DENSITIES OF NITRIC-OXIDE SYNTHESIZING NERVES IN SMOOTH MUSCLES OF HUMAN GUT DURING FETAL DEVELOPMENT

Background/Purpose: Nitric oxide (NO) plays a role in inhibitory neuro transmission in the sphincteric and nonsphincteric smooth muscles. How ever, the relative contribution of NO synthesizing innervation to thes e functionally diverse parts of the gut, particularly during developme nt, is unknown. Methods: Gastrointestinal sphincters and adjoining non sphincteric bowel segments were obtained from 14 human fetuses (gestat ion, 12 to 23 weeks). NO synthesizing nerves were examined by nicotina mide adenine deoxinucleotide phosphate (NADPH) diaphorase histochemist ry. The densities of NADPH-positive nerves in the smooth muscles were quantified using a computerized image analyzing system on random secti ons. Results: The NO synthesizing nerve density in intestinal smooth m uscles decreased during fetal development as a result of increased int erspacing between myenteric ganglia and a disproportionately larger in crease in smooth muscle area than neuronal area. The nerve densities w ere lower in sphincteric regions than the adjoining nonsphincteric reg ions at the same gestation. Conclusion: These findings may have releva nce to the occurrence of congenital dysmotility disorders of the sphin cteric regions. Copyright (C) 1997 by W.B. Saunders Company.