Abstract
In anesthetized dogs, intravenous injections of 30μg/kg of leucine- and methionine-enkephalin (L- and M-enk respectively) produced a significant reduction of mean blood pressure (MBP) and heart rate (HR). The peak decreases in MBP and HR occurred within 1min after injection and recoveries to pre-injection levels within 3min. The depressor responses to both L-enk and M-enk were abolished by intracis-ternal pretreatment with yohimbine (0.5mg/kg) but not with prazosin (0.1mg/kg). Pretreatment with either drug did not alter the bradycardia. All cardiovascular effects of both L-enk and M-enk were prevented by intravenous pretreatment with naloxone (2mg/kg). These results suggest that central α2-adrenoceptors may participate in the central actions of enkephalins on blood pressure regulation. HR responses to enkephalins may be elicited by a different mechanism.
