Regulation of rat liver glycogen synthesis and activities of glycogen cycle enzymes by glucose and galactose

Sparks, John W.; Lynch, Almorris; Glinsmann, Walter H.

doi:10.1016/0026-0495(76)90159-1

Cited by 33 publications

(26 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…When the combination of glucose, galactose, and insulin was added to the perfusate, synthetase was not only activated 10-fold, but also the degree of activation was proportional to perfusate glucose concentration. This is qualitatively similar to the glucose concentration dependence observed in the adult rat liver perfused under similar conditions (28), and this concentration dependence of synthetase activation may be important for the rapid synthesis of glycogen during feeding.…”

Section: Discussionsupporting

confidence: 84%

“…Although it is generally assumed (1, 23) that galactose is metabolized to glycogen in infants, both increased and decreased liver glycogen levels have been observed after large galactose feedings in adults (3,14). In a recent study using the isolated perfused adult rat liver, we demonstrated increased liver glycogen after perfusion with galactose (28). We also noted that galactose regulated the activities of glycogen synthetase and phosphorylase.…”

Section: Discussionsupporting

confidence: 50%

“…Additionally, the perfused newborn monkey liver regulates pH, pCO,, and p 0 2 within an appropriate range, and we have previously shown maintainance of potassium with the normal range (I I). Finally, using the same perfusion system, the adult rat takes up glucose during hyperglycemia (28). For these reasons, we conclude that the lack of net glucose uptake by the perfused near term monkey liver is not artifactual, and it is possible that this may be characteristic of newborn primate liver.…”

Section: Discussionmentioning

confidence: 76%

“…The effects of these stimuli in monkey are thus similar to their effects in isolated, perfused liver of the adult rat (1 1, 20). However, the effects of hyperglycemia in the near term monkey were significantly different from its effects in adult rat liver (4,13,28). In the near term monkey (lo), hyperglycemia did not stimulate glycogen synthesis, glucose uptake, or activation of glycogen synthetase.…”

Section: Discussionmentioning

confidence: 90%

“…In an companion study (28), we have provided evidence that galactose as well as glucose regulates glycogen cycle enzyme activit~es and promotes glycogen synthesis in the isolated perfused liver of the adult rat. Galactose and glucose form lactose, the principal dietary carbohydrate in milk (6).…”

mentioning

confidence: 99%

See 4 more Smart Citations

Glycogen Regulation in Isolated Perfused Near Term Monkey Liver

et al. 1976

Self Cite

View full text Add to dashboard Cite

ExtractGlycogen metabolism was studied in the isolated perfused liver of the monkey conceptus at 90% of gestation using an in situ recirculating perfusion system. Net uptake of glucose and galactose and the activities of the enzymes, glycogen synthetase and phosphorylase, were studied in response to varied perfusate composition. Synthetase activity was expressed as %I, the percentage of total synthetase activity in the active form. Perfusate glucose concentrations a s high as 700 mg/ 100 ml did not lead to net glucose uptake or to an increase in the baseline %I synthetase ( 4 1, mean & SEM). In the presence of 300 mg/100 ml glucose, insulin a t M increased %I to 8 i 2, and galactose > 75 mg/100 ml increased %I to 8 & 1. The combination of galactose, glucose, and insulin increased %I to 40 A 5. With this latter combination, synthetase activity was proportional to perfusate glucose concentration above 100 mg/100 ml. Phosphorylase activity was diminished by either galactose or insulin, and phosphorylase activity was lowest in the group receiving galactose, glucose, and insulin. Galactose was taken up by all livers, but net glucose uptake was not observed under any condition; net hexose uptake was observed in perfusions with galactose. Glycogen levels did not vary significantly with varied perfusate composition during the 30-min perfusion periods. Speculation W e speculate that galactose may be uniquely important for neonatal liver glycogen synthesis, and that its action is mediated through reciprocal changes in the activities of the enzymes, glycogen synthetase and phosphorylase. If liver glycogen is important for acute neonatal glucose homeostasis, then galactose may also be essential for maintaining circulating glucose concentration by ensuring glycogen synthesis during feeding.

