Hsien-Hui Chung

Plasma glucose lowering mechanisms of catalpol, an active principle from roots of Rehmannia glutinosa, in streptozotocin-induced diabetic rats.

Catalpol is one of the active principles from roots of Rehmannia glutinosa Steud (Scrophulariaceae) that is widely used to treat diabetic disorders in Chinese traditional medicine using the name of Di-Huang, which is used to investigate the mechanisms for lowering of plasma glucose in streptozotocin-induced diabetic rats (STZ-diabetic rats). Catalpol decreased plasma glucose in a dose-related manner, and this action was reduced by pretreatment with naloxone or naloxonazine. An increase of plasma β-endorphin by catalpol was also observed in parallel. The plasma glucose lowering action of catalpol was deleted in bilateral adrenalectomized rats. Moreover, catalpol enhanced β-endorphin release from the isolated adrenal medulla of STZ-diabetic rats. Otherwise, plasma glucose lowering action of catalpol failed to produce in opioid μ-receptor knockout mice. Also, repeated administration of catalpol for 3 days in STZ-diabetic rats resulted in a marked reduction of phosphoenolpyruvate carboxykinase (PEPCK) expression in liver and an increased expression of glucose transporter subtype 4 (GLUT 4) in skeletal muscle. These effects were also reversed by blockade of opioid μ-receptors. Our results suggested that catalpol increased glucose utilization through increase of β-endorphin secretion from adrenal gland in STZ-diabetic rats.

Silymarin Decreases Connective Tissue Growth Factor to Improve Liver Fibrosis in Rats Treated with Carbon Tetrachloride

Silymarin is an herbal product showing potential as protection against hepatic disorders. In an attempt to develop the agent for the treatment of hepatic fibrosis, we screened the effects of silymarin on a rat model of hepatic fibrosis induced by carbon tetrachloride (CCl4). Intraperitoneal administration of CCl4 to rats for 8 weeks not only increased the plasma levels of glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) but also induced a marked increase in the formation of hepatic fibrosis. Moreover, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were also reduced in the liver of rats treated with CCl4. Oral administration of silymarin (200 mg/kg, three times daily), in parallel, decreased the plasma levels of GOT and GPT. Furthermore, in addition to the improvement of hepatic fibrosis, the hepatic levels of hydroxyproline and connective tissue growth factor (CTGF) were both markedly decreased by silymarin. Silymarin also elevated the activities of SOD and GPx in liver isolated from CCl4‐treated rats. The results suggest that oral administration of silymarin protects against CCl4‐induced hepatic fibrosis in rats, likely due to the decrease in fibrotic parameters such as CTGF. Copyright

Activation of Peripheral Opioid µ-Receptors in Blood Vessel May Lower Blood Pressure in Spontaneously Hypertensive Rats

Background/Aims: The role of opioid receptors in the regulation of vascular function remains unclear. In the current study, we evaluated the ability of loperamide, a peripheral opioid receptor agonist, to regulate blood pressure in spontaneously hypertensive rats (SHRs) and examined the mechanism(s) by which loperamide exerts its effects. Methods: In male SHRs, mean arterial pressure (MAP) was measured and hemodynamic analysis was recorded. Additionally, the isometric tension of aortic rings isolated from SHRs was determined. Results: Loperamide dose-dependently decreased MAP in SHRs but not in the normal group of Wistar-Kyoto rats. This reduction of MAP in conscious SHRs was abolished by the selective opioid µ-receptor antagonist cyprodime, but not by naloxonazine, the µ1-opioid receptor antagonist. However, cardiac output was not altered by loperamide in anesthetized SHRs. Moreover, loperamide-induced relaxation in isolated aortic rings precontracted with phenylephrine or vasopressin. This relaxation was abolished by cyprodime, but not by naloxonazine. Loperamide-induced relaxation was also attenuated by glibenclamide, an ATP-sensitive potassium (KATP) channel blocker. Additionally, vasodilatation by loperamide was reduced by an inhibitor of protein kinase A (PKA) and enhanced by an inhibitor of phosphodiesterases. Conclusion: We suggest that loperamide can lower MAP in SHRs via µ2-opioid receptor-dependent cAMP-PKA pathway that induces vascular relaxation by opening KATP channels.

