Capsaicin In Rats Research Articles

Up-regulated Expression of a TOR2A Gene Product-Salusin-β in the Paraventricular Nucleus Enhances Sympathetic Activity and Cardiac Sympathetic Afferent Reflex in Rats with Chronic Heart Failure Induced by Coronary Artery Ligation.

Enhanced cardiac sympathetic afferent reflex (CSAR) promotes sympathetic hyperactivation in chronic heart failure (CHF). Salusin-β is a torsin family 2 member A gene product and a cardiovascular active peptide closely associated with cardiovascular diseases. We aimed to determine the roles of salusin-β in the paraventricular nucleus (PVN) in modulating enhanced CSAR and sympathetic hyperactivation in rats with CHF induced by coronary artery ligation and elucidate the underlying molecular mechanisms. CSAR was evaluated based on the responses of mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) to the epicardial administration of capsaicin in rats under anaesthesia. Salusin-β protein expression was up-regulated in the PVN of the CHF compared with sham-operated rats. Salusin-β microinjection into the PVN dose-dependently increased MAP and RSNA and enhanced CSAR, while anti-salusin-β IgG exerted opposite effects. The effect of salusin-β was inhibited by reactive oxygen species (ROS) scavenger or NAD(P)H oxidase inhibitor but promoted by superoxide dismutase inhibitor. The effect of anti-salusin-β IgG was interdicted by nitric oxide (NO) synthase inhibitor. Furthermore, chronic salusin-β gene knockdown in PVN attenuated CSAR, reduced sympathetic output, improved myocardial remodelling and cardiac function, decreased NAD(P)H oxidase activity and ROS levels, and increased NO levels in the CHF rats. Increased salusin-β activity in the PVN contributes to sympathetic hyperactivation and CSAR in CHF by inhibiting NO release and stimulating NAD(P)H oxidase-ROS production. Reducing endogenous central salusin-β expression might be a novel strategy for preventing and treating CHF in the future.

Antidepressant effects of capsaicin in rats with chronic unpredictable mild stress-induced depression

Purpose: This study was conducted to assess the antidepressant effects of capsaicin in chronic depressive rats and elucidate the mechanism underlying its effects.Methods: Male Wistar rats (280~320 g, 8 weeks of age) were subjected to depression induced by chronic unpredictable mild stresses. The rats were exposed to 8 kinds of stresses for 8 weeks. In the last 2 weeks, fluoxetine or capsaicin was injected subcutaneously. The dose of fluoxetine was 10 mg/kg (body weight), while the doses of capsaicin consisted of low (1 mg/kg), middle (5 mg/kg), and high (10 mg/kg). The forced swim test (FST) was conducted to evaluate the immobility time of rats. The immobility time indicates despair, one of symptoms of depression. The change of tryptophan hydroxylase (TPH) in the dorsal raphe was investigated using immunohistochemistry. In the hippocampus cornu ammonis (CA) 1 and 3, glucocorticoid receptor (GR) expression was measured.Results: The immobility time in the FST was significantly lower (p < .05) in the low-dose (M = 32.40 ± 13.41 seconds) and middle-dose (M = 28.48 ± 19.57 seconds) groups than in the non-treated depressive rats (M = 90.19 ± 45.34 seconds). The amount of TPH in the dorsal raphe was significantly higher (p < .05) in the middle-dose (M = 249.17 ± 35.02) and high-dose (M = 251.0 ± 56.85) groups than in the non-treated depressive rats (M = 159.78 ± 41.16). However, GR expression in the hippocampus CA1 and CA3 did not show significant differences between the non-treated depressive rats and the capsaicin-injected rats.Conclusion: This study suggests that capsaicin produces an antidepressant-like effect on chronic unpredictable mild stress-induced depression in rats via the serotonin biosynthesis pathway.

