Modulation of circulatory responses to enkephalins by cyclooxygenase inhibitors

1. Experiments were undertaken to examine the hemodynamic effects of intravenously administered leucine and methionine enkephalin and to determine if prostaglandin synthesis is involved in these responses. 2. Intravenous administration of leucine and methionine enkephalin (10, 30 and 100 micrograms/kg) resulted in a dose dependent and transient decline in mean arterial blood pressure in pentobarbital anesthetized cats. 3. A significant difference was observed, however, between the hemodynamic responses to leucine and methionine enkephalins before sodium meclofenamate (1 mg/kg) administration compared to post-meclofenamate induced hemodynamic changes. 4. This was confirmed with ibuprofen. 5. These findings indicate that cyclooxygenase inhibition modulates the circulatory responses to enkephalins. 6. Since cyclooxygenase is the first enzyme in the biosynthetic pathway of arachidonic acid, it is possible that prostaglandins, endoperoxides, thromboxanes or other prostanoids may be involved in mediating the circulatory responses to enkephalins.