Effects of exogenous glucagon on lipids in lipoproteins and liver of lactating dairy cows

Decreased concentrations of phospholipids, free cholesterol, and cholesteryl ester in plasma and liver are associated with fatty liver, a major metabolic disease of dairy cows in early lactation. The objective was to test whether daily subcutaneous injections of 7.5 and 15 mg of glucagon, which can decrease concentrations of liver triacylglycerol, affect concentrations of plasma lipoprotein components and liver lipids other than triacylglycerol. Multiparous Holstein cows (n = 32) were grouped on the basis of liver triacylglycerol concentrations at d 8 postpartum into "normal" (n = 8; triacylglycerol <1% liver wet wt) and "susceptible to fatty liver" (n = 24; triacylglycerol >1% liver wet wt) cows. Susceptible cows were assigned randomly to three groups and beginning at d 8 postpartum received 0 (same for Normal cows), 2.5, or 5 mg of glucagon by subcutaneous injections every 8 h for 14 d. In comparison to saline injections, subcutaneous injections of glucagon either increased or tended to increase concentrations of phospholipids and free cholesterol in liver, with greater increases of the latter during ambient temperatures below 35degreesC. Glucagon injections decreased or tended to decrease concentrations of very low-density lipoprotein-triacylglycerol, high-density lipoprotein(1)-phospholipids, and high-density lipoprotein(2)-free cholesterol in plasma, with no changes of the latter two during ambient temperatures below 35degreesC. The results indicate that subcutaneously administered glucagon has only minor effects on the lipid transport in plasma of dairy cows in early lactation with more beneficial effects occurring during ambient temperatures below 35degreesC and, most importantly, no indications that glucagon has negative effects.