The actions of prostanoids in various physiological and pathophysiological conditions have been being examined using mice lacking different prostanoid receptors.Prostaglandin(PG)I2 worked not only as a mediator of inflammation but also as an antithrombotic agent.PGF2α was found to be an essential inducer of labor.Several important actions of PGE2 are exerted via each of the four PGE2 receptor subtypes:EP1, EP2, EP3 and EP4.PGE2 participated in colon carcinogenesis via the EP1.PGE2 also participates in ovulation and fertilization and contributes to the control of blood pressure under high−salt intake via the EP2.PGE2 worked as a mediator of febrile responses to both endogenous and exogenous pyrogens and as a regulator of bicarbonate secretion induced by acid−stimulation in the duodenum via the EP3.It regulated the closure of ductus arteriosus and showed bone resorbing action via the EP4.PGD2 was found to be a mediator of allergic asthma.These studies have revealed important roles of prostanoids, some of which had not previously been known.
We investigated the antinociceptive effect of pentazocine hydrochloride(pentazocine)in combination with morphine hydrochloride(morphine)using two antinociceptive tests;i.e., the tail−immersion and scald−pain tests, in rats.In the tail−immersion test, the rat’s tail was immersed in warm water at 47°C, and the latency to a nociceptive response was measured.In the scald−pain test, the right hind foot was scalded by immersion into hot water at 57°C.Two hours later, additional thermal stimulus was applied to the same foot, and the latency to a nociceptive response was measured.Subcutaneous treatment with either pentazocine(6, 12, 24 mg/kg)or morphine(1.5, 3, 6 mg/kg)alone dose−dependently showed antinociceptive effects in both tests.The ED50 values(95% confidence limit)of pentazocine and morphine were 13.0(5.4−31.5)and 2.4(1.6−3.7)mg/kg in the tail−immersion test and 11.0(4.5−26.6)and 3.8(1.8−7.2)mg/kg in the scald−pain test, respectively.Simultaneous treatment with pentazocine at the similar dose augmented the morphine(1.5 mg/kg)−induced antinociception, but did not diminish the morphine(6 mg/kg)−induced antinociception in both tests.These results suggest that the simultaneous administration of pentazocine at the antinociceptive dose and morphine exerts additional antinociceptive activity against thermal and scald−induced inflammatory pain.
The regulatory mechanism of degranulation of guinea pig peritoneal eosinophils was studied by determination of eosinophil peroxidase(EPO)release.β−Agonists, such as isoproterenol, salbutamol and fenoterol, effectively inhibited A23187−induced EPO release from guinea pig eosinophils.The inhibitory effects of β−agonists were attenuated by pretreatment with either propranolol, a non−selective β−antagonist, or ICI 118, 551, a selective β2−antagonist.Both theophylline and dibutyryl−cAMP(db−cAMP)also significantly inhibited A23187−induced EPO release.The inhibition of EPO release induced by db−cAMP was attenuated by pretreatment with KT5720, a protein kinase A inhibitor.In addition, calphostin C as well as cytochalasin D effectively inhibited A23187−induced EPO release.From the results of the present study, it was concluded that an increase in intracellular Ca2+ concentration may lead to exocytosis of eosinophil granules through activation of protein kinase C and microfilaments.β−Agonists and theophylline were effective in inhibiting degranulation of eosinophils by increasing intracellular cAMP level coupled with the activation of protein kinase A.
We examined influences of certain antibiotics on the release of chemical mediators from isolated rat peritoneal mast cells in vitro.Isolated peritoneal mast cells were obtained from male Wistar strain rats.Everninomicin(0.06−1.2 mg/ml), vancomycin(0.05−1.0 mg/ml), teicoplanin(0.07−1.4 mg/ml)and concanavalin A(0.01 mg/ml)were used.Isolated mast cells were incubated in the presence of various concentrations of the test compound at 37°C for 10 min.Histamine contents of the supernatant and cell pellet were measured by an automated fluorometric method.Prostaglandin D2(PGD2)contents of the supernatant were determined by enzyme immunoassay.Everninomicin(0.06−1.2 mg/ml)had no influence on histamine and PGD2 release from mast cells.On the other hand, vancomycin significantly released both histamine(0.5 and 1.0 mg/ml)and PGD2(1.0 mg/ml)from mast cells, but vancomycin did not affect concanavalin A−induced histamine and PGD2 release.Teicoplanin(more than 0.07 mg/ml)significantly stimulated histamine and PGD2 release from mast cells and it also significantly potentiated concanavalin A−induced histamine and PGD2 release.These results suggest that everninomicin causes no chemical mediator release from mast cells, different from vancomycin and teicoplanin.
