We studied the role of the L-arginine-nitric oxide (NO) pathway in 
non-adrenergic, non-cholinergic (NANC) relaxation of the rabbit sphincter of 
Oddi by recording changes in isometric tension in response to electrical field 
stimulation in two series of experiments. In a first set of experiments, biliary 
sphincters of Oddi removed from New Zealand white rabbits were placed 
horizontally in an organ bath containing oxygenized, buffered (pH 7.4) Krebs 
solution. Contractile responses of the whole sphincter to field stimulation were 
determined. In the second set of experiments, sphincter of Oddi was divided into 
two parts and the effects of field stimulation were studied separately on areas 
close to the duodenal papilla (area I) and areas close to the common bile duct 
(area II). In the whole sphincter of Oddi, field stimulation induced an initial 
twitch-like contraction followed by relaxation proportional to the number of 
stimuli (3 and 10 stimuli at 20 Hz, 50 V, 0.1 ms). The magnitude of the 
contractile responses was considerably reduced by 1 microM atropine, 
phentolamine and oxprenolol (NANC solution). Field stimulation produced 
dose-dependent contractions of both segments of sphincter of Oddi in response to 
the same protocol as used with whole sphincter of Oddi. However, preincubation 
with NANC solution produced monophasic relaxations in response to field 
stimulation in area I, whereas area II preparations such as the whole sphincter 
of Oddi responded with contractions followed by minimal relaxations. Field 
stimulation failed to induce either contractions or relaxations in the presence 
of 1 microM tetrodotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)