In vitro antiangiogenic activity of selective somatostatin subtype-1 receptor agonists

BACKGROUND

Endothelial cells of human blood vessels (arteries and veins) show high levels of somatostatin subtype-1 receptor (sst(1)). The aim of the present study is to investigate the inhibitory effects of novel somatostatin analogs, highly selective for human sst(1), on in vitro angiogenesis and their modulation of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor-2 (VEGFR-2) expression.

MATERIALS AND METHODS

Somatostatin analogs BIM-23745 and BIM-23926 were tested for their ability to prevent proliferation and migration of human endothelial HMEC-1 cells, to modulate VEGF and VEGFR-2 expression and to inhibit sprouting of microvessels from cultured human placental vessel explants in fibrin matrix for 28 days.

RESULTS

The somatostatin sst(1 )receptor-selective agonists, BIM-23745 and BIM-23926 showed a suppression of endothelial proliferation (e.g. 10(-6) M BIM-23475, 40.0 +/- 2.1% vs. 100% of controls; 10(-7) M BIM-23926, 55.3 +/- 3.3% vs. 100% of controls), migration (e.g. 10(-7) M BIM-23475, 35.0 +/- 1.56% vs. 100% of controls; 10(-7) M BIM-23926, 53.7 +/- 1.77% vs. 100% of controls) and microvessel sprouting (e.g. 10(-8) M BIM-23475, 42.8 +/- 5.6% vs. 100% of controls; 10(-7) M BIM-23926, 17.2 +/- 11.8% vs. 100% of controls). A small but significant percentage of cells exposed to BIM-23745 and BIM-23926 for 24 h and for 72 h presented typical apoptotic morphology. Moreover, both the analogs significantly inhibit VEGF and VEGFR-2 gene expression in endothelial cells grown for 144 h in a fibrin matrix and the VEGF secretion in conditioned media.

CONCLUSIONS

The inhibition of endothelial activities suggests potential therapeutic utility for administration of somatostatin sst(1 )receptor-selective agonists in the proliferative diseases involving angiogenesis.

Cholecystokinin CCK2 receptors mediate the peptide's inhibitory actions on the contractile activity of human distal colon via the nitric oxide pathway

BACKGROUND AND PURPOSE

Cholecystokinin is known to exert stimulant actions on intestinal motility via activation of type 1 cholecystokinin receptors (CCK(1)). However, the role played by cholecystokinin 2 (CCK(2)) receptors in the regulation of gut motility remains undetermined. This study was designed to examine the influence of CCK(2) receptors on the contractile activity of human distal colon.

EXPERIMENTAL APPROACH

The effects of compounds acting on CCK(2) receptors were assessed in vitro on motor activity of longitudinal smooth muscle, under basal conditions as well as in the presence of KCl-induced contractions or transmural electrical stimulation.

KEY RESULTS

Cholecystokinin octapeptide sulphate induced concentration-dependent contractions which were enhanced by GV150013 (CCK(2) receptor antagonist; +57% at 0.01 microM). These effects were unaffected by tetrodotoxin. The enhancing actions of GV150013 on contractions evoked by cholecystokinin octapeptide sulphate were unaffected by N(omega)-propyl-L-arginine (NPA, neuronal nitric oxide synthase inhibitor), while they were prevented by N(omega)-nitro-L-arginine methylester (L-NAME, non-selective nitric oxide synthase inhibitor). In the presence of KCl-induced contractions, cholecystokinin octapeptide sulphate elicited concentration-dependent relaxations (-36%), which were unaffected by NPA, but were counteracted by GV150013 or L-NAME. The application of electrical stimuli evoked phasic contractions which were enhanced by GV150013 (+41 % at 0.01 microM).

CONCLUSIONS AND IMPLICATIONS

CCK(2) receptors mediate inhibitory actions of cholecystokinin on motor activity of human distal colon. It is suggested that CCK(2) receptors exert their modulating actions through a nitric oxide pathway, independent of the activity of the neuronal nitric oxide synthase isoform.

Constitutive expression of cyclooxygenase-2 in the neuromuscular compartment of normal human colon

Prostaglandins regulate various functions throughout the gastrointestinal system. Their biosynthesis depends on cyclooxygenase isoforms, named COX-1 and COX-2. The initial hypothesis that COX-2 is an inducible enzyme has been challenged and its constitutive expression in the stomach has been established. In this study, an immunohistochemical analysis was performed to evaluate the distribution and cellular localization of COX-2 in normal human colon. Colonic surgical specimens were processed for COX-2, protein HuC/HuD, neurofilament, S-100 protein and CD117/c-kit immunodetection. COX-2 protein was found to be constitutively expressed in the colonic wall: detectable amounts were localized in mucosal, submucosal and muscular layers, mainly in the neuromuscular compartment. In particular, COX-2 was expressed in muscularis mucosae, submucosal ganglia, longitudinal muscle layer and myenteric ganglia, the neurons of which displayed different degrees of immunostaining. Intramuscular interstitial cells of Cajal, regarded as important sites for the regulation of enteric neuromuscular activity, were also partly COX-2 immunoreactive. This study provides a detailed mapping of COX-2 expression in human colon, and allows better understanding of the roles played by this isoenzyme in gut physiology.

