Effect of methionine-enkephalin on the spontaneous electrical and mechanical activity of the smooth muscle of the rat portal vein.
In the longitudinal smooth muscle of the isolated rat portal vein, methionine-enkephalin (Met-enkephalin) increased the spontaneous contraction with a concentration as low as 10(-8)M. When the membrane activity was recorded using a microelectrode, Met-enkephalin enhanced the spike burst activity but without any effect on the resting membrane potential. Naloxone, phentolamine, atropine and reserpine pre-treatment did not inhibit the excitatory effect of Met-enkephalin on the spontaneous contraction. These results suggest that the excitatory effect of Met-enkephalin on the mechanisms involved in the automaticity may be a direct action on smooth muscle or relate to presynaptic action on a non-adrenergic non-cholinergic system.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004594:Electrophysiology / Q000187:drug effects; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D009270:Naloxone / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011169:Portal Vein / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains
D009270:Naloxone; D004744:Enkephalin, Methionine; D001285:Atropine; D010646:Phentolamine