Pulmonary noradrenergic innervation of rat and monkey: a comparative study.

, , 167-174. The noradrenergic innervation of rat and monkey lungs was studied using the fluorescence histochemical method for norepinephrine of Falck (1962). In both species the noradrenergic nerves enter the lung at the hilum in association with the bronchial arteries. Major differences were noted in the distribution and pattern of these nerves, the most important of which are as follows: (1) Noradrenergic nerves have terminal varicosities in all divisions of the rat bronchial artery but are varicose in only the medium and small bronchial arteries of the monkey. (2) Noradrenergic terminals (varicosities) are in direct association with the bronchial smooth muscle in the monkey, but in the rat most of the noradrenergic nerves pass through the smooth muscle layer without forming terminal varicosities. Smooth muscle noradrenergic innervation is seen only at bifurcation points. (3) In the monkey pulmonary artery, noradrenergic terminals are restricted to the adventitio-medial junction while they appear in the media of the rat pulmonary artery. (4) Noradrenergic terminals are present in pulmonary vein divisions of the monkey whereas in the rat the large pulmonary veins lack noradrenergic nerves. Both rat and monkey bronchial arteries and pulmonary veins were found to have adrenergic terminal varicosities deep in the medial layer. The rat pulmonary artery also has such medial terminations. In both species there is a preponderance of noradrenergic terminals in the vasa vasorum, and we think that this may be important in regulating the delivery of humoral substances to vascular walls.