Sympathetic hyperactivity in Wistar rats with insulin-resistance

Yeast exposure in the preparation of steamed rehmannia root improving its effects on alloxan-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

The root of Rehmannia glutinosa (Gaertn.) DC. has been used in China for more than 2000 years to treat various diseases including diabetes mellitus (DM) and its complications. Steamed rehmannia root (SRR) is one of the mainly used forms. During its preparation, the material has the chance to be exposed to microorganisms, particularly yeast. The aim of this study is to verify the effect of SRR on diabetes complications and the necessity of yeast exposure.

MATERIALS AND METHODS

Water extract of SRR was incubated with alcohol yeast to obtain fermented SRR (FSRR). Alloxan-induced diabetic rats were administrated with medicated animal chows for 8 weeks. Urine volume, fasted blood glucose and food intake were monitored, and open field test and tail immersion test were conducted in the last week, plasma and urine samples were subjected to biochemical examinations.

RESULTS

In DM rats, defecation in open field test was found reduced, and tail flick latency in tail immersion test increased. In the meantime, urinary excretions of Na(+), K(+), aldosterone, albumin and creatinine increased, and plasma concentrations of Na(+), K(+) and creatinine reduced and those of aldosterone, TXB₂/6-Keto-PGF(1α) and urea nitrogen elevated. Most of these indicators were significantly improved by FSRR administration, but the effects of SRR were relatively inferior in several aspects. However, SRR and FSRR could not improve the typical symptoms of DM.

CONCLUSIONS

Our data demonstrated that both SRR and FSRR have no obvious hypoglycemic effect, but have the potential to prevent the onset and development of diabetes complications, and this function can be improved by yeast exposure.

Effects of tempol on endothelial and vascular dysfunctions and insulin resistance induced by a high-fat high-sucrose diet in the rat

We investigated the effects of treatment with tempol (an antioxidant) on vascular and metabolic dysfunction induced by a high-fat high-sucrose (HFHS) diet. Rats were randomized to receive an HFHS or chow diet with or without tempol treatment (1.5 mmol·(kg body mass)−1·day−1) for 4 weeks. Blood pressure, heart rate, and blood flow were measured in the rats by using intravascular catheters and Doppler flow probes. Insulin sensitivity and vascular responses to insulin were assessed during a euglycemic–hyperinsulinemic clamp. In-vitro studies were performed to evaluate vascular reactivity and endothelial and inducible nitric oxide synthase (eNOS; iNOS) expression in vascular and muscle tissues. Endothelin, nitrotyrosine, and NAD(P)H oxidase expressions were determined in vascular tissues, and glucose transport activity and glucose transporter 4 (GLUT4) expression were examined in muscles. Tempol treatment was found to prevent alterations in insulin sensitivity, glucose transport activity, GLUT4 expression, and vascular reactivity, and to prevent increases in plasma insulin, blood pressure, and heart rate noted in the untreated HFHS-fed rats. These were associated with increased levels of eNOS expression in vascular and muscle tissues, but reductions in nitrotyrosine, endothelin, NAD(P)H oxidase, and iNOS expressions. Therefore, oxidative stress induced by a relatively short-term HFHS diet could contribute to the early development of vascular and metabolic abnormalities in rats.

Serotonin enhances β-endorphin secretion to lower plasma glucose in streptozotocin-induced diabetic rats

Although serotonin, serotonin uptake inhibitors and serotonin precursors (including tryptophan or 5-hydroxytryptophan) are known to have hypoglycemic action in rodents or human, it is not clear whether serotonin has hypoglycemic effect in streptozotocin-induced diabetic rats (STZ-diabetic rats). The aim of this study was to investigate the action of serotonin in regulating the plasma glucose STZ-diabetic rats. Plasma glucose, insulin, beta-endorphin and adrenaline were assessed after intraperitoneal administration of serotonin. Serotonin produced hypoglycemic effects without altering plasma insulin and adrenaline levels but increasing beta-endorphin level in STZ-diabetic rats. The glycogen content in soleus muscle was increased at 90 min after application of serotonin (0.3 mg/kg) in STZ-diabetic rats. Dihydroergotamine (non-selective 5-HT receptor blocker) and pimozide (5-HT(7) receptor blocker) abolished the hypoglycemic effect of serotonin in STZ-diabetic rats. Serotonin-induced hypoglycemic effect in association with the increase of beta-endorphin release was abolished in bilaterally adrenalectomized STZ-diabetic rats. In isolated adrenal gland of STZ-diabetic rats, the increase of beta-endorphin secretion in response to serotonin was reduced by either dihydroergotamine or pimozide. Pretreatment with naloxone (1.0 mg/kg, i.p.) prevented serotonin-induced plasma glucose lowering effect in STZ-diabetic rats. The results demonstrated that serotonin may activate 5-HT(7) receptor on rat adrenal gland to enhance of beta-endorphin secretion, which then stimulates the opioid receptor to increase peripheral glucose utilization, resulting in decreased plasma glucose levels in STZ-diabetic rats.

