Tzong-Cherng Chi

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.

Investigations of the mechanism of the reduction of plasma glucose by cold-stress in streptozotocin-induced diabetic rats

Exposure to a cold environment may increase the activity of the sympathetic nervous system inducing an elevation of plasma norepinephrine and may result in hyperglycemia. In the present study, we found that a hypoglycemic effect was produced in streptozotocin-induced diabetic rats after cold-exposure at 4 degrees C for 1 h. In addition to the blockade of this hypoglycemic effect by guanethidine (a ganglion-blocking agent) and prazosin (an alpha1-adrenoceptor antagonist), an increase of plasma norepinephrine was also observed in streptozotocin-induced diabetic rats receiving this cold-stress. Participation of sympathetic hyperactivity can thus be considered. Furthermore, naloxone, in a dose (0.5 mg/kg, i.p.) sufficient to block opioid receptors, reversed this hypoglycemia. Also, an increase of plasma beta-endorphin-like immunoreactivity was observed in streptozotocin-induced diabetic rats receiving this cold-stress. Intravenous injection of beta-endorphin into streptozotocin-induced diabetic rats produced a lowering of plasma glucose. Administration of methoxamine at a dose sufficient to activate the alpha1-adrenoceptors produced hypoglycemia and a similar increase of plasma beta-endorphin-like immunoreactivity in streptozotocin-induced diabetic rats. However, plasma beta-endorphin-like immunoreactivity level was not modified by similar treatment with methoxamine or cold-stress in normoglycemic rats. Therefore, beta-endorphin appears to be responsible for the induction of hypoglycemic effects in streptozotocin-induced diabetic rats after cold exposure which is different to the response in normal rats.

Activation of adenosine A1 receptors by drugs to lower plasma glucose in streptozotocin-induced diabetic rats.

To examine the role of the adenosine A1 receptor in glucose regulation in the absence of insulin, the present study investigated the changes of plasma glucose in male streptozotocin-induced diabetic rats (STZ-diabetic rats) using dipyridamole to increase endogenous adenosine and N6-cyclopentyladenosine (CPA) to activate the adenosine A1 receptor. Intravenous injections of dipyridamole or CPA induced a dose-dependent decrease of plasma glucose in fasting STZ-diabetic rats. Plasma glucose lowering action of dipyridamole, like that of CPA, was inhibited in a dose-dependent manner by pre-treatment with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) or 8-(p-sulfophenyl)theophylline (8-SPT) at which block the adenosine A1 receptors. Action of the adenosine A1 receptors can thus be considered. In isolated skeletal muscle, CPA enhanced the glucose uptake in a concentration-dependent manner. Blockade of this action by DPCPX and 8-SPT again supported the mediation of the adenosine A1 receptor. Also, CPA produced an increase of glycogen synthesis in isolated soleus muscle. Moreover, CPA decreased plasma triglyceride and cholesterol levels significantly in STZ-diabetic rats. These results suggest that activation of adenosine A1 receptors can increase glucose utilization in peripheral tissues by increasing tissue uptake and glycogen synthesis to lower plasma glucose in rats lacking insulin.

Loss of plasma glucose lowering response to cold stress in opioid μ-receptor knock-out diabetic mice

Opioid mu-receptor plays an important role in the regulation of glucose homeostasis in diabetic rats lacking insulin. Opioid mu-receptor knockout mice were employed to identify the essential role of this receptor in the present study. Western blotting analysis characterized the deletion of opioid mu-receptor in liver of knockout mice as compared to that of normal (wild-type) mice. We found that the plasma glucose concentration of diabetic mice induced by intraperitoneal injection of streptozotocin was markedly decreased after exposure to cold-stress in a cold room for 1 h. However, this plasma glucose lowering response to cold-stress was disappeared in diabetic mice lacking opioid mu-receptor. The important role of opioid mu-receptor in the plasma glucose lowering response to cold stress can thus be considered. Moreover, bilateral adrenalectomy abolished this plasma glucose lowering response to cold stress in diabetic mice with opioid mu-receptor, as compared to the shamed-operated animals. Therefore, activation of opioid mu-receptor by opioid from adrenal gland appears to be responsible for the plasma glucose lowering response to cold-stress in diabetic mice with insulin deficiency.

Stimulation of insulin release in rats by Die-Huang-Wan, a herbal mixture used in Chinese traditional medicine

Die‐Huang‐Wan is a herbal mixture widely used in Chinese traditional medicine to treat diabetic disorders. We have investigated the effect of Die‐Huang‐Wan on plasma glucose concentration in‐vivo. Die‐Huang‐Wan was administered orally (5.0, 15.0 or 26.0 mg kg−1) to three rat models. Wistar rats were used as the normal animal model, rats with insulin‐resistance (induced by the repeated thrice daily injection of human long‐acting insulin) were used as the non‐insulin‐dependent diabetic model, and streptozotocin‐induced diabetic rats were used as the insulin‐dependent diabetic model. In normal rats, approximately 1 h after oral administration of Die‐Huang‐Wan the plasma glucose concentration decreased significantly in a dose‐dependent manner, from 5 to 26.0 mg kg−1. A similar effect was observed in rats with insulin‐resistance. However, this effect was not observed in streptozotocin‐induced diabetic rats, even at an oral dose of 26.0 mg kg−1. These results suggested an insulin‐dependent action, a view supported by the increase of plasma insulin‐like immunoreactivity in normal rats receiving Die‐Huang‐Wan. The results indicated that Die‐Huang‐Wan had an ability to stimulate the secretion of insulin and this preparation seemed helpful in improving the diabetic condition, especially hyperglycaemia in type‐II diabetes.

Sympathetic hyperactivity in Wistar rats with insulin-resistance

In an attempt to know the effect of sustained hyperinsulinemia on sympathetic function, plasma norepinephrine (NE) and glucose levels were measured in Wistar rats with insulin resistance. Both the basal plasma glucose and the plasma NE levels in insulin-resistant rats were markedly higher than that obtained in normal or streptozotocin (STZ)-induced diabetic rats. Treatment with guanethidine and prazosin reversed these sympathetic hyperactive responses in insulin-resistant rats. Moreover, increase of plasma insulin in rats receiving an intraperitoneal glucose challenge test confirmed the mediation of endogenous insulin in this sympathetic hyperactivity. These results suggest an increase of sympathetic activity in insulin-resistant state that may be related to the hypertension-prone associated with diabetes mellitus in clinics.

Less of insulin desensitization in sympathetic nerve terminals from Wistar rats with insulin resistance

In an attempt to determine the effect of hyperinsulinemia on sympathetic function, release of norepinephrine (NE) from isolated aorta by insulin was measured in Wistar rats with insulin resistance. Insulin resistance was produced when the hypoglycemic action of glibenclamide at a dose of 10 mg/kg was almost abolished in rats that received daily injections of long-acting insulin for 15 days. Moreover, the stimulatory effect of insulin on glucose uptake was markedly reduced in both skeletal muscle strips and white adipocytes obtained from these rats with insulin resistance. However, the stimulatory effects of insulin at concentrations from 5 to 15 U/l on the release of NE from the aortic strip of insulin-resistant rats were not modified in the same manner but only slightly reduced compared with that of normal rats. These results suggest that insulin desensitization was produced later in sympathetic nerve terminals than in other organs in insulin-resistant rats and this may be helpful to explain the sympathetic hyperactivity associated with diabetes in clinics.