Accumulation of radioiodine in thiouracil-hyperplastic thyroids of chicks.

Kinetics of accumulation of radioiodine was studied in thyroids of chickens before, during, and following ingestion of 0.25% thiouracil (TU). After a latent period of about 5 days, weight of the thyroid gland increased, reaching its maximum (42 mg/100 g body wt) after 21 days of TU ingestion; thyroid weight decreased immediately on withdrawal of TU but tended to plateau at a higher level than that of controls. One-way clearance increased by day 4 of ingestion of TU and reached its peak early during hyperplasia; it very quickly reverted to a control level on withdrawal of TU. Exit-rate constant increased markedly during early hyperplasia and decreased to a level less than normal after withdrawal of TU. Concentration of 127I decreased by a factor of 18 by 2 wk of feeding TU; it increased to practically a normal level by 1 wk after withdrawal of TU.

Variations in plasma prolactin, thyroid hormones, gonadal steroids and growth hormone in turkeys during the induction of egg laying and moult by different photoperiods.

1. Concentrations of prolactin, growth hormone, testosterone, progesterone, thyroxine and triiodothyronine were measured in the blood plasma of female turkeys during successive periods of egg laying, a decline in lay, a moult induced by a short photoperiod (6 light: 18 dark) and a resumption of egg laying induced by a long photoperiod (16L:8D). 2. Concentrations of prolactin, growth hormone, testosterone and progesterone were higher in laying birds than in birds which were moulting or not laying. 3. The concentration of testosterone, but not of the other hormones studied, increased significantly during the period of profuse moult. 4. Concentrations of the thyroid hormones did not change with the varying physiological condition of the birds. However, the concentration of thyroxine was depressed by the long photoperiod.

Dietary iodine and accumulation of radioiodine in thyroids of chickens.

Groups of hatchling white leghorn cockerels were fed a basic, semisynthetic low-iodine diet to which various amounts of iodide were added: 0 up to 100 microgram I/g feed. Growth rates were unaffected by the range of dietary iodine content. A transitory goiter occurred only in the group fed the basic low-I diet. Half-life of 131I in the thyroid increased directly and fractional turnover rate inversely with increase of dietary iodine. Trichloroacetic acid-soluble iodine in serum did not accurately reflect variation of dietary iodine. However, effective clearance and binding rate constants did decrease proportionally to dietary iodine increase beyond the first 3-5 days. Concentration of iodine in thyroid was directly proportional to dietary iodine after 10 days. There was no consistent correlation between thyroxine or triiodothyronine and dietary iodine except in general terms of high and low dietary iodine groups. The avian thyroid exhibits great lability in adjusting functionally to a wide range of dietary iodine contents.

Dietary iodine and thyroidal iodide transport in chickens: organic binding blocked.

Experimental data concerning the increase in T/S [I-] (ratio of concentration of radioiodide in thyroid to that in serum) during equilibration after a single injection of radioidide were obtained from chickens in which protein binding of radioidide was inhibted by methimazole. Equilibration data were obtained from chickens fed a low-iodine diet (2 mo) as well as the low-iodine diet to which various amounts of NaI had been added. Experimental data were compared with productions based on the open two-compartmental model of Wollman and Reed (Am. J. Physiol. 196: 113-120, 1959). Thyroidal clearance (C/m) of radioiodide (the rate at which radioiodide is transferred from blood into the thyroid and equal to the radioiodide content of C microliter serum per minute) varied inversely to iodine content of feed. Exit rate constant (KTB, the fraction of thyroidal radioiodide transferred to serum per minute) was relatively more constant. The experimental data fitted the predictions from the model within experimental error. Thirty days of feeding the low-iodine diet was required before C/m stabilized at 50 microliter/min per mg and KTB at 0.065; stabilization of C/m and KTB occurred in 12 days with the highest iodine diet.

Thyroxine and triiodothyronine in blood after ingestion of iodinated casein by chicks.

White Leghorn cockerels were fed a broiler ration containing 0 (controls), 0.02 or 0.04% Protamone (iodinated casein) either continuously or for 10-14 days after which the 0.02% Protamone ration was switched to control or vice versa. Body growth rate was temporarily suppressed during the first 14 days of feeding 0.02% Protamone. Thyroid weight was promptly depressed during feeding of Protamone and increased more slowly when Protamone was removed from the feed. Only a fleeting increase in oxygen consumption rate was detectable in birds fed either 0.02 or 0.04% Protamone. Serum T4 and T3 promptly rose when Protamone was fed; continued feeding resulted in compensatory adjustments in secretion and perhaps peripheral metabolism of iodohormones within 2-3 days so that a level close to 200 ng. T3 or 2.5 mug T4/100 ml. serum was subsequently maintained.