The effect of naloxone on feeding and spontaneous locomotion in the wolf.

The effect of naloxone on food intake and activity levels was studied in the wolf (Canis lupus). Naloxone decreased food intake at both the 1 mg/kg and 5 mg/kg dose. There was no quantitative difference in the magnitude of the decrease in food intake produced by naloxone in winter or summer. Wolves ate significantly greater amounts of deer meat than dog chow after naloxone when expressed on a mass basis but there was no difference when the amounts of food ingested were expressed in calories. This suggests a role for endogenous opiates in the regulation of energy intake. The putative satiety factor, cholecystokinin-octapeptide, had no effect on food intake in wolves. Naloxone decreased spontaneous locomotion and increased time spent resting in wolves. The effects of naloxone on activity were significantly more marked in winter compared to summer.