Comparative thyroid function in adult Japanese quail and ring doves: influence of dietary iodine availability

Thyroid function was studied in Japanese quail, Coturnix japonica, and Ring doves, Streptopelia risoria, when both were fed the same dietary iodine (I; 930 micrograms I/kg). We also compared thyroid function in groups of doves receiving low I (less than 100 micrograms I/kg) or moderate I (930 micrograms I/kg). We measured thyroid gland (TG) weight, TG stable I content, TG 125I uptake, and 125I labeling of thyroid hormones. Triiodothyronine (T3) and thyroxine (T4) concentrations in TGs and serum were also determined. Our results indicate that doves and quail receiving the same dietary I show similar serum T3 (the presumed metabolically active hormone) and TG functional state but that there are some differences between the species in the way in which this functional state is achieved. We also assessed the effects of differences in I availability on thyroid function in doves. With low dietary I doves show decreases in some measures of thyroid function (reduced serum T4 and TG-hormone stores) compared to doves with moderate I but maintain a comparable level of serum T3. This regulation of T3 appears to be independent of serum T4 or TG-hormone stores.