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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The inotropic effects of isoproterenol (ISO), as well as the beta-adrenoceptors population, were measured in cardiac tissues from normal and short-term (3 days) diabetic rats. ISO increased the tension of both normal and diabetic ventricles, but the efficacy (Emax) of the concentration-response curve was greater on ventricles from diabetic rats than in those from the normal control. This phenomenon was accompanied by a decrease in the number of beta-adrenoceptor sites (Bmax) during diabetes. Insulin-treated diabetic hearts partially reversed the phenomenon. Propanolol blocked, in a competitive manner, the positive inotropic action of ISO in both types of ventricles. Inhibition of the synthesis and receptors of thromboxane (TX) reduced the hyperreactivity to ISO and increased the number of beta-adrenoceptors during diabetes, producing Bmax values almost similar to those of the normal heart. Additionally, the diabetic heart generated and released a greater amount of TXB2 than the normal heart, even in the presence or absence of ISO. The stimulatory effect of ISO upon TXB2 release was altered by the specific beta-adrenergic blockade and by verapamil. In addition, the drugs able to induce a sustained increase of endogenous cAMP also inhibited the release of TXB2 by diabetic ventricles. Exogenous TXB2 exerted the same type of hyperreactivity in diabetic ventricles. This phenomenon was accompanied by an inhibition of Na+ + K+-ATPase activity. These results suggest that beta-adrenergic inotropic stimulation is secondary to receptor-mediated hydrolysis of arachidonic acid with subsequent release of thromboxanes, which, in turn, may be responsible for both the superreactivity and the decrease in the number of beta-adrenoceptors during diabetes. The abnormal reactivity to beta-agonists also could be associated with alterations of the diabetic cardiac Na+ + K+-ATPase activity induced by TXB2 whose production is increased during diabetes.
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PMID:Role of thromboxanes in alterations of the diabetic beta-adrenergic system. 255 22

Adipocytes from streptozotocin-diabetic rats showed a markedly reduced lipolytic response to glucagon concomitant with a 90% or greater decrease in the number of glucagon receptors per cell. In contrast, beta-adrenergic receptors assessed by [3H]dihydroalprenolol binding and lipolysis stimulated by isoproterenol, dibutyryl 3'5'-cyclic AMP and 3-isobutyl-1-methylxanthine were reduced by only 10-25% in diabetic rats compared with controls. Furthermore, quantitative analysis of the relationship between the amount of cell-bound glucagon and the hormone-stimulated lipolysis revealed that the function of the remaining 10% of glucagon receptors remained intact in cells from diabetic animals. These findings suggest that the lipolytic cascades, including beta-adrenergic receptors, in adipocytes are not greatly impaired by diabetes, and therefore, the unresponsiveness of these cells to glucagon is mostly due to a marked reduction in the number of glucagon receptors, probably as a result of a down-regulation by postprandial hyperglucagonemia.
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PMID:Decreased glucagon binding and glucagon-stimulated lipolysis in adipocytes from streptozotocin-diabetic rats. 255 94

Treatment of pancreatic acini from diabetic rats with insulin resulted in a dose-dependent increase in the phosphorylation of ribosomal protein S6 when analyzed by two-dimensional gel electrophoresis. To study the presence of the protein kinase mediating this phosphorylation, soluble extracts of intact acini that had been previously treated with insulin were prepared and assayed for protein kinase activity with rat pancreatic ribosomes as a substrate. Activation of S6 kinase activity, observed in a time-dependent manner, was maximal after 20-30 min and, in a dose-dependent manner, was half-maximal at 1 nM and maximal at 10 nM insulin concentration. Based on cofactor requirements, substrate specificity, and a slow activation of the enzyme, the S6 kinase was distinct from cAMP-dependent, Ca2+-calmodulin-dependent, and Ca2+-phospholipid-dependent protein kinases and protease-activated kinase II. The S6 kinase activated by insulin was highly specific for the ribosomal protein S6 when compared with various substrates, including casein, glycogen synthase, phosphorylase b, phosvitin, histone HIII-S, and histone HVIII-S. Protein S6 phosphorylation in intact acini and activation of the S6 kinase by insulin showed similar dose-response curves, consistent with the S6 kinase being responsible for the protein S6 phosphorylation in intact acini. The comparison of the dose-response curves for S6 phosphorylation and protein synthesis in acini suggests that there is a close correlation between these two insulin actions.
Diabetes 1989 May
PMID:Insulin and ribosomal protein S6 kinase in rat pancreatic acini. 265 25

