Ultrastructure of isoproterenol-induced myocardial damage in chick embryos.

Isoproterenol is known to cause severe myocardial lesions when given in toxic doses to adult homoiotherms. Previous studies on chick embryos revealed myocardial damage with scattered necroses in the outer layer of ventricular myocardium. The present ultrastructural study, performed on embryos 6 to 20 days old, has shown various types of cellular lesions; mainly cellular oedema, mitochondrial swelling, necroses of isolated cardiac muscle cells, fatty degeneration, accumulation of glycogen, and signs of increased proteosynthesis in the surviving muscle cells. Morphological features of the lesions differed from those which are known to be induced by isoproterenol in adult animals and seemed to depend on the stage of embryonic development.