Effects of hypo and hyperthyroidism on the response to glucose loading of blood glucose, ketones and insulin and liver glycogen as studied in the fasted rat

After receiving an i.p. glucose load, 24 h fasted thyroidectomized rats showed a progressive increase in blood glucose and a slow decrease in blood ketone bodies. Both liver glycogen and plasma insulin levels showed no differences within 60 min of the glucose administration. It is suggested that the glucose intolerance in these animals is partly due to an insulin deficiency. Thyroidectomized rats treated daily with 25 microgram of L-thyroxine/100 g body weight for 40 days responded to the glucose test with a supranormal and more persistent elevation of blood glucose but with a faster and a greater fall in blood ketone bodies, as compared to controls. Sixty min after the glucose loading, liver glucogen levels were lower and plasma insulin were slightly higher than controls. It is suggested that a diminished extraction of glucose during transhepatic passage can be responsible for the impaired glucose tolerance observed in the hyperthyroid animals.     

Effects of iodine upon the structure and function of mitochondria

The influence of iodine in its positive and negative monovalent form upon the oxygen consumption in euthyroid and thyroidectomized rats and the oxidative phosphorylation in liver mitochondria isolated from both groups of animals, as well as the spontaneous swelling and total ATPase activity of mitochondria have been studied.It was established that the administration of ICI increased the oxygen consumption of normal and thyroidectomized rats while under the same conditions no effect was found with NaI. IBr stimulated the oxygen consumptionin vitro in liver mitochondria isolated both from normal and thyroidectomized rats and decreased the P/O ratio while NaI had no effect. I₂ and IBr increased the swelling and inhibited the ATPase activity of isolated rat liver mitochondria, while these effects were not observed when KI was used. The thyroidstatic 1-methyl-2-mercaptoimidazol decreased the stimulating effect of iodine upon the swelling of mitochondria and to a certain extent lowered its inhibiting effect upon the ATPase activity.It is concluded that iodine in its positive monovalent form has a thyroxine-like effect upon the structure and function of isolated rat liver mitochondria, as well asin vivo upon the respiration of euthyroid and thyroidectomized rats.     

Enzymatic,metabolic and secretory perturbations in pancreatic islets of thyroidectomized rats

In thyroidectomized rats, the activity of FAD-linked glycerophosphate dehydrogenase was severely diminished in liver homogenates but not affected significantly in pancreatic islet homogenates, whilst the activity of 2-ketoglutarate dehydrogenase was decreased modestly in both liver and islet homogenates. Likewise, in intact islets of thyroidectomized rats, the generation of³HOH from [2-³H]glycerol was not decreased, and the ratio between oxidative and total glycolysis not significantly lower than in islets from sham-operated rats, at least in the presence of a high concentration of D-glucose. Nevertheless impaired oxidation of both D-[3,4-¹⁴C]glucose and D-[6-¹⁴C]glucose was observed in islets of thyroidectomized rats, the relative magnitude of such a decrease being more pronounced at a low than at a high D-glucose concentration. Such metabolic anomalies coincided with a lower level of plasma insulin and a decreased output of insulin by islets incubated at low (2·8 mM ), but not higher, concentrations of D-glucose. It is concluded that hypothyroidism does not mimic the deficiency in islet FAD-linked glycerophosphate dehydrogenase activity found in rats with inherited or acquired non-insulin-dependent diabetes.     

Regulation of oxidative phosphorylation by adrenaline and insulin, effect of the insulin-dependent cytoplasmic factor

The insulin-dependent cytoplasmic factor-regulator (IDR) was shown to inhibit pyruvate and succinate oxidation by the rat liver mitochondria. In view of the fact that insulin increases and adrenaline decreases IDR activity in the liver cytoplasm it is suggested that oxidation of the substrate in mitochondria in vivo is regulated by changes in IDR content in cytoplasm. It was shown that adrenaline-activated oxidation apart from decreased activity of IDR in cytoplasm is induced by a different mechanism not related to IDR content.     

Role of thyroid hormone in intermediary metabolism of propranolol or alloxan-treated Calotes versicolor.

