Heat and cold stresses exert disparate effects on expression of proenkephalin, and concentrations of Met-enkephalin in the hypothalamus, pituitary and adrenal glands, plasma concentrations Met-enkephalin, Leu-enkephalin, β-endorphin and corticosterone and opioid receptor binding in chickens.

Effects of heat and cold stress on opioid peptides and their receptors together with plasma concentrations of corticosterone was examined in 12-week-old female chickens. There were increased plasma concentrations of Met-enkephalin, Leu-enkephalin β-endorphin and corticosterone in pullets exposed to elevated environment temperature (30°C) for 12 hours. In contrast, cold stress (0°C) for 12 hours was accompanied by decreased plasma concentrations of Met-enkephalin, no effect on plasma concentrations of Leu-enkephalin but increased plasma concentrations of β-endorphin and corticosterone. Heat and, to a less extent, cold stressed pullets had decreased concentrations of Met-enkephalin in hypothalamic, anterior pituitary and adrenal tissues but increased concentrations of total Met-enkephalin (enzymically released) and proenkephalin (PENK) expression. There were also effects of heat- or cold- stress on delta (Δ), kappa (K) and mu (M) opioid receptor binding in the hypothalamus, anterior pituitary and adrenal glands.