Pharmacological analysis of α2-adrenoceptor subtypes mediating analgesic, anti-inflammatory and gastroprotective actions

Our previous findings suggest that α₂-adrenoceptor stimulants induce gastroprotective action, the effect is likely to be mediated by α_2B-adrenoceptor subtype. Clonidine (0.094 μmol/kg p.o.) and rilmenidine (0.014 μmol/kg p.o.) in gastroprotective dose range, as well as ST-91 (2.2 μmol/kg p.o.), a clonidine analogue showing higher affinity to α_2B-adrenoceptor subtype than to α_2A-one, inhibited the carrageenan-induced hyperalgesia in Randall-Selitto test, the antinociceptive action was reversed by yohimbine (5 μmol/kg s.c.) and the α_2B-adrenoceptor antagonist prazosin (0.24 μmol/kg i.p.). Similarly, clonidine and rilmenidine in the same dose range reduced the oedema formation induced by carrageenan, yohimbine and the α_2A-adrenoceptor antagonist BRL-44408 (3 μmol/kg i.p.) inhibited the anti-inflammatory effect; however, prazosin failed to affect it. These results suggest that α_2B/C-like adrenoceptor subtype may be involved in the antihyperalgesic action, but not in the antiphlogistic effect of α₂-adrenoceptor stimulants. The later effect may be mediated by α_2A-like adrenoceptor subtype.     

Gastroprotective effect of lupeol on ethanol-induced gastric damage and the underlying mechanism

The effect of lupeol, a natural pentacyclic triterpene on ethanol-induced gastric damage in mice was evaluated. The gastroprotection was assessed by determination of changes in mean gastric lesion area, quantification of mucosal non-protein sulfhydryls (NP-SH), and characterized using drugs that influence the endogenous prostaglandins, α₂-adrenoceptors, nitric oxide, K_ATP-channels, and intracellular calcium. Orally administered lupeol (3, 10, and 30 mg/kg) significantly and dose-dependently attenuated the ethanol-induced gastric damage by 39–69%, whereas the positive control N-acetylcysteine (NAC, 300 mg/kg, i.p.) afforded 32% protection. Both lupeol and NAC restored the NP-SH depleted by ethanol but the lupeol effect was only marginal. Lupeol gastroprotection was attenuated by indomethacin and L-NAME, the respective COX and NO-synthase inhibitors and was weakly sensitive to α₂-adrenergic antagonist yohimbine and K_ATP-channel blocker glibenclamide, but more profoundly to calcium blocker verapamil. These pharmacological effects of lupeol may synergistically contribute to alleviating the ethanol-associated gastric damage, which is multifactorial.     

Role of vagal nerve in defence mechanisms against nsaid-induced gastrointestinal mucosal damage

Many papers suggested only an aggressive role of the vagus nerve on the gastrointestinal (GI) mucosa; however, the essential role of the vagus nerve was proven in GI mucosal defence against different chemicals, e.g., ethanol, HCl, non-steroidal anti-inflammatory drugs (NSAIDs). In order to evaluate the role of the vagus nerve in the development of GI mucosal damage evoked in the rat by the administration of NSAIDs, the present studies were designed to: (1) compare the changes in the NSAID-induced GI mucosal damage after acute surgical and chemical (atropine treatment) vagotomy; (2) investigate the effect of sensory nerve stimulation and chemical deafferentation on the NSAID-induced gastric mucosal damage; (3) evaluate the cytoprotective action of prostacyclin under the above experimental conditions; (4) study the effect of surgical vagotomy on the gastroprotection induced by different drugs. Gastric mucosal damage was produced by intragastrically (acidified salicylates) or systemically (indomethacin) applied NSAIDs, while the small intestinal and large bowel mucosal injury was produced by systemic indomethacin application. Results (1) acute surgical vagotomy aggravated, whereas, chemical vagotomy prevented the GI mucosal damage produced by topically and systemically applied NSAIDs; (2) indomethacin produced significantly more damage in the small intestine than in the large bowel and stomach (order is small intestine > stomach > proximal colon) which is aggravated by acute surgical vagotomy in all these areas of the GI tract; (3) stimulation of capsaicin-sensitive sensory nerves with the capsaicin analogue resiniferatoxin protected against gastric mucosal damage by acidified salicylates and indomethacin; (4) chemical deafferentation enhanced the aspirin-induced gastric mucosal injury, while it did not interfere with the prostacyclin-induced gastric cytoprotection; (5) the mucosal protective effects of PGI₂, atropine, cimetidine, sucralfate and scavengers (β-carotene) disappeared after acute surgical vagotomy.     