Endomorphin−1 is a novel endogenous peptide that is highly selective for the μ−opioid receptor over the δ−and κ−opioid receptors.The structural basis of high selectivity of endomorphin−1 to the μ−opioid receptor was examined using chimeric receptors between μ− and δ−opioid receptors and those between μ− and κ−opioid receptors.The chimeric receptors were constructed by using restriction enzyme sites intrinsically possessed by or introduced to the μ−, δ− and κ−opioid receptor cDNAs.The junctions for the construction were located at the first intracellular loop(Bbs I site), third transmembrane domain(Afl III site)and fifth transmembrane domain(Bgl II site).The competitive binding assay using chimeric receptors revealed that the region from the Bbs I site to the Afl III site, including the first extracellular loop, contributes to the discrimination between μ− and δ−opioid receptors by endomorphin−1 more than any other regions.However, the region from the Afl III site to the Bgl II site and that from the Bgl II site to the carboxy terminal also somewhat contribute to the discrimination between μ− and δ−opioid receptors.For the discrimination between μ− and κ−opioid receptors, two regions, that is, the region from the Bbs I site to the Afl III site and that from the Bgl II site to the carboxy terminal, were shown to be important.The present results show that endomorphin−1 discriminates the μ−opioid receptor from the other two types of opioid receptors by recognizing the differences in several amino acid residues widely distributed through the receptor structure.We previously reported that DAMGO, a synthetic highly μ−selective peptide, discriminates between μ− and δ−opioid receptors by recognizing the difference in only one amino acid residue and discriminates between μ− and κ−opioid receptors by recognizing the difference in four residues localized in the restricted region.Although both endomorphin−1 and DAMGO are μ−opioid receptor selective peptides, molecular mechanisms for μ−selectivity are different between these peptides.
The senescence accelerated mouse(SAM)is known as a murine model of aging.SAM consists of senescence accelerated−prone mouse(SAMP)and senescence accelerated−resistant mouse(SAMR).Previous studies reported that SAMP10 exhibits age−related learning impairments and behavioral depression in a tail suspension test after 7 months.We investigated the changes in emotional behavior in a forced swimming test and in receptors for dopamine and 5−hydroxytryptamine(5−HT)in SAMP10.SAMP10 at 8 months showed an increase of immobility in the test compared with SAMR1.Treatment with desipramine(25 mg/kg, i.p., 3 days)in SAMP10 caused a decrease in immobility.In the cortex from SAMP10, [3H]quinpirole binding to D2/D3 dopamine receptors increased significantly compared with control SAMR1.In the hippocampus from SAMP10, [3H]8−hydroxy DPAT binding to 5−HT1A receptor increased.In midbrains from SAMP10, bindings of [3H]quinpirole and [3H]8−hydroxy DPAT increased.[3H]SCH23390 binding to D1/D5 receptors and [3H]ketanserin binding to 5−HT2 receptor in brain regions examined in SAMP10 were similar to those in SAMR1.The present findings represent the first neurochemical evidence of an increase of D2/D3 and 5−HT1A receptors in SAMP10.SAMP10 may be a useful model of aging associated depressive behavior.
We have recently found that the infection with herpes simplex virus type−1(HSV−1)of primary sensory neurons induces nociceptive hypersensitivity to noxious mechanical(hyperalgesia)and tactile stimulation(allodynia)in mice.In the present experiments, we determined the distribution of HSV−1 in the dorsal root ganglia and examined the effects of four analgesic agents on hyperalgesia and allodynia.HSV−1 was inoculated on the unilateral shin.HSV−antigen−positive cells were detected in the L4 and L5 dorsal root ganglia on days 5 and 7, but not day 3, post−inoculation.About 80% of the positive cells were small in size.Allodynia and hyperalgesia appeared on day 5 post−inoculation.Antinociceptive effects of analgesic agents were examined on day 6 post−inoculation.Morphine(1−5 mg/kg, subcutaneous)and gabapentin(10−100 mg/kg, peroral)dose−dependently inhibited both allodynia and hyperalgesia.Diclofenac(10−100 mg/kg, intraperitoneal)also produced antinociceptive effects, but there was a ceiling for the effect on hyperalgesia.Amitriptyline(3, 10 mg/kg, subcutaneous)did not affect allodynia and hyperalgesia.The results suggest that mechanical allodynia and hyperalgesia appeared when HSV−1 proliferated in the sensory neurons.This mouse model may be useful for studying the mechanisms of acute herpetic pain and anti−neuropathic pain agents.
The purpose of this study was to test the potential utility of mexiletine for the treatment of drug−induced long QT syndrome in vivo.Beagle dogs were anesthetized with halothane inhalation(n=7).Monophasic action potential(MAP)of the right ventricle, ECG, systemic and left ventricular pressure, cardiac output and effective refractory period(ERP)of the right ventricle were measured.The electrically vulnerable period was estimated by the difference between MAP duration and ERP.An intentionally high dose of 1 mg/kg, i.v.of cisapride decreased the heart rate, mean blood pressure, left ventricular contraction and cardiac output and prolonged the ventricular repolarization phase and ERP, in which the increment was greater in the former than in the latter, indicating the increase of electrical vulnerability.The left ventricular end−diastolic pressure and atrioventricular as well as intraventricular conduction were hardly affected.Additional administration of an antiarrhythmic dose of 3 mg/kg, i.v.of mexiletine increased the heart rate, decreased the left ventricular contraction and cardiac output, suppressed the atrioventricular as well as intraventricular conduction, and prolonged the ERP, but shortened the ventricular repolarization phase.There was no change in the afterload and preload of the left ventricle.Thus, mexiletine decreased the electrical vulnerability of the heart during cisapride overdose, suggesting that it may become a potential pharmacological strategy for drug−induced long QT syndrome.
