Administration of recombinant bovine tumor necrosis factor-alpha affects intermediary metabolism and insulin and growth hormone secretion in dairy heifers.

Four experiments were conducted to clarify the effect of intravenous (i.v.) administration of recombinant bovine tumor necrosis factor alpha (rbTNF) on selected metabolites and on hormone secretion in Holstein heifers (n = 6; 347.0 kg average BW). In Exp. 1, rbTNF was injected at three dosage levels in a Latin square; 0 (CONT), 2.5 (TNF2.5), or 5.0 (TNF5) microg/kg BW. Plasma glucose and triglyceride concentrations were at first elevated (P < .05) by rbTNF treatment and then were decreased (P < .05) by TNF2.5 and TNF5. Plasma NEFA concentrations were increased (P < .05) in rbTNF-treated groups. The injection of rbTNF resulted in an increase in plasma insulin levels (P < .05 with TNF5) during the period between 2 and 24 h, except for the period between 6 and 8 h, after the treatment. In Exp. 2, 3, and 4, each heifer received i.v. injections of glucose (.625 mM/kg BW) + rbTNF (5 microg/kg) or glucose + saline (10 mL) (Exp. 2), insulin (0.2 U/kg) + rbTNF or insulin + saline (Exp. 3), and GHRH (0.25 microg/kg) + rbTNF or GHRH + saline (Exp. 4) at 1-wk intervals. In Exp. 2, rbTNF inhibited (P < .05) glucose-stimulated insulin secretion during the initial phase. Thereafter, plasma insulin was higher (P < .01) with the glucose + rbTNF treatment than with the glucose + saline treatment. Treatment with rbTNF inhibited the insulin-stimulated glucose utilization (Exp. 3) and GHRH-stimulated GH secretion (Exp. 4) during the initial phase. These results suggest that rbTNF directly and(or) indirectly affects the intermediary metabolism and hormone secretion in Holstein heifers.