Int.J. Biochem. Vol. 23,No. 10,~~. 1025-1030, 1991 Printed in Great Britain. All rights resewed 0020-71 IX/91 $3.00+0.00 Copyright 0 1991 Pergamon Press plc zyxwvut THE RESPONSE OF RAT LIVER LIPID PEROXIDATION, ANTIOXIDANT ENZYME ACTIVITIES AND ~L~ATHIONE CONCENT~TION TO THE THYROID HORMONE PAOLA MORINI, ELISABETTA CASALINO,CESARR SBLANOand CLEMENTE LANDRISCINA* Laboratory of Biochemistry, Faculty of Veterinary Medicine, University of Bari, Via Gentile 182, 70126 Bari, Italy [Tel. (080) 3349061 (Received I7 October 1990) Ah&act-1. In liver microsomes from hyperthyroid rats NADPH-dependent lipid peroxidation induces a hydroperoxide formation 56% higher than that in euthyroid ones. 2. The addition of 5 PM Fe2+ (or Fe)+) strongly decreases the hydroperoxide level in favour of that of TBA-reactive substances. Higher iron concentrations (30 PM) have no significant effect. 3. In hepatocytes from hy~~yroid rats Ccl,-induced lipid peroxidation produces an amount of TBA-reactive substances four times higher than that in those from euthyroid rats. 4. In the liver of h~~hyroid rats a GSH concentration decrease (by about 35%) is found while the opposite occurs in the blood of the same animals where GSH increases 2.5 times. 5. It is shown that in the liver of hyperthyroid rats, besides higher lipid peroxidation, a more active defence mechanism is operating since both glutathione peroxidase and glutathione reductase specific activities are higher than in euthyroid rats. INTRODUCTION The thyroid hormone has been shown to significantly influence a number of activities in various organs, particularly in the liver (Horrum et al., 1986; Colston and Cleave, 1986; Landriscina et al., 1976; Hoch, 1988; Lippolis et al., 1988; Mutvei and Nelson, 1989). An increase in NADPH-oxidase activity has been found in the livers of rats given triiodothyronine for several consecutive days (Fernandez et al., 1985). It has been observed that the enzyme-catalysed, unlike the non-enzymatic lipid peroxidation rate is strongly stimulated in the liver microsomes from hyperthyroid rats (Fernandez et al., 1985; Landriscina et al., 1988). The activity of NADPH-cytochrome P-450 reductase has also been found to be much increased in these microsomes (Landriscina et al., 1988). The lipid per- oxidation process involves PUFA oxidative degra- dation in membrane lipids which causes many types of damage to tissues and cells (Van der Zee et al., 1989; Poli ei al., 1987). As hy~~hyroidism induces a major fluidity in biological membranes (Hulbert, 1978; Ruggiero et at., 1984), it is important to examine whether the high PUFA content is a determining factor in making these membranes more prone to peroxidation. We observed lipid peroxidation in liver microsomes from hyperthyroid rats when ferrous ions were not added and when they were added to the reaction mixture. The activity in both cases was much higher than that observed in euthyroid rat liver microsomes. *To whom all correspondence should be addressed, at Istituto di Chimica, Facolta’ di Medicina Veterinaria de~unive~i~’ di Bari, Via Gentile 182, 70126 Bari, Italia. The fatty acid pattern following lipid peroxidation indicated that in the presence of NADPH plus 5 PM Fe*+ the PUFA decrease was about 30% higher than that with NADPH only. Lipid peroxidation stimulated by carbon tetrachloride in a culture of isolated hepato- cytes from hy~~hyroid rats was four times higher than that observed in hepatocytes from eu~yroid rats. In order to examine the state of the liver defence mechanism in this pathological condition, the activities of the antioxidant enzymes, glutathione peroxidase and glutathione reductase, were also measured. These were found to be significantly stimulated in hyper- thyroid rats while no appreciable alteration was detected in hypothyroid rats. The decreased hepatic GSH concentration and the concomitant serum level increase observed in hyperthyroid rats is discussed in relation to the enhanced lipid peroxidation in these animals. MATERIALS AND METIZODS Male Wistar rats weighing 180-200 g maintained on a standard diet were used. They were made hyperthyroid by daily i.p. injection for 6 consecutive days of 3,3’,5-L-tri- iodothyronine (30 fig/l00 g body weight), dissolved in 0.9% NaCl-propylenglycol (40:60, v/v; Lippolis et al,, 1988). Hypothyroidism was induced by administering 6n-propyl- 2-thiouracil in drinking water (O.OS%, w/v) for 15-20 days (Laker and Mayes, 1981). In euthyroid rats this treatment resulted in a decrease in the specific activity of liver L-a-glycerophosphate dehydrogenase from 0.62 f 0.05 to 0.12 f 0.02 pmol cytochrome c reduced/n& per mg protein (mean rt SD, n = 4). The liver mit~hond~a heme a f a3 content also decreased from 0.22 f 0.04 to 0.14 * 0.02 gmol/mg protein (n = 3). This response was taken to be a reliable indication of the hypothyroid state of the rats. 1025