Comparative effects of prolyl-leucyl-glycinamide and naloxone on morphine-induced inhibition of gastrointestinal transit

The effects of prolyl-leucyl-glycinamide (MIF) and naloxone on the gastrointestinal transit in mice were investigated using the charcoal meal test. MIF administered intraperitoneally (IP) (1-10 mg/kg) or intracerebroventricularly (ICV) (10 micrograms/mouse) had no effect on the transit. Administration of morphine by subcutaneous (SC) route significantly inhibited the gastrointestinal transit. The morphine-induced inhibition of the transit was not affected by MIF whether given by IP or ICV route. Administration of the opiate antagonist naloxone (1 mg/kg, IP or 10 micrograms/mouse, ICV) had no effect on the gastrointestinal transit, but it significantly antagonized the inhibition produced by morphine. Some earlier studies have indicated narcotic antagonistic effect of MIF. However, in the present study, evidence for such an action of MIF was not obtained. It is suggested that MIF does not appear to have narcotic antagonistic activity and further supports an earlier study from this laboratory that MIF may not interact with opiate receptors.