H2-receptor Blockade Research Articles

Proton pump inhibitor use and fracture risk — effect modification by histamine H1 receptor blockade. Observational case–control study using National Prescription Data

It remains unknown why proton pump inhibitor (PPI) use may be associated with risk of osteoporotic fractures; evidence of direct effects on calcium absorption or on the osteoclast in humans is weak or absent. However, the ensuing increased gastrin levels may cause histamine production through hypertrophy of gastric enterochromaffin like cells, which could lead to bone loss. We speculated that H1 receptor antagonists (H1RA) used for allergies would then reduce the effect of PPI on bone. We therefore conducted a register-based case–control study comprising 124,655 patients with hospital treated fractures, who were matched 3:1 with non fracture control subjects of the same age and gender. Use of prescription medications was retrieved from the National Prescription Database and data was analyzed using conditional logistic regression analysis.We observed a significant interaction between PPI and H1RA use on fracture risk in general (adjusted OR 0.92, 95% CI 0.87–0.98) though not on hip fracture risk (adjusted OR 0.99, 95% CI 0.85–1.16). There was a significant modification of the interaction by age (p<0.05 for both fracture categories). As previously shown, fracture risk was higher in PPI users both for fractures in general and for hip fractures. Irrespective of PPI use, H1RA users had lower risk of hip fractures than non-users (adjusted OR 0.86, 95% CI 0.79–0.93). This short report suggests that the effects of PPI on bone could be driven by in part by increased histamine release as the increased fracture risk can be modified by H1RA.

Histamine is required for H3 receptor‐mediated alcohol reward inhibition, but not for alcohol consumption or stimulation

Conflicting data have been published on whether histamine is inhibitory to the rewarding effects of abused drugs. The purpose of this study was to clarify the role of neuronal histamine and, in particular, H₃ receptors in alcohol dependence-related behaviours, which represent the addictive effects of alcohol. Alcohol-induced conditioned place preference (alcohol-CPP) was used to measure alcohol reward. Alcohol-induced locomotor stimulation, alcohol consumption and kinetics were also assessed. mRNA levels were quantified using radioactive in situ hybridization. Low doses of H₃ receptor antagonists, JNJ-10181457 and JNJ-39220675, inhibited alcohol reward in wild-type (WT) mice. However, these H₃ receptor antagonists did not inhibit alcohol reward in histidine decarboxylase knock-out (HDC KO) mice and a lack of histamine did not alter alcohol consumption. Thus H₃ receptor antagonists inhibited alcohol reward in a histamine-dependent manner. Furthermore, WT and HDC KO mice were similarly stimulated by alcohol. The expression levels of dopamine D₁ and D₂ receptors, STEP61 and DARPP-32 mRNA in striatal subregions were unaltered in HDC KO mice. No differences were seen in alcohol kinetics in HDC KO compared to WT control animals. In addition, JNJ-39220675 had no effect on alcohol kinetics in WT mice. These data suggest that histamine is required for the H₃ receptor-mediated inhibition of alcohol-CPP and support the hypothesis that the brain histaminergic system has an inhibitory role in alcohol reward. Increasing neuronal histamine release via H₃ receptor blockade could therefore be a novel way of treating alcohol dependence.

Effect of H1- and H2-histamine receptor blockade on postexercise insulin sensitivity

Following a bout of dynamic exercise, humans experience sustained postexercise vasodilatation in the previously exercised skeletal muscle which is mediated by activation of histamine (H1 and H2) receptors. Skeletal muscle glucose uptake is also enhanced following dynamic exercise. Our aim was to determine if blunting the vasodilatation during recovery from exercise would have an adverse effect on blood glucose regulation. Thus, we tested the hypothesis that insulin sensitivity following exercise would be reduced with H1- and H2-receptor blockade versus control (no blockade). We studied 20 healthy young subjects (12 exercise; eight nonexercise sham) on randomized control and H1- and H2-receptor blockade (fexofenadine and ranitidine) days. Following 60 min of upright cycling at 60% VO2 peak or nonexercise sham, subjects consumed an oral glucose tolerance beverage (1.0 g/kg). Blood glucose was determined from “arterialized” blood samples (heated hand vein). Postexercise whole-body insulin sensitivity (Matsuda insulin sensitivity index) was reduced 25% with H1- and H2-receptor blockade (P < 0.05), whereas insulin sensitivity was not affected by histamine receptor blockade in the sham trials. These results indicate that insulin sensitivity following exercise is blunted by H1- and H2-receptor blockade and suggest that postexercise H1- and H2-receptor–mediated skeletal muscle vasodilatation benefits glucose regulation in healthy humans.

