Carbachol-induced potentiation and inhibition of acid secretion by guinea pig gastric gland

The effects of muscarinic ligands on acid secretion were examined by estimating the accumulation of [14C]aminopyrine in gastric glands isolated from guinea pigs. The accumulation of [14C]aminopyrine in the presence of 0.1 mM histamine was potentiated by 1 microM carbachol but suppressed by 1 mM. These two effects of carbachol were abolished by atropine, pirenzepine and AF-DX 116. Assuming that the binding of carbachol to one site (Site 1) increases [14C]aminopyrine accumulation but its binding to the other site (Site 2) reduces [14C]aminopyrine accumulation, we analysed the dose-response curves for the carbachol effects in the absence and presence of different concentrations of atropine, pirenzepine and AF-DX 116. The dissociation constants determined for these ligands at Sites 1 and 2 were as follows: carbachol, 0.28 and 7.1 microM; atropine, 0.28 and 0.54 nM; pirenzepine, 45 and 560 nM; and AF-DX 116, 380 and 4400 nM, respectively. The binding of [3H]N-methylscopolamine to the gastric glands indicated the presence of two populations of binding sites with different affinities for the above ligands, other than atropine. The apparent dissociation constants, which were estimated by analysing the displacement curves for [3H]N-methylscopolamine binding, were as follows: carbachol, 0.18 microM (10%) and 31 microM (90%); atropine, 1.24 nM; pirenzepine, 15 nM (16%) and 220 nM (84%); and AF-DX 116, 370 nM (10%) and 2970 nM (90%). These results suggest that there are two kinds of muscarinic acetylcholine receptors in the guinea pig gastric gland, one potentiating and the other inhibiting the acid secretion induced by histamine.     

Idebenone and vinpocetine augment long-term potentiation in hippocampal slices in the guinea pig

The effects of idebenone and vinpocetine which reportedly prevent impairment of learning and memory were studied in vitro, on the long-term potentiation of the population spike in the pyramidal layer of CA3 region of slices of hippocampus in the guinea pig. Idebenone (10(-9) M-10(-6) M) or vinpocetine (10(-7) M-10(-6) M) significantly augmented long-term potentiation in the mossy fibre-CA3 pyramidal cell system, without any significant changes in population spikes in the absence of tetanic stimulation. These results suggest that both drugs have direct actions on the hippocampal neurones to augment long-term potentiation at fairly small concentrations. Further, when the two drugs were applied together, the augmenting effects were additive.     

Effects of fexofenadine hydrochloride in a guinea pig model of antigen-induced rhinitis

Allergic rhinitis is an inflammatory disease of the nasal mucosa, induced by histamine, leukotrienes, and other substances released from mast cells. Fexofenadine hydrochloride, the active metabolite of terfenadine, is a novel, nonsedating antiallergic drug having H1 receptor antagonistic activity. Fexofenadine is effective for the treatment of allergic rhinitis. However, its mechanism of action in attenuating nasal congestion has not yet been elucidated. Therefore, we first examined the effects of fexofenadine on a guinea pig model of antigen-induced rhinitis. We also evaluated the effects of mepyramine, zafirlukast and ramatroban in this model; these drugs are an H1 receptor antagonist, a selective leukotriene antagonist and a selective thromboxane antagonist, respectively. Rhinitis was induced by ovalbumin (OVA) instillation into the nasal cavity of animals that had been sensitized by two earlier OVA injections (s.c. and i.p.). The nasal airway resistance was measured for 45 min after the challenge. Fexofenadine hydrochloride (20 mg/kg) and terfenadine (20 mg/kg) administered orally 70 min prior to the challenge significantly inhibited (fexofenadine, p < 0.001, terfenadine, p < 0.05) the increase in nasal airway resistance. Ramatroban (30 mg/kg) administered orally 60 min prior to the challenge also significantly inhibited (p < 0.05) the increase in nasal airway resistance. In contrast, mepyramine (3 mg/kg i.v.) and zafirlukast (3 mg/kg p.o.) failed to reduce the increase in nasal airway resistance. These results suggest that thromboxane may be involved in the increase in the nasal airway resistance in this model. Accordingly, fexofenadine may reduce the increase in nasal airway resistance by inhibiting the release of chemical mediators, including thromboxane, that are involved in the increase in nasal airway resistance in this model.     

