Increase in intake with sham feeding experience is concentration dependent

Most sham feeding studies show that about three sham feeding tests are requ ired for intake to reach maximum. One study, however, using a dilute soluti on, reported maximum sham intake in the first sham feeding test, suggesting that the progressive rise in sham intake may be concentration dependent. W e tested this hypothesis with six groups of rats given five sham feeding te sts each with one of six concentrations of sweetened condensed milk (0.5:1, 1:1, 2:1, 4:1, 8:1, 16:1, water-to-milk dilutions). It took three sham tes ts for intake to reach maximum with the three most concentrated solutions, but only one with the three weakest. Thus the intake of concentrated soluti ons of milk is limited by two negative feedback signals, one derived from t he accumulation of fluid in the gastrointestinal tract, the other from a la bile signal that loses its effectiveness with sham feeding experience. In c ontrast, the intake of weak concentrations is limited only by the nonlabile negative feedback signal because the labile signal is missing.