Abstract
Thyroid dysfunction can compromise physical capacity. Here, we analyze the effects
of hyperthyroidism and hypothyroidism on maximum swim time in rats subjected to acute
forced swimming, as an indicator of anaerobic capacity. Animals were forced to swim
against a load (5% of body weight) attached to the tail and were killed 48 hours after
the last test. Hyperthyroid rats were treated with thyroxine (50 μg/100 g body weight,
i. p. for 7 days). The hypothyroid group received 0.03% methimazole in the drinking
water for 4 weeks. Thyroid state was confirmed by alterations in serum thyroid-stimulating
hormone (TSH), triiodothyronine (T3), thyroxine (T4), and liver mitochondrial glycerol
phosphate dehydrogenase (mGPD) activity. Hyperthyroid rats presented significantly
lower visceral fat mass (VFM) and higher food intake (p<0.05) with unchanged body
weight. Maximum swim time (MST), glycogen content (skeletal muscle and liver), and
leptin levels were lower while corticosterone was higher (p<0.05). In hypothyroid
rats body weight was lower (p<0.05), without changes in VFM. Tested at 7-day intervals,
MST was lower for tests 2, 3, and 4 (p<0.05). Muscle glycogen was higher in extensor
digitorum longus (EDL) and soleus (p<0.05), without changes in liver. Serum corticosterone
was lower, while leptin was higher (p<0.05). These results suggest that in hyperthyroid
and hypothyroid rats, thyroid hormones together with corticosterone and/or leptin
may impair exercise capacity differently through its known effects on glycogen metabolism.
Key words
thyroid hormones - physical capacity - glycogen - leptin - corticosterone
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Correspondence
pclisboa@uerj.br patricialisboa@pesquisador.cnpq.br
