The effect of a chromogranin A-derived peptide (CgA4-16) in the writhing nociceptive response induced by acetic acid in rats

The nociceptive effects of i.p administration of a synthetic peptide (CgA4-16) derived from chromogranin A (CgA) were studied on a model of inflammatory (somato-visceral) pain. Inflammatory mediators participate in controlling the activity of enterochromaffin cells that store and release chromogranins. Adult male Wistar rats were injected i.p with diluted acetic acid (AA) to induce abdominal writhes. Pharmacological agents were injected prior to CgA4-16 and/or AA together. While i.p CgA4-16 alone did not produce any effect, the peptide increased the number of abdominal constrictions induced by i.p AA administration in a dose-related manner. To determine the possible mechanisms involved in CgA4-16 produced pronociceptive effect, i.p diltiazem or indomethacin were tested. The pronociceptive effect induced by CgA4-16 was blocked by pretreatment of either substance. I.p administration of CGRP, substance P (SP) or capsaicin evoked dose-related abdominal writhing. CgA4-16, 20 min prior to CGRP or capsaicin, potentiated the nociceptive effects induced by CGRP or capsaicin, but not those induced by SP. Taken together, these data suggest for the first time that a CgA-derived peptide may modulate inflammatory pain.     

Interactions of chromogranin A-derived vasostatins and monolayers of phosphatidylserine, phosphatidylcholine and phosphatidylethanolamine

Vasostatin-I (CgA1-76) is a naturally occurring and biologically active N-terminal peptide derived from chromogranin A (CgA), produced and secreted at high concentrations by neuroendocrine tissues and also from a range of neuroendocrine tumors. This study aims to examine the hypothesis that in the absence of classical protein receptors CgA1-76 may, like its two derived peptides CgA1-40 and CgA47-66, perturb the lipid microenvironment of other membrane receptors, as a basis for the largely inhibitory activities of these CgA peptides. The nature of the interactions between phospholipids and vasostatin-derived fragments was studied in the Langmuir film balance apparatus at 37 degrees C. The synthetic peptides CgA1-40 and CgA47-66 and a recombinant fragment (VS-I) containing vasostatin-I (Ser-Thr-Ala-CgA1-78) were compared for their effects on monolayers of phosphatidylcholine and phosphatidylethanolamine from pig brain and defined species of phosphatidylserine. Marked differences in surface pressure-area isotherms and phase-transition plateaus were apparent with the three classes of phospholipids on VS-I, CgA1-40 and CgA47-66 in physiological buffer or pure water. The results indicate that VS-I and CgA47-66 at 5-10 nM concentrations may engage in electrostatic as well as hydrophobic interactions with membrane-relevant phospholipids at physiological conditions, VS-I in particular enhancing the fluidity of saturated species of phosphatidylserine.     

Laetispicine, an amide alkaloid from Piper laetispicum, presents antidepressant and antinociceptive effects in mice

In the present work, we studied the effect of laetispicine, an amide alkaloid isolated from the stems of Piper laetispicum (Piperaceae), in forced swimming, open field, acetic acid writhing and formalin tests in KM mice to assess antidepressant and antinociceptive effects. A significant and dose-dependent decrease in the immobility time, as evaluated by the forced swimming test, was observed after laetispicine administration (38.18, 39.79, 58.77 and 67.28% decreased at the doses of 5, 10, 20, 40 mg/kg, respectively), suggesting an antidepressant effect. Furthermore, in the open field test, laetispicine at the given doses did not alter the number of crossings and rearing, as compared to controls. Results from writhing and formalin tests showed that laetispicine reduced the number of writhing in mice in a dose-dependent manner, attenuated the licking and spiting time of the injected paw in the first phase of formalin test. The antinociceptive effect of laetispicine was not affected by pre-treatment (i.p.) with naloxone (2 mg/kg). In conclusion, we showed that laetispicine possessed significant antidepressant and antinociceptive properties, making this drug potentially useful in depression and pain.     

