Isoproterenol-induced ultrastructural alterations in hearts of alloxan-diabetic rabbits

1. The effects of isoproterenol (ISO) on the ultrastructure of hearts from 10-week alloxan diabetic rabbits were examined. 2. Following alloxan injection, all rabbits developed severe hyperglycemia, hyperlipidemia and hypoinsulinemia. 3. Injection of ISO induced marked alterations in both control and diabetic rabbit hearts including accumulation of lipid and swelling of sarcoplasmic reticulum. 4. Myofibrils in both groups of animals were dispersed and appeared as a homogeneous mass with poorly defined Z-bands. 5. The most marked effect of ISO treatment in both groups of animals was damage to mitochondria. Mitochondria were extensively damaged and showed partial or complete disruption of their cristae network. 6. Glycogen granules were few in number or not detectable in both groups of animals. 7. The diabetic animals treated with ISO showed greater clumping and margination of nuclear chromatin, fewer intact mitochondria and a greater number of amorphous dense bodies in and around the mitochondria. 8. The presence of greater sarcolemmal damage in diabetic animals was inferred from the significantly greater accumulation of calcium and decreased magnesium in the myocardium.