Attenuation of morphine analgesia by alpha-MSH, MIF-I, melatonin and naloxone in the rat.
In two experiments the effects of the pituitary peptide alpha-MSH, the hypothalamic tripeptide MIF-I (P-L-G-NH2) and the pineal hormone melatonin were investigated on the attenuation of morphine analgesia measured by a tail flick test. In Experiment 1, alpha-MSH had minimal effect on morphine analgesia, whereas, MIF-I and melatonin clearly delayed the onset of morphine analgesia, and melatonin also shortened the duration of analgesia. Experiment 2 was designed to investigate the possible synergistic effect of MIF-I and melatonin. The combined treatment of MIF-I and melatonin significantly delayed the onset of morphine analgesia, and melatonin alone shortened the duration of analgesia. The relationships among the pituitary, hypothalamus and the pineal for the modulation of pain and response to morphine were discussed.
D000698:Analgesia; D000818:Animals; D009075:MSH Release-Inhibiting Hormone / Q000494:pharmacology*; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology*; D008550:Melatonin / Q000494:pharmacology*; D009020:Morphine / Q000037:antagonists & inhibitors*; D009270:Naloxone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time
D009270:Naloxone; D009020:Morphine; D009074:Melanocyte-Stimulating Hormones; D009075:MSH Release-Inhibiting Hormone; D008550:Melatonin