The involvement of nitric oxide in the analgesic effects of ketamine

We investigated the contribution of NO-cyclic GMP (cGMP) pathway to the antinociceptive effects of ketamine in mice by using the nitric oxide synthase inhibitor, nitro(g)- L-arginine methyl ester (L-NAME). Intraperitoneal (i.p.) (1, 5 or 10 mg/kg) or intrathecal (i.th.) (10, 30 or 60 microg/mouse) administration of ketamine produced dose-dependent antinociceptive effects in the acetic acid-induced writhing and formalin tests but not in the tail-flick nor in hot-plate tests. Pretreatment of mice with L-NAME (10 mg/kg, i.p.) which produced no antinociception on its own, significantly inhibited the antinociceptive effect of ketamine (1, 5 or 10 mg/kg, i.p.). However, L-NAME (30 microg/mouse) was given intrathecally, it neither modified the antinociceptive effect of i.th. ketamine (10, 30 or 60 microg/mouse) nor did it produce an antinociceptive effect alone. These data suggest that the activation of the NO-cGMP pathway probably at the supraspinal level, but not spinal level, contributes to the antinociceptive effects of ketamine.     

Effect of corticoliberin fragment CRF(4-6) on pain sensitivity in rats

The effects of corticoliberin fragment CRF(4-6) (Pro-Pro-Ile) on pain sensitivity of rats in "hot plate" test were investigated. Intracerebroventricular administration of tripeptide CRF(4-6) (6, 30, 150 nmol/head) induced dose-dependent antinociception: the latency of paw lick response increased by 7.4 +/- 1.4, 10.1 +/- 1.5 and 16.7 +/- 4.2 s respectively from the basic level of 10.2 +/- 0.9 s. Duration of tripeptide antinociceptive action was 30 min (for 6 nmol) and 60 min (for 30 and 150 nmol). Pretreatment with corticotropin-releasing factor antagonist alpha-helical CRF(9-41) (6.5 nmol/head) 60 minutes before tripeptide administration completely abolished the antinociceptive effects of CRF(4-6) (6 nmol). Therefore corticoliberin receptors seem to be involved in realization of tripeptide influence on pain sensitivity. The data obtained suggest that CRF(4-6) can either directly interact with corticoliberin receptors or modulate activity of CRF-ergic neurons.     

Anxiogenic and antinociceptive effects induced by corticotropin-releasing factor (CRF) injections into the periaqueductal gray are modulated by CRF1 receptor in mice

Chemical or electrical stimulation of the dorsal portion of the midbrain periaqueductal gray (dPAG) produces anxiogenic and antinociceptive effects. In rats, chemical stimulation of dPAG by local infusion of the neuropeptide corticotropin-releasing factor (CRF) provokes anxiogenic effects in the elevated plus-maze test (EPM). CRF also produces antinociception when injected intracerebroventricularly in rats, however it remains unclear whether this response is also observed following CRF injection into the dPAG in mice. Yet, given that there are CRF1 and CRF2 receptor subtypes within the PAG, it is important to show in which receptor subtypes CRF exert its anxiogenic and antinociceptive effects in the dPAG. Here, we investigated the role of these receptors in the anxiogenic (assessed in the EPM) and antinociceptive (assessed by the Formalin test: 2.5% formalin injection into the right hind paw) effects following intra-dPAG infusion of CRF in mice. The results show that intra-dPAG injections of CRF (75 pmol/0.1 μl and 150 pmol/0.2 μl) produced dose-dependent anxiogenic and antinociceptive effects. In addition, local infusion of NBI 27914 (5-chloro-4-(N-(cyclopropyl)methyl-N-propylamino)-2-methyl-6-(2,4,6-trichlorophenyl)-aminopyridine; 2 nmol/0.2 μl), a CRF1 receptor antagonist, completely blocked both the anxiogenic and antinociceptive effects induced by local infusion of CRF, while that of antisauvagine 30 (ASV30; 1 nmol/0.2 μl), a CRF2 receptor antagonist, did not alter the CRF effects. Present results are suggestive that CRF1 (but not CRF2) receptors play a crucial role in the anxiogenic and antinociceptive effects induced by CRF in the dPAG in mice.     

