triiodothyronine--reverse and Dwarfism

Topics: Adrenal Gland Diseases; C-Peptide; Diabetes Mellitus; Dwarfism; Glucagon; Growth Hormone; Humans; Insulin; Parathyroid Diseases; Radioimmunoassay; Thyroglobulin; Thyroid Diseases; Thyroxine; Thyroxine-Binding Proteins; Triiodothyronine; Triiodothyronine, Reverse

Plasma concentrations of thyroxine (T4), triiodothyronine (T3), reversed triiodothyronine (rT3), and insulin-like growth factors I and II (IGF-I, IGF-II) together with peripheral 5'-monodeiodination activity were measured in both normal and sex-linked dwarf embryos between day 14 of incubation and day 1 posthatch. Plasma T4 levels increased gradually during embryonic development while T3 concentrations remained low until day 20, when a sharp increase was observed. rT3 levels also increased from day 14 and dropped on day 20 when T3 levels started to increase. 5'-monodeiodination activity was high on day 14 of incubation, decreased thereafter, and showed an increase at the time of air sac penetration together with increased T3 levels. At this stage, differences between normal and dwarf embryos were observed; the latter had lower nonsignificant 5'-Monodeiodination activity and lower (P less than 0.01) plasma T3 levels. Plasma IGF-II levels were high during the whole embryonic period studied. Dwarf embryos had lower (P less than 0.05) IGF-II levels at the time of hatching. IGF-I levels were high on days 14 and 16, declined afterwards, and started to increase again around hatching. With the exception of T3 and IGF-II levels, introduction of the dwarf gene did not cause major changes in the hormonal parameters studied. This may explain the identical body weight at hatching.

Topics: Animals; Chick Embryo; Dwarfism; Genetic Linkage; Iodide Peroxidase; Sex Chromosomes; Somatomedins; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The effect of an injection of thyrotrophin releasing hormone (TRH) on plasma levels of thyroid hormones was studied in dwarf and normal Rhode Island Red chickens with similar genotypes other than for the sex-linked dwarf gene dw. The sex-linked dwarf chickens had different plasma iodothyronine levels from control normal chickens: high thyroxine (T4), low triiodothyronine (T3) and similar reverse T3 (rT3) levels. The injection of TRH (10 micrograms/kg) in 5-day- and 5-week-old normal chickens increased the plasma T4 within 30 min without a significant increase in T3, whereas the injection of TRH in 11-and 26-week-old normal chickens increased plasma T3 60 min later. In dwarfs the response of T4 to TRH was the same as that in normals but no increased T3 response was observed. The plasma level of rT3 was not influenced by the TRH injection in either strain. These results suggest that although in the sex-linked dwarfs thyroidal response to exogenous TRH is similar to that of normals, the dwarf gene dw inhibits the conversion of T4 to T3 in peripheral tissues without any inhibitory effect on rT3 production.

Topics: Aging; Animals; Chickens; Dwarfism; Female; Injections, Intravenous; Injections, Subcutaneous; Male; Poultry Diseases; Sex Chromosomes; Thyroid Hormones; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse