1978 Volume 6 Issue 1 Pages 27-32
The uptake of cholesterol by the isolated hepatocytes of rats at 4°C from the incubation medium containing rat serum was low and did not increased by the prolongation of the incubation time up to 2hrs. However, the hepatocytes took up cholesterol very actively at 37.5° from serum as well as cholesterol/phospholipid dispersion. The amount of the uptake increased linearly as a function of the incubation time. The cholesterol uptake from the liposome dispersion by the cells increased linearly to the increase of the cholesterol concentration of liposome, but that from serum reached to the maximum at 70mg/100ml of cholesterol concentration and remained a plateau level at the higher concentration. Cholesterol was tansfered from every serum lipoproteins, though the uptake ratio was the highest in low density lipoprotein fraction. The uptake ratio decreased in like manner observed in the incubation with the whole serum, as lipoprotein concentration was elevated.
The labeled ester cholesterol in the serum decreased more rapidly than the free cholesterol during the incubation, but the cholesterol in the hepatocytes was mainly found as the free form, suggesting that ester cholesterol taken up by the cells was hydrolyzed rapidly.
The outflux rate of synthesized cholesterol increased as the elevation of the concentration of serum and liposomes in the medium and reached to a plateau level as high as 50-70mg/100ml of cholesterol concentartion. But there was no significance difference between the outflux rate from the incubated hepatocytes into serum and liposome suspension.
Cholesterol accumulation was not observed in the hepatocytes incubated in the medium containing serum, though cholesterol content was increased in the cells after the incubation in the medium with liposome of the high cholesterol concentration. The cholesterol/phospholipid ratios of the liposome between 0.2-0.8 did not influence the increase of cholesterol contents of the hepatocytes by the increase of cholesterol concentration in the medium.
The uptake of cholesterol diminished in old rats or hypothyroid rats who had high serum cholesterol levels. The isolated hepatocytes from rats hyperresponding to a high cholesterol diet took up more cholesterol than those from the hyporesponders. The difference of the amount of cholesterol uptake between two groups became larger as cholesterol concentration in the incubated medium increased.
In conclusion, the uptake of cholesterol by the hepatocytes from serum is probably carried out by different process from that from liposome dispersion, which is considered to be a physicochemical phenomenon. The uptake of cholesterol by the hepatocytes may be one of the important regulatory mechanism of serum cholesterol concentration.
