Fig. 3.

Effect of acute, central administration of amino acids on food intake. A: rats bearing 3rd-ventricular cannulas were fasted for 24 h and subsequently injected (icv; 7 rats/group) with vehicle, 1 μg of leucine, or a cell culture-based amino acid mixture (10× RPMI; 2 μl) that contained 1 μg of leucine in addition to other essential amino acids. Injection of both the amino acid mixture and leucine significantly suppressed 4- and 24-h food intake (*P < 0.05). B: a separate group of icv-cannulated rats was fasted as above and injected icv with increasing doses of leucine (1, 3, and 10 μg; 7–9 rats/group), and food intake during the subsequent 24 h was determined. Icv injection of leucine dose-dependently suppressed 4 and 24-h food intake, with 1 μg leucine exerting a modest anorectic effect at 24 h (P = 0.06) and 10 μg leucine robustly suppressing intake (*P < 0.01).