Suppression of sympathetic nerve activity by methionine enkephalin: additive interaction with clonidine in intact anesthetized rabbits

Abstract

In order to study the role of methionine enkephalin (met-enkephalin) in cardiovascular system, interaction between clonidine and met-enkephalin on the rate of sympathetic nerve discharge was investigated. In anesthetized rabbits multiunit renal nerve activity (RNA) was monitored after the treatment of met-enkephalin alone or met-enkephalin plus clonidine pretreatment. Met-enkephalin suppressed RNA, and reduced heart rate and blood pressure. Treatment of met-enkephalin after clonidine (2 to 20 micrograms/kg) increased the duration of RNA suppression. The data suggests that the cardiodepressive action of met-enkephalin is mediated by the stimulation of central presynaptic adrenergic alpha 2 receptor as proposed for clonidine.