Regulatory mechanism of the ventromedial hypothalamus in enhancing glucose uptake in skeletal muscles

To evaluate roles of the sympathetic nervous system in enhancing glucose uptake in skeletal muscles in response to electrical stimulation of the ventromedial hypothalamic nucleus (VMH), the effects of guanethidine treatment and adrenal demedullation on the response were examined in rats anesthetized and injected with muscle relaxant, pancuronium bromide. Pretreatment with guanethidine effectively suppressed the increase in the rate constant of glucose uptake, measured by the 2-deoxy-d-[³H]glucose method, in skeletal muscles upon VMH stimulation. However, bilateral adrenodemedullation had no significant effect. These results suggest that the VMH is intimately concerned in the regulation of glucose uptake in skeletal muscles through intermediation of the sympathetic nerves.     

Inhibition of central GABAA receptors enhances hepatic glucose production and peripheral glucose uptake

Previous studies have demonstrated that intracerebroventricular (ICV) injection of bicuculline methiodide (BMI), a gamma-amkrobutyric acid receptor antagonist, increases plasma glucose concentrations. The purpose of the present study was to determine whether the hyperglycemic response was due to an increased rate of hepatic glucose production (HGP) or a change in the rate of glucose utilization. In vivo glucose flux was assessed in catheterized, conscious overnight fasted rats using [3-³H]glucose. ICV injection of BMI (10 nmol) increased glucose levels 60% after 30 min. This hyperglycemia resulted from a rapid increase in HGP that exceeded an increased rate of glucose utilization. No alteration in the glucose metabolic clearance rate, an index of the avidity of the body's tissues for glucose, was detected in BMI-Injected rats. BMI enhanced both hepatic gluconeogermals and glycogenolysis, since the reduction in War glycogen (19 μmol/g liver) could not totally account for all of the increased HGP. These metabolic alterations were associated with sustained increases in circulating concentrations of corticosterone, giucagon and catecholamines. Prior adrenalectomy completely abolished the BMI-induced increase in glucose flux and the reduction in tissue glycogen, despite the persistent hyperglucagonemia. These data indicate that, in the fasted condition, the hyperglycemia produced by central administration of BMI results from an increased rate of HGP (both gluconeogenesis and glycogenolysis) and not a reduction in the ability of tissues to use glucose. The concomitant elevation in glucose disposal was the result of an increased mass action effect. The enhanced glucose metabolic response to BMI appears mediated exclusively by an increased secretion of epinephrine from the adrenal medulla.     

Effects of two estradiol antagonists upon the estradiol uptake in the rat brain and peripheral tissues.

Two estradiol antagonists, Parke-Davis CI 628 and CI 680, were studied for their inhibitory potency against labeled estradiol uptake within the hypothalamus, cerebral cortex, pituitary and uterus of the ovariectomized rat. Both drugs, tested from 15 min to 24 h prior to estradiol, induced a fast and long-lasting decrease of the hormone uptake. Three degrees of inhibition were observed depending on the tissue studied: (a) the most important inhibition concerned uterus and pituitary, where the estradiol uptake was prevented by up to 90% by the largest doses of antagonists used (6.3 and 6.1 mg, respectively, for CI 268 and CI 680); (b) in the hypothalamus, the estradiol uptake was counteracted to a lower degree; the inhibition being 39% for anterior hypothalamus and 22% for medial posterior hypothalamus; (c) cerebral cortex uptake was completely unaffected by pretreatments with the antagonists. After subcellular fractionation it was observed that the nuclear uptake of estradiol was completely abolished in both hypophyseal and hypothalamic tissues if the hormonal injection was preceded by the administration of 6.3 mg of CI 628.     