Intramuscular insulin administration potentiates sympathetic and pressor responses to capsaicin in rats

Insulin centrally activates the sympathetic nervous system. However, little is known about the effects of insulin on peripheral primary sensory neurons. Transient receptor potential vanilloid 1 (TRPV1), of which capsaicin (CAP) is an agonist, is widely expressed in small dorsal root ganglia (DRG) neurons subserving skeletal muscle thin‐fiber afferents expressing sensory nociceptors and/or metabolically sensitive skeletal muscle receptors. Evidence suggests that insulin increases the sensitivity of these sensory receptors as well as translocation of TRPV1 from cytosol to plasma membrane in DRG neurons. We therefore hypothesized that insulin potentiates the responsiveness of thin fiber muscle afferents to TRPV1 activation.PurposeThe aim of this investigation was 1) to examine whether TRPV1 and insulin receptors (IR) are co‐localized in small‐diameter (< 30 µm) DRG neurons subserving thin‐fiber afferents (C‐fibers or A‐delta fibers), and 2) to determine the effects of insulin on renal sympathetic nerve activity (RSNA) and mean arterial blood pressure (MAP) responses to stimulation of TRPV1 by injection of CAP into the arterial supply of the hindlimb in decerebrated rats.MethodsL4‐L6 DRGs were harvested from Sprague‐Dawley rats (n=3, 19 weeks, body weight: 518 ± 6 g). The percentage of neurons that expressed IR and/or isolectin B4 binding (IB4, a C‐fiber neuronal marker) in TRPV1 positive small DRGs neurons were assessed. RSNA and MAP responses to intra‐arterial administration of CAP (0.3 µg/100 µL) were measured in decerebrate Sprague‐Dawley rats (10 ± 1 weeks, body weight: 330 ± 43 g) before and after intramuscular injection of either insulin (5 U/mL, 30 µL) or saline (vehicle control, 30 µL). To avoid insulin/saline spill over into the systemic circulation, a vascular occluder placed around the abdominal aorta was inflated immediately prior to intramuscular administration of insulin or saline.ResultsImmunohistochemical staining demonstrated that 22 % of TRPV1 positive DRG neurons expressed IR and IB4 binding. Intramuscular insulin administration did not change blood glucose as well as plasma insulin levels assessed from the jugular vein. The RSNA response to CAP after insulin administration was significantly greater than post injection of vehicle (vehicle: 25 ± 24, n=9, vs. insulin: 54 ± 32 %, n=8, P=0.04). While the MAP response to CAP was not significantly changed by vehicle injection (before: 26 ± 13 vs. after: 24 ± 12 mmHg, n=18), insulin administration significantly increased MAP responsiveness (before: 24 ± 1 vs. after: 29 ± 15 mmHg, n=22, P=0.01).ConclusionThe data demonstrate that 1) TRPV1 and IR co‐localize on small DRG neurons and 2) intramuscular insulin administration significantly augments sympathetic and pressor responses to chemical stimulation of skeletal muscle afferents. These findings suggest that insulin potentiates TRPV1 responsiveness at the muscle tissue level, possibly contributing to insulin‐induced sympathoexcitation.

Bioavailability of a Capsaicin Lipid Multi-particulate Formulation in Rats

Background and ObjectiveBecause of the stomach-burning sensation it induces, capsaicin has been used at relatively low doses as a nutritional supplement, which has limited its bioavailability. The objective of this study was to investigate the serum bioavailability of capsaicin supplementation with or without a lipid multi-particulate (LMP) formulation.MethodsThirty-five rats were divided into five groups and administered capsaicin at either 0.2 or 1 mg/kg with or without the LMP formulation. Capsaicin bioavailability was assessed based on the area under the concentation–time curve (AUC), the time to peak concentration (Tmax), and the peak serum concentration (Cmax).ResultsFor each formulation, the capsaicin Cmax was reached at 90 min and decreased thereafter. Serum capsaicin concentrations were greater in rats administered the higher dose of capsaicin (1 mg/kg) in the LMP formulation at all measurement times (P ≤ 0.05). The AUC showed a significant increase, about 20%, when capsaicin was administered in the LMP formulation at the high dose (P = 0.002). The Tmax for oral capsaicin was similar whether or not administration was via the LMP formulation (P = 0.163). However, the Cmax of capsaicin increased in a dose-dependent manner (P < 0.05). Although the LMP formulation of the high dose of capsaicin resulted in a numerically higher Cmax, it was not statistically significantly higher (P = 0.068).ConclusionsThe present work demonstrated that administration of capsaicin via the LMP formulation significantly impacted the pharmacokinetic parameters and the serum bioavailability of orally administered 1 mg/kg capsaicin in rats. The bioavailability of capsaicin in humans may also be increased by using the LMP formulation.

