The effect of fatty acids and starvation on the metabolism of gluconeogenic precursors by isolated sheep liver cells

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising from in vivo studies

At the crossroad between nutrient supply and requirements, the liver plays a central role in partitioning nitrogenous nutrients among tissues. The present review examines the utilisation of amino acids (AA) within the liver in various physiopathological states in mammals and how the fates of AA are regulated. AA uptake by the liver is generally driven by the net portal appearance of AA. This coordination is lost when demands by peripheral tissues is important (rapid growth or lactation), or when certain metabolic pathways within the liver become a priority (synthesis of acute-phase proteins). Data obtained in various species have shown that oxidation of AA and export protein synthesis usually responds to nutrient supply. Gluconeogenesis from AA is less dependent on hepatic delivery and the nature of nutrients supplied, and hormones like insulin are involved in the regulatory processes. Gluconeogenesis is regulated by nutritional factors very differently between mammals (glucose absorbed from the diet is important in single-stomached animals, while in carnivores, glucose from endogenous origin is key). The underlying mechanisms explaining how the liver adapts its AA utilisation to the body requirements are complex. The highly adaptable hepatic metabolism must be capable to deal with the various nutritional/physiological challenges that mammals have to face to maintain homeostasis. Whereas the liver responds generally to nutritional parameters in various physiological states occurring throughout life, other complex signalling pathways at systemic and tissue level (hormones, cytokines, nutrients, etc.) are involved additionally in specific physiological/nutritional states to prioritise certain metabolic pathways (pathological states or when nutritional requirements are uncovered).

Effects of Feeding Propionate and Calcium Salts of Long-Chain Fatty Acids on Transition Dairy Cow Performance

Multiparous Holstein cows (n = 40) were used in a randomized complete block design to determine the effects of feeding Ca and Na salts (1:1, wt/wt) of propionate and Ca salts of long-chain fatty acids (LCFA) on transition cow performance. All cows were fed the same basal diet once daily for ad libitum intake. Treatments (g/d) were 320 cornstarch (CS) as a control, 120 propionate (PRO), 120 propionate and 93 LCFA (PF1), and 178 propionate and 154 LCFA (PF2). Treatments were hand-mixed into the upper one-third of the TMR from 2 wk pre- through 3 wk postpartum. Intakes were recorded from 21 d pre- through 21 d postpartum. Energy density and crude protein were 1.54 and 1.65 Mcal/kg and 14.4 and 18.8% for pre- and postpartum diets, respectively. All cows received a common diet from 22 to 70 days in milk (DIM). Milk composition was analyzed on d 7, 14, and 21. Blood was sampled at 14, 7, and 2 d prepartum and 2, 7, 14, and 21 DIM. Pre- and postpartal dry matter intake (DMI) averaged 11.9 and 16.4 kg/d, respectively, and did not differ among treatments. A diet x week interaction for postpartal DMI was observed as cows fed PF2 consumed 2 kg/d less DM during wk 2 relative to other treatments. Milk yields from 22 to 70 DIM were 48.8, 48.5, 47.8, and 51.3 kg/d for CS, PRO, PF1, and PF2, respectively, and were not significantly affected by treatments. Milk true protein (3.32 vs. 3.16%) was increased and MUN (12.5 vs. 14.4 mg/dL) was decreased for CS relative to other treatments. Milk fat yield from cows fed PRO tended to be greater than those fed PF1 (1.58 vs. 1.29 kg/d). Plasma glucose, insulin, and beta-hydroxybutyrate were not affected by treatments. The PF2 treatment tended to decrease NEFA in plasma relative to PF1 over all times measured (492 and 670 muEq/L) and significantly decreased plasma NEFA relative to those fed PF1 postpartum (623 and 875 muEq/L). Relative to PF1, feeding propionate and LCFA at the higher level in this experiment improved energy balance postpartum as evidenced by decreased concentrations of plasma NEFA.