Ability of the tissues to assimilate glucose and the pyruvate and lactate levels after intravenous glucose load in patients with peripheral facial paralysis

In 60 control subjects and 48 patients with peripheral facial nerve palsy carbohydrate metabolism was tested performing a rapid intravenous glucose tolerance test with 0.5 g glucose per 1 kg of actual body weight and with determination of concentrations of glucose, pyruvate and lactate at rest in fasting state and after intravenous glucose load. Glucose was determined in capillary blood by the orthotoluidine method, pyruvate and lactate in venous blood by the enzymatic method. In the group of patients with facial nerve palsy a significantly lower number of subjects had a normal ability of glucose assimilation by tissues and a significantly higher frequency of pathological results of glucose tolerance test with a high prevalence of fasting hyperglycaemia. In patients with abnormal glucose tolerance test the fasting pyruvate concentration was high. After an intravenous glucose load the concentration of pyruvate in the 120th minute of the test was significantly increased (p less than 0.05) in patients with facial nerve palsy independently of the degree of glucose tolerance impairment. In patients with pathological result of the glucose tolerance test disturbances were observed also in lactate concentration. The production of lactate was decreased in the initial phase and then it was increased in the time up to 120 minutes. No direct correlation was observed between the disturbances of pyruvate concentration and the preserved ability of glucose assimilation by the peripheral tissues.     

Role of alpha1A-adrenoceptor in the regulation of glucose uptake into white adipocyte of rats in vitro

In an attempt to know the functional role of alpha1A-adrenoceptors in adipose tissue, white adipocytes (WAT) of Wistar rats were used to investigate the change of glucose uptake after pharmacological activation of alpha1-adrenoceptors. Methoxamine enhanced the uptake of radioactive glucose into isolated WAT in a concentration-dependent manner. Translocation of glucose transporter (GLUT4) from cytosol to membrane was also stimulated with methoxamine. Action of methoxamine to raise glucose uptake was abolished in WAT pre-incubated with the antagonists, both tamsulosin and WB 4101, at concentrations sufficient to block alpha1A-adrenoceptors. However, chlorethylclonidine (CEC). the antagonist of alpha1B-adrenoceptors, showed the inhibition of methoxamine-induced action only at a higher concentration. Even under the treatment with maximal concentration of CEC, methoxamine can produce action about 80% of the vehicle-treated control. The major role of alpha1A-adrenoceptors in the stimulation of glucose uptake by methoxamine can thus be considered. In the presence of specific inhibitor of phospholipase C (PLC), U73312, methoxamine-stimulated glucose uptake into WAT was reduced in a concentration-dependent manner and U73343, the negative control of U73312, did not affect the action of methoxamine. Moreover, chelerythrine and GF 109203X diminished the methoxamine-stimulated glucose uptake at a concentration sufficient to inhibit protein kinase C (PKC). Inhibition of phosphoinositide-3 kinase (PI-3 kinase) by LY294002 also abolished methoxamine-stimulated glucose uptake. Therefore. the obtained data suggest that an activation of alpha1A-adrenoceptors, presence in WAT, by agonist and/or neurotransmitter may increase the glucose uptake via PLC-PKC pathway and the activation of PI-3 kinase.     

Effects of glucose on multiple-unit activity of the hypothalamus in female rats.

Multi-unit activity was recorded from diencephalic and nondiencephalic sites in female rats. Increased, decreased, or unchanged levels of activity were equally probable responses to injections of 30% glucose at all recording sites, so that it was not possible to define a locus within the diencephalon of the female rat which responded to glucose in a consistent and specifiable manner. Lesions of the medial hypothalamus did not consistently eliminate the lateral hypothalamic response to glucose. The results are discussed in terms of the glucostatic control of feeding behavior in the rat and in terms of possible species differences between rats and cats.     

