[Diurnal rhythms of thyroid hormones in rooster chicks (Gallus domesticus). 3. Studies on the changes in deiodination rate of thyroxine-I-131].
As a measure for the availability and efficiency of the so-called free hormone to repress the thyreotropin-secretion (Mouriz et al., Endocr. 79, 248-260 (1966) we investigated the deiodination of thyroxine-I-131 (T4-I-131). This was done with special regard to a possible cyclic variation. By means of the reutilisation we could measure the removed radio-iodide in the thyroid 1-1/2 hours after T4-I-131 application. Using I-125 as a reference-isotope for the radioiodine uptake we could specify the actual extent of deiodination. The deiodination had a diurnal variation: The minimal values at 9 am and 9 pm ("deiodination" 10 or 9 percent) were significantly different (2 P less than 0.025) from the maximal values at 3.00 am and 3.00 pm ("deiodination-rate" about 17 percent). We propose the following explanation: 1) While the deiodination is decreasing in the morning and evening the pituitary releases more thyreotropin; 2) Thereby the thyroid releases more hormone and so the protein-bound iodine and the so-called free hormone raises. This would be in good agreement with our prior investigations.
D000818:Animals; D002645:Chickens / Q000502:physiology*; D002940:Circadian Rhythm; D004032:Diet; D007455:Iodine / Q000097:blood / Q000378:metabolism; D007457:Iodine Radioisotopes; D008297:Male; D013961:Thyroid Gland / Q000378:metabolism* / Q000502:physiology; D013972:Thyrotropin / Q000378:metabolism; D013974:Thyroxine / Q000097:blood / Q000378:metabolism*
D007457:Iodine Radioisotopes; D013972:Thyrotropin; D007455:Iodine; D013974:Thyroxine
Tageszykliche Schwankungen der Schilddrüsenhormone bei Hähnchen (Gallus domesticus). III. Untersuchungen zu Anderungen der Dejodierungsrate von Thyroxin-J-131