Hepatic lobular patterns of phosphoenolpyruvate carboxykinase, glycogen synthase, and glycogen phosphorylase in fasted and fed rats.

Giffin, Bruce F.; Drake, Richard L.; Morris, Randal E.; Cardell, Robert R.

doi:10.1177/41.12.8245433

Cited by 24 publications

(22 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, the mass of synthase protein, determined by Western blotting, was similar as has been reported previously [28]. However, the mRNA abundance was increased approximately 1.7-fold in normal fed compared to 24 h fasted rats.…”

Section: Discussionsupporting

confidence: 62%

Effect of feeding, fasting, and diabetes on liver glycogen synthase activity, protein, and mRNA in rats

Gannon

Nuttall

1997

Diabetologia

View full text Add to dashboard Cite

Our laboratory [1], as well as many others [2][3][4][5][6][7][8] , have reported an increase in total synthase activity in liver from diabetic rats. The increase in hepatic synthase activity could be due to an increased mass of the enzyme or to the presence of a more catalytically efficient form(s) of the enzyme. Akatsuka et al. [5] reported changes in the M r of synthase in liver from streptozotocin diabetic rats. They attributed this to an increase in the phosphorylation state of synthase, which in turn resulted in greater total synthase activity. In contrast, in alloxan diabetic rats, Bahnak and Gold [3] reported that the increase in hepatic synthase activity was due to an increased mass of the enzyme. This was associated with an increased synthesis and increased turnover rate. They could not confirm the presence of an altered form of the enzyme [9].The purpose of the present study was to determine whether the increase in total synthase activity observed previously in diabetic rats was associated with an increase in enzyme protein mass and whether the reported increase in enzyme turnover was associated with an increase in mRNA abundance. Therefore, Diabetologia (1997) Summary Hepatic glycogen synthase activity is increased in diabetic animals. However, the relationship between enzymic activity, enzyme protein mass, and mRNA abundance has not been well characterized. In the present study, these relationships were determined in 3-and 8-day diabetic, fed and fasted rats. The results were compared to data obtained in normal fed and fasted animals. In normal rats, total synthase specific activity and protein mass were similar in the fed and fasted state. However, in fed animals, the synthase mRNA abundance was increased 1.7-fold. In 3-day diabetic rats, total synthase specific activity was increased approximately 29 % compared to normal controls. It was unaffected by feeding and fasting and was associated with an approximate 15 % increase in enzyme mass. Synthase mRNA was increased 1.8 and 2.6-fold in fasted and fed animals, respectively. In 8-day diabetic rats, total synthase specific activity was increased more than 2-fold compared to controls. However, the enzyme protein mass was decreased by approximately 20 %. The mRNA abundance in 8-day diabetic fasted rats was only 30 % of controls, while in fed rats it was increased by 40 %. These data indicate that feeding and fasting have a major effect on synthase mRNA abundance which is independent of synthase activity, or protein mass, or both, in normal and diabetic animals. Total synthase specific activity increased with duration of diabetes. This was associated with only a modest change in protein mass. Thus, diabetes induces an increase in synthase catalytic efficacy. The specific activity of phosphorylase is decreased in diabetic rats. [Diabetologia (1997) 40: 758-763]

show abstract

Section: Discussionsupporting

confidence: 62%

Effect of feeding, fasting, and diabetes on liver glycogen synthase activity, protein, and mRNA in rats

Gannon

Nuttall

1997

Diabetologia

View full text Add to dashboard Cite

show abstract

“…Many kinds of hormones and physiological factors can affect PEPCK gene expression, such as cAMP, insulin, glucagon, steroid, and thyroid hormone. In STZ-diabetic rats with a very limited insulin level, the PEPCK gene is overexpressed in the liver (Giffin et al, 1993;Chang et al, 2003). The mechanism and the causal relation between resveratrolinduced plasma glucose lowering effect and decreasing PEPCK expression in STZ-diabetic rats remains to be clarified.…”

