Biomedical subjects

L Morviducci

Publications and source records attributed to L Morviducci.

7 recordsLinked to original sources

PubMed2001

Acute hyperglycemia and acute hyperinsulinemia decrease plasma fibrinolytic activity and increase plasminogen activator inhibitor type 1 in the rat.

Decreased plasma fibrinolysis may contribute to accelerated atherothrombosis in diabetes. To observe whether hyperglycemia and hyperinsulinemia, common findings in type 2 diabetes, acutely affect plasma fibrinolysis in vivo, we evaluated plasma fibrinolysis (lysis of fibrin plates, free PAI-1 activity and t-PA activity) in the rat after a hyperglycemic euinsulinemic clamp (n=8), an euglycemic hyperinsulinemic clamp (n=7) or a saline infusion (n=15). Plasma fibrinolytic activity was sharply reduced after both the hyperglycemic and hyperinsulinemic clamps as compared to the respective controls (mean lysis areas on the fibrin plate, 139+/-21 vs. 323+/-30 mm2, p<0.001; 78+/-27 vs. 312+/-27 mm2 p<0.001, respectively). Plasma PAI-1 activity was greater after both hyperglycemic and hyperinsulinemic clamps as compared to saline infusion (6.6+/-2.6 vs. 1.6+/-0.6 IU/ml, p<0.001; 26+/-4 vs. 1.3+/-0.7 IU/ml, p<0.0001, respectively). Plasma t-PA activity was significantly reduced both after the hyperglycemic (0.36+/-0.15 vs. 2.17+/-0.18 IU/ml in controls, p<0.001) and the hyperinsulinemic (0.3+/-0.1 vs. 2.3+/-0.3 IU/ml in control, p<0.001) clamps. These data show that in vivo both acute hyperglycemia and acute hyperinsulinemia can decrease plasma fibrinolytic potential and that this is due to increased plasma PAI-1 and decreased free t-PA activities.

Animals↗

PubMed1999

Evidence for glucose/hexosamine in vivo regulation of insulin/IGF-I hybrid receptor assembly.

Hybrid receptors composed of an insulin alphabeta-hemireceptor and a type 1 IGF alphabeta-hemireceptor are formed in tissues expressing both molecules. We recently reported an increased hybrid receptor expression in skeletal muscle of type 2 diabetic patients that is inversely correlated with in vivo insulin sensitivity. It is unclear whether these changes were due to primary abnormalities or to secondary derangements acting in vivo, such as hyperglycemia. To address this, we determined abundance of hybrids in skeletal muscle from three groups of rats: controls, diabetic (90% pancreatectomy), and diabetic treated with phlorizin to normalize plasma glucose levels. We found that the abundance of hybrid receptors was higher in diabetic rats compared with control and phlorizin-treated diabetic rats (percentage of 125I-insulin bound versus total added radioactivity [B/T] = 1.8+/-0.11, 0.4+/-0.01, and 0.32+/-0.04, respectively; P < 0.0001). Fasting plasma glucose levels were positively correlated with hybrids abundance (r = 0.77, P < 0.002). Hybrid receptor protein content, assessed by immunoblotting, was 2.4-fold higher in diabetic rats as compared with control and phlorizin-treated diabetic rats. Because it has been shown that some of the regulatory effects of glucose may be mediated by the glucosamine pathway, we subsequently determined the effect of an in vivo glucosamine infusion on hybrid receptor formation. We found that abundance of hybrids was significantly higher in muscle from glucosamine-treated rats compared with control rats (B/T = 0.17+/-0.02 and 0.11+/-0.01, respectively; P < 0.009). Quantitation of hybrid content by immunoblotting revealed that their abundance was 1.9-fold higher in glucosamine-treated rats. The results demonstrate that 1) elevated glucose levels in diabetic rats are associated with increased expression of hybrid receptors in muscle, 2) correction of hyperglycemia with phlorizin completely reverses increased expression of hybrids, and 3) glucosamine infused into control rats mimics the effects of hyperglycemia on hybrid receptor formation. Thus, the results support the hypothesis that glucose acting, at least in part, through the glucosamine pathway may play an important role in regulating hybrid receptor assembly in vivo.

Animals↗

PubMed1998

Relative contribution of glycogenolysis and gluconeogenesis to hepatic glucose production in control and diabetic rats. A re-examination in the presence of euglycaemia.

