Effect of endogenous opioid peptides on acetylcholine release from the cat superior cervical ganglion: selective effect of a heptapeptide.
The present experiments show the presence of both metenkephalin-like and met-enkephalin-Arg6-Phe7-like immunoreactivity in the superior cervical ganglion of the cat; this was determined by radioimmunoassay after high-pressure liquid chromatography separation of tissue extracts. There was measurable efflux of both peptides, as determined by radioimmunoassay of ganglionic perfusates; this measure was increased by thiorphan, an enkephalinase inhibitor. The effect of the 2 peptides on ACh release was determined: The stable analog of methionine-enkephalin, D-Ala2-methionine-enkephalinamide, did not affect ACh release from the ganglion; in contrast, methionine-enkephalin-Arg6-Phe7 significantly depressed evoked ACh release. The effect of met-enkephalin-Arg6-Phe7 to decrease ACh release was antagonized, although only partially, by the opioid antagonist naloxone. Thus, it appears that methionine-enkephalin-Arg6-Phe7 alters ACh release from the superior cervical ganglion by acting, at least in part, on a presynaptic opioid receptor. The results suggest that in the cat superior cervical ganglion, the heptapeptide enkephalin might have a significant role in the regulation of synaptic transmission, which is unrelated to its potential function as a precursor for methionine-enkephalin.
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002415:Cats; D004723:Endorphins / Q000378:metabolism / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D004745:Enkephalins / Q000378:metabolism; D005260:Female; D005728:Ganglia, Sympathetic / Q000378:metabolism*; D008297:Male
D004723:Endorphins; D004745:Enkephalins; D004744:Enkephalin, Methionine; C027511:enkephalin-Met, Arg(6)-Phe(7)-; C033453:enkephalin-Met, Arg(6)-Gly(7)-Leu(8)-; D000109:Acetylcholine