Soluble leptin receptor and insulin resistance as determinant of sleep apnea

OBJECTIVE

To investigate the possible associations between sleep apnea syndrome, hyperinsulinemia/insulin resistance and hyperleptinemia in subjects with different degrees of body mass index.

DESIGN

To test for the presence or absence of sleep apnea syndrome in association with hyperinsulinemia/insulin resistance and hyperleptinemia.

SUBJECTS

Twenty subjects with different body mass index (mean BMI 30.9+/-4.2).

MEASUREMENTS

Insulin action and plasma soluble leptin receptor were measured by euglycemic hyperinsulinemic glucose clamp and by ELISA method, respectively. Occurrence of sleep apnea syndrome was assessed by clinical and nocturnal monitoring using a validated sleep apnea recorder.

RESULTS

The apnea/hypopnea index (AHI) was positively correlated with plasma soluble leptin receptor (0.76; P<0.001) and negatively with the degree of insulin-mediated glucose uptake (r=-0.73; P<0.001). In a multivariate analysis AHI was associated with plasma soluble leptin receptor and insulin mediated glucose uptake independently of age, gender, BMI, plasma leptin levels and PaCO(2).

CONCLUSION

Sleep apnea syndrome is associated with plasma soluble leptin receptor and insulin resistance independently of BMI.

Sympathetic nervous system and experimental diabetes: role of adrenal medullary hormones

The sympathetic nervous system is of major importance in the regulation of various physiological functions. The present review discusses the mechanisms which control glucose homeostasis and the role of the sympathetic nervous system in experimental diabetes with special emphasis on the role of adrenal medullary hormones, over-activity of the sympathetic nervous system and its relationship to hypertension in the diabetic state and the effect of stress. The chapter also reviews the ability of various drugs and pharmacological agents to produce hyperglycemia in experimental animals and how this information can be used in screening new chemical entities and in differentiating the mode of action of these agents.

Chronic hypoxia stimulates periarterial sympathetic nerve development in chicken embryo

BACKGROUND

Epidemiological findings suggest an association between low-for-age birth weight and the risk to develop coronary heart diseases in adulthood. During pregnancy, an imbalance between fetal demands and supply may result in permanent alterations of neuroendocrine development in the fetus. We evaluated whether chronic prenatal hypoxia increases arterial sympathetic innervation.

METHODS AND RESULTS

Chicken embryos were maintained from 0.3 to 0.9 of the 21-day incubation period under normoxic (21% O(2)) or hypoxic conditions (15% O(2)). At 0.9 incubation, the degree of sympathetic innervation of the embryonic femoral artery was determined by biochemical, histological, and functional (in vitro contractile reactivity) techniques. Chronic hypoxia increased embryonic mortality (32% versus 13%), reduced body weight (21.9+/-0.4 versus 25.4+/-0.6 g), increased femoral artery norepinephrine (NE) content (78.4+/-9.4 versus 57.5+/-5.0 pg/mm vessel length), and increased the density of periarterial sympathetic nerve fibers (14.4+/-0.7 versus 12.5+/-0.6 counts/10(4) microm(2)). Arteries from hypoxic embryos were less sensitive to NE (pD(2), 5.99+/-0.04 versus 6. 21+/-0.10). In the presence of cocaine, however, differences in sensitivity were no longer present. In the embryonic heart, NE content (156.9+/-11.0 versus 108.1+/-14.7 pg/mg wet wt) was also increased after chronic hypoxia.

CONCLUSIONS

In the chicken embryo, chronic moderate hypoxia leads to sympathetic hyperinnervation of the arterial system. In humans, an analogous mechanism may increase the risk for cardiovascular disease in adult life.

Relationship between insulin resistance and cardiac sympathetic nervous function in essential hypertension

BACKGROUND

It has been suggested that hyperinsulinemia and insulin resistance participate in the pathogenesis of hypertension, in part by activating sympathetic activity.

OBJECTIVE

We aimed to examine the relationship between insulin resistance and cardiac sympathetic nervous function in patients with essential hypertension using 123I-metaiodobenzylguanidine (MIBG) cardiac scintigraphy.

METHODS AND RESULTS

Twenty-eight patients (18 men) with essential hypertension and 11 (seven men) control individuals with a mean age of 55.8+/-3.3 years were recruited. Patients with diabetes mellitus, congestive heart failure or coronary artery disease were excluded from this study. To evaluate insulin resistance, we used steady-state plasma glucose (SSPG; mg/dl) levels measured by the SSPG method. To evaluate cardiac sympathetic nervous function, we calculated the heart-to-mediastinum ratio from the delayed MIBG image (H:M-D) and the mean washout rate (WOR, %). There were significant differences (P<0.01) in SSPG, H:M-D and WOR between the essential hypertension and control individual groups (125 versus 103 mg/dl, 2.2 versus 2.4, and 32 versus 23%, respectively). Stepwise regression analysis showed that SSPG and plasma norepinephrine level are independent predictors for the cardiac sympathetic nervous function obtained from MIBG scintigraphy.

CONCLUSIONS

These findings indicate that insulin resistance is significantly related to activation of the cardiac sympathetic nervous function associated with left ventricular hypertrophy in patients with essential hypertension.