INTERACTION BETWEEN NEUROTRANSMITTERS AND EXOGENOUS NOREPINEPHRINE INISOLATED RAT ANOCOCCYGEUS MUSCLE

Continuous electrical field stimulation (EFS) elicited a sustained con traction and significantly increased the EC(50) value of norepinephrin e (NE), shifting the concentration response curve for NE to the right. Tetrodotoxin significantly reduced the continuous EFS evoked increase s in basal tone and produced further dextral shift in the concentratio n response curve for NE. N-methylhydroxylamine and N-G monomethyl L-ar ginine (L-NMMA) attenuated the ''dual'' effects of continuous EFS on N E induced contractions. L-Arginine partially reversed the inhibitory e ffect of L-NMMA. The results of the present study suggest that continu ous EFS causes simultaneous release of both excitatory and inhibitory neurotransmitters, and the interaction (or functional antagonism) betw een the inhibitory neurotransmitter (endogenous nitric oxide, NO) and the excitatory neurotransmitter (endogenous NE), as well as exogenous NE, may occur at postjunctional site(s).