EVIDENCE OF DEFECTIVE TUBULAR REABSORPTION AND NORMAL SECRETION OF URIC-ACID IN THE SYNDROME OF INAPPROPRIATE SECRETION OF ANTIDIURETIC-HORMONE

The mechanisms responsible for the increased renal clearance-of uric a cid in the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) are not fully clarified. Studies using either pyrazinamide or probenecid, or both drugs but at an interval of several days, could n ot undoubtedly distinguish the 'hypersecretory theory' from the one fa voring a defect in either post- or presecretory reabsorption. We decid ed to do a combined pyrazinamide and probenecid test in 5 patients wit h hyponatremia due to SIADH in order to evaluate more clearly the resp ective importance of these different pathways. Our results allow the c onclusion of a diminished presecretory and mainly postsecretory reabso rption (80 +/- 4.6 and 14 +/- 3% of filtered load, respectively). As f ar as the secretion of uric acid is concerned (17 +/- 10% of filtered load), we may say that this pathway is adapted to the amount of hypour icemia.