Delayed antihypoxic effect of leu enkephalin in mice

Hypobaric hypoxic hypoxia conditions were simulated by raising mice in the altitude chamber to the level of 10,500-10,700 m. Enkephalin, its analogues, morphine and naloxone were injected once 1, 2, 3, 6 and 14 days prior to the experiment, and then their effects on stability to hypoxia were investigated depending on the time of drug administration. Only leu-enkephalin after a single injection was found to have antihypoxic properties for a week. Naloxone, but not phentolamine hydrochloride, blocked delayed antihypoxic effect of penta-peptide. Leu-enkephalin is thought to be endogenous antihypoxant.