Modification of aspirin and ethanol-induced mucosal damage in rats by intragastric application of resiniferatoxin

The capsaicin analogue ‘resiniferatoxin’ (RTX) was used to investigate the role of capsaicin-sensitive sensory nerves in gastric mucosal injury caused by intragastric (ig) acidified aspirin (200 mg/kg in 2 ml of 0.15 N HCl) or ethanol (2 ml of 50% v/v or 96%) in pylorus-ligated rats. Animals were sacrificed 1, 2 and 4 h later, when gastric secretory responses, number and severity of mucosal lesions were calculated. Intragastric RTX (0.6–1.8 μg/kg) prevented mucosal injury in a dose-dependent manner induced by topical acidified aspirin. The protective effect lasted for 1h and was accompanied by inhibition of gastric acid secretion by RTX. RTX (0.6 and 1.0 μg/kg) co-administered with ethanol reduced mucosal injury caused by 50% ethanol; the protective effect of RTX being more apparent when the drug was given 15 min prior to 50% ethanol. Unexpectedly, RTX co-administered with absolute ethanol aggravated the ethanol-induced mucosal damage. It is concluded that capsaicin-sensitive sensory nerves mediated microcirculatory changes in gastroprotection and these involve inhibition of gastric acid secretion.     

Modulation of immunoreactive protein kinase C-α and β isoforms and G proteins by acute and chronic treatments with morphine and other opiate drugs in rat brain

The abundance of protein kinase C-α and β isoforms (PKC-αβ), PKC-α messenger (m) RNA and guanine nucleotide-binding G protein subunits (Gα_i1/2, Gα_o and Gβ) were quantitated in the rat cerebral cortex after acute and chronic treatments with various opiate drugs. Acute (100mg/kg for 2h) and chronic (10 to 100mg/kg for 5 days) treatment with morphine decreased similarly the immunoreactivity of PKC-αβ (28% and 32%, respectively). Acute (2h) and chronic treatment (5 days) with other μ-agonists heroin (30mg/kg and 10 to 30mg/kg) and methadone (30mg/kg and 5 to 30mg/kg) also induced similar decreases of PKC-αβ (acute: 25% and 23%; chronic: 28% and 18%). After the chronic treatments, spontaneous (48h) or naloxone (2mg/kg)-precipitated opiate withdrawal (2h) resulted in up-regulation of PKC-αβ above control levels (30-38%), and in the case of morphine withdrawal in a concomitant marked increase in the expression of PKC-α mRNA levels (2.3-fold). Acute (2h) treatments with pentazocine (80mg/kg, mixed κ/δ-agonist and μ-antagonist), spiradoline (30mg/kg, selective κ-agonist) and [D-Pen², D-Pen⁵] enkephalin (14nmol i.c.v., selective δ-agonist) induced significant decreases of PKC-αβ (19–33%). Chronic (5 days) treatment with pentazocine (10 to 80mg/kg), but not spiradoline (2 to 30mg/kg), also induced a similar decrease of PKC-αβ (35%). In pentazocine- or spiradoline-dependent rats, naloxone (2mg/kg) did not induce up-regulation of brain PKC-αβ. Acute (10mg/kg for 2h) and chronic (2×10mg/kg for 5 and 14 days) treatment with naloxone did not alter PKC-αβ immunoreactivity. Chronic, but not acute, treatment with μ-agonists (morphine, heroin and methadone) increased the immunoreactivities of Gα_i1/2 (33-37%), Gα_o (25-41%) and Gβ (10-33%) protein subunits. In heroin- and methadone-dependent rats naloxone (2mg/kg)-precipitated withdrawal (2h) did not modify the up-regulation of these G proteins induced by chronic μ-opiate treatment. In marked contrast to μ-agonists, chronic treatment with high doses of pentazocine and spiradoline or acute treatment with [D-Pen², D-Pen⁵] enkephalin did not result in up-regulation of these G protein subunits. After chronic treatment with μ-agonists, significant negative correlations were found when the percentage changes in immunoreactivity of PKC-αβ were related to the percentage changes in immunoreactivity of Gα_i1/2 (r =-0.53, n = 29) and Gβ (r =-0.41, n = 24) in the same brains. PKC-αβ abundance did not correlate significantly with the density of Gα_o (r =-0.21, n = 28). Together the results indicate that the brain PKC-αβ system may play a major regulatory role in opiate tolerance and dependence. Moreover, the possible in vivo cross-communication between this regulatory enzyme and specific inhibitory G proteins may also be of relevance in the cellular and molecular processes of opiate addiction. Received: 15 July 1996 / Accepted: 22 November 1996     

