Alterations in lipid metabolism induced by recombinant bovine tumor necrosis factor-alpha administration to dairy heifers

Endotoxin induces marked changes in lipid metabolism via its effects on cytokines. To evaluate the role of tumor necrosis factor-alpha (TNF) in mediating changes of lipid metabolism in ruminants, we performed a crossover saline-controlled study in Holstein heifers (n = 8; 394.0 kg average BW), investigating the metabolic effects of a single intravenous administration of recombinant bovine TNF (rbTNF, 5.0 microg/kg). Blood samples were taken from a jugular vein at 0 (1100, just before injection), 0.5, 6, 12, and 24 h after each treatment. Dry matter intake in the heifers was not affected by single administration of the rbTNF. The rbTNF produced early as well as later hypertriglyceridemia (P < 0.05) in dairy heifers. The rbTNF also induced an early and sustained rise (P < 0.05) in the plasma NEFA concentration. Plasma retinol concentration was decreased (P < 0.05) at 24 h after rbTNF injection, whereas the a-tocopherol concentration was not significantly affected by rbTNF treatment. At 0.5 and 24 h, there was an increase (P < 0.05) in the plasma concentration of the very-low-density lipoprotein (VLDL) fraction in rbTNF-treated heifers. Between 6 and 24 h after rbTNF treatment, concentration of the low-density lipoprotein fraction declined (P < 0.05) but the high-density lipoprotein fraction was not altered in the rbTNF-treated heifers. These results indicate that TNF produces a hypertriglyceridemic response associated with an increase of the VLDL fraction and a disturbance of retinol metabolism in dairy heifers.