Protective Effect of Lycium barbarum Polysaccharides and Capsaicin in Rats With Dextran Sulfate Sodium-Induced Ulcerative Colitis via Anti-inflammation and Antioxidation

Abstract Objectives Ulcerative colitis (UC) is a chronic inflammatory disease in the colon, and the prevalence of UC is increasing worldwide. Lycium barbarum polysaccharides (LBP) from wolfberry extract has immunomodulatory effects, and act as a prebiotics candidate. Capsaicin (CAP) as an active ingredient of chili peppers has the potential for anti-inflammation and antioxidation. This study investigated the effects of LBP and CAP on anti-inflammation and antioxidation in rats with dextran sulfate sodium (DSS)-induced UC. Methods Male Sprague-Dawley rats were divided into five groups: control, UC (DSS), UC treated with 100 mg/kg bw LBP (LBP), UC treated with 12 mg/kg bw CAP (CAP), and UC treated with a combination of 50 mg/kg bw LBP and 6 mg/kg bw CAP (MIX) groups. The treatment of LBP and/or CAP was daily given by oral gavage from week 1 to week 4, and UC was induced by 5% DSS in drinking water for 6 days during week 3. Results The DSS group significantly increased disease activity index (DAI) scores, the levels of pro-inflammatory cytokines interleukin-6 (IL-6) in the serum and tumor necrosis factor-α (TNF-α) in the colon, and serum lipid peroxidation malondialdehyde (MDA) levels compared with the control group. While the activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) in the serum were significantly decreased in the DSS group. The LBP, CAP, and MIX groups significantly decreased DAI scores on day 6 during the DSS-induced period. Compared with the DSS group, the LBP group significantly decreased serum IL-6 and serum MDA levels, but increased serum CAT activity. The CAP group significantly decreased serum IL-6 levels. The MIX group significantly reduced serum IL-6 and colon TNF-α levels, but elevated serum SOD activity. Conclusions The results suggest that administration of LBP and/or CAP attenuate DSS-induced UC symptoms in rats through the anti-inflammatory and antioxidant activities. Funding Sources This study was supported by the Ministry of Science and Technology, Taiwan (grant no. MOST 108–2320-B-038–052-MY3).

Renal Sympathetic Nerve Activity and Heart Rate Responses to Renal Pelvic Infusion of Bradykinin and Capsaicin in Rats Exposed to Intermittent Hypoxia