Clinical evaluation of piroxicam-FDDF and azithromycin in the prevention of complications associated with impacted lower third molar extraction

Combined treatments with non-steroidal anti-inflammatory drugs and antibiotics may offer significant benefits in the prevention of pain and infections associated with oral surgery. In this study, piroxicam and azithromycin were administered to patients undergoing dental extraction to examine the efficacy of piroxicam in the prevention of post-operative pain and inflammatory complications, either in the absence or in the presence of a concomitant antibiotic treatment. Thirty patients were randomly assigned to three groups and treated for 3 days, before impacted lower third molar removal, as follows: (1) sublingual piroxicam-FDDF (fast dissolving dosage formulation) 20 mg/day; (2) oral azithromycin 500 mg/day; (3) piroxicam-FDDF 20 mg/day plus azithromycin 500 mg/day. Oral acetaminophen (500 mg tablets) was allowed as rescue analgesic medication. Pain intensity was evaluated on a 100-mm visual-analogue scale after dental extraction (day 1), and at days 2, 3, 7 after surgery. Edema and trismus were estimated at days 2 and 7. At days 1 and 2, pain intensity was significantly lower in patients treated with piroxicam-FDDF, either alone (p < 0.05) or in combination with azithromycin (p < 0.05), than in patients administered with azithromycin alone. A higher acetaminophen consumption was also recorded in the latter group (p < 0.01). Pain intensity values did not differ among treatment groups at days 3 and 7. At day 2, the facial edema was significantly less intense in patients exposed to piroxicam-FDDF alone, as compared to patients treated with azithromycin, either alone (p < 0.05) or in combination with piroxicam-FDDF (p < 0.05). No significant differences were detected when comparing groups for trismus at days 2 and 7. The present results indicate that, when given alone in the pre-operative period, piroxicam-FDDF effectively counteracts post-surgical pain and inflammatory reactions in oral tissues. Upon combined treatment with piroxicam-FDDF and azithromycin, the macrolide antibiotic may reduce the influence of piroxicam on post-operative inflammation, without affecting its beneficial effect on surgical pain.

Mechanisms of protection by pantoprazole against NSAID-induced gastric mucosal damage

The use of nonsteroidal anti-inflammatory drugs (NSAIDs) can be associated with severe adverse digestive effects. In clinical settings, proton pump inhibitors have proven to be effective in preventing and healing NSAID-induced gastroduodenal lesions. The present study investigates the mechanisms of protection afforded by pantoprazole against gastric injury induced by different NSAIDs in rats. Animals were orally treated with indomethacin (100 micromol/kg), diclofenac (60 micromol/kg), piroxicam (150 micromol/kg) or ketoprofen (150 micromol/kg). Thirty minutes before NSAIDs, animals received pantoprazole 6 or 60 micromol/kg orally. Four hours after NSAIDs, the following parameters were assessed: histomorphometric evaluation of gastric mucosal damage; gastric mucosal levels of myeloperoxidase (MPO), malondialdehyde (MDA), reduced glutathione as an index of non-proteic sulfhydryl compounds (GSH), and prostaglandin E2 (PGE2); mucosal cyclooxygenase-1 and -2 (COX-1, COX-2) mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR). Separate experiments were carried out to assay the effects of pantoprazole on gastric acid secretion in pylorus-ligated rats. The in vitro influence of pantoprazole (1-10 microM) on the oxidation of low density lipoproteins (LDLs) induced by copper sulphate was also examined. All NSAIDs elicited mucosal necrotic lesions associated with neutrophil infiltration and reduction of PGE2 levels. Increments of MPO and MDA contents, as well as a decrease in GSH levels, were detected in the gastric mucosa of indomethacin-, piroxicam- or ketoprofen-treated animals. Indomethacin enhanced mucosal COX-2 expression, while not affecting COX-1. At the oral dose of 6 micromol/kg pantoprazole did not affect NSAID-induced mucosal damage, whereas at 60 micromol/kg it markedly reduced injuries provoked by all test NSAIDs. Pantoprazole 60 micromol/kg also reversed the effects of NSAIDs on MPO, MDA, and GSH mucosal contents, without interfering with the decrease in PGE2 levels or indomethacin-induced COX-2 expression. However, at both doses, pantoprazole inhibited acid secretion in pylorus-ligated rats. Furthermore, pantoprazole concentration dependently reduced the in vitro oxidation of LDLs. Our results suggest that besides inhibiting acid secretion, the protection afforded by pantoprazole against NSAID-induced gastric damage depends on a reduction in mucosal oxidative injury, which may also account for an increment of sulfhydryl radical mucosal bioavailability. It is also suggested that pantoprazole does not influence the down-regulation of gastric prostaglandin production associated with NSAID treatment.