Several studies have suggested that, in non-insulin-dependent diabetes mellitus, augmented gluconeogenesis is responsible for increased endogenous glucose production (EGP) and in the end determines fasting hyperglycaemia. However, human and animal studies have been conducted by comparing euglycaemic control subjects to hyperglycaemic diabetic probands. We measured EGP and hepatic gluconeogenesis comparing control and diabetic rats in the fasting state (with diabetic animals in hyperglycaemia), re-examining them in the presence of identical euglycaemia (with diabetic rats made acutely euglycaemic through i. v. phloridzin) or during a hyperinsulinaemic clamp. All rats were infused with [3-3H]-glucose and [U-14C]-lactate; the ratio between 14C-uridine-diphosphoglucose (reflecting 14C-glucose 6-phosphate) and 2 14C-phosphoenolpyruvate specific activities (both purified by high performance liquid chromatography from liver) measured hepatic gluconeogenesis. In diabetic animals, although overall EGP ( approximately 19.5 mg x kg[-1] x min[-1]) remained unaffected by experimental euglycaemia, the contribution of glycogenolysis largely increased (from 5.4 to 11.7 mg x kg(-1) min(-1), hyper- vs euglycaemia) while gluconeogenesis decreased (from 14.0 to 8.1 mg x kg(-1) x min[-1]); both were responsible for the augmented EGP (control rats, EGP: 12.7 mg x kg(-1) x min(-1); gluconeogenesis: 5.9 mg x kg(-1) x min(-1); glycogenolysis: 6.7 mg x kg[-1] x min[-1]). Finally, during insulin clamp, gluconeogenesis and glycogenolysis were similarly decreased, and both contributed to the hepatic insulin-resistance of diabetic animals. We conclude that, in this model of non-insulin-dependent diabetes, augmented gluconeogenesis is not primarily responsible for fasting hyperglycaemia and hepatic insulin resistance. Finally, failure to accurately match the experimental conditions in which diabetic and control humans or animals are compared affects gluconeogenesis, overestimating its role in determining hyperglycaemia.

Animals↗

PubMed1998

Expression of the two insulin receptor isoforms is not altered in the skeletal muscle and liver of diabetic rats.

Alternative splicing of the 36-base pair exon 11 of the human insulin receptor (IR) gene and of the corresponding domain of the rat IR gene results in the synthesis of two IR isoforms with distinct functional characteristics. Altered expression of these IR isoforms has been previously demonstrated in the skeletal muscle of patients with non-insulin-dependent diabetes mellitus (NIDDM); however, this observation was not confirmed by other studies and is still a matter of debate. To assess whether the reported altered isoform expression is due to the secondary metabolic derangement of diabetes, we examined alternative splicing of IR mRNAs (IR36+ and IR36-, corresponding to human Ex11+ and Ex11-) in the skeletal muscle and liver of 6-hour fasting 90% pancreatectomized insulin-resistant diabetic and control Sprague-Dawley rats, using the reverse transcriptase-polymerase chain reaction (PCR) technique. Both diabetic and control rats showed the same pattern of IR mRNA expression: the liver exclusively expressed IR36+ mRNA, whereas only IR36- mRNA was detected in muscle. In conclusion, diabetes mellitus per se does not alter the expression of IR isoforms in the liver and skeletal muscle, and therefore, at least in this animal model of NIDDM, impaired insulin action develops independently from a relative increase in IR36+ mRNA expression in skeletal muscle.

Animals↗

PubMed1995

In vivo effects of glucosamine on insulin secretion and insulin sensitivity in the rat: possible relevance to the maladaptive responses to chronic hyperglycaemia.

