Effects of cold (+4°C) on thyroid metabolism of iodine (127I and 131I) in quail (Coturnix coturnix japonica)—A comparison with the rat

Abstract 1. 1.|A kinetic study of the absolute specific activity (SA) of iodine in intrathyroidal iodotyrosines and iodothyronines, and in plasma PBI, was performed comparatively in adult male rats and quail kept at +25°C (controls) or exposed to +4°C (for 2 days or 30 days before the iodine measurements). 2. 2.|In both species, 2 days of cold exposure induced a rapid increase (20 to 50%) in the SA of intrathyroidal iodoaminoacids and plasma PBI, leading to a rapid equilibration between the SA measured. After 30 days an acceleration in iodine turnover was still measurable in rats, but the stimulation then appeared more important in quail. In addition, the acceleration of iodine turnover led to a characteristic bimodal pattern of this turnover which was apparent only in quail, and could reflect an important production of non-hormonal iodinated proteins. Although the bird thyroid has been claimed to be less reactive to cold than its mammalian homologues, the present study indicates that, at least in bird species whose thyroidal stores of iodine are not excessive, the thyroid is even more responsive to cold than the rat thyroid.