Role of cyclooxygenases 1 and 2 in the modulation of neuromuscular functions in the distal colon of humans and mice

BACKGROUND

Cyclooxygenase isoforms (COX-1, COX-2) may exert differential regulatory actions on enteric motor functions under normal or pathological conditions.

AIMS

To examine the occurrence and functions of COX-1 and COX-2 in the neuromuscular compartment of normal distal colon using human and murine tissue.

METHODS

Gene expression (human, mouse), protein expression (human), gene deletion (mouse), and the effects of dual and isoform specific COX inhibitors on in vitro motility (human, mouse) were investigated.

RESULTS

Reverse transcription-polymerase chain reaction (RT-PCR) showed mRNA expression of COX-1 and COX-2 in human and wild-type mouse colonic muscle whereas only COX-2 or COX-1 was detected in COX-1 or COX-2 knockout animals. Immunohistochemistry localised both isoforms in neurones of myenteric ganglia, COX-1 in circular layer myocytes, and COX-2 in longitudinal muscle. Indomethacin (COX-1/COX-2 inhibitor), SC-560 (COX-1 inhibitor), or DFU (COX-2 inhibitor) enhanced atropine sensitive electrically induced contractions of human longitudinal muscle. The most prominent actions were recorded with indomethacin or SC-560 plus DFU. These results were confirmed under pharmacological blockade of non-cholinergic nerves. Atropine sensitive contractions evoked by carbachol in the presence of tetrodotoxin were enhanced by indomethacin or DFU but not by SC-560. In wild-type mice, contractile responses to electrical stimulation were enhanced by indomethacin, SC-560, or DFU. SC-560 potentiated electrically induced contractions in COX-2, but not COX-1, knockout mice. In contrast, DFU enhanced the contractions elicited by electrical stimuli in COX-1, but not in COX-2, knockout mice.

CONCLUSIONS

These results indicate that COX-1 and COX-2 are expressed in the neuromuscular compartment of normal human colon where they modulate cholinergic excitatory control of colonic motility at prejunctional and postjunctional sites, respectively.

Acetylcholinesterase blockade does not account for the adverse cardiovascular effects of the antitumor drug irinotecan: a preclinical study

This study investigates the mechanisms that account for the adverse cardiovascular effects of the antitumor drug irinotecan. The activities of irinotecan, its active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), and camptothecin were assayed in urethane-anesthetized rats to determine their effects on heart rate and blood pressure. In vitro experiments were performed to assess the effects of test drugs on acetylcholinesterase activity. Intravenous irinotecan (10 micromol/kg) decreased heart rate and blood pressure, but SN-38, camptothecin, or intracerebroventricular irinotecan had no effect. The bradycardic and hypotensive responses induced by irinotecan were abolished by bilateral vagotomy or atropine. Physostigmine caused a transient bradycardia, followed by a tachycardic response, and promoted a marked increment of blood pressure. Vagotomy or atropine prevented the bradycardic action of physostigmine, whereas the tachycardic and hypertensive responses were sensitive to atropine, but not to vagotomy. Five minutes after irinotecan administration (10 micromol/kg i.v.), its concentration in plasma and atrial tissue accounted for 2.29 +/- 0.19 micromol/L and 1.08 +/- 0.16 micromol/kg, respectively. The in vitro activity of human erythrocyte acetylcholinesterase was significantly inhibited by irinotecan (-21.5% at 100 microM) or physostigmine (-84.8% at 1 microM), whereas SN-38 or camptothecin had no effect. Rat atrial acetylcholinesterase was also significantly inhibited in vitro by irinotecan (-16.9% at 100 microM). The present results indicate that irinotecan exerts depressant effects on both heart rate and arterial blood pressure. A direct activation of cholinergic receptors or an interaction with central nervous sites does not appear to account for these inhibitory actions, whereas a blockade of acetylcholinesterase seems to occur at concentrations of irinotecan that may not be relevant in clinical settings.

L-histidine decarboxylase decreases its own transcription through downregulation of ERK activity

A poorly defined negative feedback loop decreases transcription of the L-histidine decarboxylase (HDC) gene. To help understand this regulation, we have studied the effect of HDC protein expression on HDC gene transcription in transfected AGS-B cells. Expression of the rat HDC protein inhibited HDC promoter activity in a dose-dependent fashion. The region of the HDC promoter mediating this inhibitory effect corresponded to a previously defined gastrin and extracellular signal-related kinase (ERK)-1 response element. Overexpression of the HDC protein reduced nuclear factor binding in this region. Experiments employing specific histamine receptor agonists indicated that the inhibitory effect was not dependent on histamine production, and studies with the HDC inhibitor alpha-fluoromethylhistidine revealed that inhibition was unrelated to enzyme activity. Instead, an enzymatically inactive region at the amino terminal of the HDC enzyme (residues 1-271) was shown to mediate inhibition. Fluorescent chimeras containing this domain were not targeted to the nucleus, arguing against specific inhibition of the HDC transcription machinery. Instead, we found that overexpression of HDC protein decreased ERK protein levels and ERK activity and that the inhibitory effect of HDC protein could be overcome by overexpression of ERK1. These data suggest a novel feedback-inhibitory role for amino terminal sequences of the HDC protein.

