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ENDOCRINE AND DIABETES
Department of Nutrition, Case Western Reserve University School of Medicine, Cleveland, Ohio
Received July 20, 2006; accepted November 8, 2006.
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Abstract |
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; Velliquette et al., 2005). At the cellular level, defects in insulin action have been noted in skeletal muscle and the liver, as indicated by reduced insulin receptor protein, reduced levels of its substrate protein IRS-1, and impaired insulin-induced tyrosine phosphorylation of both proteins (Friedman et al., 1997). In adipocytes and in skeletal muscle, the stimulation of glucose transport by insulin is impaired. However, insulin signaling in adipocytes in the SHROB model has not yet been characterized.
Akt (protein kinase B) is a 57-kDa Ser/Thr kinase that plays a key role in the insulin induced PI3K-Akt pathway (Hanada et al., 2004; Osaki et al., 2004). The binding of insulin to its receptors leads to the phosphorylation of PI3K, which then phosphorylates phosphatidylinositols at the 3-position. Then, Akt is recruited to the inner side of plasma membrane due to the interaction between its pleckstrin homology domain and the phosphatidylinositol-(3,4,5)-trisphosphate produced by PI3K. The Thr308 and Ser473 on Akt are then phosphorylated by 3-phosphoinositide-dependent protein kinase 1/2 and mammalian target of rapamycin (Hresko and Mueckler, 2005). Once activated, Akt regulates many cellular functions related to insulin action (Hanada et al., 2004). As a key element in insulin signaling, Akt could be an efficient indicator for cellular insulin response. Here, we measured the phosphorylation level of Akt in corresponding to insulin stimulation as an indicator of insulin sensitivity in isolated rat adipocytes. We hypothesized that the inherent defect in insulin action at this step downstream in the insulin-signaling cascade might be more impaired than the early stages of insulin signaling studied previously.
Moxonidine is a centrally acting sympatholytic agent that was unexpectedly found to possess insulin-sensitizing actions through largely unknown mechanisms in humans (Haenni and Lithell, 1999; Chazova et al., 2006) and in animal models (Henriksen et al., 1997; Yakubu-Madus et al., 1999; Ernsberger et al., 1996, 1999a). Similar results have been obtained for another imidazoline agonist, rilmenidine (Penicaud et al., 1998; Velliquette and Ernsberger, 2003b; Anichkov et al., 2005). Moxonidine is a selective agonist at I1-imidazoline receptors, while also activating 
2-adrenergic receptors (Ernsberger et al., 1993). Whereas both imidazoline and 2-adrenergic receptors contribute to sympatholytic actions, only the imidazoline component improves glucose metabolism (Velliquette and Ernsberger, 2003b). Most studies have been carried out with chronic treatment, but acute improvements in glucose tolerance and insulin secretion can be detected under blockade of 2-adrenergic receptors (Velliquette and Ernsberger, 2003b).
The cellular mechanisms for the insulin-sensitizing action of moxonidine are partially known. Chronic treatment with moxonidine increases the expression of insulin receptor and IRS-1 in muscle and liver in insulin-resistant SHROB and partially restores the ability of insulin to induce tyrosine phosphorylation of these proteins (Ernsberger et al., 1999a). The impacts of moxonidine treatment on other steps in the insulin-signaling cascade or in other cell types are not known. In the present study, we focused on insulin signaling in adipocytes through the Akt phosphorylation step, a possible site of insulin resistance in human diabetes type 2 (Karlsson et al., 2005). We hypothesized that insulin-dependent Akt phosphorylation would be deficient in SHROB model of insulin resistance and that long-term treatment with moxonidine would partially restore this defect, through either a direct action on adipocytes or an indirect systemic action.