Effect of acetic acid or trypsin application on rat colonic motility in vitro and modulation by two synthetic fragments of chromogranin A

The hypothesis that Chromogranin A (CgA)-derived peptides are involved in mechanisms modulating altered colonic motility was tested. Rat distal colonic strips were studied using an organ bath technique. Acetic acid (AA)-induced effects were characterized on spontaneous mechanical activities (SMA) in the presence of CgA4-16 or CgA47-66. In preparations with mucosa, AA induced a transient hyperactivity followed by a decrease in tone. The first phase is sensitive to tetrodotoxin (TTX) and capsaicin. The second phase was sensitive to BAYK8644 but insensitive to L-nitro-arginine-methyl-ester (L-Name)/apamin together. CgA4-16 or CgA47-66 alone produced no change on SMA. The administration of CgA4-16 prior to AA increased the duration of the excitatory component and reduced tone inhibition. CgA47-66 prior to AA only decreased duration of the excitatory phase. In preparations without mucosa, AA decreased tone. This effect was sensitive to BAYK8644 and CgA4-16. Trypsin decreased basal tone. This effect was suppressed by TTX, BAYK8644 or L-Name/apamin and were reduced by CgA4-16. AA-induced effects on rat colonic motility in vitro may be mediated through activation of primary afferents and an action at L-Type calcium channels. CgA-derived peptides are shown to decrease AA-induced effects on motility.     

Analgesic and anti-inflammatory activities of a fraction rich in oncocalyxone A isolated from Auxemma oncocalyx.

In the present work we studied the antinociceptive and antiedematogenic effects of a quinone fraction (QF) isolated from the heartwood of Auxemma oncocalyx Taub. The major constituent of QF, which represented around 80% of this fraction, was a terpenoid quinone named oncocalyxone A (1). Results show that QF (10 and 30 mg/kg body wt., i.p.) significantly inhibited paw edema induced by carrageenan at the second, third, and fourth hours. The effect was dose-dependent and long lasting, and QF was less effective orally. An antiedematogenic effect was also demonstrated in the dextran-induced paw edema. In this model, however, QF was somewhat less potent. QF (1 and 5 mg/kg body wt., i.p.) inhibited acetic acid-induced abdominal contractions in mice in a dose-dependent manner. In addition, QF (5 and 10 mg/kg body wt., i.p.) inhibited only the second phase (inflammatory) in the formalin test, and showed no effect in the hot-plate test in mice. The antinociceptive activity of QF was predominantly peripheral and independent of the opioid system. The observed effects of QF are, at least in part, probably due to the presence of oncocalyxone A (1).     

Structure-activity relationships of chromogranin A in cell adhesion. Identification of an adhesion site for fibroblasts and smooth muscle cells

Previous studies showed that chromogranin A (CgA), a glycoprotein stored and co-released with various hormones by neuroendocrine cells and neurons, can modulate cell adhesion. We have investigated the structure-activity relationships of CgA using fibroblasts and coronary artery smooth muscle cells in adhesion assays. A recombinant CgA fragment 1-78 and a peptide 7-57 containing reduced and alkylated cysteines (Cys(17) and Cys(38)) induced cell adhesion after adsorption onto solid phases at 50-100 nm. Peptides lacking the disulfide loop region, including residues 47-68, 39-59, and 39-68, induced cell adhesion, either bound to solid phases at 200-400 nm or added to the liquid phase at 5-10 microm, whereas peptide 60-68 was inactive, suggesting that residues 47-57 are important for activity. The effect of CgA-(1-78) was blocked by anti-CgA antibodies against epitopes including residues Arg(53), His(54), and Leu(57). Substitutions of residues His(54), Gln(55), and Asn(56) with alanine decreased the cell adhesion activity of peptide 47-68. These results suggest that the region 47-57 (RILSILRHQNL) contains a cell adhesion site and that the disulfide bridge is not necessary for the proadhesive activity. The ability of soluble peptides to elicit proadhesive effects suggests an indirect mechanism. The high sequence conservation and accessibility to antibodies suggest that this region is important for the physiological role of CgA.     

