 hours) was administered.
• Renal function was assessed during maximal water diuresis under both high (200 mmol) and low (40 mmol) sodium diets.
• Measurements included urine osmolality, free water clearance, inulin clearance, fractional excretions of sodium, phosphate, uric acid, and FRLi.
• Urinary prostaglandin E2 (PGE2) excretion was also measured.

Main Results:

• Indomethacin significantly increased minimal urine osmolality in both high- and low-sodium diets.
• Maximal free water clearance was reduced by indomethacin only during the low-sodium diet.
• Fractional lithium reabsorption (FRLi) significantly increased during both high- and low-sodium diets.
• Indomethacin administration led to a significant reduction in 24-hour urine PGE2 excretion.
• No consistent effects of indomethacin were observed on inulin clearance or fractional excretions of sodium, phosphate, and uric acid.

Conclusions:

• The observed increase in FRLi suggests that indomethacin affects lithium reabsorption beyond the proximal tubule, likely in the loop of Henle.
• Indomethacin's effect on FRLi is independent of its influence on proximal tubular sodium reabsorption.
• Fractional lithium reabsorption may not be a reliable quantitative marker of proximal tubular sodium reabsorption in all physiological or pharmacological conditions, particularly when NSAIDs are involved.