Renal oxidative stress and inflammation are evident in individuals with obstructive sleep apnea and in animals exposed to intermittent hypoxia (IH). It is known that kidney injury alters renal afferent nerve activity disrupting reno-renal reflex mechanisms. This study investigated reno-renal reflex changes in response to intra-renal pelvic infusion of bradykinin and capsaicin in rats exposed to IH. Wistar rats were exposed to 96 cycles of IH (6% O2, n=10) or to normoxia (sham, 21% O2, n=11) daily for 14 days. On day 15, rats were anesthetized (induction: urethane, α-chloralose and sodium pentobarbitone mixture i.p. (416, 27 and 33mg/kg), maintenance: urethane and α-chloralose mixture i.v. (62 and 4mg/kg)) to record cardiovascular parameters, renal sympathetic nerve activity (RSNA), and urine flow (UF). Intra-renal pelvic infusion of three doses of bradykinin (53µg/kg, 141µg/kg, 247µg/kg, for 5 min at 20µl/min in random order) was performed, and was repeated following the blockade of bradykinin receptors 1 (BK1R) and 2 (BK2R). Finally, an intra-renal pelvic infusion of capsaicin (0.133µg/kg) was performed. During infusions, changes in blood pressure, heart rate (HR) and contralateral RSNA were recorded. Urine samples were collected from the contralateral kidney. Data are expressed as mean±SD and were analyzed using t-test or ANOVA, where appropriate. IH rats were hypertensive (128±17 vs. 112±22mmHg) with elevated HR (440±37 vs. 403±42bpm), and increased basal UF (56±18 vs. 26±12µl/min/kg); all p<0.05. IH rats had increased resting RSNA, but this was not statistically significant (% of max: 19.6±6.4 vs. 14.8±7.2, p=0.105). All intra-renal pelvic doses of bradykinin augmented RSNA in IH and sham rats (all p<0.05), without changes in blood pressure during infusions. However, UF during bradykinin infusion was unchanged in IH and sham rats. Increases in RSNA and HR in response to 247µg/kg bradykinin were blunted in IH rats compared with shams (RSNA p=0.005; HR p=0.021), with diminished increase in RSNA most evident during the last three mins of infusion (% of baseline: 126±20 vs. 108±5%, p=0.016) and attenuated increase in HR during the last 30s of infusion (∆HR: +7±7 vs. +18±15bpm, p=0.05). This was also evident by a decrease in the area under RSNA curves (AUC) in IH rats compared with shams (1884±970 vs. 5437±3950%.s, p=0.046). AUC analysis revealed that increases in RSNA in response to bradykinin were attenuated during BK1R blockade (p=0.012), and greater suppression of bradykinin-induced increase in RSNA was observed following concurrent BK2R blockade (p=0.005). Intra-pelvic infusion of capsaicin induced a similar increase in HR, RSNA and UF in IH and sham rats. Protein expression of bradykinin and TRPV1 receptors in kidney tissue was equivalent between groups. However, in isolated renal pelvic wall, BK2R expression was 53% less in IH (n=4) compared with sham (n=4), but not statistically significant (p=0.120), which might be related to the small sample size. Our results indicate a blunted reflex increase in RSNA and HR in response to intra-pelvic bradykinin in IH rats, which could be due to down-regulation of the BK2R pathway.

Evaluation of the Single-Dose Toxicity of Capsaicin Pharmacopuncture in Rats

Background: This study aimed to assess the toxicity of capsaicin (CP) pharmacopunture in an animal model.&lt;br/&gt;Methods: The toxicity of a single-muscular dose of CP (45.45 mg/mL) was evaluated in 6-week-old male and female Sprague-Dawley rats. A total of 20 rats were assigned to 2 groups which were sex and weight matched. All rats acclimatized for 1 week before receiving 1.0 mL of CP (45.45 mg/mL) or normal saline solution(control) intramuscularly. The general condition and mortality of the animals were observed. The rats were sacrificed 2 weeks after CP was administered and histopathology was performed.&lt;br/&gt;Results: No abnormal symptoms or deaths were observed, and there was no difference in body weights between the CP and control groups throughout the study. No significant differences in histopathology were observed between the groups.&lt;br/&gt;Conclusion: No toxicological changes related to the administration of CP were observed. This study indicated that the safe dose of CP in Sprague-Dawley rats was 1.0 mL of CP (45.45 mg/mL) or less. Further studies are needed to confirm the safety of CP in the human body.

Participation of satellite glial cells of the dorsal root ganglia in acute nociception

At dorsal root ganglia, neurons and satellite glial cells (SGC) can communicate through ATP release and P2X7 receptor activation. SGCs are also interconnected by gap junctions and have been previously implicated in modulating inflammatory and chronic pain.We now present evidence that SGCs are also involved in processing acute nociception in rat dorsal root ganglia. Using primary dorsal root ganglia cultures we observed that calcium transients induced in neurons by capsaicin administration were followed by satellite glial cells activation. Only satellite glial cells response was reduced by administration of the P2X7 receptor antagonist A740003. In vivo, acute nociception induced by intraplantar injection of capsaicin in rats was inhibited by A740003 or by the gap junction blocker carbenoxolone administered at the dorsal root ganglia (L5 level). Both drugs also reduced the second phase of the formalin test. These results suggest that communication between neurons and satellite glial cells is not only involved in inflammatory or pathological pain, but also in the transmission of the nociceptive signal, possibly in situations involving C-fiber activation.

Peripheral µ-opioid receptors attenuate the responses of group III and IV afferents to contraction in rats with simulated peripheral artery disease.