Chromogranin A-derived peptides: interaction with the rat posterior cerebral artery

Chromogranin A (CgA), an acidic granule protein of the regulated secretory pathway in the diffuse neuroendocrine system, is postulated to serve as a prohormone for regulatory peptides. Betagranin (rCgA(1-128)), the first N-terminal cleavage product of rat CgA, is 87% homologous to the bovine vasostatin I (bCgA(1-76)), previously shown to be vasoinhibitory in bovine resistance arteries. In this study the vasoactivity of homologous rat and bovine peptides was investigated in the rat posterior cerebral artery. Firstly, we examined the interaction of rhodamine (Rh)-labelled bCgA(7-40) and bCgA(47-70) with elements of the arterial wall by fluorescence microscopy. Secondly, rCgA(7-57), bCgA(1-40), bCgA(7-40) and bCgA(47-66) (chromofungin) were studied for effects on arterial tone and intracellular calcium as function of pressure in an arteriograph. Although without dilator or constrictor responses at 60-150 mm Hg, the rat peptide (rCgA(7-57)) evoked a significant delay in the onset of forced dilatation at 170 mm Hg, in contrast to the bovine peptides bCgA(1-40), bCgA(7-40) and bCgA(47-66) (chromofungin). Neither Rh-bCgA(7-40) nor Rh-bCgA(47-70) stained the endothelial layer, while Rh-bCgA(47-70) but not Rh-bCgA(7-40) stained the smooth muscle compartment. Analogously, bCgA(47-66) but not bCgA(7-40) reduced intracellular calcium, however without modifying the myogenic response. Thus, the betagranin peptide rCgA(7-57) and the two bovine chromofungin-containing peptides, highly homologous to the corresponding sequence (rCgA(47-66)), affected the rat cerebral artery without vasodilator effects, indicating significant species differences in vasoactivity of the N-terminal domain of CgA.     

Analysis of the antinociceptive properties of marrubiin isolated from Marrubium vulgare.

We have shown previously that Marrubium vulgare, a medicinal plant employed frequently in folk medicine to treat a variety of ailments, exhibits antispasmodic and antinociceptive effects in different experimental models. This work describes the antinociceptive profile of marrubiin, the main constituent of this plant, which was analysed in some models of nociception in mice. The results showed that marrubiin exhibits potent and dose-related antinociceptive effects, whose calculated ID50 values (micromol/kg, i.p.) were the following: 2.2 in the writhing test, 6.6 (first phase) and 6.3 (second phase) in the formalin-induced pain test and 28.8 when evaluated in the capsaicin test. It was more potent than some well-known analgesic drugs. The antinociception produced by the marrubiin was not reversed by naloxone when analyzed against the writhing test. In the hot-plate test, marrubiin did not increase the latency period of pain induced by the thermal stimuli. Its exact mechanism of action remains to be determined, but the results suggest that marrubiin, like hydroalcoholic extract of M. vulgare, does not interact with opioid systems.     

Modulation of acute morphine tolerance by corticotropin-releasing factor and dynorphin A in the mouse spinal cord.