Differential mechanisms underlie the regulation of serotonergic transmission in the dorsal and median raphe nuclei by mirtazapine: a dual probe microdialysis study

Blockade of α2 adrenoceptors and histamine H1 receptors plays important roles in the antidepressant and hypnotic effects of mirtazapine. However, it remains unclear how mirtazapine's actions at these receptors interact to affect serotonergic transmission in the dorsal (DRN) and median (MRN) raphe nuclei. Using dual-probe microdialysis, we determined the roles of α2 and H1 receptors in the effects of mirtazapine on serotonergic transmission in the DRN and MRN and their respective projection regions, the frontal (FC) and entorhinal (EC) cortices. Mirtazapine (<30μM) failed to alter extracellular serotonin levels when perfused alone into the raphe nuclei, but when co-perfused with a 5-HT1A receptor antagonist, mirtazapine increased serotonin levels in the DRN, MRN, FC, and EC. Serotonin levels in the DRN and FC were decreased by blockade and increased by activation of H1 receptors in the DRN. Serotonin levels in the MRN and EC were not affected by H1 agonists/antagonists perfused in the MRN. The increase in serotonin levels in the DRN and FC induced by DRN H1 receptor activation was attenuated by co-perfusion with mirtazapine. Furthermore, the increase in serotonin levels (DRN/FC) induced by DRN α2 adrenoceptor blockade was attenuated by concurrent DRN H1 blockade, whereas the increase in serotonin levels (MRN/EC) induced by MRN α2 adrenoceptor inhibition was unaffected by concurrent MRN H1 receptor blockade. These results suggest that enhanced serotonergic transmission resulting from α2 adrenoceptor blockade is offset by subsequent activation of 5-HT1A receptors and, in the DRN but not MRN, H1 receptor inhibition. These pharmacological actions of mirtazapine may explain its antidepressant and hypnotic actions.

Blockade of the brain histamine H3 receptor by JNJ-39220675: preclinical PET studies with [11C]GSK189254 in anesthetized baboon

RationaleThe preclinical characterization of a series of aryloxypyridine amides has identified JNJ-39220675 ((4-cyclobutyl-1,4-diazepan-1-yl)(6-(4-fluorophenoxy)pyridin-3-yl)methanone) as a high-affinity histamine H3 receptor antagonist and a candidate for further drug development particularly in the treatment of alcohol-related behaviors.ObjectiveThis study measured brain histamine H3 receptor blockade by JNJ-39220675 (1 mg/kg) in the female baboon.MethodsPositron emission tomography imaging and [11C]GSK189254, a reversible high-affinity radiotracer with specificity for the histamine H3 receptor, was used to measure histamine H3 receptor availability at baseline and after i.v. and oral administration of JNJ-39220675 (1 mg/kg) in the anesthetized baboon. Histamine H3 receptor availability was estimated as the total distribution volume (V T) in brain regions. The sensitivity of [11C]GSK189254 binding to injected mass and carryover effects was determined.ResultsJNJ-39220675 produces robust (ca. 90 %) blockade of [11C]GSK189254 binding after i.v. and oral administration. After oral administration of JNJ-39220675 (1 mg/kg), the fractional receptor occupancy was >0.9 at 90 min with a slight increase from 90 to 240 min. Similar to prior studies in humans, V T was highly sensitive to the mass of GSK189254 with ED50 estimated to be 0.16 μg/kg.ConclusionsThe robust blockade of binding of [11C]GSK189254 by JNJ-39220675 demonstrates that this compound readily penetrates the blood–brain barrier and occupies the histamine H3 receptor after oral administration at low plasma concentrations (∼1 ng/cc) supporting further drug development for alcohol addiction and other disorders. This study corroborates prior reports of the high sensitivity of [11C]GSK189254 to injected mass at doses >0.1 μg/kg.

Differential effects of the antidepressant mirtazapine on amphetamine- and dizocilpine-induced PPI deficits

