RESUMO
1. Isolated, lumen-perfused, whole stomach preparations from mouse and immature rat produced a stable basal acid output which, although not blocked by histamine H2-, acetylcholine M- or CCKB/gastrin receptor antagonists, was almostly completely blocked by the H+/K(+)-ATPase inhibitor, omeprazole, and the metabolic inhibitor, sodium thiocyanate (NaSCN). 2. Fully-defined concentration-effect curves could be obtained on both assays with the phosphodiesterase inhibitor, isobutyl methylxanthine (IBMX) and with dibutyryl cyclic AMP. 3. On the rat stomach assay, histamine H2-receptor blockade had no effect on the IBMX curve. In contrast, the IBMX response in the mouse was abolished by histamine H2-receptor blockade. On both assays responses to dibutyryl cyclic AMP were resistant to H2-receptor blockade. 4. In the absence of suprathreshold endogenous histamine, it is argued that H+/K(+)-ATPase mediated basal acid secretion from the mouse stomach assay is regulated by something other than cyclic AMP.
Assuntos
Ácido Gástrico/metabolismo , Estômago/fisiologia , 1-Metil-3-Isobutilxantina/farmacologia , Adenilil Ciclases/metabolismo , Animais , Bucladesina/farmacologia , Mucosa Gástrica/efeitos dos fármacos , Mucosa Gástrica/enzimologia , Mucosa Gástrica/metabolismo , Histamina/farmacologia , Antagonistas dos Receptores H2 da Histamina/farmacologia , Técnicas In Vitro , Masculino , Camundongos , Inibidores de Fosfodiesterase/farmacologia , Inibidores da Bomba de Prótons , Ratos , Ratos Wistar , Tiocianatos/farmacologiaRESUMO
1. Electrical field stimulation produced a tetrodotoxin-sensitive, frequency-dependent, release of acid from isolated, lumen-perfused, stomach preparations from mouse, immature rat and guinea-pig. 2. In the guinea-pig and mouse preparations, the frequency-dependent response was abolished by hexamethonium, acetylcholine (ACh) muscarinic (M) and histamine H2-receptor blockade, consistent with the hypothesis that the vagal ACh acts indirectly by stimulating the release of endogenous histamine. 3. In contrast, in the rat preparation the frequency-dependent response was partially refractory to all of these inhibitors. However, a combination of H2- and ACh M-receptor blockade did abolish the effect. 4. We conclude that vagal-stimulated acid secretion in the rat, unlike the other two species, behaves as though there is a direct innervation of the oxyntic cells by either cholinergic or noncholinergic neurones.
Assuntos
Ácido Gástrico/metabolismo , Mucosa Gástrica/metabolismo , Nervo Vago/fisiologia , Animais , Atropina/farmacologia , Colecistocinina/antagonistas & inibidores , Antagonistas Colinérgicos , Estimulação Elétrica , Mucosa Gástrica/efeitos dos fármacos , Mucosa Gástrica/fisiologia , Cobaias , Compostos de Hexametônio/farmacologia , Antagonistas dos Receptores H2 da Histamina/farmacologia , Concentração de Íons de Hidrogênio , Técnicas In Vitro , Indóis/farmacologia , Masculino , Meglumina/análogos & derivados , Meglumina/farmacologia , Camundongos , Ratos , Ratos Wistar , Receptores da Colecistocinina/antagonistas & inibidores , Especificidade da Espécie , Tetrodotoxina/farmacologiaRESUMO
1. Concentration-effect curves were obtained, in the absence and presence of histamine H2-receptor blockade, to 5-methylfurmethide (5-MeF) and McN-A 343, high efficacy and low efficacy acetylcholine (ACh) M-receptor agonists, respectively, in isolated stomach preparations from the mouse and immature rat and guinea-pig. 2. In the immature guinea-pig assay, the responses to 5-MeF and McN-A 343 were abolished by histamine H2-receptor blockade suggesting that the responses were totally dependent upon gastric mucosal histamine. However, in the mouse and immature rat assays, although the histamine H2-receptor antagonists produced small but significant rightward shifts and, in some cases, depression of the maximum of the agonist concentration-effect curves, a significant secretory response remained, presumed to be due to direct stimulation of oxyntic cells. 3. Previously, by assuming that the histamine H2-receptor blockade alters the mode of agonist-stimulated acid secretion from mainly an indirect action mediated by histamine release to direct stimulation of the oxyntic cell, we applied an operational model of agonism to similar data obtained in the mouse preparation. In that study we were able to account for the behaviour of 5-MeF and McN-A 343 by assuming that the agonists expressed 6 fold higher efficacy, tau in the operational model of agonism, at ACh M-receptors on the histamine-releasing cells than on the oxyntic cells. In this study it was possible to account for the variation in the behaviour of the agonists both between and within assays by simply varying the efficacy expressed by the agonists at each of the cells in the model. The efficacy variation could be due to receptor concentration variation.4. The data and analysis are discussed in terms of contemporary models for the role of histamine in the regulation of gastric acid secretion.
