Reduced osmotic and nonosmotic release of vasopressin after meclofenamate in the conscious dog.

Both in vivo as well as in vitro experiments suggest that prostaglandins (PG) may influence arginine vasopressin (AVP) release. Recent studies on conscious dogs have shown that cyclooxygenase inhibition with meclofenamate reduces basal AVP release as well as AVP release in response to hypoxia. The current experiments were performed in order to test whether PG synthesis inhibition affects osmotic- and nonosmotic-stimulated AVP release in a similar manner. Osmotic AVP release was tested by slowly infusing hypertonic saline intravenously in water-diuresing dogs and serially sampling plasma for AVP concentration. Experiments were performed both with and without meclofenamate (2 mg/kg and 2 mg X kg-1 X h-1 iv) pretreatment. AVP release to a comparable osmotic stimulus was greatly reduced after meclofenamate administration. Nonosmotic AVP release was tested by inducing systemic hypotension with an intravenous infusion of nitroprusside. Hypotension was associated with an increase in AVP concentration, which was partially blunted after meclofenamate administration. Experiments performed with only a saline vehicle administered showed no decrease in AVP release in response to comparable hypotension. The findings of these studies suggest that endogenous PG may be involved in both osmotic and nonosmotic AVP release in the conscious dog.