Beta-endorphin inhibition of endogenous norepinephrine release from the A2 noradrenergic nucleus in vitro: role of mu opiate receptors and Na+ ion permeability.
An in vitro approach was used to determine the opioid receptor subtype mediating beta-endorphin inhibition of endogenous norepinephrine release from the A2 nucleus in the caudal dorsomedial medulla of rats. The voltage-sensitive Na+ channel blocker tetrodotoxin was used to investigate the role of Na+-dependent action potentials in beta-endorphin inhibition of K+-evoked norepinephrine release. Human beta-endorphin(1-31) inhibited K+-evoked norepinephrine release in a concentration-dependent fashion. Activation of delta- and kappa-opioid receptors had no effect on endogenous norepinephrine release. The inhibitory effect of beta-endorphin was blocked in a concentration-dependent manner by the mu-opioid receptor antagonist CTOP (Cys2, Tyr3, Orn5, Pen7 amide). Tetrodotoxin (TTX) inhibited norepinephrine release evoked by 25 mM K+ in a concentration-dependent manner and blocked the inhibitory effects of beta-endorphin. These results indicate that beta-endorphin acts on mu-opioid receptors to inhibit K+-evoked norepinephrine release from A2 neurons and suggest that the receptors involved are not located on noradrenergic nerve terminals.
Carr
J A
JA
Department of Biological Sciences, Texas Tech University, Lubbock 79409-3131, USA.
D000320:Adrenergic Fibers / Q000187:drug effects*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D010539:Permeability / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D001615:beta-Endorphin / Q000494:pharmacology*
D017450:Receptors, Opioid, mu; D013779:Tetrodotoxin; D001615:beta-Endorphin; D012964:Sodium; D009638:Norepinephrine