Assuntos
Ácido Gástrico/metabolismo , Muscarina/análogos & derivados , Parassimpatomiméticos/farmacologia , Receptores Muscarínicos/efeitos dos fármacos , Estômago/efeitos dos fármacos , Animais , Relação Dose-Resposta a Droga , Cobaias , Antagonistas dos Receptores Histamínicos/farmacologia , Masculino , Modelos Biológicos , Muscarina/farmacologia , RatosRESUMO
1. Agonist-antagonist interactions at acetylcholine (ACh) muscarinic receptors have been analysed by use of an improved urinary bladder assay, isolated and intact, from the mouse. With 5-methylfurmethide as agonist, validated cumulative concentration-effect curves were obtained in less than 7 min by re-dosing before the response plateaux began to fade. 2. The pKB value estimated for pirenzepine was 6.76. The pKB values estimated for atropine and N-methylatropine from data obtained at concentrations which produced dose-ratios greater than 20 and 60 were 8.90 and 9.58, respectively. 3. The deviation from simple competitive behaviour at low dose-ratios with atropine and N-methylatropine was consistent with the operation of saturable antagonist removal processes. The deviation observed with atropine was corrected by pre-incubation with methylbutyrate, an alternative substrate for 'atropine esterase'. 4. The simple competitive behaviour of N-methylatropine was restored following pre-incubation with the neuronal choline uptake blocker hemicholinium-3 (HC-3). However, the pKB estimated for N-methylatropine under these conditions was low. This latter result could be accounted for by the observed behaviour of HC-3 as a competitive antagonist of ACh muscarinic receptors (pKB = 4.01). 5. We conclude that the modified mouse urinary bladder assay is suitable for the quantitative analysis of muscarinic receptor interactions. In addition, we postulate the existence of a previously undescribed uptake mechanism for quaternary muscarinic receptor antagonists.
Assuntos
Músculo Liso/efeitos dos fármacos , Receptores Muscarínicos/efeitos dos fármacos , Animais , Atropina/farmacologia , Derivados da Atropina/farmacologia , Cobaias , Hemicolínio 3/farmacologia , Técnicas In Vitro , Masculino , Camundongos , Muscarina/análogos & derivados , Muscarina/farmacologia , Antagonistas Muscarínicos , Contração Muscular/efeitos dos fármacos , Parassimpatomiméticos/farmacologia , Pirenzepina/farmacologia , Traqueia/efeitos dos fármacos , Bexiga Urinária/efeitos dos fármacosRESUMO
1. The interactions between angiotensin II (AII), two non-peptide antagonists DuP 753 and IMI, and eight peptide analogues of AII were investigated on the rabbit isolated aorta assay. DuP 753 and IMI behaved as simple competitive antagonists (pKB values 8.4 and 6.8, respectively). To different degrees, all the AII-peptide analogue interactions failed to meet the basic criteria for simple competition. In addition to rightward shift, the most significant feature was a concentration-dependent saturable depression of the upper asymptote of the AII concentration-effect curves. 2. 'Washout' and combined dose-ratio analysis experiments, in which DuP 753 was used as a reference antagonist, indicated that the profile of peptide antagonism was solely due to a reversible and syntopic action at the AII receptor. 3. By use of an operational model of agonism (Black & Leff, 1983) as a starting point, it was possible to account for the data with a new model which describes reversible receptor occupancy and occupied receptor-determined, saturable reduction in the efficacy of AII. Model-fitting gave estimates of pKB values for the peptide analogues and agonist affinity and efficacy parameters for AII. 4. The model was successfully tested by applying it to qualitatively similar results obtained in a cross-tissue analysis on guinea-pig aorta, ileum and stomach. 5. A 'molecular' interpretation of the efficacy changes, based on the concepts of receptor internalisation and expression, is offered.