Effects of the local administration of selective μ-, δ-and κ-opioid receptor agonists on osteosarcoma-induced hyperalgesia

The stimulation of peripheral opioid receptors yields analgesic responses in a model of bone cancer-induced pain in mice. In order to know the type(s) of peripheral opiate receptors involved, the paw thermal withdrawal latencies were measured in C3H/HeJ mice bearing a tibial osteosarcoma, after administering selective agonists of μ-,δ-and κ-opiate receptors. The peritumoral administration of DAGO (0.6–6 μg) inhibited the osteosarcoma-induced hyperalgesia at doses ineffective in healthy animals, the highest one even increasing the withdrawal latencies over the control values. Naloxone-methiodide (2 mg/kg) and cyprodime (1 mg/kg), but not naltrindole (0.1 mg/kg) nor nor-binaltorphimine (10 mg/kg), antagonized DAGO-induced analgesic effects, these therefore probably being mediated through peripheral μ-opioid receptors. The peritumoral injection of DPDPE (100 μg) induced analgesia which was inhibited by naloxone-methiodide and naltrindole but not by nor-binaltorphimine. Cyprodime partially antagonized the analgesia induced by 100 μg of DPDPE, but did not modify the effect induced by 30 μg of this agonist—a dose that restores the hyperalgesic latencies up to the control values. The antihyperalgesic effect induced by the peritumoral administration of U-50,488H (1 μg) was antagonized by naloxone-methiodide and nor-binaltorphimine, but not by cyprodime nor naltrindole, thus suggesting the involvement of peripheral κ-opioid receptors. In conclusion, the stimulation of peripheral μ-, δ- and κ-opioid receptors is a pharmacological strategy useful for relieving this experimental type of bone cancer-induced pain, the greatest analgesic effect being achieved by stimulating peripheral μ-opioid receptors.     

Regulation of gastric acid secretion by histamine H3 receptors in the dog: an investigation into the site of action

The involvement of histamine H₃ receptors in the regulation of gastric acid secretion was investigated in the conscious dog with gastric fistula, by the use of the selective agonist (R)-methylhistamine and the selective antagonist thioperamide. (R)-methylhistamine (0.3–1.2 mol/kg/h) induced a dose-related inhibition of the acid secretion induced by pentagastrin and by bombesin, maximum inhibition not exceeding 60–65%. The inhibitory effect of the H₃ agonist (0.6 mol/kg/h) was inhibitited by thioperamide (0.1 mol/kg/h), suggesting that the effect was entirely mediated by H₃ receptors. Thioperamide was also able to enhance the acid response to submaximal doses of pentagastrin and bombesin. The acid secretion induced by histamine was not modified by (R)a-methylhistamine (0.3–1.2 mol/kg/h) but it was significantly enhanced by thioperamide (0.1 mol/kg/h). Neither (R)-methylhistamine nor thioperamide significantly modified the increase in plasma gastrin levels induced by bombesin. In conclusion these data demonstrate that histamine H₃ receptors may represent an effective mechanism for the negative control of stimulated gastric acid secretion in the dog; however, since the inhibition was mainly evident against stimuli which involve the release of histamine, a location of H₃ receptors in paracrine cells of the gastric mucosa rather than in gastrin producing cells or parietal cells seems more likely. Correspondence to: G. Bertaccini at the above address     

Agonist of peroxisome proliferator-activated receptor gamma (PPAR-γ: A new compound with potent gastroprotective and ulcer healing properties

