['The importance of small intestinal mucosa functions has been emphasized in recent years because gut metabolism becomes better defined. One of the major activities of the enterocyte is amino acid transport, which is important not only for the organism but also for the integrity of the mucosa. Bowel rest during the postoperative period is marked by decreased calorie and protein intake with atrophy of the brush border mucosa. We sought to determine whether active amino acid transport is altered during 72 hours of fasting.', 'New Zealand white rabbits were fed (control) or fasted for 72 hours. Brush border membrane vesicles were prepared from scraped jejunal mucosa, and their purity was assessed by marker enzyme enrichment (17- to 25-fold). Transport of tritiated glutamine, arginine, alanine, methylamino-isobutyric acid (MeAIB), and leucine into brush border membrane vesicles was measured by rapid mixing filtration.', 'Fasted animals lost on average 138 +/- 51 gm of body weight. Glutamine and arginine transport were decreased in rabbits fasted for 72 hours compared with controls; alanine, MeAIB, and leucine transport were maintained. The decrease in Glutamine transport was due to a decrease in Vmax (545 +/- 22 versus 836 +/- 93 pmol/mg protein/10 sec; p < 0.05), consistent with a decrease in the number of functional transporter proteins. Km values were similar in both groups (644 +/- 25 versus 624 +/- 18 mumol/L), indicating no change in carrier affinity.'] Does starvation induce differential small bowel luminal amino acid transport?