Morphine-like analgesic effect of a pituitary hormone, β-lipotropin

The analgesic effect f β-lipotropin /β -LPH/ and its fragments administered intracerebroventricularly /ICV/ to rats was studied. β -LPH proved to be a specific, morphine-like analgesic possesing 2.2 times weaker analgesic potency than morphine, calculated on molar base. Tryptic digest of β -LPH or smaller fragments of the hormone /LPH-/61 2 65/-eptide and LPH-/61–69/-peptide/ were devoid of significant analgesic activity. The in vivo results appeared to be in contrast to those previously obtained in longitudinal muscle strip of guinea-pig ileum, in vitro. A tentative explanation of this apparent contradiction is also given.