Diet-induced obesity alters dural CGRP release and potentiates TRPA1-mediated trigeminovascular responses.

Background Clinical studies suggest a link between obesity and the primary headache disorder migraine. In our study we aimed to reveal the effect of obesity on meningeal nociceptor function in rats receiving a high-fat, high-sucrose diet. Methods Transient receptor potential ankyrin 1 (TRPA1) receptor activation-induced changes in meningeal blood flow, release of calcitonin gene-related peptide (CGRP) from trigeminal afferents and TRPA1 protein expression in the trigeminal ganglia were measured in control and obese rats. Metabolic parameters of the animals were assessed by measuring glucose and insulin homeostasis as well as plasma cytokine concentrations. Results The present experiments revealed an enhanced basal and TRPA1 receptor agonist-induced CGRP release from meningeal afferents of obese insulin-resistant rats and an attenuated CGRP release to potassium chloride. Obesity was also associated with an augmented vasodilatation in meningeal arteries after dural application of the TRPA1 agonist acrolein, a reduction in TRPA1 protein expression in the trigeminal ganglia and elevations in circulating proinflammatory cytokines IL-1ß and IL-6 in addition to increased fasting blood glucose and insulin concentrations. Conclusions Our results suggest trigeminal sensitisation as a mechanism for enhanced headache susceptibility in obese individuals after chemical exposure of trigeminal nociceptors.

Diet-Induced Obesity Enhances TRPV1-Mediated Neurovascular Reactions in the Dura Mater.

OBJECTIVE: Exploring the pathophysiological changes in transient receptor potential vanilloid 1 (TRPV1) receptor of the trigeminovascular system in high-fat, high-sucrose (HFHS) diet-induced obesity of experimental animals. BACKGROUND: Clinical and experimental observations suggest a link between obesity and migraine. Accumulating evidence indicates that metabolic and immunological alterations associated with obesity may potentially modulate trigeminovascular functions. A possible target for obesity-induced pathophysiological changes is the TRPV1/capsaicin receptor which is implicated in the pathomechanism of headaches in a complex way. METHODS: Male Sprague-Dawley rats were fed a regular (n = 25) or HFHS diet (n = 26) for 20 weeks. At the end of the dietary period, body weight of the animals was normally distributed in both groups and it was significantly higher in animals on HFHS diet. Therefore, experimental groups were regarded as control and HFHS diet-induced obese groups. Capsaicin-induced changes in meningeal blood flow and release of calcitonin gene-related peptide (CGRP) from dural trigeminal afferents were measured in control and obese rats. The distribution of TRPV1- and CGRP-immunoreactive meningeal sensory nerves was also compared in whole mount preparations of the dura mater. Metabolic parameters of the animals were assessed by examining glucose and insulin homeostasis as well as plasma cytokine concentrations. RESULTS: HFHS diet was accompanied by reduced food consumption and greater fluid and energy intakes in addition to increased body weight of the animals. HFHS diet increased fasting blood glucose and insulin concentrations as well as levels of circulating proinflammatory cytokines interleukin-1ß and interleukin-6. In obese animals, dural application of the archetypal TRPV1 agonist capsaicin resulted in significantly augmented vasodilatory and vasoconstrictor responses as compared to controls. Diet-induced obesity was also associated with enhanced basal and capsaicin-induced CGRP release from meningeal afferents ex vivo. Except for minor morphological changes, the distribution of dural TRPV1- and CGRP-immunoreactive afferents was similar in control and obese animals. CONCLUSIONS: Our results suggest that obesity induced by long-term HFHS diet results in sensitization of the trigeminovascular system. Changes in TRPV1-mediated vascular reactions and CGRP release are pathophysiological alterations that may be of relevance to the enhanced headache susceptibility of obese individuals.

Beneficial cardiac effects of cicletanine in conscious rabbits with metabolic syndrome.

