The Contribution of Chylomicron Cholesterol to Milk Cholesterol in the Rat

The contribution of chylomicron cholesterol to total milk cholesterol was studied in the lactating rat. Pregnant rats were fed a high-fat, high-cholesterol diet or standard rat diet. On the 13th day of lactation, dams were intonated with 25 μCi [³H]cholesterol (25 μCi/μmole). Milk was collected at 5 and 10 hr following intubation; plasma was collected at 5, 8, and 10 hr following intubation. There was a lower specific activity of chylomicron cholesterol in dams fed the high-fat, high-cholesterol diet compared with control animals at 5, 8, and 10 hr after intubation (P < 0.05) with radiolabeled cholesterol. There was no difference in the specific activity of milk cholesterol between both groups at 5 hr. These data indicate that chylomicron cholesterol does not significantly contribute to milk cholesterol levels in the lactating rat. At 8 and 10 hr following intubation with radiolabeled cholesterol, the specific activity of plasma cholesterol from dams fed the high-fat, high-cholesterol diet was lower than that from control animals (P < 0.05). The specific activity of milk cholesterol at 10 hr was also lower in experimental animals (P < 0.05). Taken together, these data suggest that plasma lipoproteins other than chylomicrons contribute significantly to milk cholesterol levels.