Assuntos
Angiotensina II/metabolismo , Antagonistas de Receptores de Angiotensina , Angiotensina II/análogos & derivados , Angiotensina II/antagonistas & inibidores , Animais , Aorta/efeitos dos fármacos , Comportamento Animal/efeitos dos fármacos , Compostos de Bifenilo/farmacologia , Cobaias , Íleo/efeitos dos fármacos , Imidazóis/farmacologia , Técnicas In Vitro , Losartan , Masculino , Músculo Liso/efeitos dos fármacos , Coelhos , Estômago/efeitos dos fármacos , Tetrazóis/farmacologiaRESUMO
1. Dipyridamole potentiates the effects of adenosine on the heart by inhibiting adenosine uptake. The effects of dipyridamole on both adenosine and N-ethylcarboxamidoadenosine (NECA) concentration-effect (E/[A]) curves were compared on the AV node, in guinea-pig isolated perfused hearts, and on the SA node, in isolated right atria, by measuring dromotropic and chronotropic responses, respectively. In the absence of dipyridamole, adenosine was significantly more potent on the AV node than SA node (AV p[A]5, = 4.95+/-0.10. SA p[A]50=3.62+/-0.10). In contrast, NECA and adenosine in the presence of dipyridamole were approximately equiactive in the two assays (NECA: AV p[A]50=7.07+/-0.07; SA p[A]50=7.30+/-0.08: adenosine: AV p[A]50=6.49+/-0.08; SA p[A]50=6.27+/-0.05). Dipyridamole was significantly more potent in enhancing the effects of adenosine on the SA node than on the AV node (pKi values estimated by Kenakin's method (1981): AV node 8.18+/-0.14; SA node=8.75+/-0.08). 2. The difference in pKi values did not appear to be due to dipyridamole expressing other actions because concentrations of dipyridamole which saturated the adenosine transporter had no effect on the NECA E/[A] curves in either assay. However, the test of another assumption of Kenakin's method, that adenosine taken up into cells is pharmacologically inactive, failed on the AV node assay because a significant potentiating interaction was found between adenosine and NECA. The interaction was concentration-dependent, reciprocal to the extent that pre-incubation with either agonist potentiated the other and was concluded to be due to an intracellular action of adenosine as the potentiation disappeared in the presence of dipyridamole. 3. An explanatory model was developed to account for the data obtained using existing pharmacological concepts of ligand action in isolated tissue bioassays. In the model, adenosine, but not NECA, was assumed to be subject to saturable agonist uptake, an uptake which was competitively blocked by dipyridamole. Adenosine and NECA were assumed to act extracellularly at adenosine A1-receptors. In the AV node, but not the SA node, the adenosine transported into the cells was assumed to potentiate the effects of adenosine A1-receptor activation. For the AV node assay, the model predicted that potentiation of adenosine by uptake blockade is offset by a simultaneous decrease in potentiation due to the intracellular action of adenosine. All of the experimental data obtained in the study could be accounted for by the model including the apparent differences in potency of adenosine in the absence of dipyridamole and the pKi values for dipyridamole.