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Materials and Methods |
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Animal Procedures. Adult male and female SHROB were obtained from a closed colony that has been continuously inbred since 1973 (Ernsberger et al., 1999b). Because both male and female SHROB are sterile, the strain is propagated by mating lean heterozygous carriers of the mutant fak allele. Adult male and female SHR and SHROB were used in these studies. No sex differences were noted in any experimental parameter, consistent with previous results (Ernsberger et al., 1999a). Animals were not used in any other experiments, and they were housed in pairs and were provided food (Teklad formula 8664; Teklad, Madison WI) and water ad libitum. Animals were on a 12:12-h light/dark cycle (lights on from 7:00 AM to 7:00 PM) and were maintained at a constant temperature of 21°C. These procedures were carried out with the approval of the Case Western Reserve University Animal Care and Use Committee.
Adipocyte Isolation and Incubation. SHR or SHROB were fasted 18 h. Anesthesia was induced with ether and maintained with isoflurane, and gonadal fat tissue (epididymal fat pad in males, myometrial fat pad in females; 4 g) was quickly removed and rinsed. The gonadal fat pad was used because it has been most widely used in previous studies and because of its sparse blood supply, allowing a rapid, clean dissection. Adipose tissue was minced before being digested for 1 h with shaking in 20 ml of Hanks' buffer containing 1% BSA and 25 mM HEPES at pH 7.4 with 1.0 mg/ml collagenase and 200 nM adenosinase. Then, the adipocytes were filtered through a 250-µm nylon mesh (Sefar America, Depew, NY) and rinsed with phosphate-buffered saline, pH 7.4, containing 1 mM sodium pyruvate, 0.1% BSA, 20 IU of penicillin, and 20 µg/ml streptomycin. Cells (0.5-ml packed volume) were distributed to microcentrifuge tubes and preincubated at 37°C with shaking for 1 h before insulin was applied. At the end of each experiment, tubes were placed in ice for 2 min, infranatants were removed, and 0.5 ml of Laemmli buffer with mercaptoethanol was added before boiling for 10 min. The aqueous phase was stored at –70°C for later Western blot analysis.
Western Blot Procedure. Aliquots containing 20 µg of protein were subjected to SDS-polyacrylamide gel electrophoresis on a 10% polyacrylamide gel and electrophoretically transferred to a nitrocellulose membrane for immunodetection. The blots were incubated overnight with anti-active Akt (phosphoserine 473) at a dilution of 1:5000 in 5% BSA. After repeated washes in 5% reconstituted milk, blots were incubated with horseradish peroxidase-conjugated donkey-anti-rabbit in 5% milk at room temperature. Blots were visualized with enhanced chemiluminescence (Pierce Chemical, Little Chalfont, Buckinghamshire, UK), digitized (ScanMaker 4700; Microtek, Carson, CA), and quantified by densitometry as gray scale multiplied by pixels (UN-Scan-It; Silk Scientific, Orem, UT). All blots were completely stripped with a stripping buffer (Bio-Rad, Hercules, CA) before another round of immunoblotting with anti-Akt antibody (1:1000). Data were expressed as the ratio of the densitometric signal for phospho-Akt to that of total Akt. Data were further normalized to the value of untreated controls or baseline.
Chronic Moxonidine Treatment. Moxonidine was dissolved in 20% (v/v) ethanol and mixed with powered rat chow (identical formulation to standard chow) before pelleting. SHROB were administrated moxonidine orally for 21 days at a dose of 4 mg/kg/day as described previously (Velliquette and Ernsberger, 2003a). During a 10-day run-in period, body weight and food intake were monitored to ensure accurate dosing 4 mg/kg/day. SHROB were provided food and water ad libitum. After 21 days of treatment, SHROB were fasted 18 h before sacrifice. Given the 1-h half-life of moxonidine (He et al., 2000), it was expected that no drug would be present at the time of tissue harvesting.
Acute Moxonidine Treatment and Insulin Stimulation. Moxonidine (100 nM) or 0.1% citric acid vehicle was applied into each tube of floating adipocytes 90 min before insulin stimulation. Insulin was applied into the cell incubations at a concentration of 100 nM for various time lengths from 0 to 90 min (in time-course experiments) or at various concentrations from 0.0 to 1.0 µM (in dose-response experiments) for 10 min.
