Transferts et synthèse du cholestérol chez le rat au cours de sa croissance

The isotopic equilibrium method using [4-¹⁴C]cholesterol has been applied on female rats and their progeny. It has been possible to determined the quantities of exogenous and endogenous cholesterol, of fixed (inert) and exchangeable cholesterol, and of exchangeable cholesterol of endogenous origin present not only in a entire rat at different growth stages from the 12th day of foetal life to the adult state, but also in certain of its organs (liver, brain, skin …). These results together with complementary experiments have made possible the determination of the fractional rates of appearance (exogenous and endogenous), of increase and of turn over of exchangeable cholesterol during the growth of the rat.

The most outstanding features of this metabolism are the following: (1) All fixed cholesterol is of synthetic origin. (2) The proportion of exchangeable cholesterol falls with age to the adult value (50–55%) in the second to third week. (3) In the 12th–13th-day foetus, 60–70% of cholesterol is of maternal origin. Subsequently this value decreases so that in the last days of foetal life 80–85% of the cholesterol is of synthetic origin. (3) It would appear that the source of foetal exchangeable cholesterol of synthetic origin is the placenta. (5) After birth, the milk provides about two-thirds of the exchangeable cholesterol during the first 2 weeks, but after the 3 weeks nearly 80% of exchageable cholesterol is of synthetic origin. (6) Transformation into bile acids would seem to develop simultaneously with the secretion of synthesised cholesterol. (7) The fractional rate of turn-over of exchangeable cholesterol attains its highest value (8% per day) at the 4th week. (8) 80% of the milk cholesterol originates by excretion from the plasma.