Injection of thyrotrophin-releasing hormone in turkey embryos elevates plasma thyroxine concentrations

The effectiveness of thyrotrophin-releasing-hormone (TRH) as a secretagogue in turkey embryos was tested. Fertilized turkey eggs were injected with TR H after 24 d of incubation. In an experiment to determine an effective rout e and dose for TRH administration, it was shown that a single manual inject ion of 200 muL containing 2.15 mug of TRH, into the air cell or the same in jection containing 5.0 mug through the bottom of the egg, was effective in elevating plasma concentrations of thyroxine (T-4) 60 min after injection. In a second experiment, 5 mug of TRH in a volume of 200 muL was injected th rough the bottom of each egg. Injections were performed mechanically into e ggs held in a commercial incubator. The injection increased blood plasma T- 4 for 5 h after a 30-min lag. Eggs from two genetic strains of turkeys were injected in Experiment 3. The TRH elicited a persistent response for 120 m in from one strain but resulted in a slightly depressed response from the o ther, suggesting that subtle differences in the maturation of the hypothala mo-hypophyseai-thyroid axis may exist in commercial strains of turkeys. We concluded that TRH is an effective secretagogue for T-4 in 24-d-old turk ey embryos.