Thyrotropin-releasing hormone (TRH) is not thyrotropic but somatotropic in fed and starved adult chickens.
Adult fed and starved Warren chickens, 2 yr of age, and approaching the end of the second laying year, were injected iv with 1 of the following products: 10 micrograms of thyrotropin releasing hormone (TRH); 100 micrograms of bovine thyrotropin (bTSH); 100 micrograms of ovine growth hormone (oGH); saline. The influence on plasma concentrations of thyroxine (T4), triiodothyronine (T3) or chicken GH (cGH) were followed. Prior to injection, it was clear from the control values that starvation for 3 d decreased plasma levels of T3 and increased cGH, whereas 7 d of fasting increased T4 and cGH. The plasma levels of cGH were elevated greater than 10-fold at 15 min following the TRH challenge in food-deprived chickens compared to a less than 4-fold increase in normal fed hens. This increase was followed by a rise in T3 after 1 h, which was also more pronounced in the starved animals, whereas T4 decreased or remained unaffected. Increases in T4 can, however, be obtained with 100 micrograms TSH in normal fed (2-fold) or starved animals (greater than 3-fold). Following injection of 100 micrograms oGH, a significant increase in T3 levels was observed which in fed animals was already present at 30 min, but the higher levels persisted for 1 and 2 h in fed and starved hens. At the same time, a decrease in T4 was observed in both groups of GH-treated chickens. It is concluded that TRH at the dose used is not thyrotropic but has a somatotropic effect and is responsible for the peripheral conversion of T4 into T3.
Kühn
E R
ER
Catholic University of Leuven, Zoological Institute, Belgium.
Herremans
M
M
Dewil
E
E
Vanderpooten
A
A
Rudas
P
P
Bartha
T
T
Verheyen
G
G
Berghman
L
L
Decuypere
E
E
D000818:Animals; D002645:Chickens / Q000502:physiology*; D005508:Food Deprivation / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood*; D007275:Injections, Intravenous / Q000662:veterinary; D013961:Thyroid Gland / Q000502:physiology; D013963:Thyroid Hormones / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage / Q000502:physiology*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D013963:Thyroid Hormones; D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013006:Growth Hormone; D013974:Thyroxine