When tested in insulin-deficient animal models of diabetes, islet activating protein (IAP) has been shown to increase the secretion of insulin and to improve glucose intolerance. The genetically obese fa/fa rat is an animal model of impaired oral glucose tolerance that does not have reduced insulin secretion. In this model IAP treatment increases basal insulin levels, resulting in lower basal glycemia. However, glucose tolerance following an oral glucose load was worsened by IAP. This was found to be due to an exaggerated stimulation of hepatic glucose production (HGP) following glucose, a defect that is already present in the absence of IAP. IAP has been reported to inhibit (by ADP ribosylation) the inhibitory regulatory protein (Ni) of adenylate cyclase. It is therefore suggested that the increased HGP following oral glucose in fa/fa rats either in the absence or in the presence of IAP treatment may result from a cAMP-mediated mechanism. A beta adrenergic activation or a stimulation of glucagon output could therefore be potential candidates responsible for glucose intolerance in obese fa/fa rats.
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PMID:The effects of islet activating protein on oral glucose tolerance in the genetically obese fa/fa rat. 265 21

It has been reported that Vacor, a rodenticide containing N-3-pyridylmethyl-N'-p-nitrophenyl urea, causes insulin-dependent diabetes mellitus. The pathomechanism of Vacor-induced diabetes mellitus has not been clarified yet. The effect of Vacor, therefore, was studied in terms of insulin release from isolated rat pancreatic islets. Vacor suppressed glucose-stimulated insulin release, but did not affect the insulin release induced by theophylline or 12-o-tetra-decanoylphorbol 13-acetate. It is suspected that the suppression of insulin release from pancreatic islets by Vacor may contribute to the pathogenesis of Vacor-induced diabetes mellitus and that this suppression might not be related to cAMP and C-kinase.
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PMID:Vacor inhibits insulin release from islets in vitro. 266 66

Acute insulin treatment in rats has recently been shown to cause a rapid increase in liver low-Km cAMP phosphodiesterase (PDE) activity, which selectively affects Golgi fractions. To assess the physiological significance of this observation, the cAMP PDE activity associated with liver Golgi fractions has been measured in genetically obese Zucker rats, which spontaneously develop hyperinsulinemia, in rats receiving a continuous infusion of insulin, and in rats treated with anti-insulin serum. In genetically obese Zucker rats, a significant increase in Golgi-associated cAMP PDE relative to age-matched lean animals occurred after 3 wk, coinciding with the development of hyperinsulinemia. This change was maximal at 5-8 wk and affected the light (Gl) and intermediate (Gi) Golgi fractions (100-110% increase) to a greater extent than the heavy (Gh) fraction (30% increase). After 7 wk, despite the further increase in insulinemia, the increase in Golgi-associated cAMP PDE became progressively less marked, and at 18 wk it was no longer detectable except in Gh, suggesting the development of a hepatic insulin resistance. Infusion of insulin through chronically implanted intracardiac catheters led to a 30-50% increase in Golgi-associated cAMP PDE, which occurred earlier in Gi (3 h) than in Gh (7 h) and persisted for greater than 96 h. Injection of anti-insulin serum led to a 30-50% decrease in Golgi-associated cAMP PDE, which occurred sequentially in Gl (5 min), Gi (15 min), and Gh (30 min) and affected predominantly Gl and Gh. These results suggest that the cAMP PDE associated with Golgi fractions is a physiological effector of plasma insulin in vivo.
Diabetes 1988 Jun
PMID:Changes in low-Km cAMP phosphodiesterase activity in liver Golgi fractions from hyper- and hypoinsulinemic rats. 283 52

The aim of this study was to investigate the influence of insulin on platelet function, both in vitro and in vivo. For the in vitro investigation, we evaluated whether insulin affects platelet function at a physiological hormone concentration by incubating the platelet-rich plasma (PRP) of fasting subjects with human regular insulin at the final concentration of 40 microU/ml for 30 min; we observed a significant reduction of platelet sensitivity to all the aggregating agents employed, i.e., ADP, platelet-activating factor (PAF), epinephrine, collagen, and Na+ arachidonate. To investigate whether the insulin effect on platelets is dose dependent, we incubated the PRP of fasting subjects with different concentrations of human regular insulin (40, 80, 120, and 160 microU/ml) for 5 min, and we observed that the insulin-induced reduction of platelet sensitivity to aggregating agents is a dose-dependent phenomenon. Furthermore, the comparison between the platelet responses after 5 and 30 min of incubation with insulin showed that the insulin effect on platelet aggregation is time dependent. The lack of specificity of its inhibiting activity suggests that insulin does not interfere with the initial binding of each aggregating agent at specific sites but does influence a common step of platelet aggregation. Our study rules out the possibility that insulin reduces platelet-function-modifying intraplatelet cAMP levels or thromboxane A2 production, because this hormone decreases the platelet concentrations of cAMP--a phenomenon that, per se, promotes platelet aggregation--and does not modify collagen or Na+ arachidonate--induced platelet production of thromboxane A2, measured by radioimmunoassay of its stable-metabolite thromboxane B2.(ABSTRACT TRUNCATED AT 250 WORDS)
Diabetes 1988 Jun
PMID:Insulin directly reduces platelet sensitivity to aggregating agents. Studies in vitro and in vivo. 283 53