Patients with peripheral artery disease show an exaggerated pressor response to mild exercise, an effect attributable to the exercise pressor reflex, whose afferent arm comprises the thinly myelinated group III and unmyelinated group IV afferents. Previously, we found that DAMGO, a µ-opioid agonist injected into the femoral artery, attenuated the exaggerated exercise pressor reflex in rats with ligated femoral arteries, a preparation that simulates the blood flow patterns to muscle that is seen in patients with peripheral artery disease. Continuing this line of investigation, we recorded the responses of group III and IV afferents to static contraction before and after injecting DAMGO (1 µg) into the superficial epigastric artery in rats with patent femoral arteries and in rats with ligated femoral arteries. In rats with patent arteries, DAMGO did not change the responses to contraction of either group III ( n = 9; P = 0.83) or group IV ( n = 8; P = 0.34) afferents. In contrast, in rats with ligated femoral arteries, DAMGO injection (1 µg) significantly decreased the responses to contraction of both group III afferents ( n = 9, P < 0.01) and group IV afferents ( n = 9; P < 0.01). DAMGO did not significantly attenuate the responses of either group III or IV afferents to capsaicin in rats with either patent or ligated femoral arteries. These findings are in agreement with our previous studies that showed that peripheral DAMGO injection attenuated the exercise pressor reflex in rats with ligated femoral arteries but had only a modest effect on the exercise pressor reflex in rats with patent femoral arteries. NEW & NOTEWORTHY In an animal model of peripheral artery disease, we show that the µ-opioid agonist, DAMGO reduces the afferent response rate resulting from stimulated static contraction. These results suggest that peripherally active opioid agonists that do not cross the blood-brain barrier may be therapeutic for treatment of peripheral artery disease without the negative and addictive side effects associated with opioids in the central nervous system.

Antinociceptive and Antihyperalgesic Activity of a Traditional Maya Herbal Preparation Composed of Pouteria Campechiana, Chrysophyllum Cainito, Citrus Limonum, and Annona Muricata.

Preclinical Research The purpose of this work was to assess the antinociceptive and antihyperalgesic properties of an herbal preparation, composed of four vegetal species: Pouteria campechiana (P. campechiana), Chrysophyllum cainito (C. cainito), Citrus limonum (C. limonum), and Annona muricata (A. muricata), that is commonly used in combination (PCCA) in traditional Mayan medicine for the treatment of diabetes and pain. An ethanolic extract of PCCA was prepared at a ratio of 1:1:1:1 for each plant. The systemic antinociceptive effect of PCCA extract (50-600 mg/kg, p.o.) was dose-dependent in the rat formalin (1%) producing 66% antinociceptive response at 400 mg/kg, p.o. A concentration-dependent antinociceptive effect of the PCCA extract (20-160 mg/paw) was also demonstrated in the rat capsaicin (0.2%) test. The PCCA extract (100-400 mg/kg, p.o.) had antihyperalgesic effects in alloxan diabetic rats. These findings demonstrate the antinociceptive and antihyperalgesic effects of PCCA and supports the use of the plant extracts in Mayan folk medicine. Drug Dev Res 78 : 91-97, 2017. © 2017 Wiley Periodicals, Inc.

Evodiamine suppresses capsaicin-induced thermal hyperalgesia through activation and subsequent desensitization of the transient receptor potential V1 channels.

Evodiae fructus (EF), a fruit of Evodia rutaecarpa Bentham, has long been used as an analgesic drug in traditional Chinese and Japanese medicine. However, the underlying molecular mechanism of its pharmacological action is unclear. Here, using calcium imaging, whole-cell patch-clamp recording, and behavioral analysis, we investigated the pharmacological action of EF and its principal compound, evodiamine, on the transient receptor potential (TRP) V1 channels. Dorsal root ganglion (DRG) neurons and TRPV1- or TRPA1-transfected human embryonic kidney-derived (HEK) 293 cells were used for calcium imaging or whole-cell patch-clamp recording. Twenty male adult Sprague-Dawley rats were used for the capsaicin-induced thermal hyperalgesia behavioral analyses. We found that evodiamine induced significant increases in intracellular calcium and robust inward currents in a subpopulation of isolated rat DRG neurons, most of which were also sensitive to capsaicin. The effect of evodiamine was completely blocked by capsazepine, a competitive antagonist of TRPV1. Evodiamine induced significant inward currents in TRPV1-, but not TRPA1-transfected HEK293 cells. Pretreatment with evodiamine reduced capsaicin-induced currents significantly. Furthermore, the in vivo pre-treatment of evodiamine suppressed thermal hyperalgesia induced by intraplantar injection of capsaicin in rats. These results identify that the analgesic effect of EF and evodiamine may be due to the activation and subsequent desensitization of TRPV1 in sensory neurons.

