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.

Effects of food deprivation on intake of solid and liquid sugars in the rat.

In free-feeding rats, glucose at 0.025 M or 2 M evokes a vigorous bout of drinking. Powdered sucrose evokes more feeding than would occur without it, but powdered glucose does not. Food deprivation has little effect on intake of 2 M glucose, but it markedly augments intake of the powders, which rises to caloric-intake values higher than that of the 2 M solution. This occurs even if the powders are offered only after solution intake has come to an end and at a time when it would remain inhibited. We conclude: 1. Some sweet-tasting commodities will evoke ingestive behavior in free-feeding rats, but others, some of them even sweeter, will not. 2. Solid carbohydrates follow different laws from concentrated carbohydrate solutions, in that the former, but not the latter, rise with deprivation. Intake of powders must therefore be limited or satiated by different and more permissive mechanisms from the ones that limit solution intake.

"De-satiation": the reinstatement of feeding in glucose-satiated rats.

In rats "satiated" for glucose in solution, feeding can be reinstated by presentation of the same commodity (glucose) in powdered form. The effect is not reciprocal, so it is not a response to change or variety per se; and it does not reflect a greater palatability of the powder, which is rejected in favor of the solution in choice tests. Sucrose powder leads to an even larger "second meal" than glucose powder, showing that intake in the solution-sated rat remains sensitive to the stimulus properties of the diet. We conclude that the postingestive conditions necessary for satiety must be set by the stimulus properties of the diet--including, but not limited to, the properties that specify a diet's nutrient composition.

Glucose solution intake in the rat: the specificity of postingestive satiety.

Hungry rats were permitted to drink a concentrated glucose solution to 'satiety', as indicated by (1) cessation of drinking, (2) the appearance of behaviors correlated with satiety (grooming and exploring followed by resting), and (3) refusal to drink appreciable further quantities when access to the solution was prolonged. Yet such rats returned to vigorous and prolonged feeding when offered laboratory pellets, powered chow, or even glucose itself in powered form. "Satiety" for a glucose solution does not reflect a generalized suppression of hunger or of a specific carbohydrate hunger. Its properties are more specific than existing theories of energy intake regulation would lead us to suppose.