BACKGROUND AND PURPOSE: High-fat diet and consequent metabolic syndrome (MS) can lead to elevated risk for cardiac arrhythmias. This preclinical study was to investigate if cicletanine (CIC) could produce cardioprotective effects in conscious rabbits exhibiting the main symptoms of MS. METHODS: NZW rabbits that had undergone an 8-week-long cholesterol-enriched diet (1.5%) were instrumented with a pacemaker electrode and randomly assigned into 3 groups according to the oral treatment of either CIC (50 mg·kg) or sotalol (25 mg·kg) and their placebo b.i.d. over 5 days. Study groups were subjected to either "arrhythmia challenge" by programmed electrical stimulation in the "Arrhythmogenesis" study (N = 54) or global myocardial ischemia by rapid pacing in the "Ventricular Overdrive Pacing-induced Myocardial Ischemia" study (N = 18). The antiarrhythmic effect was evaluated by the establishment of the incidence of programmed electrical stimulation-induced arrhythmias. Proarrhythmia indicators (eg, QTc, Tpeak-Tend) were also measured to assess the cardiac safety profile of CIC. To evaluate the background of antiarrhythmic effect, cardiac cyclic nucleotide (cyclic 3',5'-guanosine monophosphate [cGMP], cyclic 3',5'-adenosine monophosphate [cAMP]) and nitric oxide content were determined. The antiischemic effect was characterized by change of intracavital ST segment. RESULTS: Cicletanine treatment significantly decreased the incidence of ventricular arrhythmias, increased cardiac cGMP and nitric oxide content and reduced cardiac cAMP level. Cicletanine did not modify significantly QTc and Tpeak-Tend interval. The ST-segment change in response to rapid pacing was reduced significantly by CIC. (P < 0.05). CONCLUSIONS: Cicletanine exerts beneficial cardiac effects in rabbits with symptoms of MS, which may be of influence with regard to the clinical application of the drug.

Block by nitrate tolerance of meal-induced insulin sensitization in conscious rabbits.

PURPOSE: Hemodynamic nitrate tolerance has been shown to result in an insulin-resistant state. We studied whether nitrate tolerance induced by a 7-day continuous exposure to transdermal nitroglycerin influenced the meal-induced insulin sensitization phenomenon in rabbits. METHODS: Changes in insulin sensitivity in response to feeding in conscious rabbits were determined by rapid insulin sensitivity test, in both nitrate-tolerant and nitrate-intolerant animals. In a separate series of experiments with anesthetized rabbits with or without nitrate tolerance, the hyperinsulinemic euglycemic glucose clamping methods was used to study the effect of intraportal infusion of cholecystokinin (CCK) on whole-body insulin sensitivity. RESULTS: Rabbits with normal feeding exhibited a 46 ± 6% increase in insulin sensitivity as compared with their matching fasting controls. A 7-day period of treatment with patches releasing 0.07 mg of nitroglycerin per hour yielded nitrate tolerance and a state of insulin resistance and no increase in insulin sensitivity in response to food. Intraportal infusion of CCK8 (0.3-3.0 µg/kg over 20 minutes) resulted in a dose-dependent increase in insulin sensitivity in normal but not in nitrate-tolerant, fasted anesthetized animals. CONCLUSIONS: Nitrate tolerance blocks both the meal-induced insulin sensitization phenomenon and the insulin-sensitizing effect of intraportal CCK.

Morphological, hemodynamical and hemorheological changes of mature artificial saphenous arterio-venous shunts in the rat model.

Artificial femoral arterio-venous (AV) shunts are widely used in rodent models for studying shunt maturation and to optimize various surgical techniques. However, little is known about complex circulatory, microcirculatory, and hemorheological effects of end-to-side saphenous AV shunts. We aimed to study these parameters in mature AV shunts. Studying these questions in CD rats, end-to-side anastomoses were made between the left saphenous artery and vein. On the right-side the nonoperated saphenous vessels served as own control. Furthermore healthy control animals were also investigated. On the 8th to 12th postoperative week microcirculatory and blood flow measurements were performed and blood samples were taken both from the shunt's arterial and venous limbs and from the nonoperated side vessels. Hematological parameters, erythrocyte aggregation, and deformability were determined. The entire shunt and the control vessels were removed for histological examinations. The skin microcirculation on shunt side slightly increased on thigh and decreased on paws versus the nonoperated side. Blood flow measurements made directly on the vessels showed that arterial to venous blood flow rate ratio was 1.59 ± 0.29 on nonoperated side and 1.2 ± 0.13 on the shunt side, and 1.49 ± 0.05 in control animals. Erythrocyte aggregation and deformability worsened on the shunt side. Histologically increased number of smooth muscle elements and connective tissue were found in venous limb of the shunts. The artificial AV shunt between the saphenous artery and vein seems to be a suitable model for further functional-morphological and hemorheological examinations of hemodialysis in various states and diseases.

