Functional innervation of the biliary sphincter of the guinea-pig revealedby anti-autonomic drugs

1 The roles of excitatory and inhibitory intrinsic motor nerves on contract ions reflexly evoked by wall distension were investigated in the isolated s phincter of Oddi of the guinea-pig (SO-GP). 2 Distension of the terminal bile duct for 30-60 s time periods increased t he frequency of contractions from about 2 to 12 min(-1) (n = 16). 3 Hexamethonium (HEX; 300 muM) largely prevented the distension-evoked incr ease in contraction frequency (4.5 min(-1), n = 8) as did atropine (ATR; 1 muM) (0.8 min(-1), n = 6), while tetrodotoxin (TTX; 1 muM) blocked the cont ractions triggered during distension. 4 L-nitroarginine (L-NA; 100 muM) significantly increased the frequency of contractions during and in the absence distension while apamin (APAM; 0.5 m uM) significantly increased their frequency and doubled their mean amplitud e during distension. 5 These results suggest that distension activates excitatory cholinergic mo tor nerves to increase the frequency of contractions in the SO-GP. These ac tions are modulated by the concomitant activation of intrinsic nitrergic an d non-nitrergic inhibitory motor nerves.