EFFECTS OF SMALL-INTESTINAL NUTRIENT INFUSION ON APPETITE AND PYLORICMOTILITY ARE MODIFIED BY AGE

The mechanisms responsible for the reduction in appetite and slowing o f gastric emptying in older persons are unknown. The aims of this stud y were to evaluate the effects of aging on small intestinal regulation of appetite and pyloric motility. Eight healthy older (age 65-75 yr) and seven healthy young (age 20-34 yr) male subjects received isocalor ic (2.9 kcal/min) intraduodenal infusions of lipid and glucose for 120 min, each on separate days. During the intraduodenal infusions, perce ptions of hunger, desire to eat, and fullness were assessed by visual analog scales. Pyloric motility (isolated pyloric pressure waves and t onic pyloric pressure) was measured by manometry during the intraduode nal lipid infusion. On each day, after completion of the intraduodenal nutrient infusion the subject was offered a buffet meal and food inta ke was quantified. Before intraduodenal nutrient infusions, sensations of hunger (P < 0.01) and desire to eat (P < 0.05) were less in the ol der compared with the young subjects. In the young, intraduodenal lipi d suppressed hunger to a greater extent than intraduodenal glucose (P < 0.05). In older persons, neither intraduodenal nutrient infusion sup pressed hunger. Intraduodenal lipid and glucose increased fullness in both age groups (P < 0.05 for both), with no significant difference be tween the two nutrients. There was no significant difference in food i ntake from the buffet meal between the elderly and young subjects. Int raduodenal lipid infusion stimulated phasic pyloric pressure waves in both age groups (P < 0.01 for both), and this response was greater (P < 0.05) in older persons. There was an increase (P < 0.01) in tonic py loric pressure during intraduodenal lipid infusion that was not signif icantly different between the two age groups. We conclude that the eff ect of small intestinal lipid infusion on hunger is attenuated, and th e stimulation of phasic pyloric pressure waves increased in healthy ol der persons compared with healthy young males. Increased feedback from small intestinal nutrients does not appear to be responsible for the physiological anorexia of aging.