The turnover time of dietary cholesterol in the lactating rat

The secretion of dietary 4‐14C‐cholesterol into milk of the rat was determined as a function of post‐feeding time by a single dose technique. The time interval which elapsed before maximum specific radioactivity was reached in milk (17–20 hr after maximum activity in the serum) suggests a route through the mammary gland involving transport of the cholesterol by intracellular membranes. It also suggests that the exogenous cholesterol is incorporated into the milk fat globule membranes rather than into the fat globules during their synthesis within the cell.