Net flux of nonesterified fatty acids, cholesterol, triacylglycerol, and glycerol across the portal-drained viscera and liver of pregnant ewes

The objective of this study was to determine the pattern of nutrient flux across portal-drained viscera (PDV) and liver in ewes with varying numbers of fetuses. Catheters were placed in the hepatic portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta of each ewe. Plasma flow and net cholesterol, nonesterified fatty acids (NEFA), and glycerol release across the PDV and liver were determined prior to exposure to rams. Ewes were subsequently mated. Two ewes were not pregnant, six ewes gave birth to singles, and 11 ewes gave birth to twins. Additional measurements were taken 103, 82, 61, 39, 19, and 6 d before parturition. There was a net PDV uptake of nonesterified cholesterol in the nonpregnant ewes and a net release in the ewes with singles and twins. Net nonesterified cholesterol hepatic release did not differ with days from parturition (P = .77). There was a net hepatic release of nonesterified cholesterol in the ewes with twins and a net hepatic uptake in the ewes with singles and in nonpregnant ewes (P = .03). There was a net PDV release of NEFA; however, it did not differ with litter size (P = .59) or days from parturition (P = .63). Hepatic NEFA uptake increased with litter size (P = .03) and increased as gestation progressed (P = .006). There was an interaction (P = .04) between litter size and days from parturition for net PDV glycerol release. Net PDV glycerol release in the nonpregnant ewes decreased over time, but release in pregnant ewes tended to increase over time. Hepatic glycerol uptake increased with litter size and increased as gestation progressed. There was a net PDV uptake of triacylglycerol, but it did not differ with litter size (P = .11) or with days from parturition (P = .06). There was a net hepatic release of triacylglycerol, but it did not differ with litter size (P = .59) or with days from parturition (P = .67). Liver utilization of glycerol and NEFA as substrates for metabolism increases as pregnancy progresses. In the nonpregnant ewe, the combined contribution of glycerol and NEFA carbon accounted for 10% of the carbon taken up by the liver, and in ewes pregnant with twins, the combined contribution accounted for 42% of the carbon uptake 19 d before parturition. In conclusion, these data demonstrate NEFA are an important metabolite when determining carbon balance across the liver and their relative contribution to carbon balance increases as pregnancy progresses.