Lipid peroxidation levels in rat cardiac muscle are affected by age and thyroid status

Abstract

Free radicals, hydroxyperoxides and H 2 O 2 are all known to damage cell components. This study was designed to compare the concentrations of hydroxyperoxide and free radical scavengers in the cardiac muscles of old rats in the hyper-or hypothyroid condition, to determine whether rates of peroxidation would differ with age, thyroid status, or both.Rats were rendered hyper-or hypothyroid by administration of -thyroxine or methimazole for 4 weeks. Among the old rats, the lipid peroxide (LPO) concentrations, measured as thiobarbituric acid (TBA) reactants, were significantly greater in the hyperthyroid than in the euthyroid state and the LPO concentrations measured as TBA+Fe 3+ reactants, which may be precursors of LPO, were significantly greater in the hyperthyroid state, whereas in young rats, the LPO concentrations measured by TBA or TBA+Fe 3+ methods did not differ significantly in the hyperthyroid state. In the euthyroid state, the concentration of LPO measured as TBA+Fe 3+ reactants was significantly reduced with age. Xanthine oxidase (XOD) activity also was markedly increased with age, being more pronounced in the hyperthyroid than in the euthyroid state. The Mn and Cu/Zn superoxide dismutase activities were greater in the hyperthyroid than in the euthyroid state. Glutathione peroxidase activity decreased with age in the euthyroid and, particularly, in the hyperthyroid state. Catalase activity was not affected in the old rats. Concentrations of -tocopherol in the old rats were high in the hyperthyroid state and low in the hypothyroid state, whereas the levels of -and -tocopherols in these rats were unchanged in both conditions as compared with the euthyroid state findings.Data suggest that the site of free radical generation differs in older rats, with additional shifts in the location of intracellular lipid peroxidation being noted during hyperthyroidism. Thus, as rats age, the reduction of the free radical scavenger system and the increase in LPO and XOD activities might induce myocardial dysfunction.

Oxidative Stress and Antioxidant Status in Hypo- and Hyperthyroidism

“…Cu-Zn SOD activity increased in gastrocnemious [194] and in its white portion [12], in agreement with insensitivity of such muscle to thyroid hormone, whereas it was reported to both decrease [179] and remain unchanged [11,120] in cardiac muscle, despite the same prolonged treatment with T4. Total SOD was found to decrease in liver [180] and increase in heart from young [120,157] but not from old [120] hyperthyroid rats.…”

“…However, increased lipid peroxidation in hearts from old (1. 5 years) but not from young (8 weeks) hyperthyroid rats was also reported [120]. Thyroid hormone treatment was found to increase lipid peroxidation in lymphoid organs such as mesenteric lymph nodes and thymus, without major effects in the spleen [12], a thyroid hormoneunresponsive tissue [121].…”

“…R. Shinohara et al [120] have investigated how thyroid function might influence the production of oxygen free radicals, the lipid peroxidation process and antioxidant activity in muscle of rat myocardium. It was found that the degree of lipid peroxidation, assessed by measuring substances that react with thiobarbituric acid, significantly increases in animals with hyperthyroidism than euthyroidiene.…”

“…One is Cu-Zn SOD, mainly found in the cytoplasm of cells, while the other one is mitochondrial in nature and is known as Mn-SOD [191,192]. Mn-SOD activity in cardiac tissue was reported to both increase [11,120,179] and remain unchanged [118,193], even though in all cases hyperthyroidism was elicited by long-term treatment with T4. Mn-SOD was also found to increase in the soleus and white portion of gastrocnemious muscle from rats made hyperthyroid by combined T3 and T4 administration [12] and in soleus [11] and gastrocnemious [194] from T4-treated rats.…”

Influence of hypothyroidism on lipid peroxidation, erythrocyte resistance and antioxidant plasma properties in rabbits

“…The organic chain-breaking antioxidant potential of plasma appeared to be rather low and decreased in hypothyroidism. Such conditions may be in part caused by the low plasma primary chain-breaking antioxidant -α-tocopherol -content observed concomitantly with hypothyroid state (Constantini et al, 1998;Shinohara et al, 2000). Although the blood plasma of euthyroid rabbits possesses very high inorganic iron-binding, iron-oxidising and scavenging activities (from 77.1% to 86.9% of oxygen radicals inhibition), no alteration in these activities were noticed in hypothyroid rabbits.…”