Opposite effects of zinc and melatonin on thyroid hormones
in rats.
Baltaci AK, Mogulkoc R, Kul A, Bediz CS, Ugur A.
Department of Physiology, Meram Medical School, Selcuk University, 42080,
Konya, Turkey
The present study was conducted to investigate how thyroid function in rats is
affected by administration of 3mg per kg per day of zinc and/or melatonin.The
study was conducted with 40 Sprague-Dawley adult male rats equally divided
into four groups: 1 (controls), 2 (zinc-only), 3 (melatonin-only) and 4 (zinc-
and melatonin-supplemented). The supplementation was continued for 4 weeks
after which the animals were sacrificed and plasma samples were obtained for
determination of zinc, melatonin, free- and total triiodothyronine (T3),
thyroxine (T4) and thyroid-stimulating hormone (TSH) levels.The free T3, T4
and TSH levels were lower in the melatonin group than in all other groups
(P<0.01), while free- and total T3 levels were higher in the zinc group
(P<0.01). The group that received zinc and melatonin combined had free thyroid
hormone levels higher than the only melatonin group.These results show that
melatonin has a thyroid function suppressing action, just the opposite to the
actions of zinc. When zinc is administered along with melatonin, its thyroid
function suppression is diminished.