Pioglitazone, a specific ligand for peroxisome proliferator-activated receptor gamma (PPAR-γ), was recently implicated in the control of inflammatory processes and in the modulation of the expression of various cytokines such as tumor necrosis factor alpha (TNF-α), but its role in the mechanism of gastric mucosal integrity has not been studied extensively. This study was designed to determine the effect of pioglitazone on gastric mucosal lesions induced in rats by topical application of 100% ethanol and by 3.5 h of water immersion and restraint stress (WRS) with or without pretreatment with indomethacin (5 mg/kg i.p.) to inhibit cyclooxygenase-1 (COX-1) and COX-2 enzyme activities and L-NNA (20 mg/kg i.p.) to suppress nitric oxide (NO)-synthase. In addition, the effect of pioglitazone on ulcer healing in rats with chronic acetic acid ulcers (ulcer area 28 mm²) was determined. Rats were killed 1 h and 3.5 h after ethanol administration or WRS exposure or at day 9 upon ulcer induction, and the number and area of gastric lesions were measured by planimetry, the gastric blood flow (GBF) was determined by H₂-gas clearance technique and the mucosal PGE₂ generation and gene expression and plasma concentration of TNF-α and IL-1β were also evaluated. Pre-treatment with pioglitazone dose-dependently attenuated gastric lesions induced by 100% ethanol and WRS; the dose reducing these lesions by 50% (ID₅₀) being 10 mg/kg and 7 mg/kg, respectively. The protective effect of pioglitazone was accompanied by the significant rise in the GBF, an increase in PGE₂ generation and the significant fall in the plasma TNF-α and IL-1β levels. Strong signals for IL-1β-and TNF-α mRNA were recorded in gastric mucosa exposed to ethanol or WRS, and these effects were significantly decreased by pioglitazone. Indomethacin which suppressed PG generation by about 90%, while augmenting WRS damage, and L-NNA, that suppressed NO-synthase activity, significantly attenuated the protective and hyperaemic activity of this PPAR-γ ligand. In the chronic study, pioglitazone significantly reduced the area of gastric ulcers on day 9 and significantly raised the GBF at the ulcer margin. The acceleration of ulcer healing by PPAR-γ ligand was accompanied by a significant increase in the expression of PECAM-1 protein, a marker of angiogenesis. We conclude that (1) pioglitazone exerts a potent gastroprotective and hyperaemic actions on the stomach involving endogenous PG and NO and attenuation of the expression and release of proinflammatory cytokines TNF-α and IL-1β, and (2) PPAR-γ ligand accelerates ulcer healing, possibly due to the enhancement in angiogenesis at ulcer margin.     

Effects of subunit selective nACh receptors on operant ethanol self-administration and relapse-like ethanol-drinking behavior

Rationale and objectives  The sensitivity to ethanol central effects is partially determined by the subunit composition of brain nicotinic acetylcholine receptors (nAChRs). Thus, the effects of intraventral tegmental area (VTA) administration of the nicotinic subunit-specific antagonist, α-conotoxin MII (αCtxMII, α₃β₂*, β₃*, α₆*), were compared to those of systemic mecamylamine (MEC, an allosteric negative modulator of the nAChR), dihydro-β-erythroidine (DHβE, α₄β₂*), and methyllycaconitine (MLA, α₇*) to elucidate involvement of different subunits of nAChRs in operant ethanol self-administration and relapse-like activation of ethanol consumption after ethanol deprivation in rats. Methods  The effects of drugs were studied in rats trained for operant oral self-administration of ethanol (FR = 1). For ethanol deprivation, trained animals were subjected to a period of alcohol deprivation for 10 days. αCtxMII was given directly into the VTA through implanted permanent intracranial cannulae, whereas MEC, DHβE, and MLA were administered systemically. Results  αCtxMII reduced operant ethanol self-administration and blocked the deprivation-induced relapse-like ethanol consumption. MEC reduced operant ethanol self-administration and inhibited the deprivation-induced increase in alcohol consumption. DHβE did not alter ethanol self-administration in the lower-dose range but inhibited ethanol intake at a higher dose (4 mg/kg), although this effect might have been nonspecific. MLA failed to block self-administration of ethanol and relapse-like drinking after deprivation. Conclusions  Our results indicate that nAChRs are involved in the modulation of operant alcohol self-administration and relapse-like alcohol drinking behavior in rats. Our observations support the working hypothesis that systemically active selective ligands for nAChR α₃β₂*, β₃, and/or α₆* receptor subunits might be of therapeutic value for the treatment of alcoholism.     

Intracerebroventricular injection of clonidine releases beta-endorphin to induce mucosal protection in the rat