Glucose Uptake Assay. Gonadal adipose tissue was taken from nonfasted rats for each experiment at the same of day (9:00 AM). Following collagenase digestion as described above, the adipocytes were filtered through mesh and rinsed with wash buffer (phosphate-buffered saline, pH 7.4, containing 1 mM sodium pyruvate, 0.1% BSA, 25 mM HEPES, 2.5 mM MgCl2, and 2.5 mM CaCl2) at least three times. Cell suspensions were equally distributed into 20-ml plastic tubes shaking at 100 rpm in a 37°C water bath, each containing 106 cells in a total volume of 1 ml. Various concentrations of insulin (100, 10, 1, or 0.1 nM) or vehicle (wash buffer) were applied to the cell suspensions for 30 min before exposure to [3H]2-deoxy-D-glucose. Nonspecific uptake was determined in the presence of 10 µM cytochalasin-B added 10 min before [3H]2-deoxy-D-glucose to block glucose transport. At the end of incubation, 150 µl of cell suspension from each tube was transferred into a 300-µl elongated centrifuge tube on top of 70 µl of mineral oil. Uptake was initiated by adding 50 µl of 2.5 mM [3H]2-deoxy-D-glucose containing a total of 0.33 µCi of 3H labeling. In 3 min, the reaction was stopped by spinning 10 s at 5000g to separate cells from media. The cell fraction was removed from the rest of medium by slicing through the oil layer, and the top portion of the tube containing adipocytes was put into a scintillation vial with 4 ml of scintillation fluid (EcoScint A; National Diagnostics, Atlanta, GA). Vials were counted in a scintillation counter for 5 min, and specific glucose uptake was defined as [3H]2-deoxy-D-glucose incorporation minus incorporation in the presence of cytochalasin-B. The rate of uptake was expressed as picomoles per 105 cells per 3 min. Assays were carried out with triplicate cell aliquots, and the results were averaged.
Statistics. Results are presented as means ± standard error of the mean. Dose-response curves were analyzed by nonlinear curve fitting to a logistic equation (Prism 4.0; GraphPad Software Inc., San Diego, CA). Groups were compared by one- or two-way analysis of variance followed by Newman-Keuls tests.
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A representative set of Western blots illustrating the time course of Akt activation by insulin is shown in Fig. 1. Immunoreactivity to the phosphospecific antibody is shown in the top image, and the immunoreactivity for total Akt protein is shown in the corresponding image below, which was obtained from the same blot after stripping. Note the large sustained increase in phosphospecific immunoreactivity, whereas total Akt is relatively constant, indicating equal loading of the lanes. Adipocytes isolated from SHROB show an equivalent amount of total Akt immunoreactivity, but the increase in phosphospecific immunoreactivity elicited by insulin at each time point is noticeably less.
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In dose-response experiments, after chronic moxonidine treatment the maximum response (Emax) to insulin expressed as -fold increase at 10 min rose to 7.5 ± 0.6 compared with 3.7 ± 0.8 from untreated SHROB (Fig. 4). The EC50 for insulin also fell to 2.6 ± 0.6 from 29 ± 3.8 nM. Thus, moxonidine treatment in vivo increased the maximal response to insulin as well increasing the sensitivity to low concentrations of insulin.
Since all of the data are expressed as a ratio of phosphospecific to total immunoreactivity, it is possible that changes in unstimulated basal Akt phosphorylation may have contributed to the apparent effect of drug treatment. To evaluate this possibility, we compared the ratio of phosphospecific to total Akt immunoreactivity for adipocytes incubated in the absence of insulin. As shown in Fig. 5, adipocytes from SHR, SHROB, and SHROB treated with moxonidine all showed identical levels of unstimulated baseline Akt activation. Thus, the insulin resistance of SHROB adipocytes and the insulin-sensitizing action of chronic in vivo moxonidine were not mediated by changes in baseline activation.
