[Studies on early stage changes of peroxide lipid in isoproterenol-induced myocardial injury]

Protective effect of fish oil on changes in the activities of membrane-bound ATPases and mineral status in experimentally induced myocardial infarction in Wistar rats

The present study evaluated the protective effect of fish oil in isoproterenol-induced myocardial infarction in rats. The results of the present study indicate that the IPH administration decreases the activities of membrane-bound ATPases compared to control animals. Fish oil pretreatment brought about significant increase in the activity of these membrane-bound ATPases in IPH (isoproterenol hydrochloride)-treated animals. Significant increase in serum potassium level with concomitant decrease in the values of sodium, magnesium, and calcium were observed in IPH-treated rats compared to control rats, fish oil pretreatment reversed these changes to near normal. Significant elevation of sodium and calcium levels with concomitant decrease in the levels of potassium and magnesium were observed in the myocardial tissue of IPH-administered rats compared to control rats, fish oil pretreatment followed by IPH administration brought these levels to near normal. The levels of lipid peroxidation (LPO) in both serum and tissue were increased in IPH-treated rats compared with control rats, whereas pretreatment with fish oil in IPH-treated rats maintained near-normal LPO levels. The results of the present study reveals that the pretreatment of fish maintains the activities of membrane-bound ATPases and the mineral levels at near normal by the inhibition of lipid peroxidation.

Protective effect of betaine on changes in the levels of membrane-bound ATPase activity and mineral status in experimentally induced myocardial infarction in Wistar rats

Cardiovascular diseases are emerging as a major public health problem in most parts of the world even in developing countries still afflicted by infectious diseases, undernutrition, and other illnesses related to poverty. In the present study, we investigated the protective effect of betaine, a potent lipotropic molecule, on changes in the levels of membrane-bound ATPase activities, lipid peroxidation, sulfhydryl activities, and mineral status in isoprenaline-induced myocardial infarction in Wistar rats, an animal model of myocardial infarction in man. Oral administration of betaine (250 mg/kg body weight/day for a period of 30 days) significantly (p < 0.05) reduced the isoprenaline-induced abnormalities noted in the levels of sodium, potassium, and calcium in plasma and heart tissue. Pretreatment with betaine significantly attenuated isoprenaline-induced membrane-bound ATPase depletion in the heart tissue and preserved the myocardial membrane-bound ATPase activities at levels comparable to that of control rats. Oral administration of betaine significantly attenuated the isoprenaline-altered sulfhydryl groups in the heart tissue and preserved the myocardial sulfhydryl activities at levels comparable to that of control rats. It also significantly counteracted the isoprenaline-mediated lipid peroxidation and maintained the level at near normal. In the results of the present study, betaine administration significantly prevented the isoprenaline-induced alterations in the activities of membrane-bound ATPases, lipid peroxides, myocardial sulfhydryl levels, and maintained the mineral status at near normal.

Lipolysis is an important determinant of isoproterenol-induced myocardial necrosis

The cardiotoxic effect of isoproterenol (ISO) is associated with, and possibly due to, calcium overload. Prior work suggests that calcium entry into cardiac myocytes after ISO administration occurs in two phases: an early rapid phase, followed by a slow phase beginning about 1 hour after ISO injection, leading to a peak myocardial calcium level after about 4 hours. We have tested the relationship of these phases to myocardial necrosis (MN) by determining the time after ISO administration at which the commitment to MN occurs. This was done by administration of propranolol at various times before and after ISO. In addition, since ISO induces lipolysis, and lipids can be toxic, experiments were conducted to determine if adrenergically-activated lipolysis could play a significant role in ISO-MN. We found that propranolol protected the myocardium equally well when administered anytime within 2 hours of ISO injection, but had no effect when given 4 hours after ISO. This showed that metabolic events taking place more than two hours after ISO injection are required for ISO-MN. As expected from prior work, there was a small and consistent amount of propranolol-resistant ISO-MN. Lipolysis, assessed by measuring serum glycerol levels, increased to tenfold above base line at one hour after ISO administration and returned to near basal levels at 4 hours. Potentiation of lipolysis by intravenous injections of phospholipase A2 (PLA2) or lipoprotein lipase (LPL) to rats treated with ISO substantially augmented MN. Propranolol completely blocked the increase in necrosis produced by PLA2 when given with ISO. Lipases induced only minimal necrosis in the absence of ISO. Administration of adenosine (an anti-lipolytic agent), oxfenicine (an inhibitor of mitochondrial palmitoyl carnitine transferase), or vitamin C (an anti-oxidant) resulted in a 55-60% reduction in MN. These results suggest that critical necrosis-determining events occur between 2 and 4 hours after ISO administration and imply a relationship between ISO-induced lipolysis, calcium influx, and ISO-MN. We hypothesize that importance of lipolysis as a determinant of ISO-MN is related to the generation of free fatty acids, their oxidized/metabolic products, or direct damage to plasma membrane.