Hypoxia influences enkephalin release in rats.

To investigate hypoxia effects on leucine-enkephalin (L-ENK) levels of median eminence (ME) of hypothalamus in rats, and the possible glucocorticoid involvement in modulation. Hypoxia was stimulated in a hypobaric chamber. L-ENK levels were measured by specific radioimmunoassay during acute, and a comparison of L-ENK alteration was taken for bilateral adrenalectomy (ADX) with or without a replacement of dexamethasone (DEX). Acute hypoxia 10.8% O 2 for 30min and 2h h markedly enhanced L-ENK levels of ME from 23.99 ± 7.25 in control to 51.26 ± 16.96 (P<0.01) and 53.29 ± 26.10 ng/mg protein (p<0.01), and acute hypoxia at 8.2% O 2 significantly increased L-ENK of ME to 36.76 ± 15.25 (p<0.05) and 32.09 ± 3.58 ng/mg protein (p<0.05). The increased L-ENK was returned to normoxic level when hypoxia (10.8% O 2 ) exposure lasted for 24h. After ADX, 10.8% O 2 hypoxia induced a sharp decline of L-ENK in the ME, but this decline was completely reversed by treatment with DEX (500 μg/rat, i.p.). Acute hypoxia increases L-ENK level of hypothalamic ME in rats, which may present a reduced and /or inhibited release of L-ENK, acting through a fast negative feedback mechanism of acute hypoxia activated high circulating glucocorticoid level.