Aspects of the control of feeding: application of quantitation in psychobiology

In rhesus monkeys equipped with indwelling gastric cannulae and studied in the unanesthetized state, it is possible to demonstrate that their feeding is a precisely regulated behavior functioning to maintain caloric intake quite constant. The infusion of nutrients into the stomach through the cannula results in a reduction in their feeding by an amount that is equivalent to the caloric value of the infusion. A similar precise recovery from caloric deficits by overeating can also be demonstrated. One means of controlling intake of food may derive from a remarkable change in gastric function that occurs with feeding. If the stomach is filled with non-nutrient saline it functions like a physiological "pump" expelling its contents into the small bowel in an exponential fashion--more rapidly with increasing volume. If the stomach is filled with nutrients then it functions like a precise "valve," delivering its contents at a constant and linear rate of 0.4 kcal/min to the duodenum regardless (within limits) of the volume, concentration or character (carbohydrate, fat, protein) of the nutrient meal. This change in gastric activity is provoked by the calories that are passed into the duodenum and sustained for a period depending on the amount of calories in the duodenum. The relation of these physiological events to the control of feeding is discussed.