Dexamethasone-induced increase in the rate of appearance in plasma of gut-derived glucose following an oral glucose load in rats

The influence of goutweed (Aegopodium podagraria L.) tincture and metformin on the carbohydrate and lipid metabolism in dexamethasone-treated rats

Background

Diabetes mellitus and metabolic syndrome are the common problems of the modern society. The interest in herbal medicines increases, and often they are used in combination with conventional drugs. Aegopodium podagraria L. (goutweed) is a plant widely used in traditional medicine. Hypoglycemic effect of goutweed aerial part tincture has been previously shown in alloxan-induced diabetic mice and in rats receiving excess of fructose and hydrochlorothiazide. The effects of co-administration of the tincture with widely used antihyperglycemic drugs have not been verified. The objective of this study is to determine the efficacy of goutweed tincture and its combination with metformin using the model reproducing the pathogenetic mechanisms of the metabolic syndrome and type 2 diabetes.

Methods

The animals were divided into 5 groups, as follows: intact control, dexamethasone (untreated), dexamethasone + metformin, 50 mg/kg; dexamethasone + A. podagraria tincture, 1 ml/kg intragastrically; dexamethasone + metformin, 50 mg/kg intragastrically + A. podagraria tincture, 1 ml/kg intragastrically. Dexamethasone was used at a dose of 5 mg/kg subcutaneously for 5 days. Insulin tolerance test and oral glucose tolerance test were performed, triglycerides, total lipids, total and HDL cholesterol content in plasma were determined, LDL cholesterol content was calculated, glycogen content in the liver was measured.

Results

Goutweed tincture combined with metformin increased its effect on the basal glycemia and on the results of the short insulin test. In the oral glucose tolerance test the lowest area under glucose curve and average glycemia value were seen in animals receiving this combination. Only metformin tended toward the reduction of liver glycogen. The decrease in triglycerides and increment of HDL cholesterol content (caused by the tincture), as well as tendency towards the decrease in total lipids level (caused by metformin) were observed against a background of the investigated combination, though the ability of GW tincture to reduce LDL cholesterol content and the same tendency seen against a background of metformin were eliminated when these preparations were administered together.

Conclusion

It has been shown that goutweed tincture combined with the respectively low dose of metformin partially increases the efficacy of the latter in dexamethasone-treated rats.

Graphical abstract

Goutweed tincture combined with the respectively low dose of metformin partially increases the efficacy of the latter in dexamethasone-treated rats

Chronic prednisolone treatment aggravates hyperglycemia in mice fed a high-fat diet but does not worsen dietary fat-induced insulin resistance

Synthetic glucocorticoids such as prednisolone have potent antiinflammatory actions. Unfortunately, these drugs induce severe adverse effects in patients, many of which resemble features of the metabolic syndrome, such as insulin resistance. In this study, we investigated whether adverse effects of prednisolone on glucose homeostasis are aggravated in mice with compromised insulin sensitivity due to a high-fat diet by applying various methods to analyze changes in insulin sensitivity in mice. C57BL/6J mice were fed a high-fat diet for 6 wk and treated with either prednisolone (10 mg/kg · d) or vehicle for the last 7 d. Insulin sensitivity and blood glucose kinetics were analyzed with state-of-the-art stable isotope procedures in different experimental conditions. Prednisolone treatment aggravated fasting hyperglycemia and hyperinsulinemia caused by high-fat feeding, resulting in a higher homeostatic assessment model of insulin resistance. In addition, prednisolone-treated high-fat diet-fed mice appeared less insulin sensitive by detailed analysis of basal glucose kinetics. Remarkably, using hyperinsulinemic-euglycemic or hyperglycemic clamp techniques, neither hepatic nor peripheral insulin resistance was worsened in the group that was treated with prednisolone. Yet analysis of hepatic glucose metabolism revealed that prednisolone did alter glycogen balance by reducing glycogen synthase flux under hyperinsulinemic as well as hyperglycemic conditions. In addition to elevated insulin levels, prednisolone-treated mice showed a major rise in plasma leptin and fibroblast growth factor 21 levels. Our data indicate that prednisolone-induced adverse effects on glucose metabolism in high-fat diet-fed mice do not reflect impaired insulin sensitivity but may be caused by other changes in the hormonal regulatory network controlling glucose metabolism such as fibroblast growth factor 21 and leptin.