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We then tested adipocytes from chronic moxonidine-treated (21 days, 4 mg/kg/day) SHROB and SHR to see whether the insulin-sensitizing effect detected with Akt activation was reflected in glucose uptake. As expected and consistent with Akt activation results, the glucose uptake in SHROB adipocytes stimulated with 10 nM insulin was increased to 3.9 ± 0.41 nmol/105 cells/3 min by 21 day chronic oral administration of moxonidine, whereas the basal glucose uptake remained almost unchanged: 1.3 ± 0.16 nmol/105 cells/3 min. However, in contrast to Akt activation, the EC50 values for insulin in adipocytes from the three groups were quite close to each other: the logEC50 was close to –9.0 for all three groups (Fig. 6A).
We also compared adipocyte glucose uptake between control SHR and SHR-treated with moxonidine for 21 days (Fig. 6B). Results for the untreated control SHR were similar to those of the previous experiment. In contrast to SHROB, SHR treated with moxonidine showed no difference relative to vehicle-treated controls in either basal uptake or insulin-stimulated uptake.
Effect of Acute Moxonidine Treatment. To test for a direct effect of moxonidine on Akt activation, we tested the effect of treatment with 100 nM moxonidine for 90 min. This concentration and duration of treatment has previously been shown to trigger multiple cell-signaling events in other cell types (Edwards et al., 2001; Edwards and Ernsberger, 2003). Akt activation in adipocytes treated with moxonidine alone was normalized to the control group treated with vehicle alone. Both SHR and SHROB adipocytes showed no change in basal Akt activation level in response 90 min acute in vitro treatment with moxonidine (Fig. 7). Thus, moxonidine does not directly activate Akt in adipocytes.
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Discussion |
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; Ernsberger et al., 1999b). In the present study, we isolated adipocytes from SHROB and SHR to test insulin responses in the absence of the physiological milieu. We assayed Akt activation, which is a key element in insulin cell signaling downstream of both the insulin receptor and IRS-1. Since the results were obtained from isolated cells, the insulin response was independent of influence from blood hormones and should reflect the function of adipose tissue only. Results of this study showed that adipose tissue, one of the major sites of insulin action, expresses profound insulin resistance with impaired Akt activation resulting from insulin stimulation. Insulin-induced uptake of glucose into adipocytes was also impaired, and this cellular defect might contribute to the whole-body insulin resistance syndrome.
The insulin-sensitizing effect of chronic moxonidine treatment has been observed in both animal and human experiments (Velliquette and Ernsberger, 2003a; Jacob et al., 2004). Results of this study were quite consistent with those studies in that chronic moxonidine treatment shows significant beneficial effects on the sensitivity and responsiveness to insulin. As in other recent studies, moxonidine at a dose of 4 mg/kg/day had no effect on body weight or fat depot size in either SHR or SHROB, ruling out any effect due to loss or gain of weight.
Lean SHR adipocytes did not show an enhancement of insulin action on glucose uptake. This is consistent with the much smaller effect of chronic moxonidine treatment on insulin resistance in SHR than in SHROB (Ernsberger et al., 1999a; Velliquette and Ernsberger, 2003a). Furthermore, the lipid-lowering actions of moxonidine can be detected in SHROB but not in SHR (Velliquette et al., 2006). In human studies, beneficial metabolic effects have been detected in diabetic and insulin-resistant subjects, but in unselected hypertensive subjects (Kaan et al., 1995; Lithell, 1998). Similar results have been obtained with another imidazoline agonist, rilmenidine (Meredith and Reid, 2004; Anichkov et al., 2005).
