Vitesses des processus de renouvellement du cholestérol contenu dans son espace de transfert, chez le rat: IV. Influence de l'âge, du poids, du sexe, de la gestation et de la lactation

Abstract

The isotopic equilibrium method was applied to 24-month-old male rats of varied weights and to virgin, pregnant or lactating female rats. Compared with young adult rats (350 g), the rate of cholesterol synthesis decreases (50%) in old rats whose weights were kept constant (335 g) by a restricted caloric intake. This decrease is explained mainly by this restriction. The synthetic rate expressed per 100 kcal and 100 g of body weight is only 25% lower than that of young adult rats. The same result is obtained with old rats fed ad libitum and weighing 560 g. In both groups, the turnover time of cholesterol is increased (35 and 37 days) as compared to that of young adult male rats (24 days). The cholesterol turnover time of female rats is practically equal to that of male rats, but its dynamic equilibrium differs on three points: (1) synthesis rate, expressed as percentage of total body weight and of caloric intake, is lower (35%), (2) proportionally to the external secretion, the fecal excretion of cholesterol is higher, (3) the urinary excretion of steroids must be take into account for the balance. These two last points are more important in pregnant or lactating rats. For these females, the synthetic rates of cholesterol are increased 2- and 3-fold, respectively. The contributions of placenta, mammary glands, intestine and liver to these increases are considered and discussed.