Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activities (mumol X min-1 X g liver) and zonal distributions of key enzymes of carbohydrate metabolism were studied in livers of streptozotocin-diabetic rats and compared to the values in alloxan-diabetes. Streptozotocin led to a non-ketotic diabetes with blood glucose being increased by more than fivefold but ketone bodies being in the normal range, while alloxan produced a ketotic diabetes with blood glucose, acetoacetate and beta-hydroxybutyrate being elevated by more than fivefold. Portal insulin was decreased to about 20% in streptozotocin- and more drastically to about 7% in alloxan-diabetes. Conversely, portal glucagon was increased in the two states to about 250% and 180%, respectively. The glucogenic key enzyme phosphoenolpyruvate carboxykinase (PEPCK) was enhanced in streptozotocin- and alloxan-diabetes to over 300%, while the glycolytic pyruvate kinase L (PKL) was lowered to 65% and 80%, respectively. The normal periportal to perivenous gradient of PEPCK of about 3:1, as measured in microdissected tissue samples, was maintained with elevated activities in the two zones. The normal periportal to perivenous gradient of PKL of 1:1.7 was diminished with lowered activities in the two zones. The glucogenic glucose-6-phosphatase (G6Pase) was increased in streptozotocin- and alloxan-diabetes to 130% and 140%, respectively, while the glucose utilizing glucokinase (GK) was decreased to 60% and 50%, respectively. The normal periportal to perivenous gradient of G6Pase, demonstrated histochemically, remained unaffected. Carnitine palmitoyltransferase (CPT) was increased to over 190% and acetyl-CoA carboxylase (ACC) was decreased to 60% in streptozotocin, non-ketotic diabetes, while the two enzymes were altered more drastically to 400% and 50%, respectively, in alloxan, ketotic diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Gluconeogenic-glycolytic capacities and metabolic zonation in liver of rats with streptozotocin, non-ketotic as compared to alloxan, ketotic diabetes. 302 62

Flux through the glucose/glucose 6-phosphate cycle in cultured hepatocytes was measured with radiochemical techniques. Utilization of [2-3H]glucose was taken as a measure of glucokinase flux. Liberation of [14C]glucose from [U-14C]glycogen and from [U-14C]lactate, as well as the difference between the utilization of [2-3H]glucose and of [U-14C]glucose, were taken as measures of glucose-6-phosphatase flux. At constant 5 mM-glucose and 2 mM-lactate concentrations insulin increased glucokinase flux by 35%; it decreased glucose-6-phosphatase flux from glycogen by 50%, from lactate by 15% and reverse flux from external glucose by 65%, i.e. overall by 40%. Glucagon had essentially no effect on glucokinase flux; it enhanced glucose-6-phosphatase flux from glycogen by 700%, from lactate by 45% and reverse flux from external glucose by 20%, i.e. overall by 110%. At constant glucose concentrations cellular glucose 6-phosphate concentrations were essentially not altered by insulin, but were increased by glucagon by 230%. In conclusion, under basic conditions without added hormones the glucose/glucose 6-phosphate cycle showed only a minor net glucose uptake, of 0.03 mumol/min per g of hepatocytes; this flux was increased by insulin to a net glucose uptake of 0.21 mumol/min per g and reversed by glucagon to a net glucose release of 0.22 mumol/min per g. Since the glucose 6-phosphate concentrations after hormone treatment did not correlate with the glucose-6-phosphatase flux, it is suggested that the hormones influenced the enzyme activity directly.
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PMID:Antagonistic regulation of the glucose/glucose 6-phosphate cycle by insulin and glucagon in cultured hepatocytes. 302 41

A minimal model of glycogen metabolism can allow the estimation of the flux rates in the glycogen pathway from the time course of the intermediates in the pathway, measured during substrate administration and hormonal stimulation. The comprehensive model of El-Refai & Bergman (Am. J. Physiol. 231, 1608, 1976) consisting of six compartments and 26 non-estimable parameters has successfully accounted for the responses of hepatic glycogenic intermediates in response to a glucose load in hepatocytes (Katz et al., J. biol. Chem. 253, 4530, 1978), in perfused liver (Nordlie et al., J. biol. Chem. 255, 1834, 1980) and during refeeding in vivo (Van DeWerve & Jeanrenaud, Am. J. Physiol. 247, E271, 1984). The comprehensive model is here reduced to a minimal model, consisting of five compartments representing extracellular and intracellular glucose, glucose-phosphate, uridine diphosphate glucose (UDPG), glycogen, and five parameters estimated from the hepatic response to a given stimulus. Estimation of these parameters requires the measurement of the net hepatic glucose balance, the net gluconeogenic flux, and the time course of glycogenic intermediates responding to a hormone or substrate stimulus. The hepatic glycogenolytic response predicted by the comprehensive model in response to an increase in glucagon is closely fitted by the minimal model. When Gaussian distributed random error was added, 0-5% SD in the glucose and glycogen compartments and 0-10% SD in the glucose-phosphate and UDPG compartments, the hepatic response predicted by the minimal model was virtually free of the added error, and the model parameters were found to be within 30% of their true values. When the minimal model was used to interpret the experimental response to an increase in glucose concentration it predicted that: (1) glucokinase can phosphorylate glucose at rates similar to maximal rates of net glycogen synthesis; (2) futile cycling at the glycogen/glucose-1-phosphate level can limit glycogen synthesis; and (3) glucose-6-phosphatase inhibition by glucose has a significant role in net glycogen synthesis.
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PMID:A minimal model of liver glycogen metabolism; feasibility for predicting flux rates. 325 24