The effect of sulfonylureas tolbutamide and glyburide on adenylate cyclase- and cAMP-dependent protein kinase (A-kinase) was examined in rat liver cytosol. Both tolbutamide and glyburide inhibited the A-kinase activity in a dose-dependent manner. Half-maximal inhibition was obtained at 10 mM with tolbutamide and at 0.2 mM with glyburide, indicating that glyburide was 50-fold as potent as tolbutamide. Neither tolbutamide nor glyburide affected [3H]cAMP binding to the protein kinase, but both inhibited the activity of catalytic units of the A-kinase. Lineweaver-Burk double-reciprocal plots revealed that the inhibitory effects of these drugs were noncompetitive with respect to the protein substrate histone, as well as to the phosphate-donor substrate ATP. Thus, tolbutamide and glyburide inhibited the A-kinase activity in rat liver cytosol, and it was suggested that, through the inhibition of A-kinase, the sulfonylureas would affect the carbohydrate metabolism in the liver. In fact, the relative potencies of these two drugs on A-kinase activity corresponded well with those of their reported antidiabetic effects.
Diabetes 1988 Jul
PMID:Effect of tolbutamide and glyburide on cAMP-dependent protein kinase activity in rat liver cytosol. 283 57

In isolated islets, the hydrolysis of membrane phosphoinositides (PI) participates in the transduction of both extracellular and intracellular signals into an effective insulin secretory response. A wide variety of potential second-messenger molecules are generated during the phospholipase C-mediated cleavage of these strategically situated membrane phospholipids. Several distinct but interrelated issues are addressed in this perspective. These include 1) methodological approaches utilized to assess PI turnover, 2) the synergistic relationship between PI-derived second messengers and cAMP, 3) the contribution of changing PI turnover rates to the biphasic pattern of insulin output induced by 20 mM glucose, and 4) the role played by PI turnover in the phenomenon of "memory" displayed by islets after prior stimulation with various agonists. The concept that events unique to PI turnover contribute to beta-cell activation is well founded. Because of uncertainty regarding the exact nature of all PI-derived messengers, however, it is not yet possible to mold the available information into a comprehensive theory of beta-cell activation. Future studies will have to address various important unresolved issues.
Diabetes 1988 Feb
PMID:Modulation of insulin secretion from beta-cells by phosphoinositide-derived second-messenger molecules. 283 85

In this study on purified rat pancreatic beta-cells, we show that the second-generation sulfonylurea glyburide stimulates insulin release through a direct interaction with the beta-cells. During static incubations, 2 microM glyburide releases 0.16 pg insulin per beta-cell, which corresponds to a half-maximal glucose stimulation. This effect occurs independently from the glucose-recognition unit, being detectable at both nonstimulatory and stimulatory glucose concentrations and proceeding without alterations in the rate of glucose oxidation. The secretagogue action of glyburide appears not to be mediated through cAMP but is potentiated by cAMP-generating substances such as glucagon (10(-8) M; 0.31 pg insulin released per beta-cell). Its 10-fold higher potency in isolated islets is attributed to the markedly higher cAMP levels that are maintained in islet beta-cells under the influence of locally released glucagon. Perifused pancreatic beta-cells respond to glyburide with a biphasic insulin release. After removal of the drug, the cells continue to secrete insulin at the same rate for greater than or equal to 30 min. This prolonged secretory activity coincides with a cellular accumulation of the drug, primarily in association with membranes of secretory vesicles and mitochondria. Tolbutamide also stimulates insulin release from pure beta-cells, but it is less powerful on a molar basis and does not lead to a sustained hormone release after its removal from the extracellular medium. We conclude that the hypoglycemic action of glyburide is at least partly the result of a direct interaction with pancreatic beta-cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Diabetes 1988 Aug
PMID:Interaction of sulfonylureas with pancreatic beta-cells. A study with glyburide. 283 87


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