Previously, we have demonstrated that intrathecally (i.t.) administered corticotropin-releasing factor (CRF) in mice produces stimulus-specific antinociception and modulation of morphine-induced antinociception by mechanisms involving spinal kappa opioid receptors. Recently, we also have found that CRF releases immunoreactive dynorphin A, a putative endogenous kappa opioid receptor agonist, from superfused mice spinal cords in vitro. Dynorphin A administered intracerebroventricularlly (i.c.v.) to mice has been shown to modulate the expression of morphine tolerance. In the present study, the possible modulatory effects of i.t. administered CRF as well as dynorphin A on morphine tolerance were studied in an acute tolerance model. Subcutaneous administration of 100 mg/kg of morphine sulfate (MS) to mice caused an acute tolerance to morphine-induced antinociception. The antinociceptive ED50 of MS was increased from 4.4 mg/kg (naive mice) to 17.9 mg/kg (4 hours after the injection of 100 mg/kg MS). To study the modulatory effects of spinally administered CRF and dynorphin A on the expression of morphine tolerance, CRF and dynorphin A were injected i.t. at 15 min and 5 min, respectively, before testing the tolerant mice by the tail-flick assay. The antinociceptive ED50 of MS in tolerant mice was decreased to 8.8 mg/kg and 7.1 mg/kg, respectively, after i.t. administration of CRF (0.1 nmol) and dynorphin A (0.2 nmol). In contrast, 0.5 nmol of alpha-helical CRF (9-41), a CRF antagonist and 0.4 nmol of norbinaltorphimine, a highly selective kappa opioid receptor antagonist, when administered i.t. at 15 min before the tail-flick test in tolerant mice, increased the antinociceptive ED50 of MS to 56.6 mg/kg and 88.8 mg/kg, respectively. These data confirmed the modulatory effect of dynorphin A on morphine tolerance and suggested that CRF, which releases dynorphin A in several central nervous system regions, also plays a modulatory role in the expression of morphine tolerance.     

Antinociceptive mechanisms of orally administered decursinol in the mouse

Antinociceptive profiles of decursinol were examined in ICR mice. Decursinol administered orally (from 5 to 200 mg/kg) showed an antinociceptive effect in a dose-dependent manner as measured by the tail-flick and hot-plate tests. In addition, decursinol attenuated dose-dependently the writhing numbers in the acetic acid-induced writhing test. Moreover, the cumulative response time of nociceptive behaviors induced by an intraplantar formalin injection was reduced by decursinol treatment during the both 1st and 2nd phases in a dose-dependent manner. Furthermore, the cumulative nociceptive response time for intrathecal (i.t.) injection of TNF-alpha (100 pg), IL-1 beta (100 pg), IFN-gamma (100 pg), substance P (0.7 microg) or glutamate (20 microg) was dose-dependently diminished by decursinol. Intraperitoneal (i.p.) pretreatment with yohimbine, methysergide, cyproheptadine, ranitidine, or 3,7-dimethyl-1-propargylxanthine (DMPX) attenuated inhibition of the tail-flick response induced by decursinol. However, naloxone, thioperamide, or 1,3-dipropyl-8-(2-amino-4-chloro-phenyl)-xanthine (PACPX) did not affect inhibition of the tail-flick response induced by decursinol. Our results suggests that decursinol shows an antinociceptive property in various pain models. Furthermore, antinociception of decursinol may be mediated by noradrenergic, serotonergic, adenosine A(2), histamine H(1) and H(2) receptors.     

Evaluation of the anti-inflammatory and antinociceptive properties of p-cymene in mice

We attempted to identify the antinociceptive and anti-inflammatory actions of the monoterpene p-cymene. Firstly, behavioural screening was carried out to verify the influence of p-cymene [25, 50, and 100 mg/kg intraperitoneal (i.p.)] on the central nervous system (CNS) activity. The antinociceptive activity of p-cymene was evaluated by the acetic acid-induced writhing response, formalin, and hot-plate test, respectively. The leukocyte migration induced by injection of carrageenan was used to assess the anti-inflammatory activity. p-Cymene showed depressant activity on CNS after 4 h of treatment and also a possible action on the autonomous nervous system (ANS), mainly at the dose of 100 mg/kg (i.p.). It was found that p-cymene (50 and 100 mg/kg, i.p.) significantly (p < 0.05) reduced the writhing responses induced by acetic acid. p-Cymene also decreased the licking time in the first and second phase, respectively, of the formalin test. The results of the hot-plate test showed that all doses of p-cymene increased significantly the latency time of the response to the thermal stimulus in both licking and jumping parameters. In addition, there was a significantly (p < 0.05) decreased leukocyte migration at all doses of p-cymene. The experimental data demonstrate that p-cymene possesses antinociceptive and anti-inflammatory activities.     

