[Inhibition of prostaglandins in the syndrome of inappropriate secretion of antidiuretic hormone (SIADH)].

The role played by prostaglandins in the secretion of ADH and modulation of its action was investigated by testing the effects of prostaglandin synthesis inhibition in patients with SIADH of cerebral or pulmonary origin. Three patients with SIADH of central origin and 3 with SIADH of peripheral origin were subjected to 4 successive water-loading tests. In the first and fourth tests, the patients absorbed water 20 ml/kg bodyweight; in the second test they absorbed alcohol 2.5 ml/kg followed by water 17.5 ml/kg. The third test was preceded by a 3-day inhibition of prostaglandin synthesis with indomethacin 200 mg/day and aspirin 1.5 g/day. In patients with SIADH of peripheral origin the percent water-load excreted after 4 hours was low (less than 35%) with the 4 tests, whereas it reached 80% (p less than 0.001) with the third test (prostaglandin inhibition) in those with SIADH of central origin. Alcohol did not significantly correct the antidiuretic effect in any of the patients in both groups. It is concluded that prostaglandins reduce ADH secretion in central SIADH but do not modify antidiuresis in peripheral SIADH, since ectopic secretion probably does not depend on prostaglandins. The prostaglandin inhibition test therefore seems to be more helpful than the alcohol test to differentiate between central and peripheral SIADH. Further studies, however, are required to confirm these findings.