| Effects
of melatonin on the oxidative stress induced by thyrotoxicosis
in rats by Ewa
Sewerynek, Joanna Wiktorska & Andrzej Lewinski
Key words:
thyrotoxicosis;
melatonin; malondialdehyde; conjugated dienes; Schiff bases
Abstract
High
concentrations of thyroid hormones can affect the metabolism
of oxygen in aerobic conditions and stimulate free radicals
generation in mitochondria. Reactive oxygen species are toxic
to biomembranes and lead to peroxidation of lipids unless they
are not removed by free radical scavengers. A few years ago
melatonin (MEL), a pineal hormone, was described as a scavenger
of free radicals, especially of hydroxyl and peroxyl radicals.
The goal of the
study was to examine the parameters of oxidative stress [the
levels of conjugated dienes (CD), malondialdehyde (MDA) and
Schiff bases (SB)] in male rats with thyrotoxicosis, induced
by the injection of L-thyroxine (L-T4) in a dose of 100 µg/kg
B.W. After one week of treatment with L-T4, the animals received
MEL in a dose 5 mg/kg B.W., i.p., daily, for 7 days. Diagnosis
of thyrotoxicosis was confirmed, using hormonal assays.
We observed the increased concentration
of free T4 (fT4) and free T3 (fT3) after L-T4 injections. The
concentration of fT3 was diminished after MEL in L-T4-injected
animals. In the liver, we did not observe any changes in the
content of both CD and MDA after L-T4 injections but the content
of SB was higher after L-T4 injections when compared to the
control group. In the liver, melatonin did not change any parameters
of oxidative stress, either alone or after L-T4. The changes
in the parameters of oxidative stress were better expressed
in the kidney, compared to the liver. Melatonin decreased the
concentration of CD and SB in the kidneys of a group of animals
with thyrotoxicosis. Additionally, MEL decreased the basal concentrations
of CD and SB, when compared to the control group.
|
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Letters 1999
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