We tested the hypothesis that glucosamine, a putative activator of glucose toxicity in vitro through acceleration of the hexosamine pathway, may determine in vivo the two key features of glucose toxicity in diabetes, namely, peripheral insulin resistance and decreased insulin secretion. Two groups of awake rats were studied either with intraarterial administration of glucosamine (5 mumol.kg-1.min-1) or saline. Insulin secretion was determined after arginine, glucose (hyperglycaemic clamp), and arginine/glucose infusions, while insulin-mediated glucose metabolism was assessed by the euglycaemic hyperinsulinaemic clamp in combination with [3-3H]-glucose infusion. Glucosamine had no effects on arginine-induced insulin secretion both at euglycaemia and hyperglycaemia, but significantly (40-50%) impaired glucose-induced insulin secretion (both first and second phases). During euglycaemic hyperinsulinaemic clamp studies, glucosamine decreased glucose uptake by approximately 30%, affecting glycolysis (estimated from 3H2O rate of appearance) and muscle glycogen synthesis (calculated from accumulation of [3H]-glucosyl units in muscle glycogen) to a similar extent. Muscle glucose 6-phosphate concentration was markedly reduced in the glucosamine-infused rats, suggesting an impairment in glucose transport/phosphorylation. Therefore, an increase in hexosamine metabolism in vivo: 1) inhibits glucose-induced insulin secretion, and 2) reduces insulin stimulation of both glycolysis and glycogen synthesis, thereby mimicking in normal rats the major alterations due to glucose toxicity in diabetes.

Animals↗

PubMed1994

Regulation of rat insulin receptor tyrosine kinase by hypoglycemia.

To investigate the effect of hypoglycemia on the regulation of muscle-derived insulin receptor tyrosine kinase activity, four groups of Sprague-Dawley rats were studied: two groups in which either insulin (4 mU/kg.min) or phloridzin (3 mg/kg.min) was infused to acutely reach hypoglycemia (mean, 3.2-3.5 mM); and two control groups in which either saline or phloridzin (3 mg/kg.min) was infused, while maintaining euglycemia. Plasma glucose was maintained constant for 40 min in the hypoglycemic group and for 60 min in the phloridzin-infused euglycemic groups by a variable glucose infusion. Insulin receptors were isolated under conditions designed to preserve their in vivo phosphorylation state, and their tyrosine kinase activity toward poly(Glu-Tyr) was measured in the absence and presence of in vitro exposure to insulin. Insulin infusion resulted in an enhanced in vivo tyrosine kinase activity. Surprising was the finding of a slight increase of the in vivo tyrosine kinase activity in the phloridzin-infused hypoglycemic rats. The in vitro insulin dose-response curves of tyrosine kinase activity showed no significant differences between insulin-infused and control rats. In contrast, there was a marked increase of the insulin-stimulated kinase activity in phloridzin-infused hypoglycemic rats; at 100 nM insulin, tyrosine kinase activity was 1.8-fold more responsive when compared with either insulin-infused rats or control groups. Moreover, in phloridzin-infused hypoglycemic rats, the half-maximal stimulation of tyrosine kinase activity was greater than 10-fold (0.36 +/- 0.01 nM) more sensitive to insulin than both insulin-infused (3.8 +/- 0.03 nM, mean +/- SE) and control groups (4.2 +/- 0.05 and 4.1 +/- 0.04 nM in saline- and phloridzin-infused euglycemic rats, respectively, mean +/- SE). In conclusion, hypoglycemia associated with low plasma insulin concentrations determines a hypersensitization of the intrinsic tyrosine kinase of the insulin receptor.

Animals↗

PubMed1992

Idiopathic reactive hypoglycemia: a role for glucagon?

We previously reported that patients with idiopathic reactive hypoglycemia (plasma glucose concentration lower than 2.5 mmol/L 2-4 h after the ingestion of 75 g of glucose) display reduced or absent counterregulatory response of the glucagon secretion and increased insulin sensitivity. In order to examine the effect of glucagon on the increased insulin sensitivity in these patients, 12 subjects with idiopathic reactive hypoglycemia underwent a two-step hyperinsulinemic (1 mU/kg.min) euglycemic glucose clamp and were compared with 12 normal control subjects matched for age, weight and sex. During the first step of the glucose clamp (only insulin + glucose infusion) the patients with Idiopathic Reactive Hypoglycemia required higher glucose infusion rates to maintain euglycemia than normal subjects (9.09 +/- 0.29 mg/kg. min vs 7.61 mg/kg.min). When basal glucagon secretion was replaced (+ somatostatin and glucagon, second step of the clamp) the glucose infusion rates required to maintain euglycemia in patients with Idiopathic Reactive Hypoglycemia significantly decreased (to 7.17 +/- 0.40 mg/kg.min) and resulted similar to normal subjects (7.64 +/- 0.41 mg/kg.min). Thus, in patients affected by Idiopathic Reactive Hypoglycemia, glucagon secretion may play an important role in the pathogenesis of the increased insulin sensitivity and hypoglycemia.

Adult↗