The possibility that the endogenous opioid system could be involved in the central nervous system (CNS)-mediated gastroprotective effect of clonidine was investigated. Intracerebroventricularly (i.c.v.) injected clonidine (470 pmol/rat) inhibited the gastric mucosal lesions induced by (orally administered) acidified ethanol in a significant manner in the rat. The gastroprotective effect of the centrally administered clonidine was antagonised by i.c.v. or intracisternally (i.c.) administered presynaptic alpha-2 adrenoceptor antagonist, yohimbine; the non-selective opioid receptor antagonist, naloxone; and the delta opioid receptor antagonist naltrindole. These results suggest that an interaction between central alpha-2 adrenoceptors and endogenous opioid systems is involved in mediating the mucosal protective effect. beta-endorphin antiserum (i.c.) also antagonised the gastroprotection induced by intracerebroventricularly injected clonidine indicating that beta-endorphin release is likely to be a key factor in the gastroprotective effect of clonidine. Furthermore, the i.c.v. or i.c. injection of beta-endorphin produced a potent gastroprotection in the picomolar range. The mucosal protective effect of clonidine was abolished after vagotomy indicating that the central effect may be conveyed to the periphery by vagal efferents. Since atropine (1 mg/kg i.v.) failed to modify, but hexamethonium (10 mg/kg i.v.) antagonised the gastroprotective effect of clonidine, it would appear that in the periphery nicotinic, but not muscarinic, cholinergic receptors are likely to be involved in the mucosal protective effect of clonidine. In conclusion, clonidine (i.c.v.) induces gastroprotective action by releasing an endogenous opioid substance - most likely beta-endorphin - in the rat. The clonidine-induced central gastroprotection requires the integrity of vagal pathway; cholinergic nicotinic - but not muscarinic - receptors might mediate the effect in the periphery.     

Anticonvulsant effects of GABAA modulators microinfused into area tempestas or substantia nigra in rats exposed to soman

Enhancement of GABAergic neurotransmission has anticonvulsant effects against nerve agent-induced seizures. However, systemic administration of drugs with GABA_A agonist-like effects does not differentiate well between their anticonvulsant impact. In the present study, GABA_A modulating drugs (1 μl) were microinfused bilaterally into the seizure controlling substrates, substantia nigra (SN) or area tempestas (AT), of rats subjected to seizures induced systemically by soman (100 μg/kg). The results showed that infusion of ethanol (0.47 μmol) and propofol (20 μg) in both SN and AT had anticonvulsant effects (prevention of seizures or increased latency to seizures). Anticonvulsant effects were also obtained when muscimol (120 ng) was infused into AT or when diazepam (5 μg) was infused into SN. Pentobarbital (50 μg) did not attenuate soman-elicited seizures in any of the injection sites. Results from control experiments showed that the effects from the microinfusions were site-specific, and that the absence of effects of pentobarbital was not a result of too low dose of the drug. The microinfusion technique may allow a more detailed examination of anticonvulsant properties of drugs than by the use of systemic administration.     

Role of the soluble guanylyl cyclase α1/α2 subunits in the relaxant effect of CO and CORM-2 in murine gastric fundus

Carbon monoxide (CO) has been shown to cause enteric smooth muscle relaxation by activating soluble guanylyl cyclase (sGC). In gastric fundus, the sGCα₁β₁ heterodimer is believed to be the most important isoform. The aim of our study was to investigate the role of the sGCα₁/α₂ subunits in the relaxant effect of CO and CORM-2 in murine gastric fundus using wild-type (WT) and sGCα₁ knock-out (KO) mice. In WT mice, CO (bolus)-induced relaxations were abolished by the sGC inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), while CORM-2- and CO (infusion)-induced relaxations were only partially inhibited by ODQ. In sGCα₁ KO mice, relaxant responses to CO and CORM-2 were significantly reduced when compared with WT mice, but ODQ still had an inhibitory effect. The sGC sensitizer 1-benzyl-3-(5′-hydroxymethyl-2′-furyl-)-indazol (YC-1) was able to potentiate CO- and CORM-2-induced relaxations in WT mice but lost this potentiating effect in sGCα₁ KO mice. Both in WT and sGCα₁ KO mice, CO-evoked relaxations were associated with a significant cGMP increase; however, basal and CO-elicited cGMP levels were markedly lower in sGCα₁ KO mice. These data indicate that besides the predominant sGCα₁β₁ isoform, also the less abundantly expressed sGCα₂β₁ isoform plays an important role in the relaxant effect of CO in murine gastric fundus; however, the sGC stimulator YC-1 loses its potentiating effect towards CO in sGCα₁ KO mice. Prolonged administration of CO—either by the addition of CORM-2 or by continuous infusion of CO—mediates gastric fundus relaxation in both a sGC-dependent and sGC-independent manner.     

