Vitamin A status and the metabolism of cholesterol in the rat.

The importance of blood lipids in general and cholesterol in particular in the pathogenesis of atherosclerosis has led to a search for dietary regimens to control hypercholesterolaemia. Dietary fish oils are effective in lowering serum cholesterol (Bronte-Stewart, Antonis, Eales & Brock, 1956; Anderson, Keys & Grande, 1957; Ahrens, Insull, Hirsch, Stoffel, Peterson, Farquhar, Miller & Thompson, 1959; DeGroot & Reed, 1959). In studies using chickens Wood (1960) demonstrated that vitamin A was the active hypocholesterolaemic factor in fish oils. Later, it was shown that vitamin A feeding prevented the rise in serum and liver cholesterol levels induced by dietary cholesterol in rats (Bring, Ricard & Zaehringer, 1965) and chickens (Wood & Topliff, 1961 ; Beeler, Rogler & Quackenbush, 1962; March & Biely, 1963). Sampson & Potter (1947) in a brief communication reported that vitamin A-deficient rats stored more cholesterol than controls when maintained on a diet containing cholesterol. On the other hand, Green, Horner, Lowe & Morton (1957) concluded that cholesterol feeding decreased liver vitamin A storage in male rats. All these studies suggest an inverse relationship between cholesterol and vitamin A but the exact mechanism by which this is manifested is not fully understood. The most likely processes through which vitamin Aor cholesterol may control the metabolism of each other are (a) absorption across the intestine, (b) transport and storage in the liver, and (c) turnover rate. The present investigations were undertaken in an attempt to elucidate the complex interrelationships between cholesterol and vitamin A metabolism.