Exhaustive exercise and vitamins C and E modulate thyroid hormone levels at low and high altitudes

Abstract

Thyroid hormones play an important role in cell growth and differentiation and regulation of oxygen consumption and thermogenesis. The effect of altitude and vitamin supplementation on thyroid hormone levels in animals or humans performing acute exhaustive exercise have not been investigated before. Therefore, we thought to test whether exhaustive exercise-induced stress with antioxidant supplementation was capable of modulating the level of thyroid hormones at different altitudes. Serum levels of T4 (Thyroxin), T3 (Triiodothyronine), and TSH (Thyroid Stimulating Hormone) were measured in rats (N=36) born and bred in low altitude (600 m above sea level) and high altitude (2200 m above sea level) following forced swimming with or without vitamins C and E (25 mg/kg) pre-treatments. Thyroid levels were significantly decreased in resting rats at high altitude compared to low altitude, and swimming exercise moderately increased T3 and TSH at both high and low altitudes, whereas T4 was markedly increased (62 %) at low altitude compared to a moderate high altitude increase (28 %). Co-administration of vitamins C and E augmented the observed forced swimming-induced thyroid release. However, the conversion of T4 to T3 was reduced in both altitude areas following swimming exercise and vitamin pre-treatment had no effect. We conclude that acute stress induced thyroidal hormones in rats, which was augmented by antioxidant drugs in both high and low altitude areas. These findings may play an important role in the human pathophysiology of thyroid gland at different altitudes.

Keywords: altitude; exhaustive exercise; thyroid hormones; vitamins.

Figure 1. High altitude suppresses baseline levels of thyroid hormones. Values are given as Mean ± SD for groups of six rats each. Analysis by one way ANOVA. Values are statistically significant at *p<0.05. LA: Low altitude. HA: High altitude

Figure 2. T3/T4 ratio in all experimental groups at low and high altitude. Analysis by one way ANOVA. Values are given as Mean ± SD for groups of six rats each. Values are statistically significant at p<0.05. Control: Resting rats. Stress (A): Rats under swimming excercise stress. Stress (B): Rats under swimming exercise stress and treated previously with combined vitamins E and C. *: significantly different when compared to its control group, a: significantly different when compared to same area stress (A). b: significantly different when compared to low altitude similar group

Figure 3. Exhaustive exercise induces thyroidal hormones at both low and high altitudes. Values are given as Mean ± SD for groups of six rats each. Analysis by one way ANOVA. Values are statistically significant at p<0.05. LA: Low altitude. HA: High altitude. Control: Resting rats. Stress (A): Rats under swimming excercise stress. *: Significantly different when compared to its area specific control group. Ω: Significantly different when compared to LA control group. π: significantly different when compared to stress group (A) at LA

Figure 4. Suggested model that investigates the effect of vitamins E and C on stress induced thyroid hormonal changes in rats in both low and high altitudes

Figure 5. Vitamin C and E augment exhaustive exercise - induced thyroidal hormones. Values are given as Mean ± SD for groups of six rats each. Analysis by one way ANOVA. Values are statistically significant at p<0.05. LA: Low altitude. HA: High altitude. Control: Resting rats. Stress (B): Rats under swimming exercise stress and treated previously with combined vitamins E and C. *: Significantly different when compared to its area specific control group. Ω: Significantly different when compared to LA control group. π: significantly different when compared to stress group (B) at LA. λ: Significantly different when compared to stress group (A) at LA. &: Significantly different when compared to stress group (A) at HA.