NITRIC-OXIDE (NO) INHIBITS RELEASE OF ACETYLCHOLINE FROM NERVES OF ISOLATED CIRCULAR MUSCLE OF THE CANINE ILEUM - RELATIONSHIP TO MOTILITY AND RELEASE OF NITRIC-OXIDE

A method was developed to study simultaneously 1) release of ACh from nerve varicosities and terminals in and 2) motility of the myenteric p lexus-free circular muscle of the canine ileum. Tissues were incubated with H-3-choline. Release of H-3 was analyzed before and during elect rical field stimulation of nerves in the presence and absence of choli ne oxidase. The major components released into the superfusate during field stimulation were (in the absence of choline oxidase) H-3-ACh and H-3-choline as determined by column chromatography and (in the presen ce of choline oxidase) the choline metabolite H-3-betaine as isolated by tetraphenylboronbutyronitrile extraction. Addition of tetrodotoxin (1 x 10(-6)M) or superfusion with Ca++ free Krebs reduced motor activi ty and the release of H-3-ACh, which confirmed that release was mediat ed from nerve varicosities. Addition of N-w-nitro L-arginine methyl es ter or N-w-nitro L-arginine increased field-stimulated H-3-ACh release . This effect was reduced in the presence of L-arginine but not D-argi nine. Motility was also increased by the addition of N-w-nitro-L-argin ine methyl ester and N-w-nitro L-arginine. In contrast, the addition o f L-arginine did not restore motor activity to control levels, and D-a rginine had no effect. Our findings that inhibition of nitric oxide sy nthesis amplifies ACh release during field stimulation suggest that fi eld stimulation releases both ACh and nitric oxide from nerve terminal s of the deep muscular plexus and that this nitric oxide inhibits fiel d-stimulated ACh release and circular muscle contractility.