Interaction between neurotransmitters and exogenous norepinephrine in isolated rat anococcygeus muscle.
Continuous electrical field stimulation (EFS) elicited a sustained contraction and significantly increased the EC50 value of norepinephrine (NE), shifting the concentration-response curve for NE to the right. Tetrodotoxin significantly reduced the continuous EFS-evoked increases in basal tone and produced further dextral shift in the concentration-response curve for NE. N-methylhydroxylamine and NG-monomethyl-L-arginine (L-NMMA) attenuated the "dual" effects of continuous EFS on NE-induced contractions. L-Arginine partially reversed the inhibitory effect of L-NMMA. The results of the present study suggest that continuous EFS causes simultaneous release of both excitatory and inhibitory neurotransmitters, and the interaction (or functional antagonism) between the inhibitory neurotransmitter (endogenous nitric oxide, NO) and the excitatory neurotransmitter (endogenous NE), as well as exogenous NE, may occur at postjunctional site(s).
Mudumbi
R V
RV
Research Service (151), Department of Veterans Affairs Medical Center, Boise, ID 83702, USA.
Parmeter
L L
LL
McIntyre
M S
MS
Leighton
H J
HJ
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000187:drug effects*; D009569:Nitric Oxide / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019323:omega-N-Methylarginine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D009638:Norepinephrine