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PubMedDate not supplied

Triiodothyronine effect on some parameters of carbohydrate metabolism in rat blood and liver. I. In vivo effect of triiodothyronine on liver glycogen content, blood metabolites and serum glycogenolytic activity.

Short (7 days) T3-treatment has no influence on the plasma glucose and FFA concentration and blood lactate level, as well as on the hepatic glycogen content in the rats. The rise in T3 levels, observed in our study, was accompanied by a fall in T4 concentrations, indicating suppression of the endogenous T4 production. On the other hand, glycogenolytic activity of rat serum in vitro is the highest in the system: control liver slices-serum of rats pretreated with T3 as compared to the system: control liver slices-control serum. These observations may lead to conclusions, that serum of rats pretreated with T3 contains factors exhibiting the greater ability to mobilize glucose from liver slices than the control serum (euthyroid). The possibility, that pretreatment with T3 may cause a decrease in the number and/or affinity of beta-adrenergic receptors in the rat liver, is discussed.

Animals↗
PubMed1983

The alpha particulate liver glycogen. A morphometric approach to the kinetics of its synthesis and degradation.

Electron micrographs of rat hepatocytes with a glycogen content between 0.36 and 2.55% (w/w) were submitted to morphometrical analysis. From the number and size of glycogen profiles, the distribution of radius and volume of glycogen alpha particles were computed. The 7-fold difference in glycogen content was accompanied by an only 1.8-fold increase in the mean volume of the particles while their number increased by a factor of 4. On the basis of these observations, it is proposed that the population of glycogen particles can be divided in two groups. The first one is made of growing particles, still associated with glycogen synthase; they are the only particles present at low glycogen concentration and their number is limited. Application of a simple mathematical model allows to estimate their number in hepatocytes as 49 X 10(12) particles . ml-1. The second group is made of glycogen particles which have reached their maximal size and the number of which is in principle unlimited. The maximal particle size is estimated to be 0.36 X 10(-15) ml, corresponding to an average molecular weight of 178 X 10(6). The average molecular weight of glycogen, as measured from the actual size of the particles, varied from 89 X 10(6) to 161 X 10(6).

Animals↗
PubMed1985

Intravenous thiobarbital anaesthesia for determination of liver glycogen phosphorylase activity in rats subjected to various forms of stress.

Glycogen phosphorylase activity was determined in rat livers obtained by laparotomy in thiobarbital (Inactin, PROMONTA) anaesthesia induced by injection of the drug via a polyethylene catheter into a jugular vein as described previously [Németh et al. 1983a]. Intact rats and animals exposed to open field stress without or after i.p. injection of the alpha blocker phentolamine (Regitine, CIBA; 20 mg kg-1, 90 min before stress) or the beta blocker propranolol (Inderal, ICI; 2 mg kg-1, 30 min before stress) were studied. In stressed animals a net increase of phosphorylase activity was observed. This response was abolished after alpha blockade, while after beta blockade it was potentiated. In a further series on animals subjected to the same type of anaesthesia, the activating effect of immobilization stress on phosphorylase activity was confirmed in both fed and fasted animals, the response of the latter issuing from a lower initial level but being of the same extent as in the fed rats.

Animals↗
PubMed1979

Rat liver glycogen metabolism in the perinatal period.

