MIF-1 does not act like naloxone in antagonizing the cardiovascular activity of leucine-enkephalin in the conscious dog.
MIF-1 (Pro-Leu-Gly-NH2), a hypothalamic tripeptide, has been demonstrated to stimulate naloxone in antagonizing the effects of opioid peptides in a number of experimental systems including enkephalin-induced analgesia in the tail-flick assay, beta-endorphin induced hypothermia and hypomotility, deprivation-induced drinking, and analgesia in goldfish. MIF-1, however, has no effect upon the activity of enkephalins in the mouse vas deferens or enkephalin binding in the rat striatum. We have studied the interactions of MIF-1 with Leu5-enkephalin (Leu5-ENK) in the conscious, chronically instrumented dog. Although naloxone inhibits both the elevations of heart rate and blood pressure produced by IV Leu5-ENK in the conscious state and the depressions in these variables produced by Leu5-ENK after pentobarbital anesthesia, MIF-1 has no effect upon the Leu5-ENK response in either state. However, both naloxone and MIF-1 seem to raise mean arterial pressure in the conscious dog. These results indicate that MIF-1 does not act like naloxone in antagonizing the peripheral effects of Leu5-ENK and lend further support to the existence of mechanistic differences among opiate-mediated behavior, analgesia, and cardiovascular activity.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D004285:Dogs; D004743:Enkephalin, Leucine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects*; D007028:Hypothalamic Hormones / Q000494:pharmacology*; D009075:MSH Release-Inhibiting Hormone / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D010424:Pentobarbital / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000187:drug effects
D007028:Hypothalamic Hormones; D010455:Peptides; D011957:Receptors, Opioid; D009270:Naloxone; D004743:Enkephalin, Leucine; D009075:MSH Release-Inhibiting Hormone; D010424:Pentobarbital