INNERVATION PATTERN OF GUINEA-PIG PULMONARY VASCULATURE DEPENDS ON VASCULAR DIAMETER

The pulmonary vasculature is supplied by various neurochemically disti nct types of nerve fibers, including sensory substance P-containing an d autonomic noradrenergic, nitrergic, and cholinergic axons. Pharmacol ogical experiments have suggested that various segments of the pulmona ry; vascular tree respond differently to the respective neuromediators . We, therefore, aimed to determine histochemically and, immunohistoch emically for each of these neurochemically distinct perivascular axons their quantitative distribution along tile vascular tree fi um the ex trapulmonary trunks to the smallest intraparenchymal ramifications in control guinea pigs (n=5). Generally arterial innervation was more dev eloped than that of veins. Along the arterial tree, noradrenergic and substance P-containing axons were ubiquitous from the pulmonary trunk to smallest intraparenchymal vessels, whereas nitrergic axons were pra ctically restricted to large (>700-mu m) extrapulmonary arteries. Chol inergic axons were regularly present at arteries down to 100 mu m in d iameter and innervated two-thirds of small arteries (50-100 mu m). The results demonstrate that the noradrenergic vasoconstrictor innervatio n extends throughout the pulmonary vascular system whereas the innerva tion pattern with various types of vasodilator fibers changes with vas cular diameter, parallel to known pharmacological differences in choli nergic and nitrergic vasodilator effects.