Section: Discussionmentioning

confidence: 98%

Phosphatidylinositol-3-kinase is involved in the antihyperglycemic effect induced by resveratrol in streptozotocin-induced diabetic rats

et al. 2007

View full text Add to dashboard Cite

“…The reason for the decreased synthesis of phosphorylase and whether insulin plays any role in this process or in regulation of the phosphorylase gene are not known. Phosphorylase protein levels are not altered in the fed/fasted state, which indicates that the phosphorylase gene is not under nutritional regulation (19). The abnormal expression of the phosphorylase gene has been reported in muscle tissue in altered physiological conditions such as regenerated muscles in rats (20) and dystrophic muscles in mice (21).…”

mentioning

confidence: 96%

The Effects of Streptozotocin-induced Diabetes and Insulin Supplementation on Expression of the Glycogen Phosphorylase Gene in Rat Liver

Rao

Pugazhenthi

Khandelwal

1995

Journal of Biological Chemistry

View full text Add to dashboard Cite

We have previously observed that the chronic effects of streptozotocin-induced diabetes cause a decrease in the total hepatic glycogen phosphorylase activity with a corresponding reduction in the phosphorylase protein levels. These effects were normalized by insulin administration to diabetic rats. There was no change in the total glycogen synthase activity as a result of diabetes or insulin supplementation. These results are extended to examine the effects of diabetes and insulin administration to diabetic animals on the expression of phosphorylase and glycogen synthase enzymes. The expression (i.e. mRNA levels) of phosphorylase was down-regulated (45% of normal levels) in diabetic livers, and this was normalized by insulin supplementation to diabetic animals. Diabetes or insulin supplementation to diabetic rats showed no effect on the transcription rate of phosphorylase. As expected, diabetes (or insulin administration to diabetic animals) did not cause any alteration in the mRNA levels or in the transcription rate of hepatic glycogen synthase. The stability of phosphorylase mRNA was then examined using hepatocytes prepared from normal and diabetic rats. Diabetes caused a decrease in the half-life of phosphorylase mRNA from 14 h in normal hepatocytes to 6.5 h in diabetic hepatocytes. Insulin supplementation to the medium of diabetic hepatocytes increased the half-life of phosphorylase mRNA to a level comparable with normal values. This study indicates that the chronic effect of insulin on the activation of the total hepatic phosphorylase activity (and protein) is mediated through the stabilization of its mRNA levels.It is now well established that reversible phosphorylation is one of the major mechanisms by which hormones exert their effects on the regulation of metabolic pathways. Glycogen metabolism is one of the well studied metabolic processes regulated by such a mechanism involving phosphorylation-dephosphorylation of many proteins (or enzymes) (1-5). Glycogen phosphorylase and glycogen synthase are the two key regulatory enzymes that catalyze the rate-limiting steps of glycogen degradation and synthesis, respectively. Both of these enzymes exist in two interconvertible phosphorylated and dephosphorylated forms. The level of the active phosphorylated form of phosphorylase (a-form) is balanced by the opposing actions of phosphorylase phosphatase and phosphorylase kinase. Unlike phosphorylase, the dephosphorylated form of glycogen synthase (a-form) is active, and its levels are regulated by several protein kinases (including protein kinase A, protein kinase C, glycogen synthase kinase-3, casein kinase II, and phosphorylase kinase) and synthase phosphatase (protein phosphatase type 1).The liver plays a central role in the maintenance of blood glucose homeostasis. Glycogen metabolism in hepatic tissue is one of the major metabolic processes involved in such a homeostasis. It has been well established that the balance between levels of insulin and glucagon is vital for this regulation. Insulin is involved in b...

show abstract

Hepatic lobular patterns of phosphoenolpyruvate carboxykinase, glycogen synthase, and glycogen phosphorylase in fasted and fed rats.

Cited by 24 publications

References 4 publications

Effect of feeding, fasting, and diabetes on liver glycogen synthase activity, protein, and mRNA in rats

Effect of feeding, fasting, and diabetes on liver glycogen synthase activity, protein, and mRNA in rats

Phosphatidylinositol-3-kinase is involved in the antihyperglycemic effect induced by resveratrol in streptozotocin-induced diabetic rats

The Effects of Streptozotocin-induced Diabetes and Insulin Supplementation on Expression of the Glycogen Phosphorylase Gene in Rat Liver

Contact Info

Product

Resources

About