Effect of Quercetin on Exercise Tolerance in Experimental Hyperthyroidism in Male Albino Rats

Abstract
Background: This work was performed to study the effect of Quercetin on exercise tolerance in experimental hyperthy-roidism in male albino rats.
The aim of this work is to study the effect of Quercetin on exercise tolerance in experimentally induced hyperthyroid male albino rats.
Methods: 40 male rats were divided into 4 groups 10 rats each: (I) Euthyroid sedentary (ES), (normal control) group: Received (0.5ml physiological saline daily Intra-Gastric (IG) for 3 weeks). (II) Thyrotoxic Sedentary (TS), (thyrotoxic control) group: Received exogenous thyroxine (T4), eltroxin (50mg tablet) for induction of thyrotoxicosis in increasing doses (50μg to reach 200μg/kg body weight daily by (IG) administration, for 3 weeks. The rats were given 50μg/kg daily during the first week, 100μg /kg daily during the second week and 200μg/kg daily during third week. (III) Thyrotoxic adapted (TA) group: Received eltroxin in increasing doses (50μg to reach 200μg/kg body weight daily IG) for 3weeks, as (TS) group. (IV) Quercetin Treated Thyrotoxic Adapted (QTTA) group: Received eltroxin (50μg to reach 200μg/kg body weight daily IG) for 3weeks, they received also quercetin at a dose of 25mg/kg, IG on alternate days throughout the experimental period. These animals received the dose of quercetin within 2 hours before submission to the Maximal Swimming Time test (MST). All animals were submitted to MST after induction of thyrotoxicosis. However, the animals of group III, and group IV were submitted to the test after performing swim session adaptation for 2 days before doing the test.
Results: At the end of the experimental period all thyro-toxic groups showed significant decrease in total body weight compared to control group, at the same time, TS and TA groups showed significant decrease in relative liver weight, relative thyroid weight, and relative epididymal pad of fat weight compared to control group, while, QTTA group showed insignificant change compared to control group, but it showed significant increase compared to TS and TA groups. All thyrotoxic groups also showed significant increase in serum T3, T4 level, and significant decrease in serum TSH level compared to control group. On the other hand, all thyrotoxic groups showed a significant increase in liver, skeletal muscle MDA, and catalase compared to control group, while TA group showed significant increase in their levels compared to TS group, however it showed significant decrease in their levels after quercetin treatment. It also showed significant decrease in liver and skeletal muscle glycogen in all thyrotoxic groups compared to control group, similarly, it showed sig-nificant decrease in TA group compared to TS group, but, it showed significant increase after quercetin treatment. On the other hand, TS and TA groups showed a significant decrease in MST, while QTTA showed insignificant change compared to control group, TA group also showed significant decrease compared to TS group, while it showed significant increase after quercetin treatment.
Conclusion: We concluded that quercetin can improve exercise intolerance that occurs in hyperthyroidism through its antioxidant effect.