The absorption of oral cholesterol by rats was followed directly by analyses of the thoracic lymph and indirectly by calculating the deficit of fecal cholesterol under the amount fed. The two methods checked within about 20 per cent, with fecal analyses indicating the greater absorption. The absorbed cholesterol was found to be deposited in the liver, only very minor quantities being found in other organs or plasma. Bile is necessary for normal absorption of cholesterol, although very small amounts are absorbed even in its absence. Excess oral cholic acid increases the absorption of cholesterol by otherwise normal animals. The rat absorbs about 47 per cent of a single 50 mg. dose of cholesterol and about 34 per cent of a 100 mg. dose.

The administration of thiouracil induced a rise and administration of thyroid substance a decrease of the plasma cholesterol concentration in rats. The concentration and daily output of bile cholesterol was markedly reduced in hypothyroid rats and markedly increased in hyperthyroid rats. Evidence is presented which suggests that the rate of synthesis of cholesterol is significantly increased in the hyperthyroid rat and decreased in the hypothyroid rat. The first series of 8 week old male rats (Long-Evans) consisted of (a) animals fed 0.25 per cent thiouracil in their food for 33 days, (b) rats fed 0.12 per cent powdered thyroid substance in their diet for 18 days, and (c) control rats maintained on ordinary stock diet. The second series of 13 week old rats was followed for 42 days. It consisted of (a) rats maintained on 0.3 per cent thiouracil, (b) rats maintained on 0.3 per cent thyroid substance, and (c) control rats. The results obtained on the plasma and bile contents of cholesterol were essentially similar in the two series and accordingly have been grouped together.Cannulation of the bile duct, 24-hour collection and analysis of bile for cholesterol were accomplished according to previously described methods.6' 7 Food was withheld from all rats during such bile collections. Data concerning rat bile were accepted only if autopsy examination indicated that there had been neither rupture nor obstruction of the bile duct.Data on the rate of accumulation of cholesterol in plasma', 1 in the experimental animals were obtained by analyses of the plasma for cholesterol before and 24 hours after biliary obstruction. Study of the rate of disappearance of cholesterol from plasma was accomplished in both the hypo-and hyperthyroid rat by the measurement of the plasma cholesterol in each rat immediately, 1, 3, 6, 12, and 24 hours after the intravenous injection of 2 cc. of hypercholesteremic rat plasma (950 mg. per 100 cc.).The latter was prepared as described previously.13 RESULTS A. Production of Hypo-and Hyperthyroidism in Rats The administration of thiouracil and powdered thyroid substance was found, as already described,12 to produce hypo-and hyperthyroidism, respectively, in our rats. The weight gain was greatest in the control and least in

No abstract

No abstract