Anxiolytic efficacy of repeated oral capsaicin in rats with partial aberration of oral sensory relay to brain

ObjectiveThis study was conducted to examine if taste over load with oral capsaicin improves the adverse behavioural effects induced by partial aberration of oral sensory relays to brain with bilateral transections of the lingual and chorda tympani nerves. DesignMale Sprague-Dawley rats received daily 1ml of 0.02% capsaicin or water drop by drop into the oral cavity following the bilateral transections of the lingual and chorda tympani nerves. Rats were subjected to ambulatory activity, elevated plus maze and forced swim tests after 11th, 14th and 17th daily administration of capsaicin or water, respectively. The basal and stress-induced plasma corticosterone levels were examined after the end of behavioural tests. ResultsAmbulatory counts, distance travelled, centre zone activities and rearing were increased, and rostral grooming decreased, during the activity test in capsaicin treated rats. Behavioural scores of capsaicin rats during elevated plus maze test did not differ from control rats. Immobility during the swim test was decreased in capsaicin rats with near significance (P=0.0547). Repeated oral capsaicin increased both the basal level and stress-induced elevation of plasma corticosterone in rats with bilateral transections of the lingual and chorda tympani nerves. DiscussionIt is concluded that repeated oral administration of capsaicin reduces anxiety-like behaviours in rats that received bilateral transections of the lingual and chorda tympani nerves, and that the increased corticosterone response, possibly modulating the hippocampal neural plasticity, may be implicated in the anxiolytic efficacy of oral capsaicin.

High dose of QX-314 produces anti-nociceptive effect without capsaicin in rats with inflammatory TMJ pain

High dose of QX-314 produces anti-nociceptive effect without capsaicin in rats with inflammatory TMJ pain

Capsaicin-induced metabolic and cardiovascular autonomic improvement in an animal model of the metabolic syndrome

The metabolic syndrome (MetS) is associated with an increased risk of cardiac mortality, as it is characterised by the clustering of multiple cardiovascular risk factors. Studies have shown that capsaicin (red pepper) may be useful as a nutraceutical, ameliorating metabolic profile and cardiovascular function. The aim of the present study was to investigate the cardiovascular and metabolic effects of orally administered capsaicin in rats with the MetS. Neonate spontaneously hypertensive rats were injected with monosodium glutamate and subjected to one of the following three treatments by oral administration for 14d, between 27 and 30 weeks: low-dose capsaicin (CAP05, n 18, synthetic capsaicin powder diluted in a vehicle (10% ethyl alcohol) plus 0·5mg/kg body weight (BW) of capsaicin); high-dose capsaicin (CAP1, n 19, synthetic capsaicin powder diluted in a vehicle (10% ethyl alcohol) plus 1mg/kg BW of capsaicin); control (C, n 18, vehicle). Lee's index, lipid/metabolic profile, and cardiovascular parameters with the rats being conscious, including arterial pressure (AP) and heart rate (HR) variability, as well as aortic wall thickness (haematoxylin and eosin staining) and CD68 (cluster of differentiation 68) antibody levels (monocyte/macrophage immunostaining) were evaluated. Weight, Lee's index, and lipid and metabolic parameters, as well as AP and HR and aortic wall thickness, were similar between the groups. Capsaicin determined HR variability improvement (16·0 (sem 9·0), 31·0 (sem 28·2) and 31·3 (sem 19·0)ms2 for the C, CAP05 and CAP1 groups, respectively, P=0·003), increased vascular sympathetic drive (low-frequency component of systolic AP variability: 3·3 (sem 2·8), 8·2 (sem 7·7) and 12·1 (sem 8·8)mmHg2 for the C, CAP05 and CAP1 groups, respectively, P<0·001) and increased α-index (spontaneous baroreflex sensitivity). The present data show that capsaicin did not improve lipid and glucose abnormalities in rats with the MetS. However, beneficial cardiovascular effects were observed with this nutraceutical.

