Investigation of presence and absence of nitric oxide synthase (NOS) in sphincter of oddi (SO) and gallbladder (GB) from rabbits

Background and Aims: Organic nitrates confer relief on SO spasm but they are of limited influence on the GB. We studied whether the greater efficacy of nitroglycerin (NG) to relax the SO relative to the GB was underlain by a difference in bioconversion of NG to nitric oxide (NO). We investigated the presence and absence of NOS in both organs. Methods: Relaxation of isolated SO and GB muscle rings were studied by isometric tension measurement. After a stable contraction (KCl; 30 and 140 mM), the rings were exposed to cumulative increases in NG (0.1 nM –1µM) concentrations. Furthermore, we measured the relaxing effect of NG and sodium nitroprusside (SNP) after stable contraction by KCl and CCK8. NG (30 or 100µM/kg) and/or its vehicle were infused to the rabbits and the SO and the GB were sampled for NO determination by electron spin resonance analysis and for cGMP determination by RIA. Evaluation of the expression of NOS was performed by immunohistochemistry from SO and GB resultant in vitro (1µM) and in vivo (100µM/kg) NG-treated rabbits.

Results: The efficacy of SNP to induce SO relaxation was similar to that found in the GB, while the relaxing effect of NG upon the SO, however, much exceeded than that in the GB. Neither baseline tissue NO nor cGMP content of the GB increased significantly in response to iv. NG. On the contrary, both increased in the SO. Immunohistochemistry confirmed the presence of NOS in the SO and absence of NOS in the GB.

Conclusion: Our results demonstrate that the GB and the SO respond to nitrergic challenges in a different way. The weak response of the GB to NG is explained by a relatively reduced bioconversion to NO as compared to the SO. Moreover distribution of tissue NOS exhibit strong differences in the two organs.

Supported by Mecenatura Competition, Univ. of Debrecen.