Effect of Anthocyanin-Rich Tart Cherry Extract on Inflammatory Mediators and Adipokines Involved in Type 2 Diabetes in a High Fat Diet Induced Obesity Mouse Model.

Male C57BL/6J mice were used to determine the possible therapeutic effects of our previously described tart cherry extract in a chronic obesity mouse model on metabolic parameters, glucose tolerance, inflammatory mediators, and antioxidant capacity. The control group received standard mouse chow, and the high fat control group was switched to a high fat diet and tap water supplemented with 5% sucrose. The high fat + anthocyanin group received the high fat and sucrose diet, but received the anthocyanin-rich tart cherry extract dissolved in their drinking water. After six weeks, an oral glucose tolerance test was performed, and the water-soluble antioxidant capacity (ACW), superoxide dismutase (SOD) activity, and the plasma levels of insulin, C-peptide, leptin, IL-6, MCP-1, adiponectin and resistin were measured. The high fat diet increased body weight, reduced glucose tolerance, and caused an elevation in leptin, IL-6, MCP-1, and resistin levels. Furthermore, antioxidant capacity was decreased with a significant elevation of SOD activity. Anthocyanin treatment failed to reverse the effects of the high fat diet on body weight and glucose tolerance, but significantly reduced the leptin and IL-6 levels. The tart cherry extract also made a significant enhancement in antioxidant capacity and SOD activity. Our results show that chronic anthocyanin intake has a potential to enhance redox status and alleviate inflammation associated with obesity.

Isolation of allithiamine from Hungarian red sweet pepper seed (Capsicum annuum L.).

A natural fat-soluble thiamine derivative, namely N-[(4-amino-2-methylpyrimidin-5-yl)methyl]-N-[(2E)-5-hydroxy-3-(prop-2-en-1-yldisulfanyl)pent-2-en-2-yl]formamide (allithiamine) has been identified only in garlic (Allium sativum) until now. Hungarian red sweet pepper (Capsicum annuum) was found as a new source of allithiamine. Extraction procedure and analytical method were developed for the isolation of allithiamine and a chemical synthesis of the compound was also developed. First solid-liquid extraction was performed with 96 % ethanol to isolate allithiamine from pepper seeds. Thereafter, solid phase extraction was applied from ethanolic extract using C18 cartridge to concentrate and purify samples for further analysis. The structure of the synthesized and the isolated compounds was verified by reverse phase HPLC, HPLC-MS, MALD-TOF MS and NMR. Furthermore, effect of allithiamine was investigated on streptozotocin-induced diabetic mice with neuropathy. The results show that neuropathic pain sensation is improved by allithiamine treatment similarly to benfothiamine.

The inhibitory effect of proglumide on meal-induced insulin sensitization in rats.

We studied the role of cholecystokinin in meal-induced insulin sensitization in rats. Experiments were done with fed or fasted male Wistar rats. Whole-body insulin sensitivity was determined by the rapid insulin sensitivity test in either group. The fed animals were more sensitive to the hypoglycemic effect of insulin than those in the fasted group. Single intravenous doses of proglumide, a cholecystokinin-1 receptor antagonist, decreased insulin sensitivity in fed animals in a dose-dependent manner, whereas it was without effect in the fasted state. We conclude that prandial insulin sensitization strongly depends on pathways regulated by cholecystokinin.

Diabetes induced by partial hepatic sensory denervation in conscious rabbits.

Exposure of the anterior hepatic plexus to 2% perineurial capsaicin solution over three days caused transient insulin resistance confirmed by hyperinsulinaemic euglycaemic glucose clamping. Three additional perineurial capsaicin treatments divided by 3-month intervals yielded diabetes characterized by an increase in fasting blood glucose and glycated haemoglobin levels. Both insulin sensitivity and glycated haemoglobin level re-normalized over an additional 6-month period. We conclude that chronic partial hepatic sensory denervation produces diabetes in rabbits.

