Response of monkeys to intragastric preloads: limitations on caloric compensation

Food intake of rhesus monkeys was limited to a single daily 2 hr session of banana flavored pellet availability, seven days a week. Following stabilization of intake, the effects of liquid preload meals (0-80% of normal meal size) delivered through nasogastric tubes or chronic indwelling intragastric (IG) catheters were determined during test sessions by delivering preloads 15 min prior to the session. Monkeys compensated for preloads by decreasing intake by an amount nearly equal to the energy content of the preload. As the time between the delivery of an IG preload equivalent to 40% of a normal day's intake and the beginning of the session was increased, accuracy of compensation decreased. Monkeys also did not compensate for a chow meal given 2 hr before the session and compensation did not improve when this meal was given for ten consecutive days 2 hr before a session. In addition, an IG preload equivalent to 40% of a normal day's intake was given 20 hr before the session under two conditions: two hours after or immediately after the session on the day preceding testing. Only the preload given immediately after the session decreased food intake 20 hr later. However, a control volume of tap water delivered immediately after the session also decreased food intake 20 hr later. Finally, monkeys did not compensate for deprivation experienced one day by increasing their food intake the following day. In sum, these results indicate that under these conditions, the rhesus monkey does not regulate its food intake as accurately as previously reported.