Prepulse inhibition (PPI) refers to the decrease in motor startle response to salient sensory stimuli (pulses) when they are closely preceded in time by another more modest sensory stimulus (prepulse). PPI deficits can be induced by stimulation of dopamine receptors (e.g., amphetamine or apomorphine) or blockade of NMDA glutamate receptors (e.g., dizocilpine or PCP). Previously we found that antagonists of α2-noradrenergic and H1-histaminergic receptors significantly attenuate PPI impairments caused by amphetamine or dizocilpine. In the current study we assessed the effects of the antidepressant mirtazapine, which has combined antagonist effects at α2-noradrenergic, H1-histaminergic and 5-HT serotonergic receptors, on amphetamine- and dizocilpine-induced PPI deficits. In Experiment 1, rats were tested for PPI of the startle response to a tactile air-puff stimulus after auditory prepulses of three different intensities. Drug treatments consisted of combinations of amphetamine (0 and 1mg/kg) and mirtazapine (0, 0.5, 1, 2, and 5mg/kg), with all rats receiving all drug doses and combinations with different counterbalanced orders. In Experiment 2, a different group of rats was tested with drug treatments consisting of combinations of dizocilpine (0 and 0.05mg/kg) and mirtazapine (0, 0.5, 1, 2, and 5mg/kg). In Experiment 1 amphetamine (1mg/kg) significantly reduced PPI whereas mirtazapine caused the opposite effect, with the highest dose of mirtazapine (5mg/kg) effectively reversing the amphetamine-induced PPI deficit. In Experiment 2 dizocilpine (0.05mg/kg) significantly reduced PPI, but mirtazapine did not have a significant effect on the inhibition of the startle response. These results indicate that the potential beneficial effects of combined α-adrenergic, 5-HT, and H1 receptor blockade in counteracting PPI deficits may be associated to cases of sensorimotor gating disorders mediated by dopamine, but not necessarily to NMDA glutamate-induced PPI impairments.

Prevention of anaphylaxis related to mast cell activation syndrome with omalizumab

The concept of mast cell activation syndrome (MCAS) has evolved over the last several decades to describe cases involving evidence of profound mast cell degranulation without an obvious trigger or evidence of aberrant mast cell proliferation.1 In 2010, Akin, et al. proposed a set of diagnostic criteria including: 1) absence of evidence of primary or secondary causes of mast cell activation (including mastocytosis); 2) episodic symptoms consistent with mast cell mediator release affecting ≥2 organ systems; 3) evidence of an increase in a validated urinary or serum marker of mast cell activation; and 4) a decrease in severity of symptoms with anti-mediator therapy including histamine 1 and 2 receptor antagonists, leukotriene antagonists, or mast cell stabilizers.1 Treatment of MCAS involves the use of one or more of the aforementioned classes of medications,2 while prednisone, cyclosporine A, methotrexate, and azathioprine are alternatives when treatment with more conservative therapy fails.2 Treatment of refractory cases presents a difficult dilemma for the clinician. We present a case of the successful use of omalizumab (monoclonal antibody to IgE) in the treatment of a pediatric patient who met the proposed diagnostic criteria for MCAS. Our patient is an 11 year old male with a history of eczema and viral-induced wheezing who presented in September 2010 for evaluation of presumed anaphylactic reactions to both cherries and blackberries. Symptoms included hives and breathing difficulty. He had an additional episode with similar symptoms for which a trigger was not identified. In the weeks preceding these events, he reported headache, flushing, abdominal pain, diarrhea, and fatigue. Percutaneous skin prick testing using common aeroallergen extracts and cherry was negative. Complete blood count showed a white blood cell count of 12,500/μL with a lymphocyte predominance and normal numbers of eosinophils, basophils, and monocytes. Serum tryptase was 15.8 μg/dL (normal 0.4–10.9 μg/dL). A monospot was positive, which was potentially significant as the presence of heterophile antibodies can increase tryptase levels.3 Total IgE was 26 IU/mL. The child was counseled on avoidance of cherries and blackberries, prescribed an epinephrine auto-injector, and started on oral cetirizine at 10 mg twice daily. Over the next four months, he continued to experience frequent abdominal pain, diarrhea, urticaria and flushing, as well as episodic anaphylactoid reactions requiring the use of epinephrine several times per month. Tryptase levels remained elevated (17.8 μg/dL; 19.8 μg/dL). Histamine-1 receptor blockade was increased to twice daily cetirizine plus twice daily loratadine (“4× therapy”) with continuation of twice daily ranitidine. Symptoms improved but persisted, and bone marrow biopsy was obtained to exclude systemic mastocytosis or monoclonal mast cell activation syndrome (MMAS). Normal marrow morphology was noted with the absence of a large population of mast cells or spindle-shaped mast cells. CD25 staining was negative. Additionally, a chronic urticaria index, which tests for presence of autoantibodies to the high-affinity IgE (FceRI) receptor, was within normal limits. Polymerase chain reaction for the KIT (D816V) mutation commonly found in systemic mastocytosis and MMAS was unable to be performed due to lack of amplifiable nucleic acid in the specimen. Upper and lower endoscopy did not show the presence of mast cell aggregates in the bowel wall. The patient improved on a prolonged course of oral corticosteroids, but symptoms increased after their discontinuation and he was started on omalizumab as a steroid-sparing agent in April 2011. He continues to receive omalizumab 150 mg subcutaneously every 4 weeks. He had rapid improvement in symptoms and has had one episode of urticaria with shortness of breath in the 10 months on omalizumab therapy. The patient continues on H1 receptor blockade with twice daily cetirizine and loratidine and H2 receptor blockade with twice daily ranitidine. This case supports the potential efficacy of omalizumab for MCAS in children not responding to maximal anti-histamine therapy. Molderings, et al. recently reported benefit with omalizumab therapy in 1 of 2 patients with monoclonal mast cell activation syndrome.4 There have been other reports of successful treatment of systemic mastocytosis with omalizumab.5,6 The mechanisms underlying the symptomatic improvement of patients with MCAS treated with omalizumab are not fully understood. The binding and inactivation of IgE by omalizumab leads to a decreased level of IgE available for binding to mast cells, leading to downregulation of FceRI.7 Others have proposed that omalizumab may interfere with mast cell mediator release.8 In sum, omalizumab may be an efficacious therapy for treatment resistant MCAS, and further studies are needed to ascertain what factors lead to improvement in MCAS patients receiving omalizumab.