show abstract

Section: Discussionsupporting

confidence: 84%

Section: Discussionsupporting

confidence: 50%

Section: Discussionmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 90%

mentioning

confidence: 99%

See 3 more Smart Citations

Glycogen Regulation in Isolated Perfused Near Term Monkey Liver

et al. 1976

Self Cite

View full text Add to dashboard Cite

show abstract

Lobular and cellular patterns of early hepatic glycogen deposition in the rat as observed by light and electron microscopic radioautography after injection of ³H‐galactose

et al. 1984

View full text Add to dashboard Cite

Very low hepatic glycogen levels are achieved by overnight fasting of adrenalectomized (ADX) rats. Subsequent injection of dexamethasone (DEX), a synthetic glucocorticoid, stimulates marked increases in glycogen synthesis. Using this system and injecting 3H-galactose as a glycogen precursor 1 hr prior to sacrifice, the intralobular and intracellular patterns of labeled glycogen deposition were studied by light (LM) and electron (EM) microscopic radioautography. LM radioautography revealed that 1 hr after DEX treatment, labeling patterns for both periportal and centrilobular hepatocytes resembled those in rats with no DEX treatment: 18% of the hepatocytes were unlabeled, and 82% showed light labeling. Two hours after treatment with DEX, 14% of the hepatocytes remained unlabeled, and 78% were lightly labeled; however, 8% of the cells, located randomly throughout the lobule, were intensely labeled. An increased number of heavily labeled cells (26%) appeared 3 hr after DEX treatment; and by 5 hr 91% of the hepatocytes were intensely labeled. Label over the periportal cells at this time was aggregated, whereas centrilobular cells displayed dispersed label. EM radioautographs showed that 2 to 3 hr after DEX injection initial labeling of hepatocytes, regardless of their intralobular location, occurred over foci of smooth endoplasmic reticulum (SER) and small electron-dense particles of presumptive glycogen, and in areas of SER and distinct glycogen particles. After 5 hrs of treatment with DEX, the intracellular distribution of label reflected the glycogen patterns characteristic of periportal or centrilobular regions.

show abstract

Labeling of hepatic glycogen after short‐ and long‐term stimulation of glycogen synthesis in rats injected with ³H‐galactose

et al. 1990

View full text Add to dashboard Cite

The effects of short- and long-term stimulation of glycogen synthesis elicited by dexamethasone were studied by light (LM) and electron (EM) microscopic radioautography (RAG) and biochemical analysis. Adrenalectomized rats were fasted overnight and pretreated for short- (3 hr) or long-term (14 hr) periods with dexamethasone prior to intravenous injection of tracer doses of 3H-galactose. Analysis of LM-RAGs from short-term rats revealed that about equal percentages (44%) of hepatocytes became heavily or lightly labeled 1 hr after labeling. The percentage of heavily labeled cells increased slightly 6 hr after labeling, and unlabeled glycogen became apparent in some hepatocytes. The percentage of heavily labeled cells had decreased somewhat 12 hr after labeling, and more unlabeled glycogen was evident. In the long-term rats 1 hr after labeling, a higher percentage of heavily labeled cells (76%) was observed compared to short-term rats, and most glycogen was labeled. In spite of the high amount of labeling seen initially, the percentage of heavily labeled hepatocytes had decreased considerably to 55% by 12 hr after injection; and sparsely labeled and unlabeled glycogen was prevalent. The EM-RAGs of both short- and long-term rats were similar. Silver grains were associated with glycogen patches 1 hr after labeling; 12 hr after labeling, the glycogen patches had enlarged; and label, where present, was dispersed over the enlarged glycogen clumps. Analysis of DPM/mg tissue corroborated the observed decrease in label 12 hr after administration in the long-term animals. The loss of label observed 12 hr after injection in the long-term pretreated rats suggests that turnover of glycogen occurred during this interval despite the net accumulation of glycogen that was visible morphologically and evident from biochemical measurement.

show abstract

Regulation of rat liver glycogen synthesis and activities of glycogen cycle enzymes by glucose and galactose

Cited by 33 publications

References 18 publications

Glycogen Regulation in Isolated Perfused Near Term Monkey Liver

Glycogen Regulation in Isolated Perfused Near Term Monkey Liver

Lobular and cellular patterns of early hepatic glycogen deposition in the rat as observed by light and electron microscopic radioautography after injection of ³H‐galactose

Labeling of hepatic glycogen after short‐ and long‐term stimulation of glycogen synthesis in rats injected with ³H‐galactose

Contact Info

Product

Resources

About

Regulation of rat liver glycogen synthesis and activities of glycogen cycle enzymes by glucose and galactose

Cited by 33 publications

References 18 publications

Glycogen Regulation in Isolated Perfused Near Term Monkey Liver

Glycogen Regulation in Isolated Perfused Near Term Monkey Liver

Lobular and cellular patterns of early hepatic glycogen deposition in the rat as observed by light and electron microscopic radioautography after injection of 3H‐galactose

Labeling of hepatic glycogen after short‐ and long‐term stimulation of glycogen synthesis in rats injected with 3H‐galactose

Contact Info

Product

Resources

About

Lobular and cellular patterns of early hepatic glycogen deposition in the rat as observed by light and electron microscopic radioautography after injection of ³H‐galactose

Labeling of hepatic glycogen after short‐ and long‐term stimulation of glycogen synthesis in rats injected with ³H‐galactose