Evaluation of Some Pharmacological Activities of ethanol extracts of seeds, pericarp and leaves of Eugenia Jamolana in Rats

The present study investigated the effect of ethanol extracts of seeds, pericarp and leaves of Eugenia Jamolana (E. Jamolana) on inflammation, gastric ulcer, anti-oxidants and hepatoprotective in rats. The acute inflammation was induced by intra-plantar injection of carrageenan (100 μl of 1 %) in the rat hind paw. Gastric ulcer was evoked by indomethacin (25 mg/kg) oral administration. Liver damage was induced by given CCL₄ (2.5 ml/kg) orally. The median lethal (LD₅₀) of the ethanol extract of both seeds and pericarp were determined and revealed that the investigated extracts of seeds and pericarp were non toxic up to 5g/kg. The anti-inflammatory results showed that the oral administration of ethanol extract of E. Jamolana seeds (250,500 mg/kg) showed significant inhibition of oedema formation in dose-dependent manner by −27.86, −41.23, −44.73, −51.78 % and by −63.16, −37.77, −47.04, −55.36 % at 1, 2, 3 and 4 h at 1, 2, 3 and 4 h, respectively. While the pericarp given at dose (500 mg/kg) exhibited significant inhibition of the oedema formation by −34.64, −21,8, 19.23 and −33.47 % at 1, 2, 3 and 4 h, respectively post carrageenan injection as compared with saline control group. E. Jamolana leaves fraction 1 given orally at dose of 25 mg/kg, induced non significant change on oedema, while the oedema response was significantly inhibited by −25.14, −33.4, −20.57 and −26.46 % at 1, 2, 3 and 4 h, respectively in group of rats that received leaves fraction 2 at the same dose. Rats were given leaves fraction 3 extract showed inhibition of oedema formation by −4.48 % at 1^st h post- carrageenan injection, while at 2^nd, 3^rd and 4^th h showed non significant change on oedema formation. The acute gastric mucosal lesions was significantly reduced by given ethanol extract of E. Jamolana seeds, pericarp (250, 500 mg/kg) and leaves fractions 1, 2 and 3 (25 mg/kg) respectively in dose dependent manner, as compared with indomethacin treated group (control group). All tested extracts showed significant reduction in elevated serum ALT, AST and ALP levels as compared with CCl ₄ treated group. The ethanol extract of E. Jamolana seeds, pericarp and leaves fractions 1, 2, 3 showed significant elevation of blood GSH level and significant reduction in elevated plasma lipid peroxides (MDA) as compared with CCl₄ treated group. In conclusion we can see that the ethanol extracts of E. Jamolana of seeds, pericarp and leaves fractions showed anti-inflammatory, anti-ulcer, hepatoprotective and anti-oxidants activity. Received 15 June 2008; accepted 11 November 2008     

Inhibitory H3 receptors on sympathetic nerves of the pithed rat: activation by endogenous histamine and operation in spontaneously hypertensive rats

Our previous results demonstrate the occurrence of presynaptic inhibitory histamine H₃ receptors on sympathetic neurons innervating resistance vessels of the pithed rat. The present study, in which new H₃ receptor ligands with increased potency and selectivity (imetit, clobenpropit) were used, was designed to further explore the role of H₃ receptors in the regulation of the rat cardiovascular system. In particular we were interested whether these receptors may be activated by endogenous histamine and whether they are detectable in an experimental model of hypertension. All experiments were performed on pithed and vagotomized rats treated with rauwolscine 1 μmol/kg. In normotensive Wistar rats the electrical (1 Hz, 1 ms, 50 V for 20 s) stimulation of the preganglionic sympathetic nerve fibres increased diastolic blood pressure by about 35 mmHg. Two H₃ receptor agonists, R-(–)-α-methylhistamine and imetit, inhibited the electrically induced increase in diastolic blood pressure in a dose-dependent manner. The maximal effect (about 25%) was obtained for R-(–)-α-methylhistamine at about 10 μmol/kg and for imetit at about 1 μmol/kg. Two H₃ receptor antagonists, thioperamide 1 μmol/kg and clobenpropit 0.1 μmol/kg, attenuated the inhibitory effect of imetit. The neurogenic vasopressor response was increased by about 15% by thioperamide 1 μmol/kg and clobenpropit 0.1 μmol/kg and decreased by 25% by the histamine methyltransferase inhibitor metoprine 37 μmol/kg. R-(-)-α-Methylhistamine, imetit, thioperamide, clobenpropit and metoprine did not affect the vasopressor response to exogenously added noradrenaline 0.01 μmol/kg (which increased diastolic blood pressure by about 40 mmHg). Metoprine had only a very low affinity for H₃ binding sites (labelled by ³H-N^α-methylhistamine; pK_i 4.46). In pithed Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats, electrical (1 Hz, 1 ms, 50 V for 10 s) stimulation increased diastolic blood pressure by 28 and 37 mmHg, respectively. Imetit inhibited the neurogenic vasopressor response to about the same extent in WKY and SHR rats (maximal effect of about 30%). The inhibitory influence of imetit was diminished by thioperamide 1 μmol/kg to about the same degree in rats of either strain. The present study confirms the occurrence of presynaptic H₃ receptors on sympathetic nerve fibres involved in the inhibition of the neurogenic vasopressor response. Moreover, it demonstrates that these H₃ receptors are probably activated by endogenous histamine and appear to be operative in hypertension. Received: 25 July 1996 / Accepted: 24 October 1996     