Effects of Dexamethasone and Growth Hormone Treatment on Hepatic Gluconeogenic Enzymes in Calves

The hypothesis was tested that dexamethasone (DX) and bovine somatotropin (bST) alter expression or activity of gluconeogenic enzymes in neonatal calves. Holstein dairy calves (n = 24) were randomly divided in 4 groups and were treated with saline (control group), with DX at 30 microg/kg body weight per d (CDX), with 500 mg of sustained-release recombinant bST every 14 d (CbST), and with the combination of DX and bST from d 3 through 42 of life (CbSTDX). Plasma glucose and insulin concentrations were elevated throughout the study in CbSTDX, and insulin concentrations were elevated in CDX from d 7 to 28. Treatment with DX and the combination of DX and bST increased plasma glucagon concentrations from d 14 to 42, but decreased plasma cortisol concentrations on d 7 and 14 when compared with control calves. In liver, phosphoenolpyruvate carboxykinase (PEPCK) mRNA levels were reduced in CDX and CbSTDX when compared with control calves or CbST. The activity of PEPCK on d 14 was higher in CbSTDX compared with control calves. Pyruvate carboxylase mRNA levels were decreased on d 7 in CDX and CbSTDX. Pyruvate carboxylase activities on d 14 and 28 were lower in CDX and CbSTDX than in control calves or CbST. These data indicate an age-dependent response to DX for blood metabolites, expression and activities of hepatic PEPCK and pyruvate carboxylase, and for effects of bST, suggesting that glucocorticoid status is important.

Portal venous hyperinsulinemia does not stimulate gut glucose absorption in the conscious dog

The purpose of the present study was to assess whether physiological portal vein hyperinsulinemia stimulates gut glucose absorption in vivo. Chronically catheterized (femoral artery, portal vein, inferior vena cava, and proximal and distal duodenum) and instrumented (Doppler flow probe on portal vein) insulin (INS, 2 mU.kg(-1).min(-1), n = 6) or saline (SAL, n = 5) infused dogs were studied during basal (30 minutes) and experimental (90 minutes) periods. Arterial and portal vein plasma insulin were 3.3- and 3.2-fold higher, respectively, throughout the study in INS compared to SAL. An intraduodenal glucose infusion of 8 mg.kg(-1).min(-1) was initiated at t = 0 minutes. At t = 20 and 80 minutes, a bolus of 3-O-[3H]methylglucose (MG) and L-[14C]glucose (L-GLC) was injected intraduodenally. Phloridzin, an inhibitor of the Na+ -dependent glucose transporter (SGLT1), was infused from t = 60 to 90 minutes in the presence of a peripheral isoglycemic clamp. Net gut glucose output (NGGO) was 5.2 +/- 0.6 and 4.6 +/- 0.8 mg.kg(-1).min(-1) in INS and SAL, respectively, from t = 20 to 60 minutes. Transporter-mediated absorption was 87% +/- 2% of NGGO in both INS and SAL. Passive gut glucose absorption was 13% +/- 2% of NGGO in both INS and SAL. Phloridzin-induced inhibition of transporter-mediated absorption completely abolished passive absorption of L-GLC in both groups. This study shows that under physiological conditions, a portal vein insulin infusion that results in circulating hyperinsulinemia does not increase either transporter-mediated or passive absorption of an intraduodenal glucose load.

Prior exercise enhances passive absorption of intraduodenal glucose

The purpose of this study was to assess whether a prior bout of exercise enhances passive gut glucose absorption. Mongrel dogs had sampling catheters, infusion catheters, and a portal vein flow probe implanted 17 days before an experiment. Protocols consisted of either 150 min of exercise (n = 8) or rest (n = 7) followed by basal (-30 to 0 min) and a primed (150 mg/kg) intraduodenal glucose infusion [8.0 mg x kg-1x min-1, time (t) = 0-90 min] periods. 3-O-[3H]methylglucose (absorbed actively, facilitatively, and passively) and l-[14C]glucose (absorbed passively) were injected into the duodenum at t = 20 and 80 min. Phloridzin, an inhibitor of the active sodium glucose cotransporter-1 (SGLT-1), was infused (0.1 mg x kg-1 x min-1) into the duodenum from t = 60-90 min with a peripheral venous isoglycemic clamp. Duodenal, arterial, and portal vein samples were taken every 10 min during the glucose infusion, as well as every minute after each tracer bolus injection. Net gut glucose output in exercised dogs increased compared with that in the sedentary group (5.34 +/- 0.47 and 4.02 +/- 0.53 mg x kg-1x min-1). Passive gut glucose absorption increased approximately 100% after exercise (0.93 +/- 0.06 and 0.45 +/- 0.07 mg x kg-1 x min-1). Transport-mediated glucose absorption increased by approximately 20%, but the change was not significant. The infusion of phloridzin eliminated the appearance of both glucose tracers in sedentary and exercised dogs, suggesting that passive transport required SGLT-1-mediated glucose uptake. This study shows 1). that prior exercise enhances passive absorption of intraduodenal glucose into the portal vein and 2). that basal and the added passive gut glucose absorption after exercise is dependent on initial transport of glucose via SGLT-1.