H3 receptor-mediated inhibition of intestinal acetylcholine release: pharmacological characterization of signal transduction pathways

The present study investigates the mechanisms through which prejunctional histamine H3 receptors modulate intestinal cholinergic neurotransmission. The experiments were performed on longitudinal muscle-myenteric plexus preparations of guinea pig ileum, preincubated with [3H]choline, superfused with physiological salt solution containing hemicholinium-3, and subjected to electrical field stimulation. The stimulation-induced outflow of radioactivity was taken as an index of endogenous acetylcholine release. The electrically induced [3H]acetylcholine release was inhibited by histamine (EC50)=33.5 nM) or the H3 receptor agonist R-alpha-methylhistamine (EC50=41.6 nM), whereas it was not affected by pyridylethylamine (H1 agonist), impromidine (H2 agonist), pyrilamine (H1 antagonist), cimetidine (H2 antagonist), thioperamide or clobenpropit (H3 antagonists). The inhibitory effects of histamine or R-alpha-methylhistamine were antagonized by thioperamide (pKd= 8.31 and 8.53, respectively) or clobenpropit (pKd=9.44 and 9.32, respectively), but not by pyrilamine or cimetidine. The modulatory action of histamine on the evoked tritium outflow was attenuated by pertussis toxin and abolished by N-ethylmaleimide, two selective blockers of Gi/Go proteins. Tetraethylammonium or 4-aminopyridine, acting as inhibitors of voltage-dependent K+ channels, enhanced the evoked tritium outflow when tested alone, and apparently counteracted the inhibitory effect of histamine. However, the blocking actions of tetraethylammonium and 4-aminopyridine were no longer evident when their enhancing actions were compensated by appropriate reductions of Ca2+ concentration in the superfusion medium. Histamine-induced inhibition of evoked tritium output was enhanced by omega-conotoxin, a selective blocker of N-type Ca2+ channels, or low Ca2+ concentration, whereas it was not modified by nifedipine, an antagonist of L-type Ca2+ channels. In addition, the inhibitory effect of histamine was not significantly affected by forskolin (activator of adenylyl cyclase), 8-bromo-cyclic AMP (a stable analog of cyclic AMP), rolipram (a selective blocker of type IV phosphodiesterase), phorbol myristate acetate (activator of protein kinase C), H-89 (N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide, inhibitor of protein kinase A), Ro-31-8220 (2-(1-[3-(amidinothio)propyl]-1H-indol-3-yl)-3-(1-methylindol-3-yl)-maleimide, inhibitor of protein kinase C), KT5823 (N-methyl-(8R*,9S*,11S*)-(-)-9-methoxy-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo [a,g]cycloocta[c,d,e]-trinden-1-one, inhibitor of protein kinase G), or lavendustin A (inhibitor of tyrosine kinase). The present results indicate that histamine inhibits intestinal cholinergic neurotransmission through presynaptic H3 receptors coupled to Gi/Go proteins. It is suggested that adenylyl cyclase, serine-threonine protein kinase and tyrosine kinase pathways are not implicated in this regulatory action, and that Gi/Go proteins modulate the activity of N-type Ca2+ channels through a direct link, thus causing a reduced availability of extracellular Ca2+ at the level of ileal cholinergic nerve terminals.

Gastroprotective effects of pantoprazole against experimental mucosal damage

The present study investigated the gastroprotective effects of the proton pump inhibitor pantoprazole on gastric mucosal damage induced by ethanol-HCl in rats. Omeprazole was used as reference drug. The morphometric analysis of gastric histological sections revealed that pantoprazole and omeprazole dose-dependently prevented the necrotic mucosal injury evoked by ethanol-HCl (ED50 = 14.1 and 21.6 micromol/kg, respectively). These effects were associated with a marked increment of Alcian blue recovery from gastric bound mucus (ED50 = 18.8 and 29.3 micromol/kg, respectively). In addition, both pantoprazole and omeprazole inhibited gastric acid secretion in pylorus-ligated rats (ED50 = 1.5 and 3.3 micromol/kg, respectively). Further experiments indicated that the protective effects of pantoprazole were not modified by L-365,260 (a gastrin receptor antagonist), suramin (a drug able to interfere with endogenous growth factors), N(G)-nitro-L-arginine (an inhibitor of nitric oxide synthase) or systemic ablation of capsaicin-sensitive sensory nerves, whereas they were partly blocked by indomethacin (an inhibitor of prostaglandin synthesis) and fully prevented by N-ethylmaleimide (a potent blocker of sulfhydryl compounds). The present data provide histomorphometric evidence that: 1) pantoprazole is endowed with gastroprotective properties and is more active than omeprazole in preventing the necrotic mucosal damage induced by ethanol-HCl; 2) according to the rank order of ED50 values, the protective effects of both drugs appear to depend mainly on the enhancement of the gastric mucosal barrier rather than on the inhibition of acid secretion; 3) an increased production of prostaglandins, as well as an increased availability of sulfhydryl radicals at the level of the gastric mucosa may account for the gastroprotective effects of pantoprazole.