Effects of Dietary Glucogenic Precursors and Fat on Feed Intake and Carbohydrate Status of Transition Dairy Cows

Twenty-four multiparous Holstein cows were used to determine the effects of dietary fat and glucose precursors on energy status and lactation. The treatment group (T) received 409 g/d (DM basis) of a combination of calcium salts of fatty acids, calcium propionate, and propylene glycol. The control group (C) received 409 g/d of a mixture of calcium salts of fatty acids and ground barley from 14 +/- 0.9 g/d before until 21 d after calving. Dry matter intake was greater (16.1 vs. 13.6 +/- 1.3 kg/d) for T than C during the last week prepartum and did not decrease for T from the previous week, whereas, in C, DM intakes decreased by 3.2 kg/d. Production of milk and milk fat did not differ. There was a tendency for lower protein and increased lactose concentrations in milk from T cows. Milk fat percentage was lower in T at d 7 (5.5 vs. 6.4 +/- 0.5%) and 28 (4.4 vs. 5.5 +/- 0.5%) of lactation. Liver lipid content was numerically lower (7.9 vs. 9.2 +/- 0.9%) and glycogen content was significantly higher (2.4 vs. 2.0 +/- 0.1%) in T vs. C cows on d 7 of lactation. Concentrations of nonesterified fatty acids were lower in blood of T cows on d 2 and 7 of lactation. Over all time points, blood glucose concentrations were higher in T cows pre- (70.75 vs. 62.1 +/- 1.3 mg/dL) and postpartum (60.1 vs. 56.2 +/- 1.1 mg/dL). Insulin concentrations in blood were greater for T (397 vs. 314 +/- 48 pg/mL) both pre- and postpartum. Feeding glucose precursors in combination with rumen inert lipids, compared with feeding barley in combination with the lipids for 2 wk before parturition and 3 wk postpartum helped avoid prepartum feed intake depression and increased blood glucose and insulin and decreased blood NEFA.

Effect of long-chain fatty acids on triglyceride accumulation, gluconeogenesis, and ureagenesis in bovine hepatocytes

A relationship between increased lipid concentration in the liver and reduced hepatic function has been suggested; however, there is little direct evidence of change in specific hepatic functions. Hepatocytes were obtained from ruminating calves and were incubated as monolayers for 36 h. The media contained a mixture of nonesterified fatty acids (NEFA) at 0, 0.5, 1.0, and 1.5 mM NEFA with molar proportions of 0.435 oleate, 0.319 palmitate, 0.144 stearate, 0.049 linoleate, and 0.053 palmitoleate. Ureagenesis or gluconeogenesis was measured from 48 to 51 h after plating using hepatocytes that had only previous (12 to 48 h), only concurrent (48 to 51 h), or previous and concurrent (12 to 51 h) exposure to NEFA. A previous 36-h exposure to NEFA caused cell triglyceride accumulation, yielding triglyceride concentrations that corresponded with liver that is clinically described as normal to moderately fatty. Previous, prolonged exposure to NEFA reduced ureagenesis and increased gluconeogenesis. Concurrent exposure to NEFA did not significantly affect gluconeogenesis or ureagenesis and did not alter the residual effect of prolonged incubation with NEFA. Reduced ureagenesis was related to increased cell triglyceride accumulation independently of other direct NEFA effects. Decreased ureagenic capacity may play a role in the morbidity associated with periparturient fatty liver in dairy cows.

Fatty acid effects on gluconeogenesis in goat, calf and guinea pig hepatocytes

1. Regulation of hepatic gluconeogenesis by fatty acid was studied in goat, calf and guinea pig hepatocytes. 2. Fatty acid effects on gluconeogenesis were dependent upon species; fatty acid and gluconeogenic substrate. 3. Oleate and octanoate inhibited gluconeogenesis from propionate in guinea pig hepatocytes and stimulated it in goat hepatocytes. 4. Oleate and octanoate markedly inhibited gluconeogenesis from lactate in guinea pig hepatocytes whereas octanoate, but not oleate, decreased glucose production from lactate in goat hepatocytes. 5. Effects of fatty acids on gluconeogenesis in calf hepatocytes were similar to goat hepatocytes suggesting control of gluconeogenesis is similar among ruminant species but differs from guinea pigs.