Eating rates in normal and hypothalamic hyperphagic rats.

Two experiments were conducted to determine if hypothalamic hyperphagic rats eat at a faster than normal rate and if slowing the rate of eating would reduce their overeating. Experiment 1 used a 45 mg pellet eatometer to measure 24-h meal patterns and eating rates in control rats and rats made hyperphagic with medial hypothalamic (MH) knife cuts. The MH hyperphagic rats consumed larger and more frequent meals but ate at a slower rate than did control animals during both the dynamic and static phases of the syndrome. In Experiment 2, rats were given 30-min test meals with the same pellets presented in food cups (rather than one pellet at a time as with the eatometer). The MH rats consumed the pellets at the same rate as the controls, although their meals were twice as large. Experiment 1 also determined if slowing the rate of eating would reduce MH hyperphagia; eating rates were constrained by increasing the delay between successive pellet deliveries (normally < 1 s). An interpellet delay of 20 s reduced meal size and increased meal length and frequency but did not reliably reduce 24-h food intake in normal rats and dynamic or static phase MH rats. Interpellet delays of 40 or 60 s reduced daily food intake of static phase MH rats but only to control levels. These results indicate that MH hyperphagia is not associated with elevated feeding rates and is relatively unaffected by constraints on the rat's rate of eating.