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

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Abstract
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. Tri-phase absorption was observed by the dual isotope plasma ratio method. When < 300 .mu.g of cholesterol was administered, absorption increased linearly, with the coefficient of absorption being > 80%. When the amount administered was between 300-500 .mu.g, the absorption was constant. With the administration of > 500 .mu.g, absorption increased linearly but the coefficient of absorption decreased to .apprx. 55%. With the ligated-loop method, a 2nd saturation profile was obtained when between 250-400 .mu.g of cholesterol was administered to a segment. When 50-250 .mu.g of cholesterol was administered, absorption increased in proportion to the increase in cholesterol dosage. 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; the uptake of palmitate showed no significant decrease. The uptake of cholesterol decreased remarkably to 25% of the control with the lowering of body temperature from 37 to 27.degree. 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.