In response to “The effect of agomelatine on 5HT2C receptors in humans: a clinically relevant mechanism?” by Trevor Norman

We thank Dr. Norman for his interesting comments about the role of H1 receptors in the regulation of slow wave sleep. It is of course quite plausible that H1-receptor blockade could modify slow wave sleep (SWS) in humans; however, in a study with the selective H1 receptor antagonist, mepyramine, we saw no such effect (Solomon et al. 1989). Regardless of whether or not H1-receptors play a role in SWS regulation in humans, the key issue in the case of agomelatine is whether selective 5-HT2C receptor blockade is able by itself to increase SWS. In animals, there is good evidence that this is the case, and indeed, agomelatine, given in acute doses of 10 and 40 mg/kg, also increases SWS in rats, an effect mimicked by the selective 5-HT2C receptor antagonist, S32006 (Descamps et al. 2009). This suggests that a dose of agomelatine sufficient to block 5-HT2C receptors in humans should also increase SWS. However, we agree with Dr. Norman that to resolve the question of whether agomelatine does block 5-HT2C receptors in the human brain at clinically relevant doses, other models of 5-HT2C receptor activity will be needed.

A clozapine-like effect of cyproheptadine on progressive ratio schedule performance

The atypical antipsychotic drug clozapine has multiple pharmacological actions, some of which, including 5-hydroxytryptamine (5-HT₂) and histamine (H₁) receptor antagonist effects, are shared by the non-selective 5-HT receptor antagonist cyproheptadine. Atypical antipsychotics have a characteristic profile of action on operant behaviour maintained by progressive ratio schedules, as revealed by Killeen's (1994) mathematical model of schedule controlled behaviour. These drugs increase the values of a parameter that expresses the 'incentive value' of the reinforcer (a) and a parameter that is inversely related to the 'motor capacity' of the organism (δ). This experiment examined the effects of acute treatment with cyproheptadine and clozapine on performance on a progressive ratio schedule of food reinforcement in rats; the effects of a conventional antipsychotic, haloperidol, and two drugs with food intake-enhancing effects, chlordiazepoxide and Δ⁹-tetrahydrocannabinol (THC), were also examined. Cyproheptadine (1, 5 mg kg⁻¹) and clozapine (3.75, 7.5 mg kg⁻¹) increased a and δ. Haloperidol (0.05, 0.1 mg kg⁻¹) reduced a and increased δ. Chlordiazepoxide (3, 10 mg kg⁻¹) increased a but reduced δ. THC (1, 3 mg kg⁻¹) had no effect. Interpretation based on Killeen's (1994) model suggests that cyproheptadine and clozapine enhanced the incentive value of the reinforcer and impaired motor performance. Motor impairment may be due to sedation (possibly reflecting H₁ receptor blockade). Enhancement of incentive value may reflect simultaneous blockade of H₁ and 5-HT₂ receptors, which has been proposed as the mechanism underlying the food intake-enhancing effect of cyproheptadine. In agreement with previous findings, haloperidol impaired motor performance and reduced the incentive value of the reinforcer. Chlordiazepoxide's effect on a is consistent with its food intake-enhancing effect.

Mast Cells Are Critical for Protection against Peptic Ulcers Induced by the NSAID Piroxicam

Many commonly used non-steroidal anti-inflammatory drugs (NSAIDs) also cause gastrointestinal toxicity, including the development of life-threatening peptic ulcers. We report that mast cell-deficient mice have an extremely high incidence of severe peptic ulceration when exposed to the NSAID piroxicam. This enhanced ulcer susceptibility can be reversed by reconstitution with mast cells. Furthermore, wild type mice treated with diphenhydramine hydrochloride, a commonly used antihistamine that blocks histamine H1 receptors, develop a similarly high incidence of peptic ulcers following piroxicam exposure. The protective effect of mast cells is independent of TNF, blockade of H2 receptors, or acid secretion. These data indicate a critical role for mast cells and the histamine that they produce in prevention and/or repair of piroxicam-induced gastric mucosal injury. Additional studies will be required to determine whether this represents a NSAID class effect that can be exploited to develop novel therapeutic strategies to limit the incidence of NSAID-induced side effects in humans.

