April - June 2009, Volume 5, Issue 2

Petrulea MS, Duncea I, Muresan A

Thyroid hormones in exces induce oxidative stress in rats

Acta Endo (Buc) 2009, 5 (2): 155-163
doi: 10.4183/aeb.2009.155

Thyroid hormones play a crucial role in the regulation of the mitochondrial oxidative\r\nmetabolism. Hyperthyroidism caused by the acceleration of the energy metabolism leads to\r\nthe occurrence of cellular oxidative stress.\r\nThe aim is to evaluate the pro-oxidant / antioxidant balance and the effect of vitamin\r\nE supplementation in damage caused by the excessive administration of thyroid hormones.\r\nMaterials and Methods. White, male Wistar rats were used in the study. Thirty male\r\nWistar rats were divided into three groups (1:control group, 2:animals treated with LThyroxine\r\n10 &#956;g/animal/day for 30 days, 3:L-Thyroxin treated rats protected with vitamin\r\nE 10 mg/animal/day). Malondialdehyde (MDA), the marker of lipid peroxidation, carbonyl\r\nproteins, SH groups, glutathione (GSH) and superoxide dismutase (SOD) were determined\r\nfrom the serum, while MDA, carbonyl proteins, SH groups and GSH were determined from\r\nthe thyroid tissue homogenates.\r\nThe results showed increased levels of carbonyl proteins (1.31?0.33 nmol/mg protein,\r\np=0.0001) in serum in thyrotoxic group versus control, while MDA levels did not differ\r\nsignificantly from the control. Significantly low values of the SH groups, GSH and SOD were\r\nfound (p<0.001) in the plasma of Thyroxin treated rats. Vitamin E supplementation\r\nsignificantly increased plasma MDA levels in the Thyroxin treated group as compared with\r\nthe control group (p=0.01) and with the animals treated only with Thyroxin (p=0.04).\r\nCarbonyl protein levels in plasma of the hyperthyroid supplemented rats were also increased\r\nas compared to controls (p=0.0002). Antioxidant capacity markers in plasma of group 3 were\r\ndecreased compared with group 1. The marker of lipid peroxidation (MDA) significantly\r\ndecreased in thyroid homogenates of the group 2 as compared with group 1 (p=0.004).\r\nSignificantly high levels of the SH groups (p=0.0006) and low levels of GSH (p=0.0001) were\r\nfound in thyroid homogenates of the L-Thyroxin treated group as compared with controls.\r\nThese results suggest that experimental hyperthyroidism is accompanied with\r\nincreased oxidative stress and with the consumption of antioxidant enzymes in induced\r\noxidative aggressions. No protective effects of vitamin E on oxidative stress induced by\r\nexcessive administration of thyroid hormones were detected.

Keywords: Hyperthyroidism, Oxidative stress; Vitamin E, Carbonyl proteins, Antioxidant capacity

Correspondence: Mirela Petrulea, MD, Iuliu Hatieganu University of Medicine and Pharmacy,\r\nClinic of Endocrinology, P-ta Stefan cel Mare Nr. 5, 400192, Cluj-Napoca, Romania,\r\nPhone: +40-723.847.020; Fax:+40264-439258. E-mail: mirelapetruleas@yahoo.com