Yoshinori Tamaki

Comparison of thyroxine-binding plasma proteins of various vertebrates and their evolutionary aspects.

Abstract The patterns and the binding capacities of thyroxine-binding plasma proteins in various species of vertebrates were compared, and their evolutionary aspects were considered. Protein association of radioactivity in plasma-radioactive thyroxine mixtures was characterized by use of a radioautographic technique after cellulose acetate electrophoresis. Thyroxine-binding capacity of alpha-globulin was determined after adding carrier l -thyroxine to the plasma of the test animals: In Primates, prealbumin, albumin, and alpha-globulin-bound thyroxine; in cattle, albumin, post-albumin, and alpha-globulin-bound thyroxine; in other Artiodactyla, i.e., goats, sheep, muntjak deer, and swine, albumin- and alpha-globulin-bound thyroxine. In the Artiodactylas, the thyroxine-binding capacity by alpha-globulin was high compared with other orders of Mammalia and the lower classes of vertebrates. In horses and dogs, most radiothyroxine was bound to albumin and a relatively smaller amount of radioactivity was found in alpha-globulin. In cats and rabbits, the presence of thyroxine-binding alpha-globulin was questionable, and relatively strong binding of radiothyroxine was found in post-albumin and albumin. No apparent thyroxine-binding alpha-globulin was detectable in Rodentia. Bound radioactivity was found only in plasma albumin in guinea pigs, but in mice both in albumin and post-albumin. In rats, most radiothyroxine was bound to albumin and a very little amount of radioactivity was found in postalbumin. In lower vertebrates such as Aves, Reptilia, Amphibia, and Pisces, no thyroxine-binding alpha-globulin was found. Radiothyroxine concentrated in plasma albumin in some species (chicken, duck, caiman, fish), but in other species (pigeon, snake, lizard, tortoise, frog, newt), the radiothyroxine concentrated both in albumin and pre-albumin.

Comparison of the effects of thiouracil, propylthiouracil, and methimazole on I131 metabolism by the chick thyroid and measurements of thyroxine secretion rates

Abstract The effects of thiouracil, propylthiouracil, and methimazole (1-methyl-2-mercapto-imidazole) on I 131 metabolism in the chick thyroid and thyroxine secretion rates were studied. Thiouracil, propylthiouracil, and methimazole, when fed to 5-week-old cockerels at a 0.1% level in the diet, decreased thyroidal I 131 uptake to 62, 21, and 13% of that of a normally fed group, respectively. The feeding of thiouracil, propylthiouracil, and methimazole at a 0.1% level in the diet increased the release rate of thyroidal I 131 to 2.4, 3.4, and 4.1 times, respectively, that in the chick fed a normal diet. In addition, similar values about 1.5 μg/100 gm body weight per day were obtained in the estimation of the thyroxine secretion rate of 5–6-week-old cockerels both by the goiter prevention assay and by the radioiodine assay with thiouracil, propylthiouracil or methimazole as the goitrogen. The results of both assays revealed that the employed doses of the goitrogens had little effect on thyroxine secretion rates in 6–7-week-old cockerels. Thiouracil feeding at a 0.1% level in diet of 9-week-old cockerels, which had fecal fistulas for the separate collection of the urine and feces, increased (20–30%) fecal excretion and decreased (by 10%) the deiodination of radiothyroxine, compared with the nongoitrogen-treated birds. The feeding of methimazole had no such effects. The feeding of potassium perchlorate to the 13-week-old cockerels having fecal fistulas, at a 1% level in diet, severely inhibited the thyroidal uptake of I 131 recycled from metabolized radiothyroxine, but it did not increase fecal excretion of radiothyroxine. The administration of propylthiouracil to these birds increased fecal excretion by 30%, and it decreased the deiodination of radiothyroxine by 15%; methimazole had no effect. Thus, although methimazole has a stronger antithyroidal activity than thiouracil, it does not increase the fecal excretion of thyroxine as thiouracil does in the chick. The rate of thyroxine secretion is not affected by the different goitrogens.

The effects of thiourea, KClO4, methimazole, and thiouracil on the measurement of thyroxine secretion rate of cockerels

Abstract The effects of thiourea, KClO 4 , methimazole, and thiouracil on 131 I turnover by thyroid and on thyroxine secretion rate of cockerels were studied. Thiouracil, thiourea, methimazole, and KClO 4 , when fed to 5-week-old cockerels, significantly decreased thyroidal 131 I uptake, and significantly increased the release of thyroidal 131 I. No cumulative effect was observed on the release rate of thyroidal 131 I, when two of these antithyroidal drugs were given to 11-week-old cockerels simultaneously. Similar values of about 1.2 μg/100 gm body weight per day were obtained in the estimation of thyroxine secretion rate of 5- to 6-week-old cockerels by any of the radioiodine assays, goiter prevention assays, and microhistometric assays based on the height of the epithelial cells of the thyroid gland, with thiourea, methimazole, or thiouracil as the goitrogen. When KClO 4 was used as the goitrogen, the radioiodine assay, and the microhistometric assay gave similar values, whereas the goiter prevention assay could not be conducted because of a lack of enlargement of the thyroid glands. The feeding of a diet containing 1.0% KClO 4 and 0.1% thiouracil to 9-month-old cocks having fecal fistulas significantly increased (by 40%) fecal excretion of radiothyroxine, and decreased (by 10%) the deiodination of radiothyroxine, but not significantly. Feeding a diet containing 1.0% KClO 4 and 0.06% thiourea to the birds had no such effects compared with a diet containing only 1.0% KClO 4 .

A procedure for the determination of plasma thyroxine in farm animals

ラジオステレオアッセイ法による家畜の血漿中サイロキシン測定を行なうため,抽出条件の検討を行ない次の結論を得た.1) 血漿中サイロキシンの抽出溶媒としては,アルコールとケトンの類が優れているが,なかでも蛋白凝固力,蒸発除去の難易などを考慮すると血漿の2-3倍量のエタノール使用が最適である.2) 血漿に2倍量のエタノールを加えてサイロキシンを抽出した場合,抽出液にサイロキシン結合能を有する血漿蛋白質が混入した.この混入蛋白質が血漿中サイロキシン測定値を負にする主因と考えられる.3) 抽出液中の混入蛋白質は,抽出液を乾固後エタノールで再抽出する方法でほとんど除去され,サイロキシン結合能も失なわれる.すなわち,再抽出法によって蛋白質混入による血漿中サイロキシン測定値の低下は防止される.4) 抽出液の蒸発乾固によってはサイロキシンの散逸は起こらない.