Neuronal Nitric Oxide Synthase-Derived Nitric Oxide Is Involved in Gastric Mucosal Hyperemic Response to Capsaicin in Rats

Background and Aims: Activation of transient receptor potential vanilloid type 1 (TRPV1) by capsaicin leads to gastric hyperemic response through capsaicin-sensitive sensory nerves and nitric oxide (NO). The aim of the present study is to examine which isoform of nitric oxide synthase (NOS)/NO is involved in the hyperemic response to capsaicin in the rat stomach. Methods: Gastric mucosal blood flow (GMBF) was measured by laser Doppler flowmetry in rats. The localizations of TRPV1 and neuronal NOS (nNOS) in the rat gastric mucosa were detected by immunohistochemical staining. Results: The nNOS inhibitor N⁵-[imino(propylamino)methyl]-<smlcap>L</smlcap>-ornithine substantially reduced GMBF during capsaicin application, whereas the endothelial NOS (eNOS) inhibitor N⁵-(1-iminomethyl)-<smlcap>L</smlcap>-ornithine did not affect the effect of capsaicin during the application. The nonselective NOS inhibitor N^G-nitro-<smlcap>L</smlcap>-arginine methyl ester apparently inhibited the capsaicin-induced GMBF, while the inducible NOS inhibitor 1400W did not affect GMBF response to capsaicin. The immunohistochemical studies revealed nerve fibers coexpressing TRPV1 and nNOS around blood vessels in the gastric submucosa. Conclusion: We demonstrated for the first time that nNOS/NO is involved in gastric hyperemic responses to capsaicin.

Investigation of Capsaicin-induced Superficial Punctate Keratopathy Model Due to Reduced Tear Secretion in Rats

ABSTRACTPurpose: The present study investigated the usefulness of the superficial punctate keratopathy (SPK) model due to reduced tear secretion induced by the injection of capsaicin in neonatal rats.Methods: On postnatal day 4, rats were injected subcutaneously with a single dose of capsaicin. Ocular surface symptoms were evaluated by measuring corneal sensitivity, tear secretion and corneal fluorescein score. Furthermore, the effect of pilocarpine was investigated by measuring tear secretion and corneal fluorescein score in this model. The influence of discontinuation of pilocarpine application was also examined.Results: Capsaicin caused a dose-dependent reduction of tear secretion and increase of corneal fluorescein score. In addition, 50 mg/kg capsaicin-treated rats showed a sustained decrease of corneal sensitivity and tear secretion, and an increase of corneal fluorescein score compared with vehicle-treated rats. Moreover, capsaicin-treated rats showed SPK. Instillation of pilocarpine significantly increased tear secretion and tended to improve the corneal fluorescein score by repeated application, whereas tear secretion and corneal fluorescein score in the pilocarpine-treated rats returned to the same level as that of capsaicin-treated rats after discontinuation of pilocarpine application.Conclusions: Injection of capsaicin in rats induced stable SPK due to reduced tear secretion accompanied by a decrease of corneal sensitivity. Thus, it may be concluded that this model is essentially similar to SPK due to reduced tear secretion and could be used in the development of appropriate new drugs for therapy.

Administration of Ciprofloxacin and Capsaicin in Rats to Achieve Higher Maximal Serum Concentrations