Administration of L-thyroxine (T4) to thyroidectomized Calotes versicolor significantly increased the activity of glucose-6-phosphatase (G-6-Pase) (liver and kidney), the concentrations of blood glucose and total protein (liver and kidney), and decreased hepatic cholesterol when compared to thyroidectomized lizards. Propranolol injections in thyroidectomized lizards increased the cholesterol concentration and did not change the other parameters. The activity of G-6-Pase and blood glucose content was stimulated, whereas the total protein and cholesterol contents were decreased after alloxan treatment. Administration of T4 to thyroidectomized animals pretreated with propranolol or alloxan significantly elevated the activity of G-6-Pase, the concentrations of blood glucose, and total protein, and reduced hepatic cholesterol level when compared to drug-treated lizards. From the results, it is evident that thyroid hormone has an independent stimulatory influence on intermediary metabolism in C. versicolor irrespective of the involvement of adrenaline or insulin.     

A minimal model of insulin secretion and kinetics to assess hepatic insulin extraction

The liver is the principal site of insulin degradation, and assessing its ability to extract insulin is important to understand several pathological states. Noninvasive quantification of hepatic extraction (HE) in an individual requires comparing the profiles of insulin secretion (ISR) and posthepatic insulin delivery rate (IDR). To do this, we propose here the combined use of the classical C-peptide minimal model with a new minimal model of insulin delivery and kinetics. The models were identified on insulin-modified intravenous glucose tolerance test (IM-IVGTT) data of 20 healthy subjects. C-peptide kinetics were fixed to standard population values, whereas insulin kinetics were assessed in each individual, along with IDR parameters, thanks to the presence of insulin decay data observed after exogenous insulin administration. From the two models, profiles of ISR and IDR were predicted, and ISR and IDR indexes of beta-cell responsivity to glucose in the basal state, as well as during first- and second-phase secretion, were estimated. HE profile, obtained by comparing ISR and IDR profiles, showed a rapid suppression immediately after the glucose administration. HE indexes, obtained by comparing ISR and IDR indexes, indicated that the liver is able to extract 70 +/- 9% of insulin passing through it in the basal state and 54 +/- 14% during IM-IVGTT. In conclusion, insulin secretion, kinetics, and hepatic extraction can be reliably assessed during an IM-IVGTT by using insulin and C-peptide minimal models.     

Biochemical and stereological analysis of rat liver mitochondria in different thyroid states

The concentrations of the inner mitochondrial membrane markers cardiolipin and cytochrome alpha have been measured in liver homogenates and in purified mitochondria after thyroxine administration to thyroidectomized and normal rats. The biochemical results have been correlated with stereological electron micrographic analyses of hepatocytes in liver sections, and of isolated mitochondrial pellets. There were progressive and parallel increases in homogenate and mitochondrial cardiolipin concentration, and in mitochondrial cytochrome alpha concentration, after administration of 20 microgram of thyroxine on alternate days to thyroidectomized rats, and of 300 microgram on alternate days to normal rats. Electron microscope measurements showed marked differences in the shape of the mitochondria and in the number of cristae in different thyroid states. Hypothyroid mitochondria were shorter and wider than controls, and hyperthyroid mitochondria longer but of similar width. Mitochondrial volume per unit cell volume was virtually unchanged in hypo- and hyperthyroid animals. The most striking changes were a decrease in the area of the inner membrane plus cristae in thyroidectomized rats, and a substantial increase in membrane area after thyroxine administration. The biochemical and electron micrographic results indicate that, in rat liver, thyroid hormone administration leads to a selective increase in the relative amount of mitochondrial inner membranes, with little or no change in the mitochondrial volume per unit cell volume, or in total mitochondrial protein per unit total cell protein.     

Effect of thryoidectomy on the properties of rat liver mitochondria during liver regeneration]

The properties of regenerating rat liver mitochondria are not changed by the thyroidectomy. Thus, hepatectomy induces, in thyroidectomized rats as in normal ones, a decrease in the activity of the outer membrane enzymes, a stimulation of oxidative phosphorylations and an increase of the turn over rate of mitochondrial proteins. Thyroid hormones do not seem to have a major effect upon the liver regeneration mechanism.     

Evidence for the rapid direct control both in vivo and in vitro of the efficiency of oxidative phosphorylation by 3,5,3''-tri-iodo-L-thyronine in rats.

