Research note: Peripheral administration of Met-enkephalin: Novel attenuation of the adrenal medullary and thyroidal stress responses in young female chickens

Adrenal hormones play a critical response to stresses in poultry, livestock and other vertebrates. Moreover, there are stress effects on thyroid hormones. Plasma concentrations of epinephrine (EP), norepinephrine (NE), thyroxine (T₄) and triiodothyronine (T₃) were increased by restraint stress (placing pullets into a small cage in darkness) in 14-week-old pullets. There has been a complete dearth of publications on the effects of peripheral administered Met-enkephalin on endocrine systems in chickens. To remedy this, the effects of peripheral administration of Met-enkephalin per se was examined as was along with its ability to either potentiate or attenuate the responses to stress. Plasma concentrations of EP and NE were modestly increased in chickens receiving Met-enkephalin injection peripherally. The increase in plasma concentrations of EP, NE, T₃ and T₄ together with the decrease in reverse T₃ in chickens subjected to restraint stress were markedly attenuated in pullets receiving Met-enkephalin injection peripherally.