Fluorescence histochemical observations on the adrenergic innervation of the cardiovascular system in the aged rat.

The Falck-Hillarp fluorescence technique was applied to tissue samples of the heart and certain vessels of both 4 and 24 month Wistar rats. It appeared that with increasing age, the density and fluorescence intensity of the cardiac sympathetic innervation was maintained at a level comparable to the young adult (4 month) in the atria, left ventricle and in the region of the sino-atrial node. Similarly the adrenergic innervation of the coronary vasculature, particularly in the atrium was maintained into old age. In contrast the adrenergic innervation of the common and internal carotid arteries and abdominal aorta was very sparse in the 24 month rat compared to the young adult in which these vessels were surrounded by dense fluorescent plexuses. Peripheral arteriolar innervation in the pancreas was apparently similar in both age-groups. The present study suggests that the density of adrenergic innervation varies within the constituents of the cardiovascular system in aged rats.