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Q19 - Thyroid Hormone, Oxidative Stress, and the Heart

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Endocrine System Physiology

Thyroid hormones play a crucial role in metabolism and the cardiovascular system. Too much or too little thyroid hormone can result in insufficient blood flow to the heart. Insufficient blood flow generates reactive oxygen species (ROS) which damage the heart further.

Methimazole prevents the production of thyroid hormones, whilst T4 is a thyroid hormone. Either was given to rats, and the expression of antioxidant enzymes in the heart was measured.

Five bar-chart panels (a-e), each on a log-scale y-axis (0.1-10, “Axis = Fold change”) labeled SOD1, SOD2, GPX1, GPX3, and Catalase. Each panel has three bars: CTL (untreated control, ~1), MMZ (methimazole-treated), and T4 (thyroxine-treated). SOD1: MMZ elevated (~1.8), T4 near 1. SOD2: T4 slightly below 1. GPX1: MMZ elevated (~1.8), T4 below 1 (~0.5). GPX3: MMZ below 1 (~0.7), T4 near 1. Catalase: T4 significantly below 1 (~0.5, marked with an asterisk), MMZ near 1. Fig.1. Axis = Fold change (Logarithmic scale). CTL = Untreated Control group. MMZ = Treated with Methimazole. T4 = Treated with thyroxine. SOD = Superoxide dismutase. GPX = Glutathione peroxidase.

Assess how the following variables change under the conditions described below.

Q19.1. Too much OR too little thyroid hormone can starve the heart of blood flow, generating damaging ROS. Rats were given methimazole (MMZ, blocks thyroid hormone production) or T4, and antioxidant enzyme expression was measured. Assess: the expression of catalase enzyme on a thyroxine (T4) supplemented diet.
Q19.2. Assess: severity of ROS damage in patients treated with thyroid stimulating hormone (TSH).
Q19.3. Assess: SOD1 expression of thyrotropin releasing hormone (TRH) treated rats.
Q19.4. Assess: risk of heart failure in Graves' disease patients treated with methimazole, compared to untreated Graves' patients.
Q19.5. Assess: core temperature of animals on the T4 supplemented diet.
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Question reproduced from IBO 2019, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key