Effect of Thiouracil on Plasma PBI131 in the Fowl

BLOOD protein-bound iodine (PBI) level has been reported to be a useful index of thyroid status in mammals; but according to at least two reports, it is low in the fowl and is not a good criterion of thyroid activity in that species (Bumgardner and Shaffner, 1957; Mellen and Hardy, 1957). Consistent with this conclusion is the observation that hormonal radioactivity in chicken plasma is weak compared to that in rats and mice given the same dose of I131 per unit of body weight (Wentworth, 1960). An explanation for these phenomena was recently reported by Tata and Shellabarger (1959), who showed rather conclusively that chickens and ducks lack the specific thyroxine-binding globulin found in mammals. In spite of the above observations on birds, there are reports which indicate that real differences in PBI level and in the ratio of PBI to total plasma iodine can be detected by measuring PBI131…