Acid-independent gastroprotective effects of lansoprazole in experimental mucosal injury

The protective effects of the proton pump inhibitor lansoprazole on gastric mucosal damage induced by ethanol-HCl or hemorrhagic shock were investigated in the present study. The morphometric analysis of gastric histological sections revealed that lansoprazole dose-dependently reduced mucosal injury evoked by ethanol-HCl (ED50 = 24.3 micromol/kg) or hemorrhagic shock (ED50 = 38.9 micromol/kg), these effects being associated with marked increments of Alcian blue recovery from gastric bound mucus (ED50 = 31.4 micromol/kg and 27.6 micromol/kg, respectively). In addition, lansoprazole inhibited gastric acid secretion from pylorus-ligated rats (ED50 = 9.8 micromol/kg). Further experiments, performed on rats with ethanol-HCl-induced gastric injury, indicated that the protective effects of lansoprazole were not modified by L-365,260, suramin, N(G)-nitro-L-arginine, or systemic ablation of capsaicin-sensitive sensory nerves, whereas they were partly blocked by indomethacin and fully prevented by N-ethyl-maleimide. In addition, lansoprazole did not modify somatostatin concentrations in gastric mucosa. The present results provide evidence that lansoprazole prevents the necrotic damage of gastric mucosa induced by ethanol-HCl or hemorrhagic shock. According to the rank order of ED50 values, these effects appear to depend mainly on the enhancement of the gastric mucus barrier rather than on the reduction of acid secretion. It is also proposed that an increased production of prostaglandins, as well as an increased availability of sulfhydryl compounds at level of gastric mucosa may account for the gastroprotective effects of lansoprazole.

Peripheral cholecystokinin A and cholecystokinin B receptors mediate stimulation of gastric pepsinogen and acid secretion following intracerebroventricular injection of cholecystokinin-8-sulphate

BACKGROUND

Peptides of cholecystokinin family regulate various physiological actions by acting at level of central nervous system.

AIMS

To: 1) investigate possible influence of central cholecystokinin pathways on gastric pepsinogen and acid secretions; 2) characterize pharmacological profile and location of cholecystokinin receptor subtypes involved in gastric effects of centrally applied cholecystokinin-8-sulphate (cholecystokinin-8S).

METHODS

Urethane-anaesthetized rats were subjected to continuous perfusion of gastric lumen. Pepsin levels in perfusate were determined by enzymatic assay based on spectrophotometric measurement of products generated by peptic digestion of bovine haemoglobin. Acidity was measured by automatic potentiometric titration of hydrogen ions.

RESULTS

Following intracerebroventricular injection, cholecystokinin-8S increased both pepsinogen and acid output. In addition, intravenous cholecystokinin-8S stimulated peptic and acid secretions more promptly and at lower doses than after central injection. Stimulant effects of centrally applied cholecystokinin-8S were not affected by intracerebroventricular injection of devazepide (cholecystokinin A receptor antagonist) or L-365,260 (cholecystokinin B receptor antagonist) or by bilateral vagotomy. However, intravenous devazepide partly antagonized pepsigogue action of intracerebroventricular cholecystokinin-8S without affecting its acid hypersecretory effect, whereas after intravenous injection of L-365,260 peptic hypersecretion evoked by intracerebroventricular cholecystokinin-8S was partially prevented and acid response was completely blocked. Similar effects were exerted by intravenous devazepide and L-365,260 against intravenous cholecystokinin-8S. A complete blockade of pepsigogue effects induced by intracerebroventricular or intravenous cholecystokinin-8S was obtained after combined intravenous treatment with devazepide plus L-365,260. Gastric hypersecretory effects of intravenous cholecystokinin-8S were not modified by bilateral vagotomy.

CONCLUSIONS

Increase in pepsinogen output evoked by centrally applied cholecystokinin-8S does not depend on interaction with central nervous sites. Following central or parenteral injection of cholecystokinin-8S, increase in peptic secretion would result from activation of both peripheral cholecystokinin A and B receptors presumably located at the level of gastric mucosa.