Peptides from the N-terminal domain of chromogranin A (vasostatins) exert negative inotropic effects in the isolated frog heart

The negative inotropic effects of synthetic peptides derived from the N-terminus of chromogranin A (CgA) were studied in an avascular model of the vertebrate myocardium, the isolated working frog heart (Rana esculenta). The peptides were frog and bovine CgA(4-16) and CgA(47-66), and bovine CgA(1-40) with (CgA(1-40SS)) and without an intact disulfide bridge (CgA(1-40SH)). Under basal cardiac conditions, four of the peptides caused a concentration-dependent negative inotropism that was comparable to the negative inotropy reported for human recombinant vasostatin I (CgA(1-78)) and bovine CgA(7-57). By comparison of the structural characteristics of the bovine and frog sequences with their minimally effective concentrations ranging from 68 to 125 nM of peptide, the results were consistent with the natural structure (CgA(17-38SS)) being essential for the negative inotropism. In addition, the partial sequences of the frog and bovine vasostatin I were effective in counteracting the characteristic positive inotropism exerted by isoproterenol (1 nM) at minimally effective concentrations ranging from 45 to 272 nM. Taken together, these results extend the first evidence for a cardiosuppressive role of the N-terminal domain of chromogranin A known for its co-storage with catecholamines in the sympathoadrenal system of vertebrates.     

Effect of the corticoliberin fragment CRF(4-6) on blood pressure and heart rate in rats

The effects of tripeptide corticoliberin fragment CRF(4-6) (Pro-Pro-Ile) on blood pressure and heart rate of rats were investigated. Intracerebroventricularly injected CRF(4-6) (1.5-15.0 nmol/head) increases the mean arterial pressure and heart rate in conscious and anaesthetized animals in a dose-dependent manner. Corticotropin releasing factor antagonist: alpha-helical CRF(9-41) (6.5 nmol) completely abolished the influence of tripeptide CRF(4-6) (1.5 nmol) on blood pressure and heart rate in anaesthetized rats. This result indicates that corticoliberin receptors are involved in cardiovascular effects of CRF(4-6).     

Antiangiogenic and antivascular effects of a recombinant tumstatin-derived peptide in a corneal neovascularization model

Tumstatin, a cleavage fragment of collagen IV, is a potent endogenous inhibitor of angiogenesis. Tumstatin-derived peptide T8 possesses all angiostatic properties of full-length tumstatin and indirectly suppresses tumor growth. The potential of T8 to block pathological angiogenesis in the eye has not been explored yet. Here we assess antiangiogenic effects of a recombinant T8 peptide in rabbit corneal neovascularization models. The fusion protein consisting of T8 and thioredoxin was synthesized in a highly efficient Escherichia coli expression system, isolated using ion-exchange chromatography and cleaved with TEV (tobacco etch virus) protease. The target peptide was purified on an anion-exchange resin and by reversed phase high-performance liquid chromatography. The recombinant peptide suppressed the proliferation of basic fibroblast growth factor-induced SVEC-4-10 endothelial cells (simian virus 40-immortalized murine endothelial cells) and inhibited tube formation in these cells in a dose-dependent manner. In rabbit corneal neovascularization models T8 demonstrated the ability to prevent pathological angiogenesis (when injected simultaneously with the induction of neovascularization) and, moreover, to promote the regression of newly-formed blood vessels (when injected on day 8 after angiogenesis stimulation). Our results suggest that T8 may have a therapeutic potential in the treatment of ocular neovascular diseases.     