成骨细胞对葡萄糖水平的感知作用

背景：新近研究表明,骨钙素可提高胰岛素分泌水平、胰岛素敏感性,并且可阻止脂肪的积累,参与糖脂代谢,发挥此作用的主要是羧化不全骨钙素。 目的：观察不同浓度葡萄糖对成骨细胞羧化不全骨钙素分泌水平的影响。 方法：切下人肋骨骨小梁剪碎,胰酶消化后以PBS彻底冲洗直至于倒置显微镜下观察骨片表面及清洗液中无粘着及漂浮的细胞,以DMEM完全培养液清洗骨小梁1次,移入培养瓶内培养,每周更换培养液1次,1周后可见成骨细胞自骨片移出,4~6周细胞融合成单层可作传代培养。取生长活跃的传二三代细胞接种于6孔板中分成5组,待细胞融合至80%以含5.6,7.6,9.6,12.6,20.6 mmol/L葡萄糖的培养基刺激成骨细胞,同时加入维生素K2使其在培养液中最终浓度为10-5 mol/L。培养半小时后收集上清液,以放免法检测成骨细胞培养上清液中羧化不全骨钙素水平,并以上清液中总骨钙素进行校正,计算羧化不全骨钙素率。 结果与结论：在不同葡萄糖浓度下成骨细胞羧化不全骨钙素分泌水平不同,7.6,9.6,20.6 mmol/L葡萄糖浓度组羧化不全骨钙素率高于5.6 mmol/L葡萄糖浓度组[(0.27±0.02),(0.29±0.04),(0.12±0.02)%,P < 0.05]。提示成骨细胞可感知葡萄糖浓度变化,在5.6~9.6 mmol/L葡萄糖刺激下成骨细胞可呈剂量依赖性地提高自身羧化不全骨钙素分泌水平,进一步提高葡萄糖浓度时羧化不全骨钙素水平反而降低。     

Serotonergic innervation of the lateral hypothalamus: Evidence from synaptosomal uptake studies

Uptake of tritiated serotonin by synaptosomes prepared from rat lateral hypothalamus was examined. Uptake of serotonin into lateral hypothalamic synaptosomes occurred by both saturable and non-saturable processes. The saturable process was a high affinity transport with kinetic parameters that agree closely with those previously reported for serotonin uptake into synaptosomes prepared from other brain regions. Fluoxetine, a selective inhibitor of uptake into serotonergic neurons, was a potent inhibitor of serotonin uptake into lateral hypothalamic synaptosomes. Desipramine and benztropine, noradrenergic and dopaminergic uptake inhibitors respectively, were much less effective. Damage to the ascending serotonergic system, by either electrolytic lesion of the dorsal or median raphe nucleus, or by 5,7 dihydroxytryptamine injections into the midbrain serotonergic pathways, significantly reduced the uptake of serotonin by lateral hypothalamic synaptosomes. Taken together, these data provide further evidence for a serotonergic terminal field within the lateral hypothalamus.     

Electrolytic lesions of the lateral hypothalamus influence peripheral blood NK cytotoxicity in rats

Bilateral electrolytic lesions of the lateral hypothalamic (LH) area in Wistar rats result in a time-dependent blood NK cytotoxicity changes as measured by the ⁵¹Cr-release (for entire cell population) and agarose (for a single-cell) assays. NK activity against YAC-1 and K-562 cells shift from depression through enhancement to another depression on the 2nd, 5th and 21st post-lesion day, respectively, as compared to both LH sham-operated animals and the pre-lesion baselines. This effect is not attributable to malnutrition and dehydration resulting from ingestive impairments evoked by LH lesions. No significant change in NK cytotoxicity was found after destruction of the medial hypothalamus (MH). The results indicate that LH, under normal conditions, which may be considered as a dynamogenic and stressogenic hypothalamic area is essential for proper regulations of NK cytotoxicity at both population and single-cell level.     

Interleukin-1-like immunoreactivity in peripheral tissues

Rabbit antisera were raised against a synthetic peptide corresponding to the amino acid residues 169-194 in the murine interleukin-1 sequence. Immunoreactive varicose fibers were observed in the vas deferens, urinary bladder, gastrointestinal tract, and coeliac-superior mesenteric ganglion complex of the rat. Fibers were also encountered around blood vessels in several organs including the thymus, spleen, lymph nodes, liver, and kidney.     