CCK1 and CCK2 receptors regulate gastric pepsinogen secretion

The present study investigated (1) the pharmacological profile of cholecystokinin (CCK) receptor subtypes involved in the regulation of gastric pepsinogen secretion, (2) the influence of gastric acidity on peptic responses induced by CCK-8-sulfate (CCK-8S) or gastrin-I; and (3) the mechanisms accounting for the effects of CCK-like peptides on pepsinogen secretion. In anaesthetized rats, i.v. injection of CCK-8S or gastrin-I increased both pepsinogen and acid secretion. The pepsigogue effect of CCK-8S was higher than that of gastrin-I, whereas acid hypersecretion after CCK-8S was lower than that induced by gastrin-I. Peptic output following CCK-8S was partly blocked by i.v. injection of the CCK1 receptor antagonist, devazepide (-75.3%), or the CCK2 receptor antagonist, L-365,260 [3R(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3 yl)-N'-(3-methyl-phenyl)urea; -27.9%], but was fully prevented by combined administration of devazepide and L-365,260. The gastric acid hypersecretory effect of CCK-8S was enhanced by devazepide (+84.5%) and blocked by L-365,260. In contrast, the gastric secretory actions of gastrin-I were insensitive to devazepide, but abolished by L-365,260. Excitatory effects of CCK-8S and gastrin-I were not modified by vagotomy or atropine, whereas cimetidine or alpha-fluoromethylhistidine (irreversible blocker of histidine decarboxylase) partly prevented acid hypersecretion induced by both peptides without affecting their pepsigogue effects. After pretreatment with omeprazole, both CCK-8S and gastrin-I failed to stimulate acid secretion, while they increased pepsinogen output. In rats with gastric perfusion of acid solutions, CCK-8S or gastrin-I increased peptic output in a pH-independent manner either with or without pretreatment with omeprazole. Ablation of capsaicin-sensitive sensory nerves as well as application of lidocaine to the gastric mucosa failed to modify the excitatory effects of CCK-8S or gastrin-I on pepsinogen and acid secretion. Blockade of the nitric oxide (NO) synthase pathway by N(G)-nitro-L-arginine-methyl ester prevented the pepsigogue actions of both CCK-8S and gastrin-I (-61.8% and -71.7%, respectively), without affecting the concomitant increase in acid output. In addition, both these peptides significantly increased the release of NO breakdown products into the gastric lumen. The present results suggest that: (1) both CCK1 and CCK2 receptors mediate the peptic secretory responses induced by CCK-like peptides; (2) the excitatory inputs of CCK-8S and gastrin-I to chief cells are not driven through acid-dependent mechanisms or capsaicin-sensitive afferent sensory nerves; and (3) under in vivo conditions, the stimulant actions of CCK-like peptides on pepsinogen secretion are mediated, at least in part, by an increase in NO generation.

Effects of imidazoline derivatives on cholinergic motility in guinea-pig ileum: involvement of presynaptic alpha2-adrenoceptors or imidazoline receptors?

The present study investigates the possibility that imidazoline receptors mediate modulation of cholinergic motor functions of the guinea-pig ileum. For this purpose, the effects of a series of compounds with known affinity for alpha2-adrenoceptors and/or imidazoline recognition sites were examined on the cholinergic twitch contractions evoked by electrical field stimulation (0.1 Hz) of longitudinal muscle-myenteric plexus preparations. Additional experiments were carried out on ileal strips preincubated with [3H]choline, superfused with physiological salt solution containing hemicholinium-3, and subjected to electrical field stimulation (1 Hz). The stimulation-induced outflow of radioactivity was taken as an index of endogenous acetylcholine release. Alpha-methyl-noradrenaline, noradrenaline, clonidine, medetomidine, oxymetazoline and xylazine caused a concentration-dependent inhibition of twitch responses (IC50 from 0.13 to 1.05 microM; Emax from 85.9 to 92.5%). Rilmenidine and agmatine were less potent in reducing the twitch activity, and the latter compound acted also with low intrinsic activity (IC50=44.9 microM; Emax=35.5%). In interaction experiments, the inhibitory action of clonidine on twitch responses was competitively antagonized by RX 821002 (2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline), idazoxan, rauwolscine, yohimbine and BRL 44408 (2-[2H-(1-methyl-1,3-dihydroisoindole)-methyl] -4,5-dihydroimidazoline), whereas prazosin (10 microM), ARC 239 (2-(2,4-(O-methoxy-phenyl)-piperazin-1-yl)-ethyl-4,4-dimethyl- 1,3-(2H,4H)-isoquinolindione; 10 microM) and BRL 41992 (1,2-dimethyl-2,3,9,13b-tetrahydro-1H-dibenzo[c,f]imidazol[1,5-a]a zepine; 10 microM) were without effect. Rauwolscine antagonized the inhibitory effects of various agonists on ileal twitch activity in a competitive manner and with similar potency. Agmatine and idazoxan did not significantly modify the twitch contractions when tested in the presence of alpha2-adrenoceptor blockade by rauwolscine (3 microM) or RX 821002 (1 microM). Linear regression analysis showed that the affinity values of antagonists correlated with their affinity at the alpha2A and alpha2D binding sites as well as at previously classified alpha2A/D adrenoceptor subtypes, whereas no significant correlation was obtained when comparing the potency estimates of agonists and antagonists with the affinity at I1 or I2 binding sites. When tested on the electrically induced outflow of tritium, alpha-methyl-noradrenaline, noradrenaline, clonidine, medetomidine, oxymetazoline, xylazine and rilmenidine yielded inhibitory concentration-response curves which were shifted rightward to a similar extent in the presence of rauwolscine (3 microM). In the absence of further drugs, agmatine significantly reduced the evoked tritium outflow at the highest concentrations tested (10 and 100 microM), whereas idazoxan (up to 100 microM) was without effect. When RX 821002 (1 microM) was added to the superfusion medium, neither agmatine nor idazoxan modified the evoked outflow of radioactivity. The results argue against modulation by imidazoline receptors of acetylcholine release from myenteric plexus nerve terminals. They provide evidence that compounds endowed with imidazoline-like structures affect the cholinergic motor activity of the guinea-pig ileum by interacting with presynaptic alpha2-adrenoceptors belonging to the alpha2D subtype.

