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Background: Age-related changes were studied in younger and older humans, by staining of acetylcholinesterase and cholineacetyl-transferase activities on autopsy samples of pulmonary vessels (arteries, veins and micro-vessels).Methods: Samples of human pulmonary vessels were harvested and exposed to the enzymatic staining for acetylcholinesterase and cholineacetyltransferase, two enzymes linked to the metabolism of acetylcholine. The morphological data were subjected to the quantitative analysis of images and to the statistical analysis of data.Results: Both acetylcholinesterase and cholineacetyl-transferase activities are localized in the pulmonary vessels of younger and older humans. Staining of these two enzymes shows strong age-related changes. Structures resembling cholinergic nerve fibers are located in pulmonary vessels both in the extra-parenchymal and intraparenchymal branches, organized in two plexuses. The quantitative analysis of images and the statistical analysis of data demonstrate that the cholinergic innervation of pulmonary vessels (especially the extra-parenchymal branches) strongly decreases with age. Conclusion:Our opinion is that the extra and intrapulmonary branches of the artery and veins of the human lung are provided with cholinergic nerve fibers, which could control the afferent pathways of the pulmonary vascular tree. These cholinergic nerve fibers are particularly sensitive to age-related changes.

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