Role of glutamate in the amygdala and lateral hypothalamus in conditioned taste aversion

The role of glutamate in conditioned taste aversion was investigated. Both, in the amygdala (AMYG) and in the lateral hypothalamus (LH) extracellular levels of glutamate were assessed by microdialysis and capillary electrophoresis with laser induced fluorescence detection. Rats were conditioned by pairing a novel flavor (strawberry flavor) with an intraperitoneal injection of lithium chloride. When the conditioned stimulus (strawberry flavored solution) was injected into the mouth of conditioned rats, there was an increase of glutamate release in the AMYG, and a decrease in glutamate release in the LH. These results predicted that glutamate release in the AMYG and the LH was involved in CTA. This possibility was tested by MK-801 (glutamate antagonist) and glutamate microinjections. MK-801 injections in AMYG attenuated the rejection of the novel flavor, and in the LH did not cause any effect on CTA. Glutamate microinjections in the AMYG caused CTA. These results suggest that glutamatergic activity in the AMYG might be a relevant neurochemical correlate and cause of conditioned taste aversion.     

Antipsychotic drugs affect glucose uptake and the expression of glucose transporters in PC12 cells.

1. Adherence of the PC12 cell line to poly-l-lysine (PLL) on tissue culture dishes stimulated glucose transport into the cells. Fluphenazine, chlorpromazine, clozapine and haloperidol inhibited glucose uptake in this system after a short (30 min) preincubation with drug. The IC50's for this effect were typically in the range of 5-40 microM. 2. Following longer exposures of the drugs (24 hr), there was a significant increase (approximately 3-fold) in the cellular levels of the glucose transporter (GLUT) isoforms, GLUT1 and GLUT3. 3. Long-term incubation (48 hr), especially with the phenothiazine drugs, was accompanied by a marked reduction in cell growth and proliferation. The rank ordering of the potencies of the drugs was essentially the same for these various effects: fluphenazine > chlorpromazine > clozapine approximately haloperidol. 4. It is suggested that the effects on glucose transport reported here may complicate the interpretation of positron emission tomography (PET) studies that rely on the uptake of radiolabeled glucose analogs to measure the physiological response to these drugs.     

Estradiol enhances brain glucose uptake in ovariectomized rats

This study was designed to investigate the effects of 17β-estradiol benzoate (E₂B) on brain glucose uptake and transport across the blood-brain barrier (BBB). Both a time- and dose-response evaluation of the effect of E₂B on glucose uptake in the central nervous system (CNS) were conducted. E₂B, in doses ranging from 1 to 100 μg/kg body weight, was injected subcutaneousy at 2 to 24 h prior to evaluation. The 4h time point and 10 μg/kg dose of E213 produced the most widespread increases in glucose uptake. Six regions responded to E213 with elevated glucose uptake by as much as 120% when compared to oil-treated controls. We then evaluated the effects of E213 on transport of glucose across the BBB. E₂B significantly increased the extraction of labeled sugar across the BBB by 40% without affecting extraction of the internal standard. Collectlvey, these studies indicate that physiological levels of estradiol (E₂) may play an important role in modulating cerebral glucose homeostasis.     

Role of the ventromedial hypothalamus in the regulation of adenohypophyseal immunoreactive dynorphin in the rat

In this study, we have examined the role of the dorsomedial (DMH), ventromedial (VMH) and arcuate (ARH) nuclei of the hypothalamus in the control of hypothalamic and pituitary immunoreactive (ir) dynorphin (Dyn) A and ir-Dyn B in the rat, by evaluating the effect of discrete, bilateral radiofrequency lesions in these structures. Lesions limited to the VMH reduced the content of ir-Dyn in the anterior pituitary but not in the neurointermediate lobe or in the hypothalamus. Gel chromatographic analysis of anterior pituitary extracts confirmed that ir-Dyn is mainly associated with high molecular weight forms containing Dyn A and Dyn B in their sequence. Anterior pituitary extracts of VMH-lesioned rats displayed a clearly lower proportion of these forms. Destruction of the DMH affected only the hypothalamic content of ir-Dyn; ablation of the ARH did not cause any significant change. Our results suggest that ablation of the VMH may disrupt critical neuronal connections to the median eminence originating in this nucleus or crossing it and participating in control of the adenohypophyseal pool of ir-Dyn.