Adenylate cyclase (AC) activity was demonstrated histochemically using adenylate-(beta,gamma-methylene)diphosphate as substrate in cryostat sections of livers from 45 rats treated for 7-10 weeks with N-nitrosomorpholine (NNM) (120 mg/l drinking water) and from nine untreated control rats. The enzyme patterns of normal tissue, preneoplastic and neoplastic lesions were characterized and correlated with the morphologically defined stages of tumour development in the liver. Light microscopically, the enzyme activity of normal tissue was restricted to the plasma membrane, and was most pronounced along the bile canaliculi of the hepatocytes. In glycogen storage foci and mixed cell foci induced by NNM no, or only very weak, AC activity was visible. In the cells of neoplastic nodules and hepatocellular carcinomas AC activity was also clearly reduced. However, in small parts of the plasma membrane which lined lumina resembling normal bile canaliculi and in cytoplasmic vesicles closely associated with these structures, some AC activity was occasionally detected by light and electron microscopy. Whereas the tissue of normal appearance surrounding the lesions showed a marked increase in AC activity in the presence of glucagon, forskolin and cholera toxin. AC activity in the preneoplastic and neoplastic liver lesions could not, or could only weakly, be stimulated by this treatment. As demonstrated in serial sections of the foci, the reduction in AC activity corresponded to changes in the activity of other enzymes studied earlier in the same model. Thus the reduction in AC activity was accompanied by a decrease in the activity of glucose-6-phosphatase and glycogen phosphorylase, and by an increase in the activity of glucose-6-phosphate dehydrogenase. The results support the concept that the focal changes in the activity of many enzymes (including those of carbohydrate metabolism) during hepatocarcinogenesis are the consequence of aberrations in superordinate regulatory mechanisms of cell metabolism.
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PMID:Loss of adenylate cyclase activity in preneoplastic and neoplastic lesions induced in rat liver by N-nitrosomorpholine. 369 88

Insulin resistance has been measured in man by nonsteady state tracer methodology. Increase in overall glucose utilization and suppression of glucose production was measured when hyperglycemia was achieved either by infusing glucagon or glucose. With the first method, insulin resistance was assessed in obese man and in lean hypertriglyceridemic patients. With the second method, insulin resistance was assessed in lean mild type II diabetics. These methodologies can only assess deficiences in overall glucose utilization and glucose production, but cannot delineate the defect in glucose uptake by the liver. However, if a given metabolic event is essentially characteristic of only one organ, metabolic abnormalities specific to that organ can be detected in vivo provided there is a probe specific to that metabolic pathway. Therefore, in lean mild type II diabetics the liver glucose futile cycle was assessed by a double tracer method. Previously it was shown that liver glucose futile cycling is increased in diabetic dogs. In healthy control subjects in basal state and during glucose infusion, the futile cycle could not be detected, but it represented a major part of glucose metabolism in liver of type II diabetics. It appears, therefore, that most of the glucose taken up by the liver during the glucose challenge in diabetics reenters the blood stream without being oxidized or polymerized. On the basis of these studies, it was concluded that excessive hyperglycemia in the diabetics during glucose infusion is due to a decrease in irreversible glucose uptake (impaired phosphorylation and futile cycling) and to a decrease in suppression of glucose production. The relative contribution of the liver and periphery to hyperglycemia seems to be almost equivalent. The mechanism behind the increased glucose cycle activity is not clear. It may be due to a relative decrease of glycogen synthase or increase in glucose-6-phosphatase or both. These observations in mild lean type II diabetics may have implications also in some other types of diabetes, since we have observed that futile cycling is even more marked in obese type II diabetics and that it could account in part for the diabetogenic effect of growth hormone in acromegalics.
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PMID:New probes to study insulin resistance in men; futile cycle and glucose turnover. 389 64

