Effect of marginal zinc deficiency on the apolipoprotein-B content and size of mesenteric lymph chylomicrons in adult rats.

To investigate the mechanisms underlining the impaired intestinal absorption of lipids in zinc deficiency, the apo-B content and chemical composition of chylomicrons from marginally zinc-deficient rats fed 2.8 ppm of dietary zinc (ZD) were compared with those from pair-fed (PF) and ad libitum control (CT) groups fed an adequate level (30.8 ppm) of zinc. Chylomicrons, obtained by cannulating the mesenteric lymph, were isolated by ultracentrifugation at 1.3 X 10(6) g/min at 12 C and purified by 2% agarose column chromatography. Apolipoprotein- (apo) B was separated by the method of isopropanol precipitation. The apo-B concentration of chylomicrons was lowered significantly in ZD group. The apo-B contents of chylomicrons in ZD, PF and CT rats, as expressed as % chylomicron protein, were 8.7 +/- 0.1, 11.5 +/- 0.5 and 10.7 +/- 0.7%, respectively. No significant differences were noted between ZD and PF groups in total protein (TP), phospholipid (PL), triglyceride (TG) and cholesterol (CH), although there was a slight decrease in TG and an increase in CH in CT rats compared with ZD and PF groups. The ratio of the core to surface constituents, as determined by TG/(TP + PL), was significantly higher in ZD group relative to the controls, suggesting that chylomicrons from ZD rats were larger. This finding was consistent with the appearance of larger chylomicron particles in the lacteal of the intestinal mucosa following lipid ingestion. These findings suggest that the intestinal synthesis of apo-B may be defective in zinc-deficient rats and may explain in part the impaired absorption of dietary lipids observed in zinc deficiency.