Assuntos
Adenosina/antagonistas & inibidores , Nó Atrioventricular/efeitos dos fármacos , Dipiridamol/farmacologia , Nó Sinoatrial/efeitos dos fármacos , Adenosina/metabolismo , Adenosina/farmacologia , Adenosina-5'-(N-etilcarboxamida)/farmacologia , Animais , Nó Atrioventricular/metabolismo , Nó Atrioventricular/fisiologia , Sinergismo Farmacológico , Cobaias , Frequência Cardíaca/efeitos dos fármacos , Técnicas In Vitro , Masculino , Modelos Cardiovasculares , Receptores Purinérgicos P1/efeitos dos fármacos , Receptores Purinérgicos P1/fisiologia , Nó Sinoatrial/metabolismo , Nó Sinoatrial/fisiologiaRESUMO
Recently, it was demonstrated that 5-HT induces relaxation of human colon circular muscle through activation of 5-HT(4) receptors and 5-HT(7) receptors. The aim of the current study was to develop a new in vitro bioassay of human colon that would facilitate the pharmacological analysis of 5-HT responses mediated solely by 5-HT(4) receptors. Contracting circular muscle strips with KCl (80 mM) yielded a stable contractile tension and, in contrast to muscarinic cholinoceptor agonists and histamine, a profound reduction of spontaneous contractility. This allowed the establishment of reproducible, fully-defined, agonist concentration-response curves by cumulative dosing. Under these conditions, 5-HT induced a concentration-dependent relaxation (pEC(50) 7.31, Hill slope 0.91). Neither methysergide (10 microM) nor granisetron (1 microM) affected the 5-HT-induced relaxation, suggesting that 5-HT(1), 5-HT(2), 5-HT(3), 5-ht(5), 5-HT(6) or 5-HT(7) receptors are not involved. The lack of effect of tetrodotoxin (0.3 microM) indicated a direct effect of 5-HT on the smooth muscle. The selective 5-HT(4) receptor antagonists GR 113808, GR 125487 and RS 39604 competitively antagonized the 5-HT-induced relaxation (pK(B) 9.43, 10.12 and 8.53, respectively). SB 204070 (1 nM) produced a rightward shift (pA(2) 10.34) and depression of the 5-HT curve. These affinity estimates are similar to those previously reported for 5-HT(4) receptors. The selective 5-HT(4) receptor agonists, prucalopride and R076186, induced relaxations (pEC(50) 7.50 and 7.57, respectively), that were blocked by GR 113808 (3 nM), yielding pA(2) estimates of 9.31 and 9.21, respectively. To summarise, in KCl (80 mM)-contracted muscle strips, 5-HT induces relaxation through activation of a homogeneous smooth muscle 5-HT(4) receptor population. This new bioassay allows the focused, pharmacological characterization of human colonic 5-HT(4) receptors in vitro.
Assuntos
Bioensaio/métodos , Músculo Liso/metabolismo , Receptores de Serotonina/análise , Humanos , Técnicas In Vitro , Intestino Grosso/efeitos dos fármacos , Intestino Grosso/metabolismo , Relaxamento Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Músculo Liso/fisiologia , Receptores 5-HT4 de Serotonina , Antagonistas da Serotonina/farmacologia , Agonistas do Receptor de Serotonina/farmacologiaRESUMO
This study investigated the cannabinoid receptor, known to inhibit neuronally-evoked contractions of the mouse isolated urinary bladder, in bladder sections isolated from mouse, rat, dog, pig non-human primate or human. The CB(1)-like pharmacology of the cannabinoid receptor in mouse isolated bladder observed previously was confirmed in this study by the rank order of agonist potencies: CP 55940>/=WIN 55212-2>HU 210>JWH 015>anandamide, the high affinity of the CB(1) selective antagonist, SR 141716A (apparent pK(B) 8.7), and the low affinity of the CB(2) antagonist, SR 144528 (apparent pK(B)<6.5). In these studies, SR 141716A (10-100 nM) significantly potentiated electrically-evoked contractions in this tissue by an undetermined mechanism. A similar rank order of agonist potencies was determined in rat isolated bladder sections (CP 55, 940> or =WIN 55212-2>JWH 015). In this tissue, the maximal inhibitory effect of all agonists was lower than in the mouse bladder. Indeed, the effects of both HU 210 and anandamide were too modest to quantify potency accurately. In the rat isolated bladder, SR 141716A (30 nM) or SR 144528 (100 nM), reversed the inhibitory effect of WIN 55212-2 (apparent pK(B) = 8.4 and 8.0, respectively) or JWH 015 (apparent pK(B) = 8.2 and 7.4, respectively). These findings may demonstrate pharmacological differences between the rat and mouse orthologues of the CB(1) receptor. Alternatively, they may be attributed to a mixed population of CB(1) and CB(2) receptors that jointly influence neurogenic contraction of the rat bladder, but cannot be differentiated without more selective ligands. WIN 55212-2 had no effect on electrically-evoked contractions of bladder sections isolated from dog, pig, cynomolgus monkey and human. These findings suggest that the effect of cannabinoid agonists to inhibit neurogenic contraction of the mouse and rat bladder is not conserved across all mammalian species.
