I-Min Liu

An insulin-dependent hypoglycaemia induced by electroacupuncture at the Zhongwan (CV12) acupoint in diabetic rats

Summary Acupuncture at the Zhongwan acupoint has been widely used in traditional Chinese medicine to relieve symptoms of diabetes mellitus. Our study investigated the effect on plasma glucose of electroacupuncture applied at the Zhongwan acupoint in rat diabetic models. Plasma concentrations of insulin, glucagon and β-endorphin were also determined using radioimmunoassay. A decrease in plasma glucose was observed in rats after electroacupuncture (15 Hz, 10 mA) for 30 min at the Zhongwan acupoint. This was observed in normal rats and rat models with Type II (non-insulin-dependent) diabetes mellitus. No significant effect on plasma glucose was observed in rat models with Type I (insulin-dependent) diabetes mellitus; neither the streptozotocin (STZ)-induced diabetic rats nor the genetic (BB/W) rats. Further, the hypoglycaemic action of electroacupuncture stimulation disappeared in rats with insulin-resistance induced by an injection of human long-acting insulin repeated daily to cause the loss of tolbutamide-induced hypoglycaemia. An insulin-related action can thus be hypothesised. This hypothesis is supported by an increase in plasma insulin-like immunoreactivity after electroacupuncture stimulation in normal rats. Participation of glucagon was ruled out because there was no change in plasma glucagon-like immunoreactivity resulting from electroacupuncture stimulation. In addition to an increase in plasma β-endorphin-like immunoreactivity, the plasma glucose lowering action of electroacupuncture stimulation at Zhongwan acupoint was abolished by naloxone in a sufficient dose to block opioid receptors. Thus we suggest that electroacupuncture stimulation at the Zhongwan acupoint induces secretion of endogenous β-endorphin which reduces plasma glucose concentration in an insulin-dependent manner. [Diabetologia (1999) 42: 250–255]

Changes in endogenous monoamines in aged rats.

1. It has been documented that ageing may alter endogenous neurotransmitters. However, these results are controversial. Thus, in the present study, cerebral cortex and plasma from male Wistar rats aged 8 weeks and 6, 12 or 24 months were used to investigate the changes in monoamines using electrochemical detection.

The amelioration of streptozotocin diabetes-induced renal damage by Wu-Ling-San (Hoelen Five Herb Formula), a traditional Chinese prescription.

ETHNOPHARMACOLOGICAL RELEVANCE Wu-Ling-San (Hoelen Five Herb Formula) is a Chinese prescription used to promote water metabolism. AIM OF THE STUDY The present study was undertaken to characterize the effects of Wu-Ling-San on diabetic nephropathy. MATERIALS AND METHODS Streptozotocin (STZ)-diabetic rats were orally administrated with Wu-Ling-San (0.5, 1.5, 2.5 g/(kgday)) once a day for 10 weeks. Changes in the renal function related parameters in plasma and urine were analyzed at the end of 10-week administration. Kidney was isolated for pathology histology, immunohistochemistry staining and Western blot analyses. RESULTS Wu-Ling-San (2.5 g/(kgday)) partially decreased the high plasma glucose level in diabetic rats. Diabetic-dependent alterations in urinary albumin, 24-h urinary albumin excretion rate, creatinine clearance, and glomerular mesangial matrix expansion were ameliorated by Wu-Ling-San. The increased expression of nuclear factor-kB as well as transforming growth factor-beta(1) and the progressive accumulation of fibronectin in kidney of diabetic rats were attenuated by Wu-Ling-San. Not only the elevated levels of advanced glycation end products (AGEs) and mitochondrial thiobarbituric acid-reactive substance, but also the higher levels of N(epsilon)-(carboxymethyl)lysine and receptor for AGEs in kidney of diabetic rats were ameliorated by Wu-Ling-San. CONCLUSIONS : Wu-Ling-San possess an anti-diabetic property with plasma glucose lowering action accompanied with amelioration of glycation-mediated renal damage.

Hypoglycemic effect of syringin from Eleutherococcus senticosus in streptozotocin-induced diabetic rats.

Eleutherococcus senticosus (Araliaceae ) is a very powerful adaptogenic agent. In the present study, the effects of syringin, an active principle of this herb, on plasma glucose levels in streptozotocin-induced diabetic rats (STZ-diabetic rats) were investigated. Thirty minutes after syringin was intravenously injected into fasting STZ-diabetic rats, plasma glucose levels dose-dependently decreased. In normal rats, syringin at the effective dose (1.0 mg/kg) significantly attenuated the increase in plasma glucose caused by an intravenous glucose challenge. Syringin dose-dependently (0.01 to 10.0 micromol/L) stimulated glucose uptake in soleus muscle isolated from STZ-diabetic rats. Syringin treatment of hepatocytes isolated from STZ-diabetic rats enhanced glycogen synthesis . The ability of syringin to enhance glucose utilization and lower plasma glucose level in rats suffering from insulin deficiency suggest that this chemical may be useful in the treatment of human diabetes.