Improvement of Insulin Resistance by Chlorella in Fructose‐rich Chow‐fed Rats

Chlorella is a type of unicellular fresh water algae. In an attempt to develop new agents for handling insulin resistance, Chlorella was employed to screen the effect on insulin resistance in rats induced by fructose‐rich chow. A single oral administration of Chlorella for 90 min decreased the plasma glucose in a dose‐dependent manner in rats receiving 4‐week fructose‐rich chow. In addition, chronic treatment with Chlorella for 15 days also lowered plasma glucose in the same manner. Then, the insulin action on glucose disposal rate was measured using the glucose‐insulin index, values of the areas under the curves of glucose and insulin during the intraperitoneal glucose tolerance test (IPGTT). Oral administration (three times daily for 5 days) of Chlorella to rats receiving 4 weeks of fructose‐rich chow abolished the elevated value of the glucose‐insulin index, indicating that Chlorella has an ability to improve insulin resistance. An increase of insulin sensitivity by Chlorella was further evaluated using the plasma glucose lowering action of exogenous insulin in streptozotocin‐induced diabetic rats (STZ‐diabetic rats). Oral administration of Chlorella three times daily to STZ‐diabetic rats increased the response to exogenous insulin 15 days later. The obtained results suggest that oral administration of Chlorella has the ability to improve insulin sensitivity, which may be used as an adjuvant therapy for patients with insulin resistance. Copyright

Rhodiola-Water Extract Induces β-endorphin Secretion to Lower Blood Pressure in Spontaneously Hypertensive Rats

Rhodiola rosea (Rhodiola) is grown at high altitudes and northern latitudes. It is mainly used clinically as an adaptogen, but antihypertensive effects have been reported for the extract. These have not been well investigated, so in the present study, we evaluated the effect of Rhodiola‐water extract on blood pressure in spontaneously hypertensive rats (SHRs) and investigated the potential mechanism(s) for this action. In conscious male SHRs, systolic blood pressure (SBP) and heart rate were recorded using the tail‐cuff method. Plasma β‐endorphin was measured by enzyme‐linked immunosorbent assay. Rhodiola‐water extract decreased SBP in SHRs in a dose‐dependent manner, and this action was more significant than that in normal group named Wistar‐Kyoto (WKY) rats. This reduction of SBP in SHRs was inhibited by pretreatment with the selective opioid μ‐receptor antagonist, cyprodime, but not by naloxonazine, an antagonist specific to opioid μ1‐receptor. Also, the SBP‐lowering action of Rhodiola‐water extract was attenuated in adrenalectomized SHRs. Moreover, Rhodiola‐water extract dose‐dependently increased β‐endorphin release in SHRs, and the elevation of β‐endorphin in SHRs was higher than that in WKY. Thus, we suggest that Rhodiola‐water extract can induce release of β‐endorphin to lower SBP in SHRs. Copyright

Stimulatory Effect of Allantoin on Imidazoline I1 Receptors in Animal and Cell Line

Allantoin is known as the agonist of imidazoline receptor, especially the I₂ subtype. Effect of allantoin on imidazoline I₁ receptor (I₁R) relating to reduction of blood pressure and its merit in steatosis are still obscure. Also, farnesoid X receptor (FXR) plays an important role in lipid homeostasis related to I₁R activation. Thus, we administered allantoin into high fat diet (HFD)-fed mice showing hypertriglyceridemia and hypercholesterolemia. Allantoin significantly improved hyperlipidemia in HFD mice after 4 weeks of administration. Pretreatment with efaroxan, at a dose sufficient to inhibit I₁R activation, attenuated the action of allantoin. In addition, in cultured HepG2 cells, allantoin increased the expression of farnesoid X receptor (FXR). The allantoin-induced FXR expression was blocked by efaroxan. Similar changes were observed in the expressions of FXR-targeted genes. Otherwise, allantoin also lowered systolic blood pressure (SBP) in HFD mice that can be blocked by efaroxan. Taken together, allantoin has an ability to activate I₁R for improvement of metabolic disorders.

Improvement of hyperphagia by activation of cerebral I(1)-imidazoline receptors in streptozotocin-induced diabetic mice.