Sleep and Anesthesia

Sleep and Anesthesia

Differential responding of autonomic function to histamine H1 antagonism in irritable bowel syndrome

The role of histamine in the pathophysiology of irritable bowel syndrome (IBS) is largely unknown. Dysfunction of the autonomic nervous system (ANS) in IBS patients is also not fully confirmed. We hypothesized that blockade of histamine H₁ receptors affects ANS responses differently between IBS subjects and controls. Subjects were 12 IBS subjects and 12 age- and sex-matched controls. Either 100 μg kg⁻¹ chlorphenamine or the same amount of saline was administered on different days. The rectum was stimulated with electrical currents of 0 mA (sham) or 30 mA. Autonomic nervous system function was measured using mean arterial pressure (MAP), heart rate (HR), high frequency (HF) component of HR variability, low frequency/high frequency ratio (LF/HF ratio) and plasma catecholamines and histamine. Subjective perceived stress during the examination was evaluated on an ordinate scale. Mean arterial pressure showed significant effects of diagnosis (P < 0.05) and drug × diagnosis interaction (P < 0.05). The MAP significantly increased after chlorphenamine administration in IBS subjects, but not in controls. Heart rate revealed a significant drug effect (P < 0.001), which decreased after chlorphenamine administration in controls, but not in IBS subjects. Perceived stress significantly increased by rectal stimulation (P < 0.001) and a significant stimulus × diagnosis interaction (P < 0.05) was revealed, indicating greater reduction in IBS subjects by chlorphenamine. Sympathetic vasomotor tone in IBS subjects differentially responded on administration of a histamine H₁ antagonist to that of controls. These findings suggest an increased histaminergic activity in IBS subjects.

Local histamine H1- and H2-receptor blockade reduces postexercise skeletal muscle interstitial glucose concentrations in humans

Elevated blood flow can potentially influence skeletal muscle glucose uptake, but the impact of postexercise hyperemia on glucose availability to skeletal muscle remains unknown. Because postexercise hyperemia is mediated by histamine H(1)- and H(2)-receptors, we tested the hypothesis that postexercise interstitial glucose concentrations would be lower in the presence of combined H1- and H2-receptor blockade. To this end, 4 microdialysis probes were inserted into the vastus lateralis muscle of 14 healthy subjects (21-27 years old) immediately after 60 min of either upright cycling at 60% peak oxygen uptake (exercise, n = 7) or quiet rest (sham, n = 7). Microdialysis probes were perfused with a modified Ringer's solution containing 3 mmol L(-1) glucose, 5 mmol L(-1) ethanol, and [6-3H] glucose (200 disintegrations·min-1 microL(-1)). Two sites (blockade) received both H1- and H2-receptor antagonists (1 mmol L(-1) pyrilamine and 3 mmol L-1 cimetidine) and 2 sites (control) did not receive antagonists. Ethanol outflow/inflow ratios (an inverse surrogate of local blood flow) were higher in blockade sites than in control sites following exercise (p < 0.05), whereas blockade had no effect on ethanol outflow/inflow ratios following sham (p = 0.80). Consistent with our hypothesis, during 3 of the 5 dialysate collection periods, interstitial glucose concentrations were lower in blockade sites vs. control sites following exercise (p < 0.05), whereas blockade had no effect on interstitial glucose concentrations following sham (p = 0.79). These findings indicate that local H1- and H2-receptor activation modulates skeletal muscle interstitial glucose levels during recovery from exercise in humans and suggest that the availability of glucose to skeletal muscle is enhanced by postexercise hyperemia.

A histamine H2 receptor blocker ameliorates development of heart failure in dogs independently of β-adrenergic receptor blockade

