AMPK phosphorylates and activates heart PFK-2 in vitro and in intact cells. AMPK-mediated PFK-2 activation is likely to be involved in the stimulation of heart glycolysis during ischaemia.

AMP-activated protein kinase is a multisubstrate protein kinase that, in liver, inactivates both acetyl-CoA carboxylase, the rate-limiting enzyme of fatty acid synthesis, and 3-hydroxy-3-methyl-glutaryl-CoA reductase, the rate-limiting enzyme of cholesterol synthesis. AICAR (5-amino 4-imidazolecarboxamide ribotide, ZMP) was found to stimulate up to 10-fold rat liver AMP-activated protein kinase, with a half-maximal effect at approximately 5 mM. In accordance with previous observations, addition to suspensions of isolated rat hepatocytes of 50-500 microM AICAriboside, the nucleoside corresponding to ZMP, resulted in the accumulation of millimolar concentrations of the latter. This was accompanied by a dose-dependent inactivation of both acetyl-CoA carboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase. Addition of 50-500 microM AICAriboside to hepatocyte suspensions incubated in the presence of various substrates, including glucose and lactate/pyruvate, caused a parallel inhibition of both fatty acid and cholesterol synthesis. With lactate/pyruvate (10/1 mM), half-maximal inhibition was obtained at approximately 100 microM, and near-complete inhibition at 500 microM AICAriboside. These findings open new perspectives for the simultaneous control of triglyceride and cholesterol synthesis by pharmacological stimulators of AMP-activated protein kinase.

5-Amino-4-imidazolecarboxamide (AICA) riboside, the nucleoside corresponding to AICA ribotide (AICAR or ZMP), an intermediate of the de novo pathway of purine biosynthesis, was found to exert a dose-dependent inhibition on gluconeogenesis in isolated rat hepatocytes. Production of glucose from lactate-pyruvate mixtures was half-maximally inhibited by approximately 100 microM and completely suppressed by 500 microM AICA riboside. AICA riboside also inhibited the production of glucose from all other gluconeogenic precursors investigated, i.e., fructose, dihydroxyacetone, and L-proline. Measurements of intermediates of the glycolytic-gluconeogenic pathway showed that AICA riboside provoked elevations of triose phosphates and fructose-1,6-bisphosphate and decreases in fructose-6-phosphate and glucose-6-phosphate. The effects of AICA riboside persisted when the cells were washed 10 min after its addition but were suppressed by 5-iodotubercidin, an inhibitor of adenosine kinase. AICA riboside provoked a dose-dependent buildup of normally undetectable Z nucleotides. After 20 min of incubation with 500 microM AICA riboside, ZMP, ZTP, and ZDP reached 3, 0.3, and 0.1 mumol/g cells, respectively. Concentrations of ATP were not significantly modified by addition of up to 500 microM AICA riboside when the cells were incubated with lactate-pyruvate but decreased with fructose or dihydroxyacetone. The activity of rat liver fructose-1,6-bisphosphatase was inhibited by ZMP with an apparent Ki of 370 microM. It is concluded that AICA riboside exerts a suppressive effect on gluconeogenesis because it provokes an accumulation of ZMP, which inhibits fructose-1,6-bisphosphatase.(ABSTRACT TRUNCATED AT 250 WORDS)

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We have previously demonstrated that in isolated hepatocytes from fasted rats, AICAriboside (5-amino 4-imidazolecarboxamide riboside), after its conversion into AICAribotide (AICAR or ZMP), exerts a dose-dependent inhibition on fructose-1,6-bisphosphatase and hence on gluconeogenesis. To assess the effect of AICAriboside in vivo, we measured plasma glucose and liver metabolites after intraperitoneal administration of AICAriboside in mice. In fasted animals, in which gluconeogenesis is activated, AICAriboside (250 mg/kg body weight) induced a 50% decrease of plasma glucose within 15 min, which lasted about 3 h. In fed mice, glucose decreased by 8% at 30 min, and normalized at 1 h. Under both conditions, ZMP accumulated to approximately 2 mumol/g of liver at 1 h. It decreased progressively thereafter, although much more slowly in the fasted state. Inhibition of fructose-1,6-bisphosphatase was evidenced by time-wise linear accumulations of fructose-1,6-bisphosphate, from 0.006 to 3.9 mumol/g of liver at 3 h in fasted mice, and from 0.010 to 0.114 mumol/g of liver at 1 h in fed animals. AICAriboside did not significantly influence plasma insulin or glucose utilization by muscle. We conclude that in vivo as in isolated hepatocytes, AICAriboside, owing to its conversion into ZMP, inhibits fructose-1,6-bisphosphatase and consequently gluconeogenesis.