The effect of ischemia on the catecholamine content and morphology of autonomic cardiac nerves was studied in experimental myocardial infarction in 65 rats with coronary ligation. The area of infarction, of ligation and other regions of the heart were investigated at hourly and daily intervals up to 9 weeks after ligation. During the first 4 h there is a slight reduction of fluorescence in the area of infarction and a focal, inconstant diffusion of adrenergic transmitters shown by Falck method. After 4 h an increasing loss of catecholamines is observed while the fluorescence of the adrenergic nerves in the adjacent myocardium is maintained or even increased. After 8 h the fluorescence of terminal nerve fibres has decreased; such changes also take place in bigger perivascular nerve trunks. After 16 h specifically fluorescent nerves can be identified only weakly. After two days catecholamine fluorescence has faded. The serotonin fluorescence of mast cells is constant except for focal degranulation. In later stages non-specific fluorescence is caused by fatty degeneration of myocardial cells and lipid-laden phagocytes. The results are discussed in respect to the local effects of catecholamines liberated during the early phase of infarction.
