P. Prakash et al., SUPEROXIDE ANION-RADICAL PRODUCTION AS A CADMIUM-MEDIATED MECHANISM OF TOXICITY IN AVIAN THYROID - AN ELECTRON SPIN RESONANCE STUDY BY SPIN-TRAPPING, Comparative biochemistry and physiology. Part C, Pharmacology toxicology & endocrinology, 118(1), 1997, pp. 89-95
Cadmium (Cd) induced superoxide anion radical (O-2(-)) generation in v
ivo has been demonstrated in the thyroid gland of Columba livia interm
edia by electron spin resonance (ESR) spin trapping. A single dose of
Cd caused generation of O-2(-), elevated lipid peroxidation (LPO) and
superoxide dismutase (SOD) activity and depletion of glutathione (GSH)
content in the thyroid gland on the 1st and 3rd day after the treatme
nt. After the 7th and 10th day of Cd intoxication, the thyroid gland r
esumes normal reducing atmosphere characterized by a very low LPO leve
l, total decay of O-2(-) and an adaptive recovery of depleted GSH to t
hat of control. A high level of SOD activity over the experimental per
iod and return of GSH content to that of control by the 7th day of tre
atment till the 10th day suggest their role as a very effective oxyrad
ical scavenging sink during Cd-mediated oxidative assault. A low plasm
a triiodothyronine (T-3) level, decreased plasma T-3/T-4 ratio over mo
st of the study period and a transient drop in plasma thyroxine (T-4)
level during early phase of acute poisoning indicate that pigeons are
in the hypothyroid state. We propose that avian thyroid dysfunction un
der acute Cd-exposure is due to impaired thyroid hormonogenesis under
an oxidative stress and a direct Cd-inhibition of peripheral monodeiod
ination of T-4 to T-3. (C) 1997 Elsevier Science Inc.