Background: Endurance training increases insulin-stimulated muscle glucose transport and leads to improved metabolic control in diabetic patients. Objective: To analyze the effects of endurance training on the early steps of insulin action in muscle of rats. Design: Male rats submitted to daily swimming for 6 weeks were compared with sedentary controls. At the end of the training period, anesthetized animals received an intravenous (i.v.) injection of insulin and had a fragment of their gastrocnemius muscle excised for the experiments. Methods: Associations between insulin receptor, insulin receptor substrates (IRS)-1 and -2 and phosphatidylinositol 3-kinase (PI3-kinase) were analyzed by immunoprecipitation and immunoblotting. Akt-1 serine phosphorylation and specific protein quantification were detected by immunoblotting of total extracts, and IRS-1/IRS-2-associated PI3-kinase activity were determined by thin-layer chromatography.Results: Insulin-induced phosphorylation of IRS-1 and IRS-2 increased respectively by 1.8-fold ðP , 0:05Þ and 1.5-fold ðP , 0:05Þ; whereas their association with PI3-kinase increased by 2.3-fold ðP , 0:05Þ and 1.9-fold ðP , 0:05Þ in trained rats as compared with sedentary controls, respectively. The activity of PI3-kinase associated with IRS-1 and IRS-2 increased by 1.8-fold ðP , 0:05Þ and 1.7-fold ðP , 0:05Þ respectively, in trained rats as compared with their untrained counterparts. Serine phosphorylation of Akt-1/PKB increased 1.7-fold ðP , 0:05Þ in trained rats in response to insulin. These findings were accompanied by increased responsiveness to insulin as demonstrated by a reduced area under the curve for insulin during an i.v. glucose tolerance test, by increased glucose disappearance rate during an insulin tolerance test, and by increased expression of glucose transporter-4. Conclusions: The increased responsiveness to insulin induced by chronic exercise in rat skeletal muscle may result, at least in part, from the modulation of the insulin signaling pathway at different molecular levels.

The results indicate that the aqueous extract of the stem bark of Caesalpinia ferrea has hypoglycaemic properties and possibly acts to regulate glucose uptake in liver and muscles by way of Akt activation, restoring the intracellular energy balance confirmed by inhibition of AMPK activation.

Our purpose was to determine the blood amino acid concentration during insulin induced hypoglycemia (IIH) and examine if the administration of alanine or glutamine could help glycemia recovery in fasted rats. IIH was obtained by an intraperitoneal injection of regular insulin (1.0 U/kg). The blood levels of the majority of amino acids, including alanine and glutamine were decreased (P < 0.05) during IIH and this change correlates well with the duration than the intensity of hypoglycemia. On the other hand, the oral and intraperitoneal administration of alanine (100 mg/kg) or glutamine (100 mg/kg) accelerates glucose recovery. This effect was partly at least consequence of the increased capacity of the livers from IIH group to produce glucose from alanine and glutamine. It was concluded that the blood amino acids availability during IIH, particularly alanine and glutamine, play a pivotal role in recovery from hypoglycemia.

muscle denervation is a reproducible model of tissue-specific insulin resistance. To investigate the molecular basis of insulin resistance in denervated muscle, the downstream signaling molecules of the insulinsignaling pathway were examined in intact and denervated soleus muscle of rats. Short-term denervation induced a significant fall in glucose clearance rates (62% of control, P Ͻ 0.05) as detected by euglycemic hyperinsulinemic clamp and was associated with a significant decrease in insulin-stimulated tyrosine phosphorylation of the insulin receptor (IR; 73% of control, P Ͻ 0.05), IR substrate 1 (IRS1; 69% of control, P Ͻ 0.05), and IRS2 (82% of control, P Ͻ 0.05) and serine phosphorylation of Akt (39% of control, P Ͻ 0.05). Moreover, denervation reduced insulin-induced association between IRS1/IRS2 and p85/phosphatidylinositol (PI) 3-kinase. Nevertheless, denervation caused an increase in PI 3-kinase activity associated with IRS1 (275%, P Ͻ 0.05) and IRS2 (180%, P Ͻ 0.05), but the contents of phosphorylated PI detected by HPLC were significantly reduced in lipid fractions. In the face of the apparent discrepancy, we evaluated the expression and activity of the 5-inositol, lipid phosphatase SH2 domain-containing inositol phosphatase (SHIP2), and the serine phosphorylation of p85/PI 3-kinase. No major differences in SHIP2 expression were detected between intact and denervated muscle. However, serine phosphorylation of p85/PI 3-kinase was reduced in denervated muscle, whereas the blockade of SHIP2 expression by antisense oligonucleotide treatment led to partial restoration of phosphorylated PI contents and to improved glucose uptake. Thus modulation of the functional status of SHIP2 may be a major mechanism of insulin resistance induced by denervation. denervation; SH2 domain-containing inositol phosphatase; phosphatidylinositol 3-kinase MUSCLE DENERVATION is a reproducible model of insulin resistance. It is characterized by a decreased ability of insulin to stimulate glucose uptake, glycogen synthesis, and amino acid transport (9). Several studies have attempted to characterize the major mechanisms involved in the development of impaired insulin action after denervation, and as it stands now, we know that modulation of muscle blood flow (31), reduced binding of insulin to its receptor (13), and loss of mechanical activity (10) are not responsible for the phenomenon. Defects in different steps of the insulin-signaling pathway are currently under scrutiny, and some advances have been achieved. No study was able to demonstrate a major loss of insulin receptor (IR) kinase activity (1, 20), although one study (14) demonstrated a reduced insulin-stimulated IR substrate 1 (IRS1) phosphorylation after 7 days of denervation. The activity of the lipid-metabolizing enzyme phosphatidylinositol (PI) 3-kinase was shown to be unaltered 30 min and 24 h after denervation and to decrease 3 days after denervation (2, 9). The activity of Akt was shown to be unaltered at 1 day and reduced at 3 days after denervation (30), and th...

Autocrine and paracrine insulin signaling may participate in the fine control of insulin secretion. In the present study, tissue distribution and protein amounts of the insulin receptor and its major substrates, insulin receptor substrate (IRS)-1 and IRS-2, were evaluated in a model of impaired glucose-induced insulin secretion, the proteindeficient rat. Immunoblot and RT-PCR studies showed that the insulin receptor and IRS-2 expression are increased, whilst IRS-1 protein and mRNA contents are decreased in pancreatic islets of protein-deficient rats. Immunohistochemical studies revealed that the insulin receptor and IRS-1 and -2 are present in the great majority of islet cells; however, the greatest staining was localized at the periphery, suggesting a co-localization with non-insulin-secreting cells. Exogenous insulin stimulation of isolated islets promoted higher insulin receptor and IRS-1 and -2 tyrosine phosphorylation in islets from protein-deficient rats, as compared with controls. Moreover, insulin-induced IRS-1-and IRS-2-associated phosphatidylinositol 3-kinase activity are increased in islets of protein-deficient rats. The reduction of IRS-1 and IRS-2 protein expression in islets isolated from proteindeficient rats by the use of antisense IRS-1 or IRS-2 phosphorthioate-modified oligonucleotides partially restored glucose-induced insulin secretion. Thus, the impairment of insulin cell signaling through members of the IRS family of proteins in isolated rat pancreatic islets improves glucose-induced insulin secretion. The present data reinforced the role of insulin paracrine and autocrine signaling in the control of its own secretion.