Assuntos
Morfolinas/farmacologia , Naftalenos/farmacologia , Receptor CB2 de Canabinoide , Receptores de Droga/fisiologia , Bexiga Urinária/fisiologia , Acetilcolina/metabolismo , Trifosfato de Adenosina/análogos & derivados , Trifosfato de Adenosina/metabolismo , Trifosfato de Adenosina/farmacologia , Animais , Atropina/farmacologia , Benzoxazinas , Bloqueadores dos Canais de Cálcio/farmacologia , Carbacol/farmacologia , Agonistas Colinérgicos/farmacologia , Cães , Relação Dose-Resposta a Droga , Estimulação Elétrica , Eletrofisiologia , Humanos , Técnicas In Vitro , Macaca fascicularis , Masculino , Camundongos , Contração Muscular/efeitos dos fármacos , Piperidinas/farmacologia , Pirazóis/farmacologia , Ratos , Receptores de Canabinoides , Receptores de Droga/agonistas , Receptores de Droga/antagonistas & inibidores , Receptores Muscarínicos/metabolismo , Rimonabanto , Especificidade da Espécie , Suínos , Bexiga Urinária/efeitos dos fármacos , Bexiga Urinária/metabolismoRESUMO
1. The CCKB/gastrin receptors mediating pentagastrin stimulation of gastric acid secretion by histamine release and by direct stimulation of oxyntic cells have been characterized in the immature rat isolated stomach assay. This was achieved by estimating antagonist affinity values for competitive antagonists from three distinct chemical classes (L-365,260, PD134,308 and JB93190) in the absence and presence of a high concentration of the histamine H2-receptor antagonist, famotidine (30 microM). 2. Pentagastrin produced concentration-dependent stimulation of gastric acid secretion in the absence and presence of famotidine. Famotidine depressed the maximum secretory response to pentagastrin although the degree of depression varied between experimental replicates (25-60%). This variation was attributed to the histamine-release mediated component of acid secretion, as judged by the consistency of the maximum responses obtained in the presence, but not absence, of famotidine. 3. All three CCKB/gastrin receptor antagonists behaved as surmountable antagonists in the absence and presence of famotidine. JB93190 (pKB approximately 9.1, approximately 8.9, in the absence and presence of famotidine, respectively) was approximately 30 fold more potent than either L-365,260 (pKB approximately 7.4, approximately 7.1) or PD134,308 (pKB approximately 7.6, approximately 7.4). 4. It was assumed that the famotidine treatment converted pentagastrin-stimulated acid secretion from a combination of an indirect action due to the release of histamine and a direct action on the oxyntic cell to solely a direct action on the oxyntic cell. A simple mathematical model of this two-receptor system was developed. The direct and indirect components were assumed to sum to produce the total response to pentagastrin obtained in the absence of famotidine. It was found that this model could account quantitatively for the behaviour of the three antagonists without invoking a difference in antagonist affinity for the CCKB/gastrin receptors mediating the direct and indirect actions of pentagastrin. However, a conclusion of receptor homogeneity has to be qualified because the model was also used to generate simulations which indicated that the analysis could only detect antagonist affinity differences of greater than one log-unit between enterochromaffin-like (ECL) and oxyntic cell CCKB/gastrin receptor populations.