Genetically obese normotensive rats, LA/N-corpulent (cp), were fed ad libitum diets containing either 54% sucrose or cooked corn starch for 12 weeks. Twenty-four rats were used for the study; half were corpulent (cp/cp) and half were lean (cp/+ or +/+). Fasting levels of plasma insulin, glucose, corticosterone, glucagon and growth hormone, and activities of liver and epididymal fat pad glucose-6-phosphate dehydrogenase (G6PD), malic enzyme (ME), and liver and kidney glucose-6-phosphatase (G6Pase), fructose 1,6-diphosphatase (FDPase), and phosphoenolpyruvate carboxykinase (PEPCK) were measured. A significant phenotype effect was observed in insulin, corticosterone, growth hormone, and liver G6PD, ME, FDPase, and kidney PEPCK, G6Pase, FDPase, and epididymal fat pad G6PD and ME (corpulent greater than lean), and glucagon (lean greater than corpulent). Diet effect (sucrose greater than starch) was significant for plasma glucose, liver ME, and kidney G6Pase. Although not significant at the P less than 0.05 level, insulin, corticosterone, liver G6PD and FDPase and kidney FDPase tended to be higher in sucrose-fed rats. This study suggests that the corpulent rat is more lipogenic and gluconeogenic than the lean, and that the hormones responsible are effective in keeping both the lipogenic and gluconeogenic enzyme activity elevated.
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PMID:Hormonal and lipogenic and gluconeogenic enzymatic responses in LA/N-corpulent rats. 399 2

The continuous infusion of a low dose of glucagon (35 micrograms/kg/d, for 5 d) constitutes, in view of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities, a reliable experimental model of hyperglucagonemia. By conjunction of monooxygenase assays and immunoquantitation of specific isozymes of cytochrome P-450, the actual inducing ability of glucagon has been shown and it might explain some of the modifications of the drug metabolizing system in diabetic mice. The isozymic pattern of cytochrome P-450 of liver microsomes from diabetic mice appears very different from that produced by classical inducers.
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PMID:The effect of different hyperglucagonemic states on monooxygenase activities and isozymic pattern of cytochrome P-450 in mouse. 402 53

An 8-month-old female, maintained on breast feeding for 6 months, experienced numerous attacks of hyperventilation when weaned to baby food and was admitted with severe lactic acidosis (20 mM) and hypoglycemia. Physical examination was negative except for hepatomegaly. Fasting (18 hr) after stabilization on a high carbohydrate diet resulted in hypoglycemia (plasma glucose 40 mg/100 ml), lactic acidosis (6-10 mM), and a rise in plasma alanine. Glucagon produced a glycemic response after 6 hr, but not after 18 hr fasting. Intravenous galactose increased plasma glucose (Delta 45 mg/100 ml) but intravenous fructose, glycerol, and alanine caused a 40-50% fall in plasma glucose and a significant rise in lactate (Delta 3-4 mM). Liver biopsy showed fatty infiltration. Liver slices incubated with galactose, lactate, fructose, alanine, or glycerol converted only galactose to glucose. Hepatic glycolytic intermediates were increased below the level of fructose-1,6-diphosphate and decreased above. Hepatic phosphorylase, glucose-6-phosphatase, amylo-1,6-glucosidase, phosphofructokinase, fructose-1-phosphate aldolase, and fructose-1,6-diphosphate aldolase levels were normal, but no fructose-1,6-diphosphatase (FDPase) activity was detected. Further studies on the liver homogenate of this patient revealed the presence of an acid-precipitable activator of FDPase. Normal plasma glucose and lactate levels were maintained on an 800 cal diet of 66% carbohydrate (sucrose and fructose excluded). 5% protein, and 20% fat. When carbohydrate was reduced to 35% and protein or fat increased to 23 and 53% respectively, lactic acidosis and hypoglycemia recurred. These studies show that a deficiency of FDPase produced infantile lactic acidosis and hypoglycemia and can be controlled by an appropriate diet.
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PMID:Hepatic fructose-1,6-diphosphatase deficiency. A cause of lactic acidosis and hypoglycemia in infancy. 434 Oct 15

