Expression and activity of key hepatic gluconeogenesis enzymes in response to increasing intravenous infusions of glucose in dairy cows1

Abstract

The present study aimed at investigating whether increasing concentrations of glucose supply have a depressive effect on the mRNA abundance and activity of key gluconeogenic enzymes in dairy cows. Twelve Holstein-Friesian dairy cows in mid-lactation were intravenously infused with saline (SI; n = 6) or a 40% glucose solution (GI; n = 6). For GI cows, the infusion dose increased by 1.25%/d relative to the initial NE(l) requirement until a maximum dose equating to surplus 30% NE(l) was reached on d 24. Cows receiving SI received an equivalent volume of 0.9% saline solution. Blood samples were taken every 2 d, and liver biopsies were collected every 8 d. A treatment x quadratic dose interaction (P < 0.01) was observed for the concentration of plasma glucose and serum insulin. The interactions were due to positive quadratic responses of the concentrations of glucose and insulin for GI cows, whereas the concentrations of glucose and insulin did not change over time for SI cows. The concentration of beta-hydroxybutyric acid (BHBA) and serum urea nitrogen (BUN) responded in a treatment x quadratic dose manner, such that greater decreases (P < 0.01) in BHBA and BUN concentrations were observed for cows receiving GI than SI as the dosage increased. Serum NEFA concentration tended to follow a similar pattern as serum BHBA and BUN; however, the interaction was not significant (P = 0.07). The mRNA abundance of gluconeogenesis enzymes followed a linear treatment x dose interaction (P < 0.05) for only pyruvate carboxylase (PC), which was paralleled by a trend for a linear treatment x dose interaction (P = 0.13) for PC enzyme activity. The least PC expression and activity were observed at the largest glucose dosage. The activity, but not mRNA abundance, of fructose 1,6-bisphosphatase (FBPase) showed treatment x quadratic dose interactions (P < 0.05) with decreasing activity at increasing glucose dose. Activities and expression of phosphoenolpyruvate carboxykinase and glucose 6-phosphatase were not affected (P > 0.25) by treatment. In conclusion, hepatic gluconeogenic enzymes are only moderately affected by slowly increasing glucose supply, including a translational or posttranslational downregulation of FBPase activity and a decrease in the mRNA abundance of PC with possible consequences for PC enzyme activity.

Hepatic gene expression involved in glucose and lipid metabolism in transition cows: Effects of fat mobilization during early lactation in relation to milk performance and metabolic changes

“…In support of our findings, plasma glucose concentrations were not associated with protein concentrations of gluconeogenic enzymes in the liver of dairy cows (Sejersen et al, 2012). Changes in the glucose and insulin status in dairy cows by glucose or insulin treatment, or both, indicated only minor changes in gene expression of gluconeogenic enzymes, implying less regulation of gene expression of gluconeogenic enzymes by the glucose and insulin status in dairy cows around parturition (Al-Trad et al, 2010;Kreipe et al, 2011). On the other hand, a negative relationship was observed between hepatic glycogen concentration and particularly PC mRNA abundance during lactation, pointing at a feedback mechanism of stored hepatic glycogen on gluconeogenesis.…”

Gluconeogenesis in dairy cows: The secret of making sweet milk from sour dough

“…Murondoti et al (60) found coordinated depressions of PCoAC and PEPCK activities in cows with induced fatty liver, whereas Hammon et al (unpublished) discovered coordinated changes in the mRNA expression of isoform A of PCoAC and PEPCK-C in transition dairy cows. These results support the view that changes in PEPCK activity have a high predictive value for glucose production from propionate even if the concurrent changes in PCoAC (and MCM) are not known (61,62). Moreover, the bovine PEPCK gene promoter itself is positively regulated by propionate (63), constituting a feed-forward mechanism of substrate control for hepatic gluconeogenesis that is linked to the end products of rumen fermentation.…”

“…With an intravenous infusion route, extremely high glucose doses (2.65 kg/ day) were necessary to affect the activity of enzymes responsible for the exit of glucose from the gluconeogenetic pathway (fructose 1,6-bisphosphatase, FBPase) and the liver (G6-Pase). Most notably, these changes in FBPase and G6-Pase activities were not correlated with their mRNA abundance, indicating that the release of glucose from the gluconeogenesis pathway and from the liver is regulated to a large degree on a posttranscriptional level according to actual glucose status (62).…”

“…As a consequence, net glucose flux across the basolateral hepatocyte membrane is always outward driven, and the liver is always an organ of net glucose release in adult cattle (17). These evolutionary adaptations to a low glucose status imply that cattle respond to experimentally or therapeutically applied infusions of glucose predominantly with an increase in peripheral glucose utilization (especially in adipose and skeletal muscle tissues) (86), while the negative feedback on hepatic glucose output is more subtle and sometimes even missing in contrast to monogastric species (29,62,86). With an intravenous infusion route, extremely high glucose doses (2.65 kg/ day) were necessary to affect the activity of enzymes responsible for the exit of glucose from the gluconeogenetic pathway (fructose 1,6-bisphosphatase, FBPase) and the liver (G6-Pase).…”

Changes in milk performance and hepatic metabolism in mid-lactating dairy goats after being fed a high concentrate diet for 10 weeks

“…In addition, hepatic lipid synthesis is very important for developing the physical properties and quality of the milk. Among the factors involved in hepatic gluconeogenesis, glucose-6-phosphatase (G6Pase), pyruvate carboxylase (PC ) and phosphoenolpyruvate carboxykinase (PEPCK ) are the rate-limiting enzymes in the gluconeogenic process (Pershing et al, 2002;Al-Trad et al, 2010). However, whether milk production is changed in lactating ruminants after they are fed a high concentrate for a relative long time and the molecular mechanism involved in the hepatic gluconeogenic process is still unclear.…”