Diurnal Variations of Plasma Lipoproteins and Liver Lipids in Rats Fed Starch Sucrose or Fat

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Abstract
The incidence of the dietary source of energy on lipid transport and accumulation was investigated over a full nycthemeral cycle in adapted rats fed ad lib. Starch, sucrose and lard were compared. Lipoprotein composition of the plasma, liver and plasma lipids and insulinemia were analyzed every 3 h over 24 h. The pattern of VLDL [very low density lipid] concentration was dependent on the nature of the energetic substrate. Feeding starch resulted in a remarkable stability of lipoproteins, liver and plasma lipids, despite clearcut diurnal variations in plasma non-esterified fatty acids, insulinemia and liver glycogen. In sucrose-fed rats VLDL rose to a sharp maximum in the post prandial period (0900-1200 h) and were totally cleared by 1800 h. In fat-fed rats, HDL were elevated during the night, suggesting a possible stimulation of their synthesis by dietary fat in the intestine. LDL were constantly elevated with peak values at 2100 h while VLDL were very low, even at night, despite elevated levels of non-esterified fatty acids. In animals adapted to a high fat-diet, a high level of circulating non-esterified fatty acids is not sufficient to promote the synthesis of VLDL. The main regulating factor appears to be the intensity of hepatic lipogenesis which is stimulated by sucrose and inhibited by lard. No correlation was found between variations in plasma VLDL and insulinemia.

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