The role of nitric oxide in the acetylcholine-induced relaxation of the feline internal anal sphincter, in vitro.
BACKGROUND
The relaxatory effect of acetylcholine was investigated on the feline internal anal sphincter (IAS), in vitro.


RESULTS
Acetylcholine (10, 30, 100, and 1000 microM) caused a concentration-dependent relaxation of the same magnitude in strips from the proximal and distal IAS. The antagonist of nitric oxide synthase, N omega-nitro-L-arginine (L-NNA; 1, 10, and 100 microM), in a concentration-dependent and stereospecific manner, blocked the acetylcholine-induced relaxation, leaving a residual response of 10-30%. The blocking effect of L-NNA (100 microM) could not be shown in tissues that had been incubated with the substrate for nitric oxide synthase, L-arginine (1 mM).


CONCLUSIONS
The present results suggest that the acetylcholine-induced relaxation of the IAS to a major extent is due to an activation of nitrergic, inhibitory motor neurons to the IAS.
Buntzen
S
S
Dept. of Surgery, University of Göteborg, Sweden.
Nordgren
S
S
Hultén
L
L
Delbro
D
D
D000109:Acetylcholine / Q000008:administration & dosage / Q000494:pharmacology*; D001003:Anal Canal / Q000187:drug effects / Q000294:innervation; D000818:Animals; D002415:Cats; D046508:Culture Techniques; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects* / Q000502:physiology; D009569:Nitric Oxide / Q000008:administration & dosage / Q000494:pharmacology*
D009569:Nitric Oxide; D000109:Acetylcholine