Stimulatory effect of paeoniflorin on the release of noradrenaline from ileal synaptosomes of guinea-pig in-vitro

The effect of paeoniflorin (an active principle of Paeoniae Radix, commonly used in traditional Chinese medicine) on the release of noradrenaline (norepineprhine) from nerve terminals was investigated using guinea‐pig isolated ileal synaptosomes. Release was determined as the amount of noradrenaline, quantified by high‐performance liquid chromatography‐electrochemical detection, from samples incubated with paeoniflorin or vehicle. Paeoniflorin stimulated the release of noradrenaline in a concentration‐dependent manner without an effect on the level of lactate dehydrogenase in the bathing medium. Tetrodotoxin abolished the action of paeoniflorin at concentrations sufficient to block sodium channels. The depolarizing effect of paeoniflorin on the membrane potential was also illustrated by a concentration‐dependent increase in the fluorescence of bisoxonol. Moreover, the effect of paeoniflorin on bisoxonol fluorescence in ileal synaptosomes seems more potent than that of 4‐aminopyridine. That paeoniflorin causes influx of calcium ions via the depolarization of nerve terminals could be considered. The noradrenaline‐releasing action of paeoniflorin was abolished by removal of calcium chloride from the bathing medium. This action of paeoniflorin was also attenuated by Rp‐cAMP at concentrations sufficient to inhibit the action of cyclic AMP. Therefore, paeoniflorin could induce a calcium‐dependent and cyclic‐AMP‐related release of noradrenaline from sympathetic nerve terminals of guinea‐pig ileum. Guanethidine inhibited the noradrenaline‐releasing action of paeoniflorin in a concentration‐dependent manner. The effect of paeoniflorin on the increase of bisoxonol fluorescence was not modified by atropine. Release of noradrenaline by paeoniflorin from noradrenergic nerve terminals was characterized. These findings suggest that paeoniflorin can stimulate tetrodotoxin‐sensitive depolarization of membranes to result in a calcium‐dependent and cyclic‐AMP‐related release of noradrenaline from noradrenergic nerve terminals.

Inhibitory effects of potassium channel blockers on tetramethylpyrazine-induced relaxation of rat aortic strip in vitro.

Tetramethylpyrazine (TMP) is one of the active principles contained in Ligusticum chuanxiong Hort. (Umbelliferae), a herb that has been widely used to treat vascular disorders in China. In the present study, role of potassium channel in the vasodilatation of TMP was investigated using the effect of potassium channel blocker on TMP induced relaxation in isolated aortic rings from Wistar rats. TMP produced a concentration-dependent relaxation in the aortic rings precontracted with vasopressin or phenylephrine. Similar effect of TMP on vasoconstrictions by phenylephrine and vasopressin, induced through two different receptors, indicating the direct vasodilatation of TMP. Specific inhibitors for potassium channel were used to characterize the role of potassium channel in this action of TMP. Only the inhibitors specific to small conductance calcium-activated potassium (SK(Ca)) channel or ATP-sensitive potassium (K(ATP)) channel inhibited the action of TMP. Also, the TMP-induced relaxation was reversed by the inhibitor of soluble guanylyl cyclase in a way similar to that of K(ATP) channel blockade. The obtained results indicated that vasodilatation induced by TMP is related to the opening of SK(Ca) and K(ATP) channels.

Myricetin Increases Hepatic Peroxisome Proliferator-Activated Receptor α Protein Expression and Decreases Plasma Lipids and Adiposity in Rats

The aim of this study was to investigate the antiobesity and antihyperlipidaemic effects of myricetin. Myricetin exhibited a significant concentration-dependent decrease in the intracellular accumulation of triglyceride in 3T3-L1 adipocytes. The high-fat diet (HFD)-fed rats were dosed orally with myricetin or fenofibrate, once daily for eight weeks. Myricetin (300 mg kg−1 per day) displayed similar characteristics to fenofibrate (100 mg kg−1 per day) in reducing lowered body weight (BW) gain, visceral fat-pad weights and plasma lipid levels of HFD-fed rats. Myricetin also reduced the hepatic triglyceride and cholesterol contents, as well as lowered hepatic lipid droplets accumulation and epididymal adipocyte size in HFD-fed rats. Myricetin and fenofibrate reversed the HFD-induced down-regulation of the hepatic peroxisome proliferator activated receptor (PPAR)α. HFD-induced decreases of the hepatic protein level of acyl-CoA oxidase and cytochrome P450 isoform 4A1 were up-regulated by myricetin and fenofibrate. The elevated expressions of hepatic sterol regulatory element binding proteins (SREBPs) of HFD-fed rats were lowered by myricetin and fenofibrate. These results suggest that myricetin suppressed BW gain and body fat accumulation by increasing the fatty acid oxidation, which was likely mediated via up-regulation of PPARα and down-regulation of SREBP expressions in the liver of HFD-fed rats.