1. Examination of the distribution of L-tri-iodothyronine among rat liver tissue fractions after its intravenous injection into thyroidectomized rats focused attention on mitochondria at very short times after administration. By 15 min this fraction contained 18.5% of the tissue pool; however, the content had decreased sharply by 60 min and even further over the next 3 h. By contrast, the content in all other fractions was constant or increased over 4 h. About 60% of tissue hormone was bound to soluble protein. 2. Mitochondria isolated from thyroidectomized rats showed P/O ratios that were about 50% of those found in normal controls, with both succinate and pyruvate plus malate as substrates. There was no evidence of uncoupling; the respiratory-control ratio was about 6. 3. Mitochondria isolated 15 min after injection of tri-iodothyronine into thyroidectomized rats showed P/O ratios and respiratory-control ratios that were indistinguishable from those obtained in mitochondria from euthyroid animals. The oxidation rate was, however, not restored. 4. Incubation of homogenates of livers taken from thyroidectomized animals injected with L-tri-iodothyronine before isolation of the mitochondria restored the P/O ratio to normal; by contrast, direct addition of hormone to isolated mitochondria had no effect. The role of extramitochondrial factors in rapid tri-iodothyronine action is discussed. 5. Possible mechanisms by which tri-iodothyronine might rapidly alter phosphorylation efficiency are considered: it is concluded that control of adenine nucleotide translocase is unlikely to be involved. 6. The amounts of adenine nucleotides in liver were measured both after thyroidectomy and 15 min after intravenous tri-iodo-thyronine administration to thyroidectomized animals. The concentrations found are consistent with a decreased phosphorylation efficiency in thyroidectomized animals. Tri-iodothyronine injection resulted in very significant changes in the amounts of ATP, ADP and AMP, and in the [ATP]/[ADP] ratio, consonant with those expected from an increased efficiency of ADP phosphorylation. This suggests that the changes seen in isolated mitochondria may indeed reflect a rapid response of liver in vivo to tri-iodo-thyronine.     

(A1-D-alanine) insulin (author's transl)]

Starting from porcine insulin, A1-glycine was substituted by D-alanine and by L-alanine for comparison. Replacement of A1-glycine by L-alanine revealed the known decrease in the biological activity. [A1-D-Alanine]insulin, however, has the same blood sugar lowering activity as insulin and is slightly more active in its influence on the glucose uptake into the rat diaphragm. The specific binding to insulin receptors of rat liver is decreased as, compared to insulin, but increased as compared to the L-alanine analogue.     

Endocrine-metabolic relations in rats with genetic arterial hypertension

Levels of triiodothyronine, thyroxine, insulin, glucose and free fatty acids in the blood; contents of adrenaline, noradrenaline in adrenals and glycogen in the liver; activity of phenylethanolamine-N-methyltransferase in adrenals, hexokinase and glucose-6-phosphatase in the liver were studied in male Wistar rats and rats with inherited stress-induced arterial hypertension /ISIAH/. It was found that genetically caused rise of hypophyseal-thyroid systems activity in ISIAH-rats leads to a decrease of insulin blood level, activation of lipolysis and breach of glucose tolerance.     

Influence of thyroid status on the electrophoretic pattern of rat liver mitochondrial proteins]

Liver mitochondria were isolated from normal and thyroidectomized rats and their protein components analyzed by polyacrylamide gel electrophoresis. In whole mitochondria 35 protein fractions with MW ranging from 10,000 to 135,000 were characterized. In the absence of thyroid hormone secretion, the amount of a MW 54,000 fraction was always decreased. Injection of small doses of 3,5,3'-triiodo-L-thyronine to the thyroidectomized animal restored the quantity of that protein fraction to normal. Isolated outer mitochondrial membranes showed the presence of 20 protein fractions. These fractions revealed no change after thyroidectomy. The mitoplast, which contained 35 fractions, exhibited a decrease of the MW 54,000 component in thyroidectomized rats. The mitoplast was separated into several fractions. Water soluble matrix proteins presented molecular weights ranging between 40,000 and 55,000. Proteins, which were slightly bound to the inner mitochondrial membrane and could be extracted by KCl, presented molecular weights between 25,000 and 45,000. Structural proteins showed a principal specific component of MW equals 23,000. Electrophoretic patterns obtained with these submitochondrial fractions were similar in normal and thyroidectomized animals. The mitoplast fraction which contained the insoluble cytochromes (a, a3, b, c1) was isolated ; its principal constituent, of MW 54,000 was significantly decreased after thyroidectomy. Thus, the lack of thyroid hormone secretion lowered the level of a protein constituent bound to the inner membrane of liver mitochondria. The synthesis of this constituent could be controlled by mitochondrial nucleic acids.     