Both male and female animals were used in the present study. No sex differences were observed in any variable (data not shown). This finding is consistent with all previous studies in the SHROB model, which have consistently failed to find significant differences in metabolic syndrome traits between males and females (Ernsberger et al., 1999b). The SHROB model is unusual in this regard, because most rodent models of obesity and insulin resistance affect one gender more than the other (Kava et al., 1992). The lack of gender differences probably stems from severe hypogonadism (Koletsky, 1975), which results from impaired hypothalamic production of gonadotropin-releasing hormone (Rhinehart et al., 2004).
Not only chronic treatment but also acute application of moxonidine has been shown to improve glucose tolerance in SHROB within 15 min of injection (Velliquette and Ernsberger, 2003b). Thus, we asked the question that whether moxonidine works directly on the insulin-responsive tissues or cells or whether it might work through other organ systems such as the central nervous system or the endocrine pancreas in a short period such as 15 min. Although definite conclusions cannot yet be made, the results of the present study suggested that the effects of acute moxonidine treatment are not mediated by direction action on adipocytes. The site of action of acute moxonidine may be located within the pancreas, where it acts to facilitate insulin secretion and inhibit glucagon secretion (Velliquette and Ernsberger, 2003b). A number of other groups have characterized the actions of imidazoline agonists within the endocrine pancreas (Morgan and Chan, 2001). Moxonidine may alter adipocyte gene expression indirectly by affecting another organ, such as the pancreas or the liver. Recently, we have shown that moxonidine has a direct action on the liver to reduce the production and secretion of triglycerides into the plasma (Velliquette et al., 2006). Reduced delivery of triglycerides to adipocytes might produce long-lasting changes in their insulin sensitivity. The influence of plasma triglycerides on adipocyte insulin resistance has been shown in humans (Yki-Jarvinen and Taskinen, 1988).
There is a slight discrepancy in the results that in the moxonidine pretreatment experiments (Fig. 9), the peak -fold Akt activations in SHR and SHROB were both higher than the corresponding 5-min levels in Fig. 2. This seemed to be a consequence of the 90-min pretreatment period, which reduced the basal Akt activation as a result of additional exposure to serum-free medium. In addition, whereas cell-signaling responses to insulin were dose-dependent up to 1.0 µM, the activation of glucose transport fell off at 100 nM insulin for some experimental groups. This might reflect desensitization of insulin signaling pathways in vitro from prolonged exposure to higher concentrations. Differences in the susceptibility of SHR and SHROB adipocytes to insulin desensitization should be examined in future studies.
In conclusion, insulin resistance in SHROB adipocytes persists upon isolation and challenge with insulin in vitro. The phosphorylation of Akt is a step in the insulin signaling cascade that shows much stronger evidence of insulin resistance than tyrosine phosphorylation of the insulin receptor or IRS-1 we have described previously (Friedman et al., 1997; Ernsberger et al., 1999b; Velliquette et al., 2005). Thus, the SHROB adipocyte is a potential in vitro model of insulin resistance. In vivo treatment with moxonidine for 21 days increased the sensitivity of SHROB adipocytes to insulin, despite withdrawal of treatment 18 h before tissue harvesting and extensive washing during the isolation process. This suggests a durable effect of the treatment on adipocytes such as a change in gene expression. This conclusion is supported by the lack of an acute effect of moxonidine on insulin-dependent activation of Akt. Moxonidine treatment in vivo also facilitated the glucose uptake response of adipocytes to insulin, suggesting that facilitated Akt signaling may have consequences of insulin sensitivity in the whole organism, particularly in the extremely obese SHROB model where adipose tissue makes up a significant fraction of the body mass.
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Footnotes |
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS: SHROB, spontaneously hypertensive rat(s), obese substrain; IRS-1, insulin receptor substrate 1; PI3K, Phosphatidylinositol 3-kainse; BSA, bovine serum albumin.