Prejunctional histamine H3-receptors inhibit electrically evoked endogenous noradrenaline overflow in the portal vein of freely moving rats

The effects of intra-arterial injection of different doses of the selective histamine H₃-receptor agonist R-α-methylhistamine and the selective histamine H₃-receptor antagonist thioperamide on basal and electrically evoked noradrenaline overflow in the portal vein as well as on mean arterial pressure (MAP) and heart rate (HR) were investigated in permanently instrumented freely moving rats. R-α-Methylhistamine (0.01, 0.1 and 1 μmol/kg) inhibited the evoked noradrenaline overflow up to 43%, the ED₅₀ value being 0.013 μmol/kg. Thioperamide (0.1, 0.5 and 1.0 μmol/kg) antagonized the effect of 1.0 μmol/kg R-α-methylhistamine dose-dependently, evoked overflow returning to control values at 1.0 μmol/kg of the antagonist; thioperamide alone had no effect on electrically evoked noradrenaline overflow. Basal noradrenaline levels, blood pressure and heart rate were not at all influenced by R-α-methylhistamine and thioperamide, alone or in combination. The results clearly show the presence of prejunctional histamine H₃-receptors inhibiting the electrically evoked noradrenaline overflow from vascular sympathetic nerve terminals in the portal vein of freely moving rats. Received: 27 August 1996 / Accepted: 14 October 1996     

Studies on the mechanism for the gastric mucosal protection by famotidine in rats

The effect of famotidine on gastric lesions induced by the decrease in mucosal defensive resistance was investigated in rats and compared with those of cimetidine, pirenzepine and cetraxate. Famotidine (0.03, 0.1 and 0.3 mg/kg, p.o.) inhibited dose-dependently the development of gastric lesions produced by taurocholate-histamine in doses that suppressed histamine-induced acid secretion in pylorus-ligated rats. The H2-antagonist also prevented gastric mucosal lesions induced by taurocholate-serotonin, iodoacetamide, acidified aspirin and acidified ethanol. Cimetidine, pirenzepine and cetraxate showed the inhibitory effects on almost all types of the gastric lesions, but their inhibitory effects were much less potent than those of famotidine. On the other hand, famotidine inhibited the decreases of gastric mucosal blood flow induced by acidified ethanol and the mucosal contents of glycoprotein induced by water immersion restraint stress. In addition, famotidine increased the transgastric potential difference (PD) and promoted the recovery of decreased transgastric PD induced by acidified ethanol in rats. These results suggest that the preventive effect of famotidine on gastric lesions is attributable not only to suppression of acid secretion but to activation of the gastric mucosal defensive mechanisms.     

Nocloprost, a unique prostaglandin E2 analog with local gastroprotective and ulcer-healing activity

Nocloprost (9 beta-chloro-16,16-dimethyl prostaglandin E2 (PGE2)) was examined for gastroprotective and ulcer-healing activity and compared to 16,16-dimethyl PGE2 (dmPGE) in rats. Nocloprost given intragastrically (i.g.) at various doses (0.01-10 micrograms/kg) 30 min before 100% ethanol, acidified aspirin (ASA), acidified taurocholate, water immersion, or restraint stress dose dependently prevented the formation of gastric lesions, the ID50 values being 0.25, 0.58, 0.06 and 0.12 micrograms/kg, respectively. The gastroprotection provided by nocloprost given i.g. was somewhat enhanced by the presence of acid in the stomach and was reduced by inhibition of gastric acid secretion. Nocloprost given s.c. also showed protective activity against ethanol damage but was ineffective when applied intraduodenally. The protective effect of nocloprost lasted about 8 h whereas that induced by dmPGE lasted 6 h. Nocloprost (0.01-100 micrograms/kg) given i.g. failed to affect gastric acid secretion or intestinal secretion (enteropooling) but prevented the increased gastroduodenal alkaline secretion. Nocloprost alone caused only a transient increase in the mucosal blood flow but prevented the fall in blood flow caused by 100% ethanol. [3H]Nocloprost was absorbed from the small intestine but was then taken up and metabolized by the liver and excreted into the bile so that very little reached the systemic circulation in an unchanged form. Nocloprost, unlike dmPGE, accelerated the healing of chronic gastric ulcerations and enhanced mucosal growth. We conclude that nocloprost is a locally active PGE2 analog with high cytoprotective and ulcer-healing efficacy.     