Effect of experimental hypercholesterolaemia on K+ channel alpha-subunit mRNA levels in rabbit hearts.

We investigated the effect of dietary cholesterol on gene transcription of delayed rectifier (I(Kr) - ERG1 and I(Ks) - KvLQT1) and transient outward (I(to,fast) - Kv4.2 and Kv4.3) potassium channel subunits in rabbit hearts using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). While the level of Kv4.3 mRNA did not change, both Kv4.2 and ERG1 mRNAs were downregulated, whereas the level of KvLQT1 was increased in hypercholesterolaemic rabbits, indicating that hypercholesterolaemia altered ventricular K(+) channel alpha-subunit gene transcription.

Changes in tracheo-bronchial sensory neuropeptide receptor gene expression pattern in rats with cisplatin-induced sensory neuropathy.

An attenuated neurogenic broncho-constriction underpinned by a decrease in sensory neuropeptide release has been shown to be characteristic of cisplatin-induced neuropathy. The present work was to explore if beyond neuropeptide release, cisplatin at a treatment schedule attaining sensory neuropathy, produced changes in the expression of the receptors of sensory neuropeptides such as somatostatin, calcitonin gene-related peptide (CGRP) and substance P (SP) in bronchial tissue of the rat. Twenty-four Wistar rats were divided into three groups. The animals in the "Treatment groups 1 and 2" were given cisplatin (1.5mgkg(-1)) and mannitol (75mgkg(-1)) over 5 days. The rats in the "Control" group were given mannitol+isotonic saline. Four animals from each group were used to study the expression pattern of the neuropeptide receptors in bronchial tissue. The levels of somatostatin receptor 4 (SSTR 4), neurokinin 1 (NK1), neurokinin 2 (NK2) and CGRP receptor expression were examined by quantitative real time polymerase chain reaction (RT-PCR) method, 11 and 22 days after the last cisplatin/vehicle dose. The cisplatin treatment significantly increased plasma somatostatin immunoreactivity and the expression of SSTR4 receptor detected both on the 11th and 22nd post-treatment days with no change in either CGRP, NK1, and NK2 receptor gene expression or plasma CGRP and substance P levels. We conclude that cisplatin neuropathy is accompanied by an increase in plasma somatostatin immunoreactivity with an increase in SSTR4 expression in rats.

Neurogenic insulin resistance in guinea-pigs with cisplatin-induced neuropathy.

The aim of the present work was to study whether neurotoxicity produced by cisplatin modified tissue insulin sensitivity in guinea-pigs. One week after selective sensory denervation of the anterior hepatic plexus by means of perineurial 2% capsaicin treatment, hyperinsulinaemic euglycaemic glucose clamp were performed to estimate insulin sensitivity in male guinea-pigs. The guinea-pigs underwent regional sensory denervation of the anterior hepatic plexus exhibited insulin resistance, whereas systemic capsaicin desensitization increased insulin sensitivity. Intraportal administration of L-nitro-arginine methyl ester (L-NAME decreased, whereas capsaicin increased insulin sensitivity. Neither atropine nor acetylcholine produced any significant effect. In animals with preceding regional capsaicin desensitization, none of the pharmacological maneuvers modified the resulting insulin resistant state. Cisplatin pretreatment induced sensory neuropathy and decreased insulin sensitivity. Insulin sensitivity did not change after either regional or systemic capsaicin desensitization in the cisplatin-treated animals. CGRP(8-37), a nonselective calcitonin gene-related peptide (CGRP) antagonist (50 microg/kg i.v.), significantly increased insulin sensitivity in normal animals but only a tendency to insulin sensitization was seen after cisplatin treatment. Cisplatin treatment, similar to regional capsaicin desensitization of the anterior hepatic plexus, produced a significant decrease in insulin-stimulated uptake of 2-deoxy-D [L-14C] glucose in cardiac and gastrocnemius muscle with no effect on percentage suppression of endogenous glucose production by hyperinsulinaemia. We conclude that the majority of cisplatin-induced insulin resistance is related to functional deterioration of the hepatic insulin sensitizing substance (HISS) mechanism.