Address correspondence to: Dr. Paul Ernsberger, Department of Nutrition, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4906. E-mail: pre{at}po.cwru.edu
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References |
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Anichkov DA, Shostak NA, and Schastnaya OV (2005) Comparison of rilmenidine and lisinopril on ambulatory blood pressure and plasma lipid and glucose levels in hypertensive women with metabolic syndrome. Curr Med Res Opin 21: 113–119.[CrossRef][Medline]
Chazova I, Almazov VA, and Shlyakhto E (2006) Moxonidine improves glycaemic control in mildly hypertensive, overweight patients: a comparison with metformin. Diabetes Obes Metab 8: 456–465.[CrossRef][Medline]
Edwards L and Ernsberger P (2003) The I(1)-imidazoline receptor in PC12 pheochromocytoma cells reverses NGF-induced ERK activation and induces MKP-2 phosphatase. Brain Res 980: 71–79.[CrossRef][Medline]
Edwards L, Fishman D, Horowitz P, Bourbon N, Kester M, and Ernsberger P (2001) The I(1)-imidazoline receptor in PC12 pheochromocytoma cells activates protein kinases C, extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinase (JNK). J Neurochem 79: 931–940.[CrossRef][Medline]
Ernsberger P, Damon TH, Graff LM, Christen MO, and Schäfer SG (1993) Moxonidine, a centrally-acting antihypertensive agent, is a selective ligand for I1-imidazoline sites. J Pharmacol Exp Ther 264: 172–182.
Ernsberger P, Ishizuka T, Liu S, Farrell CJ, Bedol D, Koletsky RJ, and Friedman JE (1999a) Mechanisms of antihyperglycemic effects of moxonidine in the obese spontaneously hypertensive Koletsky rat (SHROB). J Pharmacol Exp Ther 288: 139–147.
Ernsberger P, Koletsky RJ, Collins LA, and Bedol DL (1996) Sympathetic nervous system in salt-sensitive and obese hypertension: amelioration of multiple abnormalities by a central sympatholytic agent. Cardiovasc Drugs Ther 10: 275–282.
Ernsberger P, Koletsky RJ, and Friedman JE (1999b) Molecular pathology in the obese spontaneous hypertensive Koletsky rat: a model of syndrome X. Ann NY Acad Sci 892: 272–288.[CrossRef][Medline]
Friedman JE, Ishizuka T, Liu S, Farrell CJ, Bedol D, Koletsky RJ, Kaung HL, and Ernsberger P (1997) Reduced insulin receptor signaling in the obese spontaneously hypertensive Koletsky rat. Am J Physiol 273: E1014–E1023.
Haenni A and Lithell H (1999) Moxonidine improves insulin sensitivity in insulin-resistant hypertensives. J Hypertens 17 (Suppl 3): S29–S35.
Hanada M, Feng J, and Hemmings BA (2004) Structure, regulation and function of PKB/AKT–a major therapeutic target. Biochim Biophys Acta 1697: 3–16.[Medline]
He MM, Abraham TL, Lindsay TJ, Chay SH, Czeskis BA, and Shipley LA (2000) Metabolism and disposition of moxonidine in Fischer 344 rats. Drug Metab Dispos 28: 446–459.
Henriksen EJ, Jacob S, Fogt DL, Youngblood EB, and Gödicke J (1997) Antihypertensive agent moxonidine enhances muscle glucose transport in insulin-resistant rats. Hypertension 30: 1560–1565.
Hresko RC and Mueckler M (2005) mTOR.RICTOR is the Ser473 kinase for Akt/protein kinase B in 3T3–L1 adipocytes. J Biol Chem 280: 40406–40416.
Jacob S, Klimm HJ, Rett K, Helsberg K, Haring HU, and Godicke J (2004) Effects of moxonidine vs. metoprolol on blood pressure and metabolic control in hypertensive subjects with type 2 diabetes. Exp Clin Endocrinol Diabetes 112: 315–322.[CrossRef][Medline]
Kaan EC, Brückner R, Frohly P, Tulp M, Schäfer SG, and Ziegler D (1995) Effects of agmatine and moxonidine on glucose metabolism: an integrated approach towards pathophysiological mechanisms in cardiovascular metabolic disorders. Cardiovasc Risk Factors 5 (Suppl 1): 19–27.