Corni fructus as the major herb of Die-Huang-Wan for lowering plasma glucose in Wistar rats

Die‐Huang‐Wan is a mixture of six herbs used to lower plasma glucose by increasing insulin secretion in normal rats. Die‐Huang‐Wan contains the herbs dioscorea (Dioscoreae rhizoma), cornus (Corni fructus), alisma (Rhizoma alismatis), holelen (Poria), rehmannia (Rehmanniae radix) and tree peony bark (Moutan radicis cortex). The present study was designed to clarify the major herb contributing to the plasma glucose‐lowering action of Die‐Huang‐Wan in rats. A decrease in plasma glucose was not observed in Wistar rats treated with the cornus‐deleted formula of Die‐Huang‐Wan; however, the action was retained in the other herb‐deleted formulas containing cornus. In normal rats, the decrease in plasma glucose and increase in plasma insulin concentrations were dependent on the dose of cornus and were similar to those produced by Die‐Huang‐Wan. Treatment of Wistar rats with each of the other five herbs separately did not result in a decrease in plasma glucose. Moreover, the increase in plasma insulin or reduction in plasma glucose resulting from cornus treatment was blocked by atropine or 4‐diphenylacetoxy‐N‐methylpiperidine methiodide mustard, indicating mediation of muscarinic M3 receptors similar to that caused by Die‐Huang‐Wan. These results suggest that cornus is the major contributor to the plasma glucose‐lowering action in Die‐Huang‐Wan in normal rats.

Antihyperglycemic action of angiotensin II receptor antagonist, valsartan, in streptozotocin-induced diabetic rats

Objectives In the present study, we use valsartan, a highly selective antagonist for angiotensin1 (AT1) receptor subtype, to investigate the effect of AT1 receptor on the plasma glucose metabolism in streptozotocin-induced diabetic rats (STZ-diabetic rats). Methods The plasma glucose concentration was assessed by glucose oxidase method and plasma insulin was measured using enzyme-linked immunosorbent assay. Systolic blood pressure (SBP) was determined by the tail-cuff method. The intravenous glucose challenge test (IVGCT) was carried out to evaluate the effect of valsartan on the glucose utilization in vivo. The mRNA levels of the subtype 4 form of glucose transporter (GLUT4) in soleus muscle and phosphoenolpyruvate carboxykinase (PEPCK) in the liver were detected by Northern blotting analysis. Moreover, the protein levels of GLUT4 in isolated soleus muscle and hepatic PEPCK were investigated using Western blotting analysis. Results A single intravenous injection of valsartan decreased the plasma glucose concentrations in a dose-dependent manner in STZ-diabetic rats. Plasma glucose-lowering action of valsartan also observed in normal rats although in a way not so effective as that in STZ-diabetic rats. Valsartan at the dose of 0.2 mg/kg that produced the maximal plasma glucose-lowering activity in STZ-diabetic rats is also effective to lower the SBP. However, oral treatment with nifedipine or nicorandil in STZ-diabetic rats at the dose sufficient to decrease SBP showed no change of plasma glucose. Otherwise, infusion of saralasin (10 μg/kg per min) into STZ-diabetic rats produced a plasma glucose-lowering activity similar to that by valsartan at 0.2 mg/kg. Moreover, valsartan (0.2 mg/kg) significantly attenuated the raise of plasma glucose induced by IVGCT in normal rats. Repeated intravenous administration of valsartan (0.2 mg/kg) in STZ-diabetic rats resulted in the lowering of plasma glucose after 3 days. The mRNA and protein levels of GLUT4 in the soleus muscle were increased after repeated intravenous administration of valsartan in STZ-diabetic rats for 3 days. Moreover, similar repeated treatment with valsartan reversed the elevated mRNA and protein levels of PEPCK in the liver of STZ-diabetic rats. Conclusions These results suggest that the plasma glucose-lowering activity of AT1 receptor antagonism was associated with an increase in the glucose utilization in peripheral tissue and/or a reduction in hepatic gluconeogenesis in the absence of insulin.

Effect of Topical Application of Chlorogenic Acid on Excision Wound Healing in Rats

This study was undertaken to evaluate the therapeutic effects of topical chlorogenic acid on excision wounds in Wistar rats. A 1 % (w/w) chlorogenic acid or silver sulfadiazine ointment was applied topically once a day for 15 days on full-thickness excision wounds created on rats. The 1 % (w/w) chlorogenic acid ointment had potent wound healing capacity as evident from the wound contraction on the 15th post-surgery day, which was similar to that produced by 1 % (w/w) silver sulfadiazine ointment. Increased rates of epithelialization were observed in the treated rats. It also improved cellular proliferation, increased tumor necrosis factor-α levels during the inflammatory phase (12 h, 24 h, 48 h, and 72 h post-wounding) of wound healing, upregulated transforming growth factor-β1 and elevated collagen IV synthesis in the chlorogenic acid-treated group. The results also indicated that chlorogenic acid possesses potent antioxidant activity by increasing superoxide dismutase, catalase, and glutathione, and decreasing lipid peroxidation. In conclusion, these results demonstrate that topical application of chlorogenic acid can accelerate the process of excision wound healing by its ability to increase collagen synthesis through upregulation of key players such as tumor necrosis factor-α and transforming growth factor-β1 in different phases of wound healing as well as by its antioxidant potential.