To test if capsaicin could improve the bioavailability of ciprofloxacin (1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid, CAS 85721-33-1, Bay q 3939) in rats, 0.01, 0.1, 0.5 and 1% capsaicin ((E)-N-[(4-hydroxy-3-methoxyphenyl)methyl]-8-methyl-6-nonenamide, trans-8-methyl-N-vanillyl-6-nonenamide, CAS 404-86-4) dissolved in ethanol and mixed with 20 mg/kg of ciprofloxacin were orally administered to groups of 10 rats each. Control groups were dosed with capsaicin-free, ethanol-containing or ethanol-free ciprofloxacin. Reference intravenous pharmacokinetics of ciprofloxacin was also established. The results revealed that capsaicin increased ciprofloxacin bioavailability by approximately 70% in groups receiving preparations containing capsaicin at a rate of 0.01, 0.1 and 0.5%. Higher concentrations failed to further increase bioavailability. However, capsaicin appears to have little or no impact on the rate of absorption or clearance of ciprofloxacin. Considering that 0.01% or 0.1% capsaicin are unlikely to upset the gastrointestinal tract, it may be worth attempting to study if a similar effect occurs in man, and to evaluate if the addition of capsaicin can be used as a method to increase the area under the curve/minimum inhibitory concentration rate, a key variable to improve clinical efficacy of ciprofloxacin.

Increased hypothalamic c‐Fos expression and anxiety‐like behaviors by oral exposure to capsaicin in rats

In this study, we examined the neurobehavioral outcome of repeated oral exposures to capsaicin in rats. Oral application of 0.02% capsaicin was performed once daily and the rats were subjected to the behavioral tests following 10 days of oral capsaicin or sacrificed for c‐Fos immunohistochemistry at 1 h after the first oral capsaicin. The control group received water orally instead of capsaicin, and for immunohistochemistry, rats were transcardially perfused with 4% paraformaldehyde. Total ambulatory counts and the distance travelled in the activity chamber did not differ between the capsaicin and the control groups; however, the central zone activities were decreased in the capsaicin group. In the elevated‐plus maze test, capsaicin rats spent more time in the closed arms than control rats. In Porsolt swim test, swimming duration was decreased, struggling increased, in capsaicin rats without statistical significance. Oral capsaicin exposure significantly increased c‐Fos expression not only in the nucleus tractus of solitarius but also in the paraventricular nucleus. Results suggest that a long‐term oral exposure to capsaicin may increase anxiety‐like behaviors, likely by affecting neural plasticity of the hypothalamic neurons. Supported by NRF(20100003642)

Discovery of potent, soluble and orally active TRPV1 antagonists. Structure–activity relationships of a series of isoxazoles

Systematic optimisation of a poorly soluble lead series of isoxazole-3-carboxamides was conducted. Substitution of the 4-position with specific polar functionality afforded the requisite balance of potency, solubility and physicochemical properties. Compound 21a was found to be efficacious in the rat Capsaicin Hargreaves assay following oral administration.

Selective Pharmacological Blockade of the TRPV1 Receptor Suppresses Sensory Reflexes of the Rodent Bladder

We investigated the pharmacological effect of TRPV1 antagonists in anesthetized rodent models of bladder function. The TRPV1 antagonists JNJ17203212 and JYL1421 were evaluated in the anesthetized rat volume induced micturition reflex model. JNJ17203212 was further evaluated in this model in capsaicin (Sigma) desensitized rats, and in rat capsaicin and mouse citric acid models of irritant induced detrusor overactivity. Systemic JNJ17203212 and JYL1421 administration in the anesthetized rat volume induced micturition reflex model resulted in an increased micturition threshold volume. JNJ17203212 also decreased bladder contraction amplitude but JYL1421 had no effect. Capsaicin desensitization significantly increased baseline micturition threshold volume and decreased bladder contraction amplitude in the volume induced micturition reflex model compared to those in sham treated controls and JNJ17203212 produced no further effect after capsaicin desensitization. JNJ17203212 was also effective in 2 models of irritant induced detrusor overactivity, preventing the decrease in micturition threshold volume and the increase in bladder contraction amplitude observed with intravesical instillation of 10 microM capsaicin, and the decreased voiding interval induced by intravesical citric acid. The TRPV1 antagonists JNJ17203212 and JYL1421 increased the threshold for activation of the micturition reflex in the anesthetized rat volume induced micturition reflex model. This effect appeared to be mediated by capsaicin sensitive afferents. JNJ17203212 also inhibited detrusor overactivity induced by intravesical capsaicin and intravesical citric acid. These data extend our understanding of the role of TRPV1 in sensory modulation of the micturition reflex under nonirritant and inflammatory conditions.