Evidence that histamine H3 receptors are involved in the control of gastric acid secretion in the conscious cat

Summary In an attempt to assess the role of histamine H₃ receptors in the control of gastric acid secretion, the effects of the selective histamine H3 receptor agonist, (R)-methylhistamine and antagonist, thioperamide were evaluated in the conscious gastric fistula cat under basal conditions and against different stimuli. (R)-methylhistamine (0.05–0.2 mol/kg/h) was ineffective against spontaneous and dimaprit-induced acid secretion; it also did not reduce significantly pentagastr-ininduced acid output, but caused a dose-dependent (0.05–0.1 mol/kg/h) and significant inhibition of the acid response to 2-deoxy-d-glucose. Thioperamide (0.02–0.04 mol/kg/h) did not modify spontaneous acid secretion, whereas it evoked a significant enhancement of the acid response to submaximal doses (50 mg/kg i. v.) of 2-deoxy-d-glucose. Thioperamide completely reversed the inhibitory effect of (R)-methylhistamine against 2-deoxy-d-glucose-induced secretion, while leaving unaffected the inhibition induced by somatostatin. These data suggest that histamine H3 receptors may be involved in the control of acid secretion stimulated by indirectly acting secretagogues. Send offprint requests to G. Bertaccini at the above address     

Analysis of the inhibiting activity of presynaptic\alpha _{2^ - } ADRENOCEPTORS against NSAID-induced gastric mucosal lesions in the ratagainst NSAID-induced gastric mucosal lesions in the rat

Clonidine at a dose of 0.00625–0.025 mg/kg (po) inhibited the gastric mucosal lesions induced by indomethacin, acidified aspirin, naproxen and piroxicam. The gastroprotective effect was reversed by the $\alpha _{2^ - } ADRENOCEPTORS$ antagonist yohimbine (5 mg/kg sc) and by the highly selective $\alpha _{2^ - } andrenoceptor$ antagonist berbane derivative, Ch-38083 (3.5 mg/kg sc). Clonidine also decreased the gastric acid secretion in pylorus-ligated rats at a dose of 0.2 mg/kg (given intraduodenally) but not at gastroprotective doses (0.00625–0.025 mg/kg). The antisecretory effect of clonidine was reversed by both yohimbine and Ch-38083. The $\alpha _{2B^ - receptor} $ antagonist prazosin (0.1 mg/kg sc) blocked the gastroprotective effect but failed to influence the antisecretory action of clonidine. Our data suggest that the $\alpha _{2B^ - androceptor} $ subtype might be involved in gastroprotection; however, the antisecretory effect is likely to be mediated by $\alpha _{2A^ - like} $ adrenoceptor subtype.     

Bremazocine reduces unrestricted free-choice ethanol self-administration in rats without affecting sucrose preference

It has been postulated that opioid systems in the brain may play a role in ethanol reinforcement. In this respect, μ- and δ-opioid receptors may mediate the rewarding effects whereas κ receptors are thought to mediate the aversive effects of opioids. Accordingly, long-acting benzomorphans such as bremazocine, that simultaneously act as μ and δ receptor antagonists and κ receptor agonists may be particularly effective in reducing ethanol self-administration. Therefore, we studied the effect of bremazocine on oral ethanol self-administration in rats using a paradigm [unrestricted free-choice drinking of 10% (v/v) ethanol], previously shown to cause long-term neuroadaptations in the nucleus accumbens and caudate putamen. Bremazocine (0.1 mg/kg, once daily for five consecutive days) reduced ethanol drinking by about 50% during the active period of the animals, whereas the intake of sucrose (3–10% w/v) was affected neither in naive nor in ethanol-experienced rats. This effect of bremazocine appeared not to be secondary to its acute sedative effect or the slight increase in total fluid consumption. Unlike bremazocine, the selective κ-opioid receptor agonist U50,488H (10 mg/kg, once daily) inhibited ethanol drinking only during the first of 5 treatment days and the opioid receptor antagonist naltrexone (0.3–10 mg/kg, once daily) only caused a modest (about 20%) suppression of ethanol drinking during the first hours after drug injection. Thus, bremazocine appears to be far more potent than the clinically applied drug naltrexone in this respect. Our data further support the role of opioid receptors in ethanol reinforcement and indicate that long-acting mixed-action opioids such as bremazocine may be useful as adjuvants for the clinical management of ethanol addiction. Received: 1 July 1998/Final version: 3 September 1998