Opioid activity of C8813, a novel and potent opioid analgesic

Compound trans-4-(p-bromophenyl)-4-(dimethylamino)-1-(2-thiophen-2-yl-ethyl)-cyclohexanol (C8813), structurally unrelated to morphine, is a novel analgesic. The present study examined the antinociception, opioid receptor selectivity and in vitro activity of C8813. The antinociceptive activity was evaluated using mouse hot plate and acetic acid writhing tests. In mouse hot plate test, the antinociceptive ED(50) of C8813 was 11.5 microg/kg, being 591 times and 3.4 times more potent than morphine and fentanyl respectively. In mouse writhing test, the antinociceptive ED(50) of C8813 was 16.9 microg/kg, being 55 times and 2.3 times more active than morphine and fentanyl respectively. In the opioid receptor binding assay, C8813 showed high affinity for mu-opioid receptor (K(i) = 1.37 nM) and delta-opioid receptor (K(i) = 3.24 nM) but almost no affinity for kappa-opioid receptor (at 1 microM). In the bioassay, the inhibitory effect of C8813 in the guinea-pig ileum (GPI) was 16.5 times more potent than in the mouse vas deferens (MVD). The inhibitory effects of C8813 in the GPI and MVD could be antagonized by mu-opioid receptor antagonist naloxone and delta-opioid receptor antagonist ICI174,864 respectively. However, the inhibitory effect of C8813 in the rabbit vas deferens was very weak. These results indicated that C8813 was a potent analgesic and a high affinity agonist for the mu- and delta-opioid receptors.     

Supraspinal antinociceptive effect of apelin-13 in a mouse visceral pain model

Apelin, as the endogenous ligand of the APJ receptor, is a novel identified neuropeptide whose biological functions are not fully understood. APJ receptor mRNA was found in several brain regions related to descending control system of pain, such as amygdala, hypothalamus and dorsal raphe nucleus (DRN). The present study was designed to determine whether supraspinal apelin-13 may produce antinociceptive effect observed in the acetic acid-induced writhing test, a model of visceral pain. Apelin-13 not only significantly produced preemptive antinociception at the dose of 0.3, 0.5, 1 and 3μg/mouse when injected intracerebroventricularly (i.c.v.) before acetic acid, but also significantly induced antinociception at a dose of 0.5, 1 and 3μg/mouse when injected i.c.v. after acetic acid. And i.c.v. apelin-13 did not influence 30-min locomotor activity counts in mice. Intrathecal (i.t.) administration of apelin-13 (1 and 3μg/mouse) significantly decreased the number of writhes, however, intraperitoneal (i.p.) injection of apelin-13 (10-100μg/mouse) had no effect on the number of writhes in the writhing test. The specific APJ receptor antagonist apelin-13(F13A), no-specific opioid receptor antagonist naloxone and μ-opioid receptor antagonist β-funaltrexamine hydrochloride (β-FNA) could significantly antagonize the antinociceptive effect of i.c.v. apelin-13, suggesting APJ receptor and μ-opioid receptor are involved in this process. Central low dose of apelin-13 (0.3μg/mouse, i.c.v.) could significantly potentiate the analgesic potencies of modest and even relatively ineffective doses of morphine administrated at supraspinal level. This enhanced antinociceptive effect was reversed by naloxone, suggesting that the potentiated analgesic response is mediated by opioid-responsive neurons.     

Antinociceptive activity of metapramine in mice. Relationship with its pharmacokinetic properties.

The antinociceptive effect of acutely and chronically (every brain elimination half-life time) administered metapramine, a tricyclic antidepressant without anticholinergic or cardiotoxic effects, was studied in three different pain tests. In the hot plate test, its action was more potent when jumping was used as a pain parameter (acute ED50 = 19 +/- 3 mg/kg, i.p.) than when pain was assessed by licking of forepaws (only 20 mg/kg, i.p. was weakly active). Five chronic doses of 15 mg/kg were as active in the tail-flick test as an acute dose of 20 mg/kg (only active dose). Metapramine was more effective in the PBQ-induced writhing test after acute (ED50 = 9.9 +/- 0.1 mg/kg, i.p.) and chronic administration. A significant linear correlation was found between the effect in this test and plasma and overall brain levels of metapramine. No correlation was observed with levels of its three desmethylated metabolites. The usefullness of using a well-defined pattern of administration based on pharmacokinetic parameters and the involvement of monoaminergic mechanisms and of some metabolites of metapramine are discussed.