The superficial buffer barrier function of the sarcoplasmic reticulum(SR)during rest and that during stimulation with Bay k 8644, an agonist of L−type Ca2+ channels, were compared in endotheliumdenuded strips of tail arteries from 13−week−old normotensive Wistar−Kyoto rats(WKY)and spontaneously hypertensive rats(SHR), by measuring the effects of cyclopiazonic acid(CPA)and thapsigargin that inhibit SR Ca2+−ATPase and the effect of ryanodine that depletes SR Ca2+.The addition of 10μM CPA induced a transient contraction that was not significantly different between WKY and SHR.The CPA−induced contraction was strongly inhibited by 100 nM nifedipine and was abolished by Ca2+−free solution in both strains.Thapsigargin(100 nM)or ryanodine(10 μM)induced similar, small transient contractions in the two strains.The addition of Bay k 8644(1−100 nM)almost failed to induce a contraction in both WKY and SHR.When the strips were preincubated with 10 μM CPA, 100 nM thapsigargin or 10 μM ryanodine, Bay k 8644 induced similar concentration−dependent contractions in the two strains.The amount of Ca2+ stored in the SR, as estimated from the 20 mM caffeine−induced contraction, was not significantly different between WKY and SHR.Our results suggest that the SR of rat tail arteries can buffer a large amount of Ca2+ that enters the cell during the rest and the Bay k 8644 stimulation, and these functions are not altered in SHR.
When 30 mg/kg, p.o.of fluvoxamine, a selective serotonin reuptake inhibitor, was administered, significant increases of 3−methoxy−4−hydroxyphenylglycol(MHPG)and 5−hydroxy indole−3−acetic acid(5−HIAA)contents in rat cerebrospinal fluid(CSF)were observed from two days after administration of fluvoxamine in both the light and dark periods and in the dark period of the light/dark cycle, respectively.In long−term treatment with 15 mg/kg, p.o.of fluvoxamine, the level of MHPG in CSF exhibited no difference, whereas the levels of 5−HIAA showed a significant increase during the light periods.These results suggest that fluvoxamine enhances the 5−HT system, but only with long−term treatment.
We investigated the effects of a continuous infusion of adenosine on responses of sinus rate and developed tension to bolus injections of adenosine and acetylcholine in isolated, blood−perfused canine right atria.Each drug was directly injected into the sinus node artery of the isolated atrium.During adenosine infusions, the negative chronotropic and inotropic responses to bolus injections of adenosine were significantly inhibited in a dose−related manner, while the negative responses to administered acetylcholine were consistently potentiated.These results indicate that adenosine infusion has an acute desensitizing action on subsequent bolus adenosine, although the cholinergic action is enhanced by a continuous infusion of adenosine.
Expression of Bcl−2 related proteins in rat microglial primary culture was examined.At relative low cell densities, serum deprivation caused cell death and nuclei condensation of cultured microglia.Expression of a pro−apoptotic protein, Bax, but not Bcl−2, was increased by the serum deprivation.SB203580, a specific inhibitor of p38MAPK, prevented both the serum deprivation−induced Bax expression and microglial death.Immunochemical staining showed that microglia expressing a high level of Bax were subjected to apoptosis−like cell death.These observations suggest that Bax expression underlies the apoptosis of cultured microglia after serum deprivation.
The term for re−entrainment to a new light−dark cycle in streptozotocin(STZ)−induced diabetic rats was significantly longer than that in control rats.In STZ−induced diabetic rats, the same level of phase delay in the suprachiasmatic nucleus neuronal firing rhythm was observed in control rats after glutamate application.Therefore, 5−HT function in the hypothalamus is thought to be decreased in STZ−induced diabetic rats.These results suggest that postsynaptic neuronal function is still maintained in the suprachiasmatic nucleus of STZ−induced diabetic rats.Therefore, 5−HT mechanisms may play an important role in the maintenance of this function.
Interferon−γ(IFN−γ)transgenic mice expressed the IFN−γ gene in the liver and developed chronic hepatitis.The expression of cyclooxygenase(Cox)−1 and −2 mRNA were studied in the livers of these mice.A faint band of Cox−1 mRNA was observed in the livers of both normal and transgenic mice.Slight expression of Cox−2 mRNA was observed in the normal mouse liver, and this mRNA expression was induced in the transgenic mouse liver.The present results showed the induction of Cox−2 mRNA expression in the livers of transgenic mice with chronic hepatitis.
Metallothionein(MT)is a metalloprotein with high affinity for certain heavy metals.In the present study, the ability of cadmium(Cd)to induce the synthesis of MT in dental pulp was investigated.Rats were injected subcutaneously with CdCl2(1.5 mg Cd/kg)daily for 7 days.Expression of the MT gene was demonstrated by reverse transcription polymerase chain−reaction techniques.The results indicate that Cd induced MT in dental pulp of rat incisor and this may be involved in the cellular defense mechanism against Cd toxicity.