Insulin sensitization induced by oral cicletanine in conscious rabbits.

The endogenous insulin sensitizing machinery termed the hepatic insulin sensitizing substance (HISS) mechanism has been shown to be nitrergic and linked to sensory fibers in the anterior hepatic plexus. We studied whether this mechanism could pharmacologically be exploited by cicletanine, a cGMP-PDE inhibitor antihypertensive drug, in conscious rabbits. Whole body insulin sensitivity and peripheral glucose uptake were determined by hyperinsulinaemic euglycaemic glucose clamping, and cardiac radiolabelled deoxyglucose (DOG) uptake in neurogenic, achieved by perineurial capsaicin treatment of the anterior hepatic plexus through defunctionalization of hepatic sensory fibers, and metabolic, induced by dietary hypercholesterolemia, insulin resistance models after single oral doses of cicletanine (3, 10 and 30 mg kg(-1)) or rosiglitazone (3 mg kg(-1)). The effect of cicletanine on cardiac and vascular tissue NO, cGMP, cAMP was measured by means of spin trapping technique and radioimmunoassay, respectively. Insulin sensitivity and peripheral DOG uptake were significantly increased by 10 and 30 mg kg(-1) cicletanine in both healthy and hypercholesterolaemic rabbits, but not in those with neurogenic insulin resistance. Rosiglitazone had no effect in healthy and neurogenic insulin resistant rabbits although it improved insulin sensitivity in hypercholesterolemic animals. The 10 mg kg(-1) cicletanine dose induced no change in either cardiac or vascular tissue NO, cGMP or cAMP concentrations. Nevertheless, at a dose of 30 mg kg(-1) producing an insulin sensitizing effect of approximately the same amplitude as seen with 10 mg kg(-1), the drug significantly increased tissue NO and cGMP concentrations. Oral cicletanine attains its insulin sensitizing effect at doses lower than those necessary to activate the NO-cGMP pathway in the cardiovascular system. This metabolic effect requires functional integrity of hepatic sensory nerves.

The prandial insulin sensitivity-modifying effect of vagal stimulation in rats.

The effect of left cervical vagal nerve stimulation was studied on insulin sensitivity to test the proposed permissive insulin-sensitizing role of hepatic vagal parasympathetic efferent pathways in fasted and fed anesthetized rats. In fed animals, electrical stimulation (square impulses: 25 V, 5 Hz, 0.5 milliseconds over 15 minutes) of the vagal nerve induced hyperglycemia and an increase in plasma insulin immunoreactivity. Atropine (1.0 mg/kg intravenously) induced insulin resistance estimated by rapid insulin sensitivity testing. This was amplified when the vagal nerve was stimulated. The insulin-resistant state developed by fasting was not modified by either treatment with atropine or electrical stimulation. We conclude that both parasympathetic cholinergic and noncholinergic vagal efferents modulate postprandial neurogenic insulin sensitivity adjustments.

Accelerated recovery of 5-fluorouracil-damaged bone marrow after rosiglitazone treatment.

Our preliminary data indicate that rosiglitazone may be myeloprotective. We investigated whether it can modify bone marrow recovery. Five-day pre-treatment with rosiglitazone significantly accelerated recovery of 5-fluorouracil-damaged bone marrow in mice. Frequency and femoral content of granulocyte-macrophage progenitors reached mean baseline faster in pre-treated groups than in 5-fluorouracil-treated controls. Consequently, neutropenia was milder. Five-day insulin pre-treatment had similar effects in vivo. Insulin supports in vitro hematopoiesis. The observed myeloprotection demonstrated the importance of insulin in vivo. Clinical use of insulin to moderate myelotoxicity is impractical but rosiglitazone, an insulin sensitizer, could offer hope. Although rosiglitazone tends to increase plasma insulin levels, the significant myeloprotection was partly due to direct effects on progenitors. In vitro rosiglitazone enhanced the survival of both murine progenitor and human mobilized blood stem cells in the presence of 5-fluorouracil, the effect of which was neutralized by a peroxisome-proliferator-activated receptor-gamma antagonist.

Decreased sensory neuropeptide release in isolated bronchi of rats with cisplatin-induced neuropathy.

