In experiments on frog urinary bladder it was found that 23 nM arginine-vasopressin (antidiuretic hormone, AVP), 10 min after addition, increased the content of free arachidonic acid (AA) in bladder tissue from 18.6 +/- 1.2 to 33.3 +/- 3.9 ng/mg protein. The exogenous AA (10(-8) - 10(-5) M) added to the serosal Ringer solution did not change the basal level of osmotic water flow, but significantly inhibited the hydroosmotic effect of 23 nM AVP in a dose-dependent manner. The inhibitory effect of AA was not eliminated in the presence of 1 microM indomethacin, 1 microM nordihydroguaiaretic acid, 100 microM ketoconazole, nor if the nonmetabolized analog of AA, eicosatetraynoic acid (1 microM), was used instead of AA. AA inhibited only the action of vasopressin, but had no effect on osmotic water flow induced by 2 mM cAMP + 50 microM 3-isobutyl-1-methylxanthine or 20 microM forskolin. These data suggest that AA is another phospholipid-derived messenger, which modulates the hydroosmotic action of vasopressin in frog urinary bladder at a point prior to cAMP formation.