Abstract. The effect of carnitine administration on levels of lipid peroxide and activities of superoxide dismutase and catalase was studied in rats administered ...
J. Biosci., Vol. 13, Number 3, September 1988, pp. 257–262. © Printed in India.
Effect of carnitine administration on levels of lipid peroxides and activities of superoxide dismutase and catalase in isoproterenol-induced myocardial infarction in rats S. SUSHAMA KUMARI and VENUGOPAL P. MENON* Department of Biochemistry, University of Kerala, Kariavattom, Trivandrum 695 581, India MS received 26 October 1987; revised 14 June 1988 Abstract. The effect of carnitine administration on levels of lipid peroxide and activities of superoxide dismutase and catalase was studied in rats administered isoproterenol to induce myocardial infarction. Levels of fatty acid were lower in rats pretreated with carnitine at the peak period and given isoproterenol than the levels in isoproterenol-treated control rats. Lipid peroxides were decreased in the heart at peak infarction in carnitine-treated rats compared to the levels in isoproterenol-treated controls. Activities of superoxide dismutase and catalase showed no change in carnitine-treated animals given isoproterenol compared to those in normal control rats, while they decreased in animals treated with isoproterenol alone. Keywords. Malondialdehyde; hydroperoxides; conjugated dienes; superoxide dismutase; catalase; free fatty acids.
Introduction A number of substances have been identified for their ability to protect against experimental myocardial infarction induced by a β-agonist isoproterenol (Wexler and Greenberg, 1978). Any substance which can prevent an attack or accelerate the process of recovery will have considerable clinical application. Carnitine (L-3-hydroxy-4-trimethylammonium butyrate) which plays an important role in the transmembrane transport of long chain fatty acids for their oxidation in the mitochondria, has been reported from our laboratory to offer protection against myocardial infarction induced by isoproterenol (Saleena et al., 1986). The molecular events underlying this phenomenon are not clear. There are some reports indicating that the level of carnitine decreases in the myocardium during ischemia (Whitmer et al., 1978). Recently we reported that one of the major events taking place during myocardial infarction is the increase in levels of myocardial lipid peroxides which may cause damage to the myocardium (Sushama and Menon, 1987). The primary substrates for the formation of lipid peroxides are fatty acids and long chain acyl coenzyme A derivatives whose concentrations have been reported to increase during myocardial infarction (Gudjarnason, 1980). In view of the observed protective action of carnitine it was thought worthwhile to study its effect on levels of lipid peroxides in animals pretreated with carnitine and administered isoproterenol. Changes in activities of two enzymes closely associated with the process, namely superoxide dismutase (SOD) and catalase, have also been studied. The results of these investigations are reported in this communication. *To whom all correspondence should be addressed. Abbreviations used: SOD, Superoxide dismutase; CPK, creatine Phosphokinase; GOT, glutamate oxalotransaminase; GPT, glutamine pyruvic transaminase.
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Materials and methods The animals used were virgin male albino rats of Sprague-Dawley strain with body weights in the range 150–200 g. The rats were grouped into (1) control group, and (2) carnitine-treated group. DL-Carnitine in physiological saline was administered daily intramuscularly at a dose of l0mg/l00g body weight for 10 days. The control group received physiological saline. At the end of the period, the animals were regrouped as follows. 1. Normal control group. 2. Normal administered isoproterenol. 3. Carnitine-treated control group. 4. Carnitine-treated rats administered isoproterenol. Isoproterenol was given at a dose of 35 mg/100 g body weight in two injections 24 h apart as previously described (Saleena et al., 1982). Rats in groups 3 and 4 continued to receive carnitine. Rats of group 4 were given isoproterenol 3 h after administration of carnitine. The isoproterenol-treated rats showed signs of shock tachycardia, dyspnea, rapid respiration, etc. The animals of group 4 showed these signs to a lesser extent. The surviving animals of group 4 continued to receive carnitine till the end of the experiment. Rats in each group (45 rats) were killed after overnight starvation at 5 h, 36 h and 7·5 days after the first injection. The control rats (15) were sacrificed along with those killed at 5 h. The heart tissue was removed to ice-cold containers for various estimations. Serum creatine Phosphokinase (CPK), glutamate oxalotransaminase (GOT) and glutamine pyruvic transaminase (GPT), free fatty acid levels in the heart and serum, activities of SOD and catalase in the heart, and levels of malondialdehyde, hydroperoxides and conjugated dienes in the heart were estimated as described earlier (Sushama and Menon, 1987). Statistical analysis was carried out using Student’s ‘t’ test (Bennet and Franklin, 1967). Results The rate of survival in rats given isoproterenol alone was 60–65% while in the case of rats pretreated with carnitine and then given isoproterenol it was 85–90%. These results are. from 5 experiments using 25 rats in each group. Serum GOT, GPT and CPK Rats treated with isoproterenol showed significantly higher values for GOT and GPT at 5 h, 36 h and 7·5 days after injection than normal rats. In the case of CPK, the values were higher only at the peak period (table 1). Rats treated with carnitine before isoproterenol injection showed lower enzyme activities at peak period of infarction than the isoproterenol-treated animals. Carnitine alone did not bring about any significant change in the enzyme activities. Levels of free fatty acid in serum and heart The data are given in table 2. The levels of free fatty acid registered an increase at
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Table 1. Activities of serum GOT, GPT and CPK in induced myocardial infarction and recovery.
Groups 2 to 4 compared with group 1. Group 4 has been compared with group 2. *P < 0·01; +P between 0·01 and 0·05;‡P < 0·01. Values given are the mean from 7 rats in each group ± SEM.
Table 2. Changes in the free fatty acids in serum and heart at different stages of infarction.
Groups 2 to 4 have been compared with group 1. Group 4 has been compared with group 2. *Ρ < 0·01; ‡Ρ < 0·01. Values given are the mean from 7 rats in each group ± SEM.
peak period of infarction in both serum and heart in rats administered isoproterenol. In the case of serum the fatty acid levels showed a sudden spurt at 5 h. In the case of rats pretreated with carnitine and given isoproterenol, the levels of free fatty acid at peak infarction in both serum and heart were lower than those in animals given isoproterenol alone. In the carnitine group the level of free fatty acid at 5 h in the heart was higher than the level in animals treated with isoproterenol. The carnitinetreated animals also showed higher level of free fatty acids in the heart than normal control rats. Levels of lipid hydroperoxides, conjugated dienes and malondialdehyde in heart The levels of hydroperoxides, conjugated dienes and malondialdehyde were higher at
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the 5 and 36 h in animals administered isoproterenol alone. On the other hand rats pretreated with carnitine and then administered isoproterenol showed significant decrease in the level at the 5 and 36 h intervals (table 3). Table 3. Changes in the levels of lipid hydroperoxides, conjugated dienes and malondialdehyde in heart at different stages of infarction.
Groups 2 to 4 nave been compared with group 1 Group 4 has been compared with group 2. *P < 0·01; ‡P < 0·01. Values given are the mean from 7 rats ± SEM.
Activities of SOD (EC·1·15 1·1) and catalase (EC 1·11·1·6) The activities of SOD and catalase showed slight increase at 5 h and then fell below the normal levels at peak infarction in animals administered isoproterenol (table 4). In animals administered isoproterenol after pre-treatment with carnitine, activity of SOD showed slight elevation at 5 h and then fell to values near normal at peak Table 4. Activities of SOD and catalase in heart at different stages of infarction.
Groups 2 to 4 have been compared with group 1. Group 4 has been compared with group 2. *Ρ < 0·01; +P between 0·01 and 0·05; ‡P