Imidazoline I1-receptors (I1R) are known to regulate blood pressure and rilmenidine, an agonist, is widely used as antihypertensive agent in clinic. However, the role of I1R in feeding behavior is still unclear. In the present study, we used the agonist of I1R to investigate the effect on hyperphagia in streptozotocin (STZ)-induced diabetic mice. Rilmenidine decreased the food intake of STZ-diabetic mice in a dose-dependent manner. The reduction of food intake was abolished by pretreatment with efaroxan at the dose sufficient to block I1R. Intracerebroventricular (icv) administration of rilmenidine into STZ-diabetic mice also significantly reduced hyperphagia, which was reversed by icv administration of efaroxan. In addition, similar results were observed in STZ-diabetic mice, which received chronic treatment with rilmenidine 3 times daily (t.i.d.) for 7 days. Moreover, the hypothalamic neuropeptide Y (NPY) level was reduced by rilmenidine that was also reversed by pretreatment with efaroxan. In conclusion, the obtained results suggest that rilmenidine can decrease food intake in STZ-diabetic mice through an activation of I1R to lower hypothalamic NPY level.

Decrease of Hyperglycemia by Syringaldehyde in Diabetic Rats

Syringaldehyde is one of the active principles from the stems of Hibiscus taiwanensis (Malvaceae) that has been mentioned to lower hyperglycemia. However, the potential mechanisms for this action of syringaldehyde remain obscure. In the present study, we used streptozotocin to induce diabetic rats (STZ-diabetic rats) as type 1-like diabetic rats and fed fructose-rich chow to rats as type 2-like diabetic rats. Then, we performed the postprandial glucose test and applied the hyperinsulinemic euglycemic clamp to investigate the actions of syringaldehyde. Also, the changes of gene expressions of enzyme relating to glucose homeostasis in muscle and liver were characterized. Syringaldehyde significantly decreased the postprandial plasma glucose in rats, while the plasma insulin was not modified by syringaldehyde. The glucose infusion rate (GIR) in fructose chow-fed rats using hyperinsulinemic euglycemic clamp was markedly improved by syringaldehyde. Additionally, repeated administration of syringaldehyde for 3 days in STZ-diabetic rats resulted in a marked reduction of phosphoenolpyruvate carboxykinase (PEPCK) expression in liver and an increased expression of glucose transporter subtype 4 (GLUT 4) in skeletal muscle. Our results suggest that syringaldehyde may increase glucose utilization to lower hyperglycemia in diabetic rats.

Improvement of obesity by activation of I1-imidazoline receptors in high fat diet-fed mice.

Imidazoline I1-receptor (I1R) is known to regulate the blood pressure, and rilmenidine, as the agonist, is used to treat hypertension in clinics. However, the role of I1R in obesity is still unclear. In the present study, we investigated the changes of obesity by activation of I1R in high fat diet (HFD)-fed mice. Chronic administration of rilmenidine into HFD-fed mice for 8 weeks significantly reduced body weight, which was reversed by efaroxan at the dose sufficient to block I1R. Also, rilmenidine significantly decreased the energy intake of HFD-fed mice. This reduction of energy intake was abolished by efaroxan at the same dosing for blockade of I1R. However, hypothalamic I1R protein expression in HFD-fed mice was markedly lower than that in normal chow-fed mice. In addition, epididymal white adipose tissue (eWAT) cell size in HFD-fed mice was decreased by rilmenidine via the activation of I1R. Moreover, effect of rilmenidine on appetite disappeared in db/db mice. Taken together, we suggest that rilmenidine can improve obesity in HFD-fed mice through an activation of I1R to ameliorate energy intake and eWAT accumulation.

Insulin resistance induced by zymosan as a new animal model in mice.

Insulin resistance (IR) is known as a main problem in diabetic disorders. Some animal models for research in IR have been mentioned. Each model shows merit with some disadvantages. Thus, a new animal model for IR is required. The present study used zymosan, a mixture of cell-wall particles from the yeast named Saccharomyces cerevisiae, to establish a new model of IR in mice. Also, we compared the difference of this model with fructose-rich chow-induced model and found some merits of this model. Moreover, we identified that this model induced by zymosan is reversible and IR can be reversed gradually after termination of treatment. Taken together, we suggest zymosan as a useful agent to induce IR through inflammatory pathway in mice.