Control of Serum Cholesterol Homeostasis by Cholesterol in the Milk of the Suckling Rat

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Abstract
This is a test with rats of both sexes of an hypothesis that cholesterol in the suckling's milk somehow helps establish a permanent mechanism for maintaining low serum cholesterol concentration in the adult animals during high cholesterol ingestion. It was found that the serum cholesterol concentrations of adult males but not females varied inversely with the concentrations of cholesterol in their dams' milks, which could be modified by diet. Serum cholesterol was about 150 mg/100 ml in those males suckled on milk containing 40 to 50 mg/100 ml, about 215 mg/100 ml in those suckled on milk containing around 30 mg/100 ml, and about 250 mg/100 ml in those suckled on milk containing 23 mg/100 ml. In the first test a simple method was devised to teach 12-day-old rats to drink formula milk from a drinking tube. They grew normally. Groups nursed on two semisynthetic formulas, one containing a residue of 5 mg of cholesterol/100 ml and the other containing added crystalline cholesterol dissolved in stripped lard to the normal rat milk concentration of 35 mg/100 ml, were compared to a group nursed on bovine milk fortified with cream to 35 mg cholesterol/100 ml, and to a mother-nursed group. In the second test the cholesterol concentrations of dams' milks were varied by diet from 21 mg up to about 50 mg/100 ml. In both tests the young were weaned at 30 days of age and then given a semisynthetic low cholesterol, 10% stripped lard diet for the second 30 days. From 2 to about 8 months of age lard containing 5% dissolved cholesterol was added to the diet at the 10% level (0.5% cholesterol). The serum cholesterol concentrations of the 8-month-old females of both tests varied from about 400 to 700 mg/100 ml with wide variations within the groups. No significant trends were found relating serum cholesterol to their milk cholesterol as sucklings. The serum cholesterol concentrations of the male rats in the first test also did not differ significantly from the cholesterol concentrations of their semisynthetic post-day-12 suckling milks. However, in the second test, in which the rats were nursed naturally on dams whose milk cholesterol was varied by diet, the serum cholesterol concentrations in the males varied inversely with the cholesterol concentrations of their mothers' milks: Milk cholesterol levels were approximately 40 to 50, 30, and 23 mg/100 ml, and the respective serum cholesterol concentrations 150, 215 and 250 mg/100 ml.