Effects of duodenal osmotic loads on spontaneous meals in pigs

Fourteen young Large White pigs were trained to press a panel switch to obtain reinforcements of food (FR 10-15). Duodenal injections (5 ml/kg) were made automatically via implanted catheters shortly after the beginning of every other meal 24 hours a day. Solutions of varying osmoconcentration and nutrient content were injected. Isosmotic solutions of glucose (5, 20 and 40%) and NaCl (0.9, 3.25 and 6.5%) equally depressed the size of ongoing meals in proportion to their hypertonicity. For example, 20% glucose and 3.25% NaCl depressed meal size to 62% of control, and 40% glucose and 6.5% NaCl to 34%. Xylose (33%) was less effective than its glucose osmotic equivalent. Tetracaine (0.5%) blocked most of the reduction of meal size. The reduced meal size was due to a decrease in meal duration. Neither rate of eating during the meal nor intermeal interval changed. The results support the hypothesis that a duodenal osmoreceptive system participates normally in the control of meal size.