No abstract

Two strains of rats were obtained by selective breeding: the IR strain, resistant to isoprenaline-induced myocardial lesions and the IS strain, sensitive to this damage. The IR rats grew more slowly, the weight of their adipose tissue was higher and the weight of m. soleus was less than that of the IS rats. The IR rats had a higher content of triglycerides in the serum and a lower isoprenaline-stimulated lipolytic activity of adipose tissue in vitro. The basal NEFA level in the serum and its rise after the administration of isoprenaline in vivo did not differ between the strains. The IR rats had a higher content of glycogen in the heart and in the muscle. After the administration of isoprenaline the glycogen content decreased more slowly in IR rats. The findings indicate a considerable importance of the glycogen stores in the heart for the resistance of myocardium to damage.

Two inbred rat strains, differing in their resistance to the induction of myocardial lesions by the administration of isoprenaline (ISO), have been developed. The extent of ISO-induced myocardial lesions (IML) was three to five times lower in the ISO-resistant (IR) strain as compared to that in the ISO-sensitive (IS) strain. The two strains differ also in a number of other genetically determined features, e.g., a higher myocardial glycogen content (MGC) and higher adipose tissue weight in IR rats. Between IML extent and MGC a significant negative correlation has been demonstrated in 2nd filial generation of IR and IS hybrids. By contrast, no correlation has been found between the resistance to the development of IML and the other genetically determined features studied. High resistance to the development of IML and a high MGC were also noted in another inbred strain, the hypertriacylglycerolemic (HTG) rats. Comparison of IML extent in HTG, IR and IS rats has revealed that the extent of IML, while depending on MGC, is independent of triacylglycerolemia. MGC can be raised in IR and IS rats by various interventions (e.g., repeated administration of ISD or fasting). Regardless of the intervention used, it entails a simultaneous increase in resistance to the development of IML. In vivo administration of glucose and insulin, however, exerts only a minimal effect on MGC and on the extent of IML. It may be concluded, therefore, that under our experimental conditions the enhanced resistance to the development of IML, whether genetically determined (IR, HTG rats) or induced by some interventions (fasting, repeated ISO administration), is closely related to an increased MGC.

For the quantitative evaluation of myocardial damage induced by isoprenaline (ISO) a method based on the uptake of 203Hg-labelled Mercurascan (MSC) in the heart was used. The increase of myocardial uptake of MSC in ISO-treated rats over control values was very rapid and might be directly proportional to the number of damaged myocardial cells actually present in the heart. MSC-uptake method of myocardial damage evaluation was more sensitive and precise than other methods tested (macroscopic evaluation according to Rona, increase of heart weight). Different modifications of MSC-uptake test may be selected in relation to experimental conditions. MSC test is especially useful for evaluation of early myocardial lesions induced by small doses of ISO (0.01 mg/kg).

Behavioral pattern was studied in two inbred strains of rats which have different responses to stress. These strains were originally developed from a randomly bred Wistar rat colony, according to high or low myocardial cells sensitivity to cardiotoxic effect of isoprenaline. One strain is very sensitive to isoprenaline cardiotoxicity (IS = isoprenaline sensitive) the other strain is more resistant (IR = isoprenaline resistant). In the IR strain the immobilization immersion stress causes high incidence of gastric ulcers, while the IS strain is prone to heart pathology. In this communication we report the differences in behavior of these two rat lines in three tests: open field, intruder's test and Porsolt's forced swimming test. The IS animals were passive and anxious in open field test, submissive in intruders test and they showed more floating time in Porsolt's forced swimming test. The IR rats were active, aggressive and dominant.