The metabolism of glucose in diaphragm muscle from normal rats, from streptozotocin-treated diabetic rats and from rats treated with anti-insulin serum

1. The metabolism of [U-¹⁴C]glucose by the isolated diaphragm muscle of normal rats, rats rendered diabetic with streptozotocin and rats with transitory insulin deficiency after an injection of anti-insulin serum was studied. 2. The incorporation of [¹⁴C]glucose into glycogen and oligosaccharides was significantly decreased in the diabetic diaphragm muscle and in the muscle from rats treated with anti-insulin serum. 3. Neither diabetes nor transitory insulin deficiency influenced the oxidation of glucose, or the formation of lactate and hexose phosphate esters from glucose. 4. Insulin fully restored the incorporation of glucose into glycogen and maltotetraose in the diabetic muscle, but the incorporation into oligosaccharides, although increased in the presence of insulin, was significantly lower than the values obtained with normal diaphragm in the presence of insulin.     

Study on the effect of a high fat diet on diaphragm and liver glycogen and glycerides in the rat

The present work was undertaken to study the effect of nutritional obesity induced by a high fat diet on the consumption of glycogen and glycerides in rat liver and diaphragm. Groups of rats were fed for five weeks from weaning either a fat-rich-carbohydrate (CHO)-poor diet, or a CHO-rich-fat-poor diet. Basal plasma glucose and free fatty acids (FFA) were significantly increased in the animals adapted to the fat-rich diet. Half of the rats were submitted to a 48-h fast. After fast, basal plasma glucose and immunoreactive insulin (IRI) fell significantly, whereas plasma FFA levels were higher than in the group fed the CHO-rich-fat-poor diet. In the liver, glycogen concentration fell in both groups after fast, with a glycogen breakdown of 1930 +/- 244 mumole glycogen glucose/liver in the fat-fed group vs 4636 +/- 216 mumole/liver in the CHO-fed group. Glycerides fell by 750 +/- 68 mumole glyceride glycerol/liver in the fat-fed rats while remaining unchanged (increased by 82 +/- 57 mumole/liver) in the CHO-fed group. In the diaphragm glycogen concentration also fell in both groups, with a glycogen breakdown of 6.0 +/- 0.3 mumole glycogen glucose/g wet tissue in the fat-fed rats vs 15.2 +/- 1.4 mumole/g wet tissue in the CHO-fed animals. Glycerides fell by 23.1 +/- 4.0 mumole/g wet diaphragm in the CHO-fed animals. The lower breakdown of glycogen in both liver and diaphragm of fat-fed rats demonstrates a decreased utilization of glycogen during fast, with energy consumption originating in larger part from triglycerides.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence that the decrease in liver glycogen is associated with the exercise-induced increase in IGFBP-1.

The purpose of the present study was to test the hypothesis that the exercise-induced increase in insulin-like growth factor binding protein (IGFBP)-1 is not always linked to a decrease in blood glucose level and to examine whether the decreasing levels of liver glycogen during exercise may be associated with the increase in IGFBP-1. Three groups of rats were submitted to a 70-min treadmill exercise. One group of rats was fed normally, and the two other groups had their food intake restricted by 50% (50% fast) the night before the experiment. One of these two 50% fasted groups of rats was infused (intravenously) with glucose throughout exercise to maintain euglycemia. Exercise in noninfused 50% fasted rats, compared with the normally fed rats, resulted in significantly lower blood glucose (minute 70) and insulin levels, significantly lower liver glycogen content, no change in IGF-I, and significantly higher increases in free fatty acid, glycerol, beta-hydroxybutyrate, and IGFBP-1. Maintenance of euglycemia during exercise in glucose-infused 50% fasted rats reduced to a large extent the decrease in insulin levels but only slightly attenuated the lipid response and the IGFBP-1 response seen in noninfused 50% fasted rats. Comparisons of all individual liver glycogen and IGFBP-1 values revealed that liver glycogen values were highly (P < 0.001) predictive of the IGFBP-1 response during exercise (R = 0.564). The present results indicate that the IGFBP-1 response during exercise is not always linked to a decrease in plasma glucose and suggest that the increase in IGFBP-1 during exercise may be related to the decrease in liver glycogen content.     

