All-or-none suppression of glucose sham feeding by an intragastric mixed meal in rats

Rats were permitted to sham feed a 1 M glucose solution after varying delays (0-40 min) following the intragastric (IG) infusion of a large, nutritionally adequate meal. (a) The meal affected sham feeding in an all-or-none way. After such a meal, sham feeding was either suppressed almost entirely, or it was not suppressed at all as compared with a no-meal control condition. (b) When it occurred, the suppression was short-lived: As little as a 20-min delay after the meal could suffice to change its suppressant effect from "all" to "none." This implies in turn that the much longer suppression found under other conditions is not a product of systemic inhibition on readiness to ingest. (c) The duration of the suppression appeared to decrease with successive exposures to the experimental conditions. After several such exposures, some rats showed no postprandial suppression at all, even immediately after the IG meal.