Background/purpose: Nitric oxide (NO) plays a role in inhibitory neurotransmission in the sphincteric and nonsphincteric smooth muscles. However, the relative contribution of NO synthesizing innervation to these functionally diverse parts of the gut, particularly during development, is unknown.
Methods: Gastrointestinal sphincters and adjoining nonsphincteric bowel segments were obtained from 14 human fetuses (gestation, 12 to 23 weeks). NO synthesizing nerves were examined by nicotinamide adenine deoxinucleotide phosphate (NADPH) diaphorase histochemistry. The densities of NADPH-positive nerves in the smooth muscles were quantified using a computerized image analyzing system on random sections.
Results: The NO synthesizing nerve density in intestinal smooth muscles decreased during fetal development as a result of increased interspacing between myenteric ganglia and a disproportionately larger increase in smooth muscle area than neuronal area. The nerve densities were lower in sphincteric regions than the adjoining nonsphincteric regions at the same gestation.
Conclusion: These findings may have relevance to the occurrence of congenital dysmotility disorders of the sphincteric regions.