Histamine has a positive inotropic effect on ventricular myocardium and stimulation of histamine H₂ receptors increases the intracellular cAMP level via Gs protein, as dose stimulation of β-adrenergic receptors, and worsens heart failure. To test whether a histamine H₂ receptor blocker had a beneficial effect in addition to β-adrenergic receptor blockade, we investigated the cardioprotective effect of famotidine, a histamine H₂ receptor blocker, in dogs receiving a β-blocker. We induced heart failure in dogs by rapid ventricular pacing (230 beats/min). Animals received no drugs (control group), famotidine (1 mg/kg daily), carvedilol (0.1 mg/kg daily), or carvedilol plus famotidine. Both cardiac catheterization and echocardiography were performed before and 4 weeks after the initiation of pacing. Immunohistochemical studies showed the appearance of mast cells and histamine in the myocardium after 4 weeks of pacing. In the control group, the left ventricular ejection fraction (LVEF) was decreased after 4 weeks compared with before pacing (71 ± 2 vs. 27 ± 2%, p < 0.05) and mean pulmonary capillary wedge pressure (PCWP) was increased (8 ± 1 vs. 19 ± 3 mmHg). Famotidine ameliorated the decrease of LVEF and increase of PCWP, while the combination of carvedilol plus famotidine further improved both parameters compared with the carvedilol groups. These beneficial effects of famotidine were associated with a decrease of the myocardial cAMP level. Histamine H₂ receptor blockade preserves cardiac systolic function in dogs with pacing-induced heart failure, even in the presence of β-adrenergic receptor blockade. This finding strengthens the rationale for using histamine H₂ blockers in the treatment of heart failure.

Effect of MK-801 on learning in rats: Evaluation of PK/PD relationship

The non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 is widely used in animal research (over 3000 publications), however its extracellular brain concentration has never been reported. Here, we investigated the brain extracellular fluid (ECF) concentration of MK-801 and dopamine after systemic injection of different doses of MK-801 in freely moving rats using in vivo microdialysis. Furthermore, we were interested in: (1) comparing these data with results from locomotor activity in the open field and a 1-day Morris water maze task, (2) the effect of different injection intervalls of MK-801, and (3) reversal of MK-801 induced behavioural alterations by a histamine H3 receptor antagonist (ABT-239). In vitro brain microdialysis combined with LCMSMS analysis was used to assess the brain ECF concentration of MK-801 (0.05, 0.1, 0.2 mg/kg) after i.p. application. Following, data were recalculated based on in vivo recovery. Locomotor activity was measured in an open field for 2 h, while spatial learning and memory was assessed in the Morris water maze (5 consecutive trials on 1 day). MK-801 was injected 30, 60, 120, or 240 min before behavioral testing began. ABT-239 (3, 10 mg/kg) was injected i.p. 45 min prior to testing. Injection of MK-801 in doses of 0.05, 0.1, or 0.2 mg/kg resulted in peak brain ECF concentration of 5, 15 or 30 nM, repectively, at 60 min after application as well as in alterations of striatal dopamine levels. Interestingly, only one injection of 0.05 mg/kg MK-801 triggered an increase of baseline ECF dopamine concentration 24 h later. Moreover, MK-801 resulted in learning impairment in the water maze and ABT-239 at the dose of 3 mg/kg was able to reverse this deficit. These data demonstrate a clear PK/PD relationship of MK-801 at doses normally used for behavioural testing resulting in brain levels corresponding to the affinity at NMDA receptors. Moreover, the observation that MK-801-induced impairment of learning can be fully reversed by a H3 receptor antagonist suggests, that blockade of H3 receptors may reverse cognitive impairment resulting from glutamatergic hypofunction.

Commentary on “An analysis of the depressor responses to histamine in the cat and dog: involvement of both H1 and H2 receptors” by JW Black, DAA Owen and ME Parsons

The qualitative part of this story was described briefly in 1972 when we reported on burimamide as a prototype histamine H2-receptor antagonist. The purpose of the present paper was to produce a quantitative account of the phenomenon. The phenomenon, namely the difficulty in blocking the hypotensive effects of histamine by antihistamine drugs, was first described by Staub in 1939. Folkow, Haeger and Kahlson in 1948 confirmed the observation and suggested that other histamine receptors might be involved. When we were developing burimamide we showed that the drug was unable to block the hypotensive effects of histamine in intact animals. My recollection is that we did not look at interactions between H1- and H2-receptor antagonists at that stage. The surprise for me happened when we started human studies. John Wylie was one of the earliest volunteers. The interaction between burimamide and histamine-stimulated gastric acid secretion was carried out on him after an intramuscular dose of the H1-receptor antagonist, mepyramine. In spite of the H1-receptor blockade the subsequent i.v. infusion of histamine produced a bright red face, engorged conjunctivae and a headache. However, when the H2-receptor antagonist was now infused all the vascular reactions to histamine (including a marked spreading flare around the vein being injected with histamine) gradually disappeared. I still love showing my colour slide of Wylie's face before and after, such was the impact of the observation on me. This paper shows that H2-receptor blockade has no effect on histamine-induced hypotension, that H1-receptor blockade produces a small shift in the dose-response curves and that after this, H2-receptor blockade can now move the dose-response curves out in parallel. We then used Ariens' two receptor model (Ariens, van Rossum & Simonis, 1959) to explain that this is the expected result where either receptor arm can produce a maximum response but the H2 receptor arm is about ten fold less potent. Another valedictory paper, this one winding up my part in the H2-receptor antagonist story.