Positive modulation of pepsinogen secretion by gastric acidity after vagal cholinergic stimulation

Parallel increments of gastric acid and pepsinogen secretion generally occur after the application of cholinergic stimuli. However, it still remains to be established whether the changes in acid output associated with cholinergic stimulation play a role in regulation of the concomitant peptic secretory activity. In the present study, an anesthetized rat model was used for the evaluation of pepsinogen secretion in order to pursue a dual purpose: 1) to assess the relative functional relevance of direct and acid-dependent control exerted by cholinergic pathways on pepsinogen output; 2) to characterize the mechanisms through which changes in acidity within the stomach lumen may affect the peptic secretory activity of gastric mucosa. Bethanechol, 2-deoxy-D-glucose or electrical vagal stimulation caused parallel and atropine-sensitive increments of peptic and acid secretions. Omeprazole, a selective inhibitor of gastric H+:K+-adenosintriphosphatase, blocked the increase in acid but not pepsinogen secretion induced by bethanechol. However, 2-deoxy-D-glucose or electrical vagal stimulation failed to increase either pepsinogen or acid secretion in omeprazole-pretreated rats. When tested in animals pretreated with both omeprazole and physostigmine (a drug able to prevent the enzymatic breakdown of vagally released ACh through the blockade of acetylcholinesterase), 2-deoxy-D-glucose or electrical vagal stimulation significantly increased pepsinogen secretion without affecting acid secretion. In omeprazole-pretreated rats, perfusion of the gastric lumen with acid solutions caused a pH-dependent and atropine-sensitive increase in peptic output only when applied in combination with electrical vagal stimulation. Functional ablation of capsaicin-sensitive sensory neurons did not modify the gastric secretory responses induced by bethanechol or electrical vagal stimulation. However, after topical application of lidocaine to the gastric mucosal surface, bethanechol stimulated both peptic and acid outputs, whereas electrical vagal stimulation only evoked acid secretion without affecting basal peptic output. The present results indicate that the activation of muscarinic receptors by vagally released ACh is not sufficient by itself to stimulate pepsinogen secretion and that a facilitatory action mediated by acid secretion is necessary to allow an increment of peptic output in response to vagal cholinergic stimuli. It is suggested that such facilitatory input is driven to chief cells by local intramural reflexes that involve capsaicin-insensitive intrinsic nerves.

Single-dose pharmacokinetics of felbamate in patients with renal dysfunction

AIMS

The purpose of this study was to evaluate the effects of renal impairment on the single-dose pharmacokinetics of the antiepileptic felbamate.

METHODS

Twelve subjects with three levels of renal dysfunction (creatinine clearance > 30-80, > 10-30 or 5-10 m min(-1)) and four controls with normal renal function (creatinine clearance > 80 ml min(-1) were studied). Plasma and urine samples were obtained for 144 h following administration of a single 1200 mg dose.

RESULTS

Compared with controls, apparent total body clearance, renal clearance and urinary excretion of felbamate were decreased, and half-life, Cmax and AUC values were increased in subjects with renal dysfunction. The magnitude of these changes was associated with the degree of renal dysfunction. Nonrenal clearance and apparent volume of distribution values were also lower in renal dysfunction subjects, but there was no association between the extent of these changes and degree of renal dysfunction. Renal clearance of felbamate accounted for approximately 30% of apparent total body clearance in the control group and from 9-22% in the renal failure patients. Renal clearance of felbamate was significantly correlated with creatinine clearance (r = 0.75; P< 0.001).

CONCLUSIONS

These data suggest that initial dosage and titration of felbamate may require adjustment in patients with renal dysfunction.

Suramin enhances ethanol-induced injury to gastric mucosa in rats

Suramin is currently used in clinical practice as antineoplastic agent because of its complex interaction with the biological activity of various growth factors involved in tumor progression. The influence exerted by suramin on gastric injury induced in rats by intraluminal injection of absolute ethanol was investigated in the present study. The morphometric analysis of gastric histological sections revealed that suramin, 18 mg/kg, administered intraperitoneally for 14 days every other day, caused a marked enhancement of ethanol-induced mucosal damage. This effect was more pronounced 1-8 hr following ethanol administration, and it was still significant after 48 hr. In suramin-treated animals the evaluation of Alcian blue recovery from gastric-bound mucus showed that the levels of adherent mucus were significantly lower than those detected in untreated rats. In addition, pretreatment with suramin did not modify basal acid secretion, but caused potentiation of acid output stimulated by pylorus ligation or electrical vagal stimulation. Overall, the present results indicate that suramin exerts a negative influence on both gastric protective and repairing mechanisms. Due to the peculiar pharmacodynamic profile of suramin, it is suggested that interference with endogenous growth factors, endowed with physiological protective activity on gastric mucosa, might account for the damage-enhancing action of this drug.