Glucagon (0.04-0.09 mg/kg/min) was given intravenously for either 2 or 3 min to eight patients with fasting-induced hypoglycemia. One child had hepatic phosphorylase deficiency, two children had glucose-6-phosphatase deficiency, two children had debrancher enzyme (amylo-1,6-glucosidase) deficiency, and two children and one adult had decreased hepatic fructose-1,6-diphosphatase (FDPase) activity. Liver biopsy specimens were obtained before and immediately after the glucagon infusion. The glucagon caused a significant increase in the activity of FDPase (from 50+/-10.0 to 72+/-11.7 nmol/mg protein/min) and a significant decrease in the activities of phosphofructokinase (PFK) (from 92+/-6.1 to 41+/-8.1 nmol/mg protein/min) and pyruvate kinase (PK) (from 309+/-39.4 to 165+/-23.9 nmol/mg protein/min). The glucagon infusion also caused a significant increase in hepatic cyclic AMP concentrations (from 41+/-2.6 to 233+/-35.6 pmol/mg protein). Two patients with debrancher enzyme deficiency who had biopsy specimens taken 5 min after the glucagon infusion had persistence of enzyme and cyclic AMP changes for at least 5 min. One child with glucose-6-phosphatase deficiency was given intravenous glucose (150 mg/kg/min) for a period of 5 min after the glucagon infusion and biopsy. The plasma insulin concentration increased from 8 to 152 muU/ml and blood glucose increased from 72 to 204 mg/100 ml. A third liver biopsy specimen was obtained immediately after the glucose infusion and showed that the glucagon-induced effects on PFK and FDPase were completely reversed. The glucagon infusion caused an increase in hepatic cyclic AMP concentration from 38 to 431 pmol/mg protein but the glucose infusion caused only a slight decrease in hepatic cyclic AMP concentration (from 431 to 384 pmol/mg protein), which did not appear to be sufficient to account for the changes in enzyme activities. Hepatic glucose-6-phosphatase and fructose-1,6-diphosphate aldolase activities were not altered by either the glucagon or the glucose infusion in any patients. Cyclic AMP (0.05 mmol/kg) was injected into the portal vein of adult rats and caused enzyme changes similar to those seen with glucagon administration in humans. Our findings suggest that rapid changes in the activities of PFK, PK, and FDPase are important in the regulation of hepatic glycolysis and gluconeogenesis, respectively, in humans and that cyclic AMP may mediate the glucagon- but probably not the glucose-insulin-induced changes in enzyme activities.
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PMID:The rapid changes of hepatic glycolytic enzymes and fructose-1,6-diphosphatase activities after intravenous glucagon in humans. 435 16

The metabolic response to the first fast experienced by all mammals has been studied in the newborn rat. Levels of fuels and hormones have been compared in the fetal and maternal circulations at term. Then, after cesarean section just before the normal time of birth, sequential changes in the same parameters were quantified during the first 16 h of the neonatal period. No caloric intake was permitted, and the newborns were maintained at 37 degrees C. Activities of three key hepatic enzymes involved in glucose production were estimated. Marked differences in maternal and fetal hormones and fuels were observed. Lower levels of glucose, free fatty acids, and glycerol but higher levels of lactate, alpha-amino nitrogen, alanine, and glutamine were present in the fetus. Pyruvate, glutamate, and ketone bodies were not significantly different. The combination of a strikingly higher fetal immunoreactive insulin and a slightly lower immunoreactive glucagon (pancreatic) resulted in a profound elevation in the insulin-to-glucagon ratio, a finding consistent with an organism in an anabolic state. The rat at birth presents a body composition with respect to fuels available for mobilization and conversion which is dominated by carbohydrate and protein, since little fat is present. However, at birth a transient period of hypoglycemia occurred, associated with a rapid fall in insulin and rise in glucagon, causing reversal of the insulin-to-glucagon relationship toward ratios such as were observed in the mother. After a lag period, hepatic activities of phosphorylase, glucose-6-phosphatase, and phosphoenolpyruvate carboxykinase increased. Concurrent with these enzyme changes, the blood glucose returned to levels at or above those of the fetus. Interestingly, the fall observed in levels of the gluconeogenic precursors, lactate and amino acids, preceded the rise in enzyme activities and restoration of blood glucose. After 4 h, however, hypoglycemia recurred, during a period of decreasing hepatic glycogen content and blood lactate, pyruvate, and glycerol levels but of stable or increasing amino acid concentrations. Hepatic gluconeogenesis in this phase of depleted glycogen stores was insufficient to maintain euglycemia. Substrates derived from fat showed early changes of smaller magnitude. The rise in free fatty acids which occurred was less than twofold the value at birth, though this rise persisted up to 6 h. Whereas glycerol rose transiently, acetoacetate did not change and beta-hydroxybutyrate concentration fell. Both ketone bodies showed a marked rise at 16 h. at a time of diminished free fatty acid levels. Plasma growth hormone, though higher in the fetal than the maternal circulation, showed no consistent change during the period of observation. The changes in levels of the endocrine pancreatic hormones at birth were appropriate in time, magnitude, and direction to be implicated as prime regulators of the metabolic response during the neonatal period in the rat.
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PMID:Fuels, hormones, and liver metabolism at term and during the early postnatal period in the rat. 475 Apr 49


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