Effect of adrenalectomy on glucose tolerance and lipid metabolism in gold-thioglucose obese mice

The effect of adrenalectomy (ADX) on body weight, lipogenesis, and glucose tolerance was investigated in mice made obese by a single intraperitoneal injection of gold-thioglucose (GTG). Five weeks after ADX the weight of GTG-obese mice was significantly decreased (GTG-obese+sham-ADX: 39.8 +/- 0.8 g; GTG-obese+ADX: 27.6 +/- 1.1 g; P < 0.05). ADX also reduced serum glucose (GTG-obese+sham-ADX: 16.5 +/- 0.6 mmol/l; GTG-obese+ADX: 10.8 +/- 0.5 mmol/l; P < 0.05) and serum insulin concentrations (GTG-obese+sham-ADX: 197 +/- 36 microU/ml; GTG-obese+ADX: 38 +/- 7 microU/ml; P < 0.05) of fed GTG-obese mice and greatly improved glucose tolerance. ADX lowered liver glycogen content and reduced the fatty acid content of liver, epididymal white adipose tissue (WAT), and interscapular brown adipose tissue (BAT) of fed GTG-obese mice. Lipid synthesis in liver and WAT of GTG-obese mice was decreased by ADX, but lipogenesis in BAT was increased, possibly to provide substrate for increased thermogenesis in this tissue. Effects of ADX on metabolism were not confined to GTG-injected mice, as ADX also reduced body weight and altered the glucose tolerance of age-matched control mice. ADX increased lipid synthesis in liver, WAT, and BAT of fed control mice without an increase in lipid deposition, indicating that there was increased lipid turnover in these lipogenic tissues of ADX mice. ADX reduced the fasting blood glucose concentration of both control and GTG-obese mice to a level below that of sham-ADX control mice (sham-ADX control: 6.0 +/- 0.4 mM; ADX control: 2.9 +/- 0.5 mM; ADX GTG-obese: 3.3 +/- 0.2 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of glucocorticoids and activated charcoal on the lethality of rats after acute poisoning with T-2 toxin, diacetoxyscirpenol, or roridin A

Lethal doses of the trichothecene mycotoxins T-2 toxin (1.5 mg/kg), diacetoxyscirpenol (DAS; 2.3 mg/kg) or roridin A (1.3 mg/kg) were intravenously administered to rats. When rats were treated with either activated charcoal (Superchar liquid, Norit A; 1 g/kg, po) or dexamethasone (8 mg/kg, iv) 30 min after poisoning with one of the trichothecenes, lethality was only marginally reduced. However, when the combination of activated charcoal (Superchar liquid or Norit A) and dexamethasone was administered, the survival rate of animals after 30 days was significantly enhanced by up to 50%. Comparison between 2 preparations of activated charcoal, Norit AR with a surface area of 1,000 m2/g and Superchar liquidR with a surface area of 3,000 m2/g, each in combination with dexamethasone, revealed no difference in their therapeutic efficacy. Prednisolone (60 mg/kg) was as effective as dexamethasone (8 mg/kg), each administered with activated charcoal, in preventing death in acute T-2 toxicosis.

Glucocorticoid induction of epinephrine synthesizing enzyme in rat skeletal muscle and insulin resistance

Rat skeletal muscle contains two enzymes which can make epinephrine: phenylethanolamine N-methyltransferase (PNMT) and nonspecific N-methyltransferase. We studied the time-course and mechanism by which the glucocorticoid dexamethasone increases muscle PNMT activity. We also examined the hypothesis that increased muscle E synthesis may contribute to glucocorticoid-induced insulin resistance. Dexamethasone (1 mg/kg s.c. for 12 d) increased muscle PNMT activity seven-fold but did not change NMT activity. Immunotitration with an anti-PNMT antibody indicated that the PNMT elevation was due to increased numbers of PNMT molecules. Dexamethasone rapidly increased PNMT activity and this elevation was largely maintained 6 d after glucocorticoid treatment stopped. Muscle epinephrine levels were transiently elevated by dexamethasone. Dexamethasone-treated rats had elevated insulin levels after a glucose load, and chronic administration of the PNMT inhibitor SKF 64139 reversed this increase. Chronic SKF 64139 improved glucose tolerance in normal rats. Dexamethasone induced muscle synthesis of the epinephrine-forming enzyme PNMT. A PNMT inhibitor lowered insulin levels in glucocorticoid-treated rats and glucose levels in untreated rats. These findings are compatible with antagonism of insulin-mediated glucose uptake by epinephrine synthesized in skeletal muscle.