1. The cardiovascular effects of enkephalins have been tested in normotensive Wistar—Kyoto rats. Methionine—enkephalin and leucine—enkephalin increased blood pressure and heart rate after infusion into the brain ventricles.
2. After intravenous injection, blood pressure was increased by methionine—enkephalin and leucine—enkephalin, but heart rate was increased by methionine—enkephalin only.
3. Propranolol treatment reduced the increases in blood pressure following intraventricular methionine—enkephalin and leucine—enkephalin, while only the methionine—enkephalin-induced increases in heart rate were reduced by propranolol.
4. Heart rate and blood pressure responses after intravenous administration of methionine— enkephalins and leucine—enkephalin were not affected by propranolol.
5. Since opioid peptides occur in the blood and in regions of the brain involved in blood pressure regulation, the demonstrated cardiovascular effects to intraventricular and intravenous enkephalins support a role of these peptides in central and peripheral mechanisms of blood pressure control.