Age-related changes of the noradrenergic innervation of rat tracheo-bronchial tree and pulmonary vasculature.

Age-related changes of the noradrenergic innervation of the tracheo-bronchial tree and of pulmonary vasculature were investigated in male Wistar rats of 3 months (young), 12 months (adult) and 24 months (old/aged), using catecholamine histofluorescence techniques associated with image analysis and by high pressure liquid chromagraphy with electrochemical detection. In young rats, blue-green fluorescent nerve fibres supply tracheo-bronchial smooth muscle and tracheal and bronchial glands, which are innervated by a delicate network of nerve fibres rich in varicosities. Pulmonary artery and vein are sparsely innervated. They are supplied with nerve fibres distributed in the vasa vasorum or the adventitia and the outer tunica media. The higher noradrenaline concentrations were found in the trachea and extraparenchymal bronchi, followed by pulmonary vein and pulmonary artery. The density and pattern of noradrenergic innervation of the tracheo-bronchial tree, or of the pulmonary vasculature, were similar in young and adult rats. In aged rats, a loss of noradrenergic innervation involving primarily the supply to the smooth muscle of the tracheo-bronchial tree was observed. Histofluorescence techniques demonstrated a higher sensitivity than noradrenaline assay in detecting changes of the sympathetic innervation of the tracheo-bronchial tree and of the pulmonary vasculature. The possible significance of reduced noradrenergic innervation of the tracheo-bronchial tree in aged rats is discussed.