Lithium's effects on rat liver glucose metabolism in vivo

Oral administration of lithium carbonate to fed-healthy rats strongly decreased liver glycogen content, despite the simultaneous activation of glycogen synthase and the inactivation of glycogen phosphorylase. The effect seemed to be related to a decrease in glucose 6-phosphate concentration and to a decrease in glucokinase activity. Moreover, in these animals lithium markedly decreased liver fructose 2,6-bisphosphate, which could be a consequence of the fall in glucose 6-phosphate and of the inactivation of 6-phosphofructo-2-kinase. Liver pyruvate kinase activity and blood insulin also decreased after lithium administration. Lower doses of lithium carbonate had less intense effects. Lithium administration to starved-healthy and fed-streptozotocin-diabetic rats caused a slight increase in blood insulin, which was simultaneous with increases in liver glycogen, glucose 6-phosphate, and fructose 2, 6-phosphate. Glucokinase, 6-phosphofructo-2-kinase, and pyruvate kinase activities also increased after lithium administration in starved-healthy and fed-diabetic rats. Lithium treatment activated glycogen synthase and inactivated glycogen phosphorylase in a manner similar to that observed in fed-healthy rats. Glycemia was not modified in any group of animals. These results indicate that lithium acts on liver glycogen metabolism in vivo in at least two different ways: one related to changes in insulinemia, and the other related to the direct action of lithium on the activity of some key enzymes of liver glucose metabolism.     

Insulin receptor exon 11+/- is expressed in Zucker (fa/fa) rats, and chlorogenic acid modifies their plasma insulin and liver protein and DNA

In vivo studies confirmed that chlorogenic acid (CGA) improved glucose tolerance and mineral pool distribution in obese Zucker (fa/fa) rats. We found a significant decrease (P<.05) in postprandial blood glucose concentrations, which may have been due to an improved sensitivity to insulin. Impaired glucose tolerance and insulin resistance have been associated with differences in the hepatic mRNA expression of the spliced variants of the insulin receptor at exon 11. Spliced variants of the insulin receptor have not been studied in obese Zucker (fa/fa) rats, and no information exists about the effects of CGA in vivo as a possible insulin sensitizer. Thus, we studied the in vivo effect of CGA on plasma insulin concentrations during a glucose tolerance test, liver protein and DNA concentrations, the hepatic activity of glucose-6-phosphatase (G-6-PASE) and the mRNA expression of the two variants of the insulin receptor at exon 11. Zucker (fa/fa) rats were implanted with jugular vein catheters. Chlorogenic acid was administered (5 mg/kg body weight per day) for 3 weeks via intravenous infusion. In the CGA-treated group, areas under the curve (AUC) for blood glucose and plasma insulin improved (P<.005), and the protein and DNA concentrations in the liver increased (P<.05). No significant differences (P>.05) were found between groups for the hepatic G-6-PASE activity. The insulin receptor exon 11(+) and the exon 11(-) variants were expressed in the liver of Zucker (fa/fa) rats without significant changes (P>.05). Chlorogenic acid improved some cellular mechanisms that are stimulated by insulin.     

Oxymatrine ameliorates insulin resistance in rats with type 2 diabetes by regulating the expression of KSRP,PETN, and AKT in the liver

Insulin resistance plays a key role in the development and progression of type 2 diabetes mellitus (T2DM). Recent studies found that insulin resistance was associated with the dysfunction of KH-type splicing regulatory protein (KSRP) expression and AKT pathway, and that oxymatrine possesses an antidiabetic effect. The aim of the present study was to investigate whether the protection of oxymatrine against T2DM was associated with the modulation of the KSRP expression and AKT pathway. Sprague-Dawley rats were fed a high-fat diet and injected with streptozotocin intraperitoneally to induce T2DM, which led to an increase in blood glucose levels and insulin resistance, and a decrease in insulin sensitivity and glycogen synthesis concomitant with KSRP downregulation, PTEN upregulation, and AKT phosphorylation deficiency. The administration of oxymatrine decreased blood glucose levels and insulin resistance, increased insulin sensitivity, and improved glycogen synthesis in the liver of T2DM rats, through a reversal in the expression of KSRP, PTEN, and AKT. On the basis of these observations, we concluded that oxymatrine can protect T2DM rats from insulin resistance through the regulation of the KSRP, PETN, and AKT expression in the liver.