We studied if attenuated neurogenic bronchoconstriction was associated with a change in sensory neuropeptide release in preparations from rats with cisplatin-induced neuropathy. Electrical field stimulation (100 stimuli, 20 V, 0.1 ms, 20 Hz) induced an increase in the release of somatostatin, calcitonin gene-related peptide (CGRP) and substance P determined by radioimmunoassay from baseline 0.18+/-0.01, 0.17+/-0.01 and 0.86+/-0.02, to 0.59+/-0.02, 1.77+/-0.04 and 5.96 fmol/mg wet tissue weight, respectively, in organ fluid of tracheal tubes from rats. This was significantly attenuated to post-stimulation values of 0.36+/-0.02, 0.45+/-0.02, 4.68+/-0.24 fmol/mg wet tissue weight for somatostatin, CGRP, and substance P, respectively, with a significant decrease in field stimulation-induced contraction of bronchial preparations from animals 11 days after a 5-day treatment period with cisplatin (1.5 mg/kg i.p. once a day). The cisplatin-treated animals developed sensory neuropathy characterized by a 40% decrease in femoral nerve conduction velocity. The results show that a decrease in tracheo-bronchial sensory neuropeptide release associates with feeble bronchomotor responses in rats with cisplatin-induced sensory neuropathy.

Effect of long-term olanzapine treatment on meal-induced insulin sensitization and on gastrointestinal peptides in female Sprague-Dawley rats.

Meal-induced insulin sensitization (MIS), an endogenous adaptive mechanism is activated post-prandially. Reduced MIS leads to diabetes, but its activation improves insulin sensitivity. MIS is preserved to single olanzapine administration, therefore we aimed to investigate the chronic effect of olanzapine on fasted-state insulin sensitivity and on MIS in female Sprague-Dawley rats. Daily food and water intake, stool and urine production and body weight were determined. The MIS was characterized by a rapid insulin sensitivity test. Fasting hepatic and peripheral insulin sensitivity were determined by a hyperinsulinaemic euglycaemic glucose clamping supplemented with radiotracer technique. Fasted and post-prandial blood samples were obtained for plasma insulin, leptin, ghrelin, amylin, GLP-1, GIP, PYY and PP determination. Adiposity was characterized by weighing intra-abdominal and inguinal fat pads. Olanzapine caused hepatic insulin resistance and a reduced metabolic clearance rate of insulin, but the MIS retained its function. Body weight and adiposity were enhanced, but olanzapine failed to increase food intake. Fasting insulin and leptin were elevated and the post-prandial reduction in ghrelin level was inhibited by olanzapine.The MIS remained functionally intact after long-term olanzapine treatment. Altered insulin, leptin and ghrelin levels indicate olanzapine-induced metabolic derangements. Pharmacological activation of MIS could potentially be exploited to treat or prevent olanzapine-induced insulin resistance.

Insulin sensitivity is modified by a glycogen phosphorylase inhibitor: glucopyranosylidene-spiro-thiohydantoin in streptozotocin-induced diabetic rats.

The major role of liver glycogen is to supply glucose to the circulation maintaining the normal blood glucose level. In muscle and liver the accumulation and breakdown of glycogen are regulated by the reciprocal activities of glycogen phosphorylase and glycogen synthase. Glycogen phosphorylase catalyses the key step of glycogen degradation and its activity can be inhibited by glucose and its analogues. Obviously, any readily accessible inhibitor of glycogen phosphorylase can be used as a potential therapy of non-insulin-dependent or type 2 diabetes. Hepatic glycogen phosphorylase has been identified as a new target for drugs that control blood glucose concentration. In our experiments glucopyranosylidene-spirothiohydantoin (TH) was tested on the insulin sensitivity and blood glucose level of control and streptozotocin-treated rats. The streptozotocin-treated rats failed to gain weight and exhibited stable hyperglycemia (4.7 ± 0.5 mmol/L glucose in control vs. 7.8 ± 0.5 mmol/L) and low plasma insulin levels (9.6 ± 1.9 µIU/mL in control vs. 3.2 ± 2.2 µIU/mL). When insulin supplementation with slow-release implants (2 IU/day) was started 8 weeks after streptozotocin injection, blood glucose concentration remained suppressed, plasma insulin level dramatically increased and the insulin sensitivity restored. TH administration significantly reduced the high blood glucose concentration and restored the insulin sensitivity of STZtreated rats.

