DIFFERENTIAL-EFFECTS OF TYR-MIF-1, MIF-1, AND NALOXONE ON PEPTIDE YY-INDUCED HYPERPHAGIA

Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and MIF-1 (Pro-Leu-Gly-NH2) act as opi ate antagonists in various behavioral systems including ingestion. Cen tral injection of peptide YY (PYY) elicits a powerful feeding response in satiated rats, and the opioid antagonist naloxone decreases eating in a variety of conditions including PYY-stimulated eating. Therefore . the aim of this study was to examine the effects of Tyr-MIF-1 and MI F-1 as opiate antagonists on a naloxone-sensitive PYY model of hyperph agia. Naloxone at doses of 1.0 and 10.0 mg/kg. SC, decreased hyperphag ia induced by 2.4 mug PYY injected in the PVN. MIF-1 and Tyr-MIF-1 had no effect on PYY-induced eating at doses comparable to naloxone (0.1 to 10.0 mg/kg, IP). These results suggest that in this model of eating behavior. Tyr-MIF-1 and MIF-1 do not act as opiate antagonists.