The correlation between blood glucose levels, the concentration of glycogen, the activities of glycogen synthase and phosphorylase and their respective kinases and phosphatases was examined in liver of rat fetuses between day 18 of gestation and one day after birth. Between day 18 and 21 there is a rapid increase in the concentration of glycogen and in the activity of synthase a and a much slower increase in the activity of phosphorylase a. The activity of the respective kinases increased rapidly during this period and reached maximum on day 21. The activity of synthase phosphatase and phosphorylase phosphatase increased after day 18, to reach a maximum on day 19 and 20, respectively, but decreased again towards day 21. The possibility that the changes in glycogen concentration and enzyme activities were related to an effect of glucose or AMP on the respective phosphatases was considered. It was found that the Km of phosphorylase phosphatase for glucose in the prenatal period was 5--7 mM, as in the adult. Since the level of blood glucose during this period was constant (2.8 mM), an effect of glucose on phosphatase activity seems unlikely. AMP concentration increased between day 18 and 21 from 6--15 nmol/g. In view of the low level of phosphorylase a activity during this period, the increase in AMP concentration is not considered to be important in the regulation of glycogen breakdown at this time. Immediately after birth blood glucose levels dropped to 5 mg/dl. This was accompanied by a rapid decrease in glycogen concentration and in the activity of glycogen synthase and a rise in phosphorylase activity. Blood glucose levels returned to the initial level within 1 h after birth, whereas the changes in glycogen concentration and enzyme activities continued for at least 3 h after birth. On day 22 all parameters examined had reached the level found in adult rat liver. It is suggested that the rapid changes observed immediately after birth are due to an effect of gypoglycemia mediated by hormones and cannot be ascribed to direct effects of metabolites on the enzyme systems involved.

Animals↗
PubMedDate not supplied

Effects of chronic ethanol ingestion on male and female rat liver glycogen phosphorylase phosphatase.

The effects of chronic ethanol ingestion on the interconversion of the active to the inactive form of glycogen phosphorylase by phosphorylase phosphatase was studied. Male and female rats also were compared. Chronic ethanol feeding decreased phosphorylase a and total phosphorylase activity in male rats. In females, no change was observed in phosphorylase a, whereas total phosphorylase activity was increased 73%. This was found to correlate with the relative activities of phosphorylase phosphatase. The data show differences between the two sexes with regard to the AMP inhibition of phosphorylase phosphatase and the caffeine stimulation of the phosphatase. Ethanol markedly enhanced the AMP inhibition of the phosphatase in males but had no effect in females. Further studies in females showed that ethanol completely obliterated the well documented stimulation of the phosphatase by caffeine; however, it did not alter the caffeine effect in males. These data suggest possible alterations in the tertiary structure of phosphorylase a.

Adenosine Monophosphate↗
PubMed1989

Effect of dietary protein on in vivo insulin action and liver glycogen repletion.

To investigate the influence of dietary manipulation on in vivo glucose metabolism, we pair fed normal rats for 10 days with one of three diets: 1) high protein-low carbohydrate (Hi-PN) (n = 20); 2) intermediate protein (I-PN) (n = 11); and 3) low protein-high carbohydrate (Lo-PN) (n = 18). Fasting glucose, postmeal plasma glucose, and insulin concentrations were as follows: 118 +/- 2 mg/dl, 138 +/- 2 mg/dl, and 4.0 +/- 0.2 ng/ml in Hi-PN; 111 +/- 3 mg/dl, 147 +/- 3 mg/dl, and 5.1 +/- 0.3 ng/ml in I-PN; 102 +/- 2 mg/dl, 162 +/- 2 mg/dl, and 6.0 +/- 0.2 ng/ml in Lo-PN, respectively. Basic hepatic glucose production (HGP) was 6.6 +/- 0.2 in Hi-PN, 6.1 +/- 0.2 in I-PN, and 5.6 +/- 0.1 mg.kg-1.min-1 in Lo-PN. Insulin sensitivity was assessed with the euglycemic clamp using two insulin infusion rates: 2 and 4 mU.kg-1.min-1. The rate of glucose disappearance was 14.8 +/- 0.4 and 25.3 +/- 0.7 in Hi-PN, 15.3 +/- 0.4 and 26.9 +/- 0.5 in I-PN, and 16.1 +/- 0.6 and 31.5 +/- 0.5 mg.kg-1.min-1 in Lo-PN, respectively. HGP was suppressed by 86 in the 2- and by 90% in the 4-mU insulin clamp in the Lo-PN, whereas HGP was suppressed by 45 and by 79% in the two steps in the Hi-PN group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