Thyrotropic activity of the ovine corticotropin-releasing factor in the chick embryo

An injection of several doses of ovine corticotropin-releasing factor (oCRF) was made into an allantoic blood vessel of 18-day-old chick embryos. All doses used (0.5, 1, 2, and 5 micrograms) induce a quick increase of plasma corticosterone concentrations after 15 and 30 min and 1 and 2 hr and this in a dose-dependent manner with the high doses having a prolonged effect lasting up to 2 hr. An increase in plasma levels of thyroxine (T4) and triiodothyronine (T3) was observed after 1 and 2 hr. After the oCRF injection, no stimulation of the hepatic 5'-monodeiodination activity was observed and there was no increase, but even a small decrease in the T3 to T4 ratio could be calculated. It was therefore concluded that oCRF in the chick embryo has a thyrotropic effect presumably by stimulating the release of thyrotropin from the pituitary.