Meal-induced insulin sensitization is preserved after acute olanzapine administration in female Sprague-Dawley rats.

Olanzapine, an atypical antipsychotic, can acutely induce fasting insulin resistance, but we do not know whether it is able to modulate the meal-induced insulin sensitization (MIS). Two main experimental groups (control and olanzapine-treated) were created with two subgroups (fasted and re-fed) within each. After oral vehicle/olanzapine administration, the first meal size and duration and the total amount of consumed food was recorded in conscious rats. Then, under anaesthesia, the carotid artery and jugular vein was prepared and cannulated to obtain samples for blood glucose and hormone determination as well as for insulin/glucose infusion, respectively. Basal insulin sensitivity and MIS was determined by homeostasis model assessment (HOMA) calculation and by rapid insulin sensitivity test, respectively. In fasted animals, olanzapine increased blood glucose and plasma insulin and reduced basal insulin sensitivity, but it failed to modify other hormone levels. Postprandial leptin and glucose-dependent insulinotropic polypeptide (GIP) levels increased, and ghrelin level decreased significantly (p < 0.05) both in vehicle- and olanzapine-treated groups, but plasma insulin increased only in vehicle-treated animals. Furthermore, decrement in ghrelin level was attenuated in olanzapine-treated animals compared to controls. There was no significant change in the first meal size and duration or in the total amount of food consumed. Olanzapine had no effect on the MIS. We demonstrated that olanzapine can induce insulin resistance without weight gain in healthy rats. Furthermore, the MIS was preserved after acute olanzapine treatment. The blunted postprandial ghrelin and insulin response could contribute to the effect of olanzapine on feeding behaviour. Pharmacological induction of MIS may improve the olanzapine-induced insulin resistance.

Sensory nitrergic meningeal vasodilatation and non-nitrergic plasma extravasation in anaesthesized rats.

The aim of the present study was to evaluate the role of nitric oxide (NO) of sensory neural origin in neurogenic inflammatory response in the trigeminovascular system. Antidromic vasodilatation and plasma extravasation in response to electrical stimulation (15 V, 5 Hz, 0.5 ms, 100 impulses) of the trigeminal ganglion were investigated in the dura mater and nasal mucosa/upper eyelid by laser Doppler flowmetry and [(125)I]-labelled bovine serum albumin, respectively. Electrical stimulation of the trigeminal ganglion of rats elicited a reproducible ipsilateral enhancement of both meningeal and nasal mucosal blood flow. N(omega)-nitro-L-arginine (L-NNA; 4, 8, and 16 mg/kg, i.v.), a nonselective inhibitor of nitric oxide synthase (NOS), inhibited antidromic vasodilatation both in the dura mater (15.86+/-2.05%, 22.82+/-2.51%, and 36.28+/-4.37%) and nasal mucosa (35.46+/-8.57%, 58.72+/-9.2%, and 89.99+/-8.94%) in a dose-dependent manner. Specific inhibitors of neuronal NOS, 7-nitroindazole (7-NI; 20 mg/kg, i.v.) and 3-bromo-7-nitroindazole (3Br-7NI; 10 mg/kg, i.v.) were administered to assess the possible role of NO released from the trigeminal sensory fibres. The meningeal vasodilatation was inhibited by both 3Br-7NI and 7-NI (63.36+/-7.7% and 49+/-6.5%, respectively). The nasal hyperaemic response was also reduced by 3Br-7NI (78.26+/-8.7%). Plasma extravasation in the dura mater and upper eyelid evoked by electrical stimulation of the trigeminal ganglion (25 V, 5 Hz, 0,5 ms, 5 min), expressed as extravasation ratios (ERs) of the stimulated vs. nonstimulated sides, was 1.80+/-0.8 and 4.63+/-1.24, respectively. This neurogenic oedema formation was not inhibited by neither L-NNA nor 3Br-7NI. It is concluded that neural nitrergic mechanisms are involved in the meningeal vasodilatation evoked by electrical stimulation of the trigeminal ganglion.