8 Kit Low Interstitial Cell of Cajal Stem Cells are a Cell of Origin of Gastrointestinal Stromal Tumors

BACKGROUND: We previously showed that the mast cell stabilizer ketotifen reduces IBS symptoms and increases the threshold of discomfort in hypersensitive IBS-patients. However, as ketotifen also has Histamine 1-receptor antagonistic properties and is known to penetrate the blood-brain barrier, its beneficial effect observed in this trial could also result from H1 receptor blockade, either at the peripheral or central level. AIM: To establish whether fexofenadine, a peripherally restricted 2nd generation Histamine 1-receptor antagonist, can mimic the effect of ketotifen and A) reverse stress-induced, mast cell dependent visceral hypersensitivity in a rat model of maternal separation (MS), and B) modulate gastrointestinal transit in MS and non-handled (NH) rats. METHODS: Adult MS and NH rats (n=9 in all groups) were subjected to acute stress (1 hr water avoidance,WA). The visceromotor response (VMR) to colorectal distension (1, 11⁄2, 2ml) was established preand 24 hours post-WA and expressed as area-under-curve (AUC, volume-vs-response, significant difference when P<0.05: Wilcoxon). Rats were then treated with fexofenadine (1,8 mg/kg or 18 mg/kg) or vehicle and re-evaluated 48 hrs post-WA. Pre-WA transit was measured in NH (n=4) and MS (n=5) rats treated with fexofenadine or vehicle by evaluating the transit (geometric centre or GC) of orally administered fluorescein-labeled dextran (MW=70.000) (1 is stomach, 2 most proximal small bowel, 11 most distal, 12 cecum, 13-15 colon). RESULTS: WA induced an increased VMR to distension in MS rats (pre-WA vs post-WA, 64±4 vs 98±6 (mean±SEM), P=0.012) which was reversed by 1.8 mg/kg fexofenadine (post-WA vs post-fexofenadine, 98±6 vs 69±5, P=0.012). High concentration fexofenadine (18 mg/kg) showed similar results (pre-WA vs post-WA, 72±4 vs 97±6, P=0.012 and post-WA vs post fexofenadine 97±6 vs 60±6, P=0.008). NH rats remained normo-sensitive under all conditions. Baseline pre-WA transit times of NH and MS were equal (10±0.2 vs 9.6±0.4). Administration of high-dose fexofenadine decreased transit time in NH (vehicle vs fexofenadine, 10±0.2 vs 6.4±1.1, P= 0.028) and MS-rats (9.6±0.4 vs 6.9±0.2, P=0.008). CONCLUSION: The peripheral H1 receptor antagonist fexofenadine effectively reverses stress-induced visceral hypersensitivity and decreases intestinal transit. As low dose fexofenadine does not cross the blood brain barrier, these data justify future IBS patient trials with 2nd generationH1-receptor antagonists.

7 The Peripheral Histamine 1-Receptor Antagonist Fexofenadine Effectively Reverses Stress-Induced Visceral Hypersensitivity in a Rat Model of Maternal Separation

BACKGROUND: We previously showed that the mast cell stabilizer ketotifen reduces IBS symptoms and increases the threshold of discomfort in hypersensitive IBS-patients. However, as ketotifen also has Histamine 1-receptor antagonistic properties and is known to penetrate the blood-brain barrier, its beneficial effect observed in this trial could also result from H1 receptor blockade, either at the peripheral or central level. AIM: To establish whether fexofenadine, a peripherally restricted 2nd generation Histamine 1-receptor antagonist, can mimic the effect of ketotifen and A) reverse stress-induced, mast cell dependent visceral hypersensitivity in a rat model of maternal separation (MS), and B) modulate gastrointestinal transit in MS and non-handled (NH) rats. METHODS: Adult MS and NH rats (n=9 in all groups) were subjected to acute stress (1 hr water avoidance,WA). The visceromotor response (VMR) to colorectal distension (1, 11⁄2, 2ml) was established preand 24 hours post-WA and expressed as area-under-curve (AUC, volume-vs-response, significant difference when P<0.05: Wilcoxon). Rats were then treated with fexofenadine (1,8 mg/kg or 18 mg/kg) or vehicle and re-evaluated 48 hrs post-WA. Pre-WA transit was measured in NH (n=4) and MS (n=5) rats treated with fexofenadine or vehicle by evaluating the transit (geometric centre or GC) of orally administered fluorescein-labeled dextran (MW=70.000) (1 is stomach, 2 most proximal small bowel, 11 most distal, 12 cecum, 13-15 colon). RESULTS: WA induced an increased VMR to distension in MS rats (pre-WA vs post-WA, 64±4 vs 98±6 (mean±SEM), P=0.012) which was reversed by 1.8 mg/kg fexofenadine (post-WA vs post-fexofenadine, 98±6 vs 69±5, P=0.012). High concentration fexofenadine (18 mg/kg) showed similar results (pre-WA vs post-WA, 72±4 vs 97±6, P=0.012 and post-WA vs post fexofenadine 97±6 vs 60±6, P=0.008). NH rats remained normo-sensitive under all conditions. Baseline pre-WA transit times of NH and MS were equal (10±0.2 vs 9.6±0.4). Administration of high-dose fexofenadine decreased transit time in NH (vehicle vs fexofenadine, 10±0.2 vs 6.4±1.1, P= 0.028) and MS-rats (9.6±0.4 vs 6.9±0.2, P=0.008). CONCLUSION: The peripheral H1 receptor antagonist fexofenadine effectively reverses stress-induced visceral hypersensitivity and decreases intestinal transit. As low dose fexofenadine does not cross the blood brain barrier, these data justify future IBS patient trials with 2nd generationH1-receptor antagonists.