Assuntos
Ácido Gástrico/metabolismo , Mucosa Gástrica/metabolismo , Histamina/farmacologia , Pentagastrina/farmacologia , Receptores da Colecistocinina/efeitos dos fármacos , Animais , Ligação Competitiva/efeitos dos fármacos , Células Enterocromafins/efeitos dos fármacos , Células Enterocromafins/metabolismo , Famotidina/farmacologia , Mucosa Gástrica/efeitos dos fármacos , Antagonistas dos Receptores H2 da Histamina/farmacologia , Técnicas In Vitro , Cinética , Modelos Biológicos , Ratos , Ratos Wistar , Receptores da Colecistocinina/antagonistas & inibidores , Estimulação QuímicaRESUMO
1. The effects of seven agonist and three antagonist adenosine receptor ligands were compared on the guinea-pig sinoatrial (SA) node (isolated right atrium) and atrioventricular (AV) node (perfused whole heart). Single agonist concentration-effect curves were obtained to 5'-N-ethylcarboxamidoadenosine (NECA), R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA), N6-cyclohexyladenosine (CHA), 2-chloroadenosine (CADO),),S(+)-N6-(2-phenylisopropyl)adenosine (L-PIA), 2-phenylaminoadenosine (CV 1808) and N6-aminoadenosine (MeAdo). Adenosine and/or NECA curves were obtained in the absence and presence of the antagonists 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), 9-chloro-2 (2-furanyl)-5,6-dihydro-1,2,4-triazolo[1,5-c]quinazolin-5-imine (CGS15943) and N6-(endonorbornan-2-yl)-9-methyladenine (N-0861). 2. A formal comparison of the agonist and antagonist potency data was made by fitting the data to a straight line using a least squares procedure based on principal components analysis to account for the variance on both axes. The antagonist affinity estimates made on the two assays did not deviate significantly from the line of identity. 3. The agonist p[A]50 data obtained on the two assays did not deviate from the line of identity, indicating that there were no significant differences in potencies between the two assays. The p[A]50 ratio of R-PIA and S-PIA was 1.24+/-0.09 in the SA node and 1.36+/-0.11 in the AV node, indicating no difference in the stereoselectivity of the PIA isomers between the two tissues. 4. The agonist potency and antagonist affinity data obtained are consistent with previous findings showing that the AV and SA node data are pharmacologically indistinguishable and belong to the adenosine A1-receptor class. No evidence for the reported A3-receptor was found.
Assuntos
Nó Atrioventricular/efeitos dos fármacos , Agonistas do Receptor Purinérgico P1 , Antagonistas de Receptores Purinérgicos P1 , Nó Sinoatrial/efeitos dos fármacos , Adenosina/análogos & derivados , Adenosina/farmacologia , Animais , Nó Atrioventricular/metabolismo , Nó Atrioventricular/fisiologia , Cobaias , Frequência Cardíaca/efeitos dos fármacos , Técnicas In Vitro , Masculino , Agonistas do Receptor Purinérgico P2 , Antagonistas do Receptor Purinérgico P2 , Receptor A3 de Adenosina , Receptores Purinérgicos P1/classificação , Nó Sinoatrial/metabolismo , Nó Sinoatrial/fisiologia , EstereoisomerismoRESUMO
BACKGROUND: Constitutive cyclooxygenase-1 enzyme synthesizes prostaglandins which are thought to play an important role in the functional integrity of the stomach gastric mucosa. Recently, it was shown that cyclooxygenase-1 deficient mutant mice did not develop spontaneous gastric pathology and appear less sensitive to indomethacin-induced gastric damage. AIM: To investigate gastric acid secretion in cyclooxygenase-1 deficient mutant mice. METHODS: The basal and histamine or isobutyl methylxanthine-stimulated acid secretion in stomachs of cyclooxygenase-1 deficient homozygous mice and the effect of indomethacin was compared with that of heterozygous and wild-type mice using isolated lumen perfused mouse stomachs, in organ baths, monitored by pH-electrodes. RESULTS: There was no significant difference in the basal or histamine stimulated gastric acid secretion between wild-type or heterozygous or homozygous mice. However, isobutyl methylxanthine was more potent in the cyclooxygenase-1 deficient and heterozygous mice than in wild-type mice. Indomethacin, at concentrations below 1 mM, had no effect on either basal or histamine stimulated acid secretion in any of the mice populations. CONCLUSION: Gastric acid secretion is maintained without prostaglandin involvement in cyclooxygenase-1 deficient mice. The finding that basal and histamine-stimulated gastric acid secretion was similar in the cyclooxygenase-1 deficient, compared to wild-type mice is consistent with the lack of spontaneous gastric pathology in the cyclooxygenase-1 deficient mice.
