Changes in cholinergic and nitrergic systems of defunctionalized colons after colostomy in rabbits.

BACKGROUND: This study was designed to assess smooth muscle function and motility in defunctionalized colonic segments and subsequent changes in pathways responsible for gastrointestinal motility.

METHODS: Two-month-old New Zealand rabbits were randomly allocated into control and study groups. Sigmoid colostomies were performed in the study group. After a 2-month waiting period, colonic segments were harvested in both groups. For the in vitro experiment, the isolated circular muscle strips which were prepared from the harvested distal colon were used. First, contraction responses were detected using KCl and carbachol; relaxation responses were detected using papaverine, sodium nitroprusside, sildenafil, and l-arginine. The neurologic responses of muscle strips to electrical field stimulation (EFS) were evaluated in an environment with guanethidine and indomethacin. EFS studies were then repeated with atropine, Nω-nitro-l-arginine methyl ester, atropine, and Nω-nitro-l-arginine methyl ester-added environments.

RESULTS: Although macroscopic atrophy had developed in the distal colonic segment of the colostomy, the contraction and relaxation capacity of the smooth muscle did not change. EFS-induced nitrergic-peptidergic, cholinergic-peptidergic, and noncholinergic nonnitrergic responses significantly decreased at all frequencies (0.5-32 Hz) in the study group compared with those in the control group (P < 0.05).

CONCLUSIONS: Although the contraction capacity of the smooth muscle was not affected, the motility of the distal colon deteriorated owing to the defective secretion of presynaptic neurotransmitters such as acetylcholine, nitric oxide, and neuropeptides.