Satieties and cross-satieties for three diets in the rat

In food-deprived rats, intake of a 2 M glucose solution is independent of deprivation level. However, subsequent intake of laboratory chow does vary with deprivation, though the immediately-preceding glucose meal did not. If deprivation is severe, the rat may eat as much chow as if the prior glucose meal had not occurred. In the converse case, a preload of chow has no suppressant effect whatever on intake of glucose, at any deprivation level. As with chow, intake of milk after a glucose load varies with food deprivation, even though the preceding intake of glucose did not. In contrast to the chow case, however, there is cross-satiety between milk and glucose in both directions; a meal of either one suppresses subsequent intake of the other. We conclude: (1) Intake of different diets is limited (satiated) by different postingestive mechanisms with different functional properties; some are sensitive to deprivation, others not. (2) Offering a new diet can change the properties of satiety, as if it recruited a new satiety mechanism and disengaged the old one. (3) The interactions among different satiety mechanisms are complex and non-reciprocal. Glucose and milk both contribute to a satiety mechanism that limits intake of both. A glucose preload can augment or accelerate satiety for chow, and thus reduce chow meal size; but the converse is not true. A single state or variable, "satiety" in the abstract, probably does not exist.