Comparative bioavailability of ceftibuten in capsule and suspension forms

The comparative bioavailability of ceftibuten, a new third-generation cephalosporin antibiotic given orally once daily, in capsule and suspension dosage forms, was assessed in healthy male subjects. In three separate studies, subjects received either a 400-mg dose as a suspension or one laboratory-batch, 400-mg capsule; one laboratory-batch, 400-mg capsule or two laboratory-batch, 200-mg capsules; or one production-batch, 400-mg capsule or two laboratory-batch, 200-mg capsules. Plasma samples were assayed for ceftibuten using high-performance liquid chromatography, and the data were assessed using pharmacokinetic and statistical methods. Confidence intervals for the maximum plasma concentration and the area under the plasma concentration-time curve extrapolated to infinity were within 80% to 125% of guidelines, demonstrating the bioequivalence of the two treatments within each of the three studies. One 400-mg capsule (laboratory or production batch) was bioequivalent to two 200-mg capsules used in a clinical efficacy trial; the 400-mg suspension was bioequivalent to a 400-mg capsule (laboratory batch). Thus we concluded that the capsule and the suspension dosage forms were bioequivalent.

Effect of felbamate on the pharmacokinetics of lamotrigine

To assess the possible interaction between lamotrigine and felbamate, a double-blind, randomized, placebo-controlled, two-way crossover study was conducted in 21 healthy male volunteers. Volunteers were given lamotrigine (100 mg every 12 hours) and felbamate (1,200 mg every 12 hours) or matching placebo for 10 days during each period of the crossover. After morning administration on day 10, blood samples were obtained over 12 hours for measurement of lamotrigine. Felbamate increased the maximum concentration (Cmax) and and area under the concentration-time curve from time 0 to 12 hours (AUC0-12) of lamotrigine by 13% and 14%, respectively, compared with placebo. The 90% confidence intervals of the log-transformed pharmacokinetic parameters were within the 80-125% bioequivalance limits, however. Felbamate had no significant effect on the urinary excretion of lamotrigine (total), unconjugated lamotrigine, or the N-glucuronide. One volunteer discontinued the study after developing a rash while taking lamotrigine and placebo. All other adverse events were primarily related to the central nervous system and gastrointestinal tract, with a higher incidence reported during coadministration of lamotrigine and felbamate than with placebo. Overall, felbamate appears to have no clinically relevant effects on the pharmacokinetics of lamotrigine.

Determination on functional basis of presynaptic alpha 2-adrenoceptor subtypes in guinea-pig duodenum

The effects of several alpha 2-adrenoceptor agonists and antagonists were examined on the cholinergic twitch contractions evoked by electrical field stimulation of guinea-pig duodenum. Oxymetazoline, xylazine, noradrenaline, alpha-methyl-noradrenaline or medetomidine (0.01-30 microM) were nearly equieffective in inhibiting duodenal twitch responses. The effects of xylazine were competitively counteracted by antagonists tested (0.03-10 microM) with the following order of potency: RX 821002 = idazoxan > rauwolscine = yohimbine = BRL 44408 >> prazosin = ARC 239 = BRL 41992. According to the current classification, it is suggested that alpha 2-heteroadrenoceptors involved in the modulation of duodenal cholinergic neurotransmission belong to the alpha ZD subtype.

Effect of Felbamate on The Pharmacokinetics of Clonazepam

To assess the possible interaction between clonazepam and felbamate, a double-blind, randomized, placebo-controlled, two-way crossover study was conducted in 18 healthy male volunteers. Volunteers were administered clonazepam (1 mg q12h) and felbamate (1200 mg q12h) or matching placebo for 10 days during each period of the crossover. Following morning dosing on day 10, blood samples were obtained over 12 h for the determination of clonazepam and the metabolites 7-amino-clonazepam and 7-acetamido-clonazepam. Felbamate increased clonazepam's C(max) and AUC(0--12 h) by 17% and 14%, respectively (p < 0.01). The 90% confidence intervals following log-transformation for each of these pharmacokinetic parameters were within the generally accepted interval (80--125%) for bioequivalence. Felbamate had no significant effect on the pharmacokinetics of 7-amino-clonazepam, whereas 7-acetamido-clonazepam concentrations were below the limit of quantification in all but one subject. Adverse events were mainly central nervous system in nature, with a greater incidence reported during coadministration with felbamate compared with placebo. Overall, felbamate appears to have no clinically relevant effects on the pharmacokinetics of clonazepam.