INTERACTION OF ENKEPHALINS WITH SUBSTANCE-P ON VASCULAR SMOOTH-MUSCLE

Abstract

Interactions between SP [substance-P] and the enkephalins were reported to occur in the CNS and the possibility of a more peripheral site of interaction was investigated. SP (10-6 to 10-4 g/ml) dose-related contractions of rabbit isolated aorta which were resistant to .alpha.-adrenoceptor blockade (phentolamine, 5 .times. 10-6 g/ml) were induced. Met- and leu-enkephalin had no intrinsic action on the aorta, but met-enkephalin at 5 .times. 10-6 g/ml significantly inhibited responses to SP but not to NE [norepinephrine]. Morphine (5 .times. 10-6 g/ml) potentiated responses to NE, but had no significant effect on SP response. SP and met-enkephalin act on a common receptor on vascular smooth muscle met-enkephalin has no intrinsic action on this receptor, and the receptor is morphine-insensitive.