Assuntos
Ácido Gástrico/metabolismo , Isoenzimas/deficiência , Prostaglandina-Endoperóxido Sintases/deficiência , 1-Metil-3-Isobutilxantina/farmacologia , Algoritmos , Animais , Ciclo-Oxigenase 1 , Inibidores de Ciclo-Oxigenase/toxicidade , Genótipo , Histamina/farmacologia , Concentração de Íons de Hidrogênio , Técnicas In Vitro , Indometacina/toxicidade , Isoenzimas/genética , Proteínas de Membrana , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Perfusão , Inibidores de Fosfodiesterase/farmacologia , Prostaglandina-Endoperóxido Sintases/genética , Prostaglandinas/metabolismoRESUMO
Cholecystokinin (CCK) produces contractions of gallbladder and colon in a number of different species. Although the effects of CCK on the human gallbladder are relatively well documented, the CCK receptors in the human colon have not been clearly characterised. Therefore, in this study, the CCK receptors in the human gallbladder and colon were compared using pharmacological techniques. Contraction of specimens of the human tissue was measured using in vitro organ bath bioassay. The effect of selective concentrations of CCK(1) and CCK(2) receptor antagonists (L-364,718 and JB93182, respectively) was determined on agonist concentration-effect (E/[A]) curves obtained by cumulative dosing with sulphated CCK. The CCK(1) antagonist L-364,718 produced a rightward shift of the CCK-8S [E/[A] curve in the human gallbladder (pA(2)=9.15 +/- 0.26) and ascending colon (pA(2)=9.20 +/- .33). In both tissues, the CCK(2) receptor antagonist, JB93182, had no effect on the CCK E/[A] curves. In addition, in the colon, pentagastrin responses were inhibited by L-364,718 but unaffected by JB93182. These data indicate that the CCK-induced contraction of the human colon and gallbladder smooth muscle is mediated solely through the CCK(1) receptor subtype, and the antagonist affinity estimates are consistent with those previously obtained in experiments on animal tissue.
Assuntos
Colecistocinina/farmacologia , Colo/efeitos dos fármacos , Colo/metabolismo , Vesícula Biliar/efeitos dos fármacos , Vesícula Biliar/metabolismo , Contração Muscular/efeitos dos fármacos , Receptores da Colecistocinina/metabolismo , Sincalida/análogos & derivados , Colo/fisiologia , Relação Dose-Resposta a Droga , Vesícula Biliar/fisiologia , Humanos , Técnicas de Cultura de Órgãos , Pentagastrina/farmacologia , Peristaltismo/efeitos dos fármacos , Sincalida/farmacologiaRESUMO
OBJECTIVE: To study the effect of nimesulide on acid secretion in mouse isolated stomach. METHODS: Isolated lumen-perfused mouse stomachs were monitored by pH-electrodes (1). Gastric acid secretion was stimulated with histamine or 5-methylfurmethide (5-MeF, a stable acetylcholine derivative), and the effect of nimesulide and indomethacin were studied alone and in combination with famotidine. RESULTS: The concentration-dependent stimulation of gastric acid output by histamine (Hill equation fitting parameters: log[A]50 5.44 +/- 0.15; p, 1.01 +/- 0.11; alpha, 0.64 +/- 0.05) was inhibited by famotidine, and also by nimesulide (log r = 0.79 +/- 0.10 at 30 microM). However, nimesulide also reduced the maximum acid output. The shift produced by nimesulide and famotidine in combination indicated a greater than additive effect, suggesting that nimesulide was not acting at histamine H2-receptors (Shankley et al., 1988) (2). Indomethacin reduced acid secretion only at the highest concentration (100 microM). Furthermore, the histamine-receptor-independent stimulation of gastric acid output by 5-MeF was greatly inhibited by nimesulide, which also suggests that nimesulide was acting on the parietal cell signaling pathway at a non-histamine-receptor site. CONCLUSION: The relatively low risk of gastric mucosal damage with nimesulide is thought to involve its weak inhibition of gastric prostaglandin synthesis and its weak acidity, but another factor might be the ability to reduce gastric acid production. However, the effect of nimesulide on human gastric acid secretion remains to be investigated.
