Influence of a prostaglandin inhibitor and a mineralocorticoid on the antidiuretic and hormonal response to an osmolar load.

To examine the influence of prostaglandins (PGs) and sodium-volume status on the urinary excretion and action of arginine-vasopressin (AVP), we studied the response to a hypertonic saline infusion (2.5% NaCl, 0.06 ml/kg/min for 3 h) in 8 healthy males under three different conditions: 1) on an ad libitum salt diet (C), 2) after 4-day treatment with indomethacin (IDM) 150 mg/d, 3) after 4-day treatment with fluorohydrocortisone (9 alpha FF) 0.6 mg/d. The rise of urine osmolality and the decrease of free water clearance were identical in all three studies. Basal urinary PGE2, PGF2 alpha and AVP were decreased during IDM and unchanged during 9 alpha FF, compared to C. The increment of urinary AVP was similar during C and IDM but significantly greater with 9 alpha FF (P less than 0.02) although urinary PGs were higher at the end of the infusion. In conclusion, despite markedly different hormonal patterns and sodium status in the three protocols, the antidiuretic response to an osmolar load is preserved suggesting an adaptive mechanism maintaining a constant balance between AVP and PGs.