Karlsson HK, Zierath JR, Kane S, Krook A, Lienhard GE, and Wallberg-Henriksson H (2005) Insulin-stimulated phosphorylation of the Akt substrate AS160 is impaired in skeletal muscle of type 2 diabetic subjects. Diabetes 54: 1692–1697.
Kava RA, West DB, Lukasik VA, Wypijewski C, Wojnar Z, Johnson PR, and Greenwood MRC (1992) The effects of gonadectomy on glucose tolerance of genetically obese (fa/fa) rats: influence of sex and genetic background. Int J Obes 16: 103–111.[Medline]
Koletsky S (1975) Pathologic findings and laboratory data in a new strain of obese hypertensive rats. Am J Pathol 80: 129–142.[Abstract]
Lithell HO (1998) Insulin resistance and diabetes in the context of treatment of hypertension. Blood Press (Suppl 3): 28–31.
Meredith PA and Reid JL (2004) Efficacy and tolerability of long-term rilmenidine treatment in hypertensive diabetic patients: a retrospective analysis of a general practice study. Am J Cardiovasc Drugs 4: 195–200.[CrossRef][Medline]
Morgan NG and Chan SL (2001) Imidazoline binding sites in the endocrine pancreas: can they fulfill their potential as targets for the development of new insulin secretagogues? Curr Pharm Des 7: 1413–1431.[CrossRef][Medline]
Osaki M, Oshimura M, and Ito H (2004) PI3K-Akt pathway: its functions and alterations in human cancer. Apoptosis 9: 667–676.[CrossRef][Medline]
Penicaud L, Berthault MF, Morin J, Dubar M, Ktorza A, and Ferre P (1998) Rilmenidine normalizes fructose-induced insulin resistance and hypertension in rats. J Hypertens Suppl 16: S45–S49.[CrossRef][Medline]
Rhinehart EK, Kalra SP, and Kalra PS (2004) Neuropeptidergic characterization of the leptin receptor mutated obese Koletsky rat. Regul Pept 119: 3–10.[CrossRef][Medline]
Velliquette RA and Ernsberger P (2003a) Contrasting metabolic effects of antihypertensive agents. J Pharmacol Exp Ther 307: 1104–1111.
Velliquette RA and Ernsberger P (2003b) The role of I(1)-imidazoline and (2)-adrenergic receptors in the modulation of glucose metabolism in the spontaneously hypertensive obese rat model of metabolic syndrome X. J Pharmacol Exp Ther 306: 646–657.
Velliquette RA, Friedman JE, Shao J, Zhang BB, and Ernsberger P (2005) Therapeutic actions of an insulin receptor activator and a novel peroxisome proliferator-activated receptor gamma agonist in the spontaneously hypertensive obese rat model of metabolic syndrome X. J Pharmacol Exp Ther 314: 422–430.
Velliquette RA, Kossover R, Previs SF, and Ernsberger P (2006) Lipid-lowering actions of imidazoline antihypertensive agents in metabolic syndrome X. Naunyn-Schmiedeberg's Arch Pharmacol 372: 300–312.[CrossRef][Medline]
Yakubu-Madus FE, Johnson WT, Zimmerman KM, Dananberg J, and Steinberg MI (1999) Metabolic and hemodynamic effects of moxonidine in the Zucker diabetic fatty rat model of type 2 diabetes. Diabetes 48: 1093–1100.[Abstract]
Yki-Jarvinen H and Taskinen MR (1988) Interrelationships among insulin's antilipolytic and glucoregulatory effects and plasma triglycerides in nondiabetic and diabetic patients with endogenous hypertriglyceridemia. Diabetes 37: 1271–1278.[Abstract]
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