Abstract: S2-2 ROLES OF INFLAMMATION AND ENDOPLASMIC RETICULUM STRESS IN THE PROGRESSION AND RAPTURE OF ATHEROSCLEROTIC PLAQUES

The goal of this work was to determine whether the blockade of histamine H2receptors is beneficial for the pathophysiology of chronic heart failure (CHF).Because CHF is one of the major life-threatening diseases, we need to find a novel effective therapy. Intriguingly, our previous study, which predicts the involvement of histamine in CHF, suggests that we should test this hypothesis in patients with CHF.We selected 159 patients who received famotidine among symptomatic CHF patients for the retrospective study. We blindly selected age- and gender-matched CHF patients receiving drugs for gastritis other than histamine H2receptor blockers as a control group. For the prospective study, 50 symptomatic CHF patients were randomly divided into 2 groups. One group received famotidine of 30 mg/day for 6 months, and the other group received teprenone.In the retrospective study, famotidine of 20 to 40 mg decreased both left ventricular end-diastolic and end-systolic lengths (LVDd and LVDs, respectively) and the plasma B-type natriuretic peptide (BNP) levels (182 ± 21 vs. 259 ± 25 pg/ml, p < 0.05) with unaltered fractional shortening (FS). In a randomized, open-label study, compared with teprenone, famotidine of 30 mg prospectively decreased both New York Heart Association functional class (p < 0.05) and plasma BNP levels (183 ± 26 pg/ml vs. 285 ± 41 pg/ml, p < 0.05); this corresponded to decreasing both LVDd (57 ± 2 mm vs. 64 ± 2 mm, p < 0.05) and LVDs (47 ± 2 mm vs. 55 ± 2 mm, p < 0.05) with unaltered FS (15 ± 1% vs. 17 ± 1%). The frequency of readmission because of worsening of CHF was lower in the famotidine group (4% and 24%, p < 0.05). On the other hand, teprenone had no effects on CHF.Famotidine improved both cardiac symptoms and ventricular remodeling associated with CHF. Histamine H2receptor blockers may have therapeutic benefits for CHF.

Chlorpheniramine impairs spatial choice learning in telencephalon-ablated fish.

This work investigated the effect of the H1 receptor blockade in the forebrain of ablated Carassius auratus in a simple stimulus-response learning task using a T-maze test with positive reinforcement. The goldfish were submitted to surgery for removal of both telencephalic lobes five days before beginning the experiment. A T-shaped glass aquarium was employed, with two feeders located at the extremities of the long arm. One of the two feeders was blocked. The experimental trials were performed in nine consecutive days. Each fish was individually placed in the short arm and confined there for thirty seconds, then it was allowed to swim through the aquarium to search for food for ten minutes (maximum period). Time to find food was analysed in seconds. Animals were injected intraperitoneally with chlorpheniramine (CPA) at 16 mg/kg of body weight or saline after every trial, ten minutes after being placed back in the home aquarium. The results show that all the training latencies of the A-SAL group were higher than the latencies of the S-SAL group. The S-SAL group had decreased latencies from the second trial on, while the S-CPA group showed decreased latencies after the fourth trial. The A-SAL group showed reduced latencies after the fifth trial, but the A-CPA group maintained the latencies throughout the experiment. This suggests that CPA impairs the consolidation of learning both on telencephalon ablated animals and in sham-operated ones through its action on mesencephalic structures of the brain and/or on the cerebellum in teleost fish.