Assuntos
Anti-Inflamatórios não Esteroides/farmacologia , Inibidores de Ciclo-Oxigenase/farmacologia , Ácido Gástrico/metabolismo , Mucosa Gástrica/efeitos dos fármacos , Mucosa Gástrica/metabolismo , Sulfonamidas/farmacologia , Animais , Relação Dose-Resposta a Droga , Interações Medicamentosas , Famotidina/farmacologia , Mucosa Gástrica/patologia , Histamina/farmacologia , Antagonistas dos Receptores H2 da Histamina/farmacologia , Concentração de Íons de Hidrogênio/efeitos dos fármacos , Técnicas In Vitro , Indometacina/farmacologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Muscarina/análogos & derivados , Muscarina/farmacologia , PerfusãoRESUMO
Does gastrin stimulate gastric acid secretion by direct action on oxyntic cells, by releasing histamine, or by being potentiated by histamine? Previous studies in the mouse pointed to gastrin-regulated histamine release. Guinea pig and rat are well known to vary in their sensitivity to histamine. Therefore, the effects of histamine and pentagastrin were compared quantitatively on isolated, lumen-perfused, stomach preparations from these species in the absence and presence of histamine H2-receptor blockade. The loss of potency of histamine in the rat was mirrored by a loss of potency of pentagastrin consistent with the idea that pentagastrin acts by releasing histamine. In the rat, a well-defined pentagastrin curve was obtained in the presence of histamine H2-receptor block as though pentagastrin acts both directly on the oxyntic cell and indirectly by releasing histamine. It was not necessary to invoke a potentiating interaction between histamine and pentagastrin at the oxyntic cell; the two effects appeared simply to add. Potentiation was observed, however, between other combinations of stimuli, for example, between vagal nerve and pentagastrin stimulation. The physiological consequences of these results are discussed.
Assuntos
Ácido Gástrico/metabolismo , Histamina/farmacologia , Pentagastrina/farmacologia , Animais , Sinergismo Farmacológico , Mucosa Gástrica/citologia , Mucosa Gástrica/metabolismo , Mucosa Gástrica/fisiologia , Cobaias , Liberação de Histamina/fisiologia , Camundongos , Células Parietais Gástricas/química , Células Parietais Gástricas/citologia , Células Parietais Gástricas/metabolismo , Ratos , Receptores Histamínicos H2/análise , Receptores Histamínicos H2/fisiologia , Estômago/citologia , Estômago/fisiologia , Nervo Vago/fisiologiaRESUMO
This study was designed to identify the need for primary prevention of cardiovascular disease in an HMO population and to develop appropriate interventions for individuals in different risk groups, based on risk stratification and comparison. The analysis is based on a cross-sectional survey of the HMO members of a large employer group. Respondents (n=17,878) were stratified based on the Framingham model; 34% of respondents without cardiovascular disease were classified as moderate to high attributable risk for the disease, and 66% were classified as low attributable risk. Results of logistic regression analyses suggest that, compared with respondents with pre-existing cardiovascular disease, moderate- to high-risk respondents are more likely to smoke, have unhealthy diets, and be overweight, hypertensive, and hypercholesterolemic. More low-risk respondents had unhealthy diets than did those with pre-existing cardiovascular disease. There were no differences between these groups for physical activity and stress. Respondents had fewer modifiable risk factors and healthier lifestyles than did those who were at risk. These findings suggest that primary prevention should be enhanced, especially among those with significantly increased risk for the disease. Moreover, the approaches of this project-population-based risk assessment, stratification, and comparison-were instrumental in identifying the target population and designing appropriate interventions. (c) 2001 by CHF, Inc.