HEART GLYCOGEN-CONTENT AND ISOPRENALINE-INDUCED MYOCARDIAL LESIONS

The role of glycogen content in the heart for the development of isopr enaline-induced myocardial lesions (IML) was studied in Wistar rats an d in two inbred rat strains: In IR rats (resistant to the development of IML) and in IS rats (sensitive to IML development). Glycogen conten t in the heart can be dramatically lowered or increased by various int erventions. IML develop during the period of very low heart glycogen c ontent (about 0.6 mg.g(-1)) induced by isoprenaline administration. In animals with increased resistance to IML, either due to genetic facto rs or induced by isoprenaline pretreatment a high glycogen content in the heart is found (up to 7.5 mg.g(-1)). The increase of resistance to IML development and increased glycogen content induced by isoprenalin e pretreatment were accompanied by lower basal or ISO-, guanylylimidod iphosphate- (Gpp/NH/p) and forskolin-stimulated activities of adenylyl cyclase. On the other hand, these parameters did not differ between I R and IS rats in spite of the presence of significant differences in t he resistance to the development of IML and in heart glycogen content in these two rats strains. These results suggest that genetically dete rmined differences between two inbred rat strains in the resistance of the heart to the development of IML and in the heart glycogen content are caused by factors which are independent of the receptor-adenylyl cyclase complex and are therefore different from those involved in the increase of resistance and glycogen content due to isoprenaline pretr eatment.