Fever induced oxidative stress: the effect on thyroid status and the 5'-monodeiodinase activity, protective role of selenium and vitamin E.

The thyroid hormones metabolism is considerably altered in many pathological processes including fever. Experiments performed on rabbits (n=62) showed that increase in the rectal temperature by 1 degrees C (after turpentine oil sc injections) decreased 5'-monodeiodinase activity, the enzyme responsible for deiodination of thyroxine to the most active thyroid hormone 3,3',5-triiodothyronine (T3), in the liver by 25% and in the kidney by 20%. Triiodothyronines concentration in serum decreased during fever from 1.57+/-0.12 to 0.52+/-0.02 nmolT3/l and from 0.17+/-0.01 to 0.07+/-0.02 nmol rT3/l. The increase in the body temperature intensified lipid peroxidation processes (malondialdehyde level increased from 1.2 times in kidney, and 1.4 times in the liver homogenates to 1.6 times in serum). The antioxidants (vitamin E and selenium) supplementation decreased lipid peroxidation processes during fever and partly restored the 5'-monodeiodinase activity. The present study confirmed our previous observations in vitro that lipid peroxidation (free radical formation) influences the 5'-monodeiodinase activity in tissues and alters the thyroid hormones metabolism.