Effects of nitric oxide in the dorsal motor nucleus of the vagus on the extrahepatic biliary system in rabbits.

To investigate whether nitric oxide (NO) in the dorsal motor nucleus of the vagus (DMV) mediated an influence on the extrahepatic biliary system, we studied the effects of microinjection of NO-producing drugs into DMV on the motilities of the gallbladder (GB) and the sphincter of Oddi (SO) in anesthetized rabbits. Microinjection of the NO precursor L-arginine into the rostral DMV produced an increase in the GB and SO motilities, which can be counteracted by both NG-nitro-L-arginine-methyl (L-NAME), an inhibitor of NOS, and reduced hemoglobin (rHb), a scavenger of NO, and were eliminated by bilateral cervical vagotomy. On the other hand, the NO donor sodium nitroprusside (SNP) was able to mimic the excitatory effect of L-arginine. This effect can be antagonized by rHb, but not by L-NAME, for SNP supplied exogenous NO without activating NOS. These results indicate that NO in the DMV mediates an excitatory effect on the extrahepatic biliary system.