Naloxone-like actions of MIF-1 do not require the presence of the pituitary.
The actions of peripherally administered MIF-1 (Pro-Leu-Gly-NH2) and naloxone in blocking the effects of morphine in the tail-flick test were measured across a wide range of five doses in hypophysectomized and intact mice. The presence of the pituitary gland failed to influence the response to MIF-1 or naloxone. Both hypophysectomized and intact mice were significantly affected by these two compounds at doses of 0.01, 0.1, 1.0, and 10.0 mg/kg IP. The greatest effect of MIF-1 occurred at 100 mg/kg, but naloxone was lethal at this dose. Preliminary experiments with other tests showed that at 10 mg/kg, naloxone, but not MIF-1, was effective in preventing the Straub-tail reflex and in precipitating withdrawal-jumping in mice implanted with morphine pellets. Only minimal activity was shown by MIF-1 in preventing blockade of electrically induced contractions of the guinea pig ileum by morphine. Neither compound was active in the frog-righting test. In summary, the results emphasize the differential actions of MIF-1 as an opiate antagonist and demonstrate that the pituitary is not required for their mediation.
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005769:Gastrointestinal Motility / Q000187:drug effects; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D009075:MSH Release-Inhibiting Hormone / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000494:pharmacology; D009068:Movement / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology*; D009949:Orientation / Q000187:drug effects; D010902:Pituitary Gland / Q000502:physiology*; D011894:Rana pipiens; D012018:Reflex / Q000187:drug effects; D013997:Time Factors
D009270:Naloxone; D009020:Morphine; D009075:MSH Release-Inhibiting Hormone