Decreased free water excretion after indomethacin in the absence of antidiuretic hormone in saline loaded hypophysectomized Wistar and hydrapaenic Brattleboro rats.

Indomethacin (40 mg kg-1 in a single dose) was applied by stomach tube to inhibit the synthesis of prostaglandins during extracellular fluid volume expansion with isotonic saline in normal and acutely (2 h) hypophysectomized Wistar rats and hydropaenic diabetes insipidus Brattleboro rats. In the normal rats indomethacin reduced urine output due to decreased free water excretion. In the rats deprived of antidiuretic hormone (ADH) by acute hypophysectomy or due to hereditary eror in ADH synthesis indomethacin also decreased the urine output and clearance of osmotically free water. It is concluded that also other mechanisms besides the established competition between ADH and prostaglandins for ADH receptors may be responsible for the indomethacin effect on the osmotic movement of water in the distal nephron.