Stimulation by glucose of gluconeogenesis in hepatocytes isolated from starved rats

Abstract

Control properties of the gluconeogenic pathway in hepatocytes isolated from starved rats were studied in the presence of glucose. The following observations were made. (1) Glucose stimulated the rate of glucose production from 20 mM-glycerol, from a mixture of 20 mM-lactate and 2 mM-pyruvate, or from pyruvate alone; no stimulation was observed with 20 mM-alanine or 20 mM-dihydroxyacetone. Maximal stimulation was obtained between 2 and 5 mM-glucose, depending on the conditions. At concentrations above 6 mM, gluconeogenesis declined again, so that at 10 mM-glucose the glucose production rate became equal to that in its absence. (2) With glycerol, stimulation of gluconeogenesis by glucose was accompanied by oxidation of cytosolic NADH and reduction of mitochondrial NAD+ and was insensitive to the transaminase inhibitor amino-oxyacetate; this indicated that glucose accelerated the rate of transport of cytosolic reducing equivalents to the mitochondria via the glycerol 1-phosphate shuttle. (3) With lactate plus pyruvate (10:1) as substrates, stimulation of gluconeogenesis by glucose was almost additive to that obtained with glucagon. From an analysis of the effect of glucose on the curves relating gluconeogenic flux and the steady-state intracellular concentrations of gluconeogenic intermediates under various conditions, in the absence and presence of glucagon, it was concluded that addition of glucose stimulated both phosphoenolpyruvate carboxykinase and pyruvate carboxylase activity.

O-GlcNAc Transferase/Host Cell Factor C1 Complex Regulates Gluconeogenesis by Modulating PGC-1α Stability

“…However, the underlying mechanism is still obscure. Consistent with previous in vivo studies (Rigoulet et al, 1987), we show that glucose treatment can directly modulate gluconeogenesis in primary hepatocytes, with a maximal effect observed at 5 mM glucose (Figure 4A). Consistent with this observation, the expression of G6pc and Pck1 is also modulated by glucose availability, with the peak level at 5 mM glucose (Figure 4B, C).…”

“…Although insulin, forskolin (a cAMP agonist mimicking the action of glucagon), and dexamethasome (a synthetic glucocorticoid) are potent regulators of gluconeogenic gene expression (Figure S4A, B), our results show that they do not modulate the association between OGT and HCF-1 (Figure S4C). It has been known that glucose itself regulates gluconeogenesis (Rigoulet et al, 1987; Sacca et al, 1978; Seglen, 1974). However, the underlying mechanism is still obscure.…”

“…Here we describe a mechanism whereby glucose determines its own production, which is through regulation of OGT/HCF-1 complex formation and subsequent O-GlcNAcylation and stabilization of PGC-1α. Compared to no glucose, low levels of glucose stimulate gluconeogenesis; on the other hand, hyperglycemia inhibits gluconeogenesis (Rigoulet et al, 1987; Seglen, 1974). Consistent with this phenomenon, we found that OGT/HCF-1 interaction, O-GlcNAcylation and expression of PGC-1α, enrichment of O-GlcNAc and HCF-1 on the G6pc promoter, and expression of gluconeogenic genes all peak under euglycemic conditions.…”

The mitochondrial consequences of uncoupling intact cells depend on the nature of the exogenous substrate

“…The increase in the cytosolic NADH\NAD + ratio with DNP was abolished when either octanoate or proline was added, the ratio being no different from that obtained with DHA alone. These values are in agreement with values previously found in isolated liver cells under similar conditions [19,20,[33][34][35][36], and initially described in rat liver by Williamson et al [28]. DNP uncoupling with DHAjethanol was responsible for a very large increase in the cytosolic NADH\NAD + ratio.…”

Use and Limitations of Modular Metabolic Control Analysis in Medicine and Biotechnology

“…Traditionally, PEP carboxykinase has been considered a ratelimiting enzyme in gluconeogenesis. However, studies of Rigoulet et al (1987) and of Groen et al (1983) demonstrated that the control coefficient of this enzyme is relatively low. In contrast, pyruvate carboxylase turned out to exert much flux control and would, therefore, be a better potential therapeutic target.…”