Mouvements des sterols dans le tube digestif du rat. Absorption du cholesterol de synthese

Abstract

Rats of approximately synchronous alimentary behaviour and known coprophagous cycle were used. During one day they were fed a diet containing [4- 14C]-cholesterol. Sterol composition and radioactivity of the content of each digestive organ (stomach, intestine divided into four fractions, caecum, colon) and of faeces were determined eight times during this 24-h period. Daily fluxes of cholesterol, coprosterol and precursor sterols (mainly lathosterol and methostenol) passing through each digestive organ were calculated. Following coprophagy, the daily influx into the stomach accounted for 2.1 mg precursor sterols, 2.8 mg coprosterol and 1.2 mg cholesterol. The dietary cholesterol influx was 2.6 mg. In addition to exogenous sterols, the stomach content was rich in endogenous sterols. Their daily influx reached 3.7 mg for precursor sterols and 3.1 mg for cholesterol. The fluxes of endogenous and exogenous sterols were simultaneous. The mean quantities of sterols and cholesterol in the contents of the intestinal fractions increased approximately as an exponential function of the length of the intestine. Besides the cholesterol from the stomach (exogenous for intestine), their content was rich in endogenous cholesterol. The ratio of endogenous to exogenous cholesterol varied all along the intestine. At the pyloric extremity there was 14 times as much endogenous as exogenous cholesterol. If we consider the intestinal content as a homogeneous mixture of exogenous and endogenous cholesterol, or as divided into two separate compartments, the “axial” and “intermediary”, respectively, quantitative deductions are unacceptable. There was in fact, a transfer (11 mg/day) of endogenous cholesterol from the “intermediary” to the “axial” compartment. Consequently, endogenous cholesterol (5 mg/day) was absorbed to a similar extent as exogenous cholesterol (5.5 mg/day). For the stomach and intestine contents we also determined the origin of endogenous cholesterol accurately. Approximatively half of it came from plasma while the rest resulted from synthesis in the digestive tract. It could be demonstrated that 4.2 mg synthetic cholesterol passed into the plasma per day by means of absorption. Coprosterol absorption conformed with classical data. In addition, the intestine contained endogenous precursor sterols besides those from the stomach. The precursor sterols were partially absorbed. The caecum and the colon were transit organs, in which only transformation of cholesterol to coprosterol took place.