A new aspect on the mechanism of intestinal cholesterol absorption in rat

In order to study the mechanism of intestinal cholesterol absorption, the relationship between the amount of cholesterol administered and the rate of absorption was investigated by the dual isotope plasma ratio method in vivo and the ligated-loop method in situ. The energy requirement of cholesterol absorption was also observed by means of the ligated-loop method. The results obtained are summarized below. 1) Tri-phase absorption was observed by the dual isotope plasma ratio method. When less than 300 microgram of cholesterol was administered, absorption increased linearly, with the coefficient of absorption being more than 80%. When the amount administered was between 300 and 500 microgram, the absorption was constant. With the administration of more than 500 microgram, absorption increased linearly, but the coefficient of absorption decreased to approximately 55%. 2) With the ligated-loop method, a second saturation profile was obtained when between 250 and 400 microgram of cholesterol was administered to a segment. When 50 to 250 microgram of cholesterol were administered, absorption increased in proportion to the increase in cholesterol dosage. 3) The mucosal uptake of cholesterol decreased to 40-60% of the control with the addition of metabolic inhibitors such as NaN3, KCN, 2,4-DNP and ouabain, whereas the uptake of palmitate showed no significant decrease. In addition, the uptake of cholesterol decreased remarkably to 25% of the control with the lowering of body temperature from 37 degrees C to 27 C. These results suggest the existence of an active transport system which has a limited capacity for cholesterol absorption and which requires energy for its operation in the physiological state.