INCREASED SARCOLEMMAL PERMEABILITY IN CARDIOMYOPATHY IN HYPERTROPHIED SHR MYOCARDIUM

To study the membrane changes in the myocardium, the sarcolemmal permeability of 16-week-old SHR and age-matched WKY myocardium was examined morphologically using horseradish peroxidase (HRP) on the first and fourth day after doxorubicin administration. No HRP was seen in either saline-treated controls or doxorubicin-treated WKY on the first day. On the fourth day, the doxorubicin-treated WKY showed, HRP around the myocytes due to an increase in the vascular permeability, whereas, the HRP-reactant product was not seen within the sarcoplasm. Electron micros-copy revealed osmiophilic, fine granular HRP-reactant products in the extracellular space of the WKY myocardium on the fourth day. On the other hand, in doxorubicin-treated SHR myocardium, HRP was seen in a portion of the papillary muscle or myocardial cells in the anterior wall on the first day and HRP-positive myocytes were scattered in the anterio-lateral wall at the fourth day. Cross striations were still visible within some HRP-positive myocytes of SHR. Electron microscopy also showed HRP-reactant products, not only in sarcotubules of normal-appearance myocytes, but also in myofibrils and/or mitochondria of highly degenerated myocytes. These results demonstrate the increase in the mem-brane permeability in the SHR myocardium, probably due to genetical disadvantage of the defense system and a proneness for membrane lipid peroxidation.