THE EFFECT OF NICOTINE ON THYROID-FUNCTION IN RATS

Very recently, it has been reported that subclinical hypothyroidism is more severe and peripheral markers of hypothyroidism are more pronoun ced in women with subclinical or overt hypothyroidism who smoke, incre ased concentrations of the known goitrogen thiocyanate, generated from cigarette smoke, have been the major explanation for the decreased th yroid function in these women but do not explain the reported increase d peripheral markers of hypothyroidism. There are no data on the effec t of the other major product of cigarettes, nicotine, on thyroid funct ion in vivo, The present studies were therefore performed to determine the effects of large doses of nicotine infused for 7 days on thyroid function, outer-ring 5'deiodinase activity (5'D-I), and hepatic malic enzyme activity ia measure of thyroid hormone action) in euthyroid, su bclinically hypothyroid ((hemithyroidectomized), and L-thyroxine (L-T- 4)-treated thyroidectomized rats, Nicotine infusion had mo effect on s erum T-4, triiodothyronine (T-3), thyrotropin (TSH), and cholesterol c oncentrations, intrathyroidal metabolism of I-125, liver and kidney 5' D-I activity, and hepatic malic enzyme activity in euthyroid and subcl inically hypothyroid rats, Nicotine administration also did not affect serum T-3, TSH, or cholesterol concentrations, liver and kidney 5'D-I activity, and hepatic melic enzyme activity in L-T-4-treated thyroide ctomized rats, These studies provide strong evidence that nicotine is not responsible for the observed adverse effects of smoking on the thy roid in humans. Copyright (C) 1998 by W.B. Saunders Company.