Role of muscarinic acetylcholine receptors in a guinea pig model of asthma

We examined the density of muscarinic acetylcholine receptor (mACh-R) subtypes (M1R, M2R and M3R) in guinea pig lung. The density of M3R in the lung tissue of ovalbumin (OA)-sensitized guinea pigs was higher than that in the control group. However, no difference was observed in the affinity of M3R between the sensitized and the control lungs. No difference was observed in the density and affinity of M1R and M2R in sensitized and control lungs. Pilocarpine, which is an M2R stimulant, increased the density of M3R in the lung tissue and the rate of the increase in sensitized guinea pigs was less than that in the control group. In contrast, methoctranine, which is an M2R antagonist, decreased the density of M3R and the rate ofthis decrease was the same in the sensitized and control groups. These results suggest that, in OA-sensitized guinea pigs, a dysfunction of M2R leads to the abnormal density of M3R.     

Triglyceride-lowering effect of pitavastatin in a guinea pig model of postprandial lipemia

The triglyceride (TG)-lowering effect of pitavastatin (CAS 147526-32-7), a potent 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, was investigated in a guinea pig model of post-prandial lipemia. Plasma TG levels started to rise 2 h after the fat load, reached the maximum at 8 h and then gradually decreased. A 14-day dose of pitavastatin at 3 mg/kg decreased the 8 h plasma TG levels by 59%, and the 0-12 h area under the curve (AUC) of TG levels above the initial levels, by 77%. This effect was also shown with 30 mg/kg of atorvastatin (CAS 134523-00-5), and the same dose of simvastatin (CAS 79902-63-9). The intensity of the action was equivalent for pitavastatin and atorvastatin, but weaker with simvastatin. In order to clarify the mechanism of this action, the effect of pitavastatin exerted on the activity of microsomal triglyceride transfer protein (MTP), which participates in the secretion to the lymph vessel of chyromicron (CM)-TG in the small intestine, and the activity of lipoprotein lipase (LPL), which is the hydrolysis enzyme of the very low density lipoprotein (VLDL)-TG and CM-TG, was examined. However, an influence on the activity of MTP or LPL by pitavastatin was not shown. These results suggested that pitavastatin lowered the postprandial TG levels in guinea pigs by accelerating the remnant clearance, probably through the enhancement of the low density lipoprotein (LDL) receptor. This effect is expected to improve postprandial lipemia.     

Toxicological scoring of Alzheimer's disease drug huperzine in a guinea pig model

Huperzine is a secondary metabolite in lycopods Huprzia and an inhibitor of acetylcholinesterase and antagonist of N-methyl-D-apartate receptor. Huperine is a suitable drug for the treatment of Alzheimer's disease as it is a part of traditional Chinese medicine. Currently, it undergoes clinical trials in the European Union and United States. The toxicological data about huperzine are missing and link between huperzine and oxidative stress has not been extensively investigated. For the above mentioned reasons, we organized experiment on a guinea pig model aimed at the investigation of adverse effects caused by huperzine. Guinea pigs were exposed to (-)-huperzine A in doses 5-625 μg/kg. Animals were sacrificed one day after exposure. Ferric reducing antioxidant power, thiobarbituric acid reactive substances, glutathione reductase, caspase 3 activity and selected biochemical markers (e.g. transaminases, blood urea nitrogen and glucose) were assayed. In frontal, parietal, temporal lobes and cerebellum, we found increase of antioxidants, glutathione reductase and oxidative stress markers in a dose dependent manner. Effects on liver, kidney and spleen were milder. We discuss ambivalent action of huperzine in the body and judge the huperzine action owing to recently reported experiments.     

Evaluation of Lassa antiviral compound ST-193 in a guinea pig model

Lassa virus (LASV), a member of the Arenaviridae family, causes a viral hemorrhagic fever endemic to West Africa, where as many as 300,000 infections occur per year. Presently, there are no FDA-approved LASV-specific vaccines or antiviral agents, although the antiviral drug ribavirin has shown some efficacy. A recently identified small-molecule inhibitor of arenavirus entry, ST-193, exhibits submicromolar antiviral activity in vitro. To determine the antiviral utility of ST-193 in vivo, we tested the efficacy of this compound in the LASV guinea pig model. Four groups of strain 13 guinea pigs were administered 25 or 80 mg/kg ST-193, 25 mg/kg of ribavirin, or the vehicle by the intraperitoneal (i.p.) route before infection with a lethal dose of LASV, strain Josiah, and continuing once daily for 14 days. Control animals exhibited severe disease, becoming moribund between days 10 and 15 postinfection. ST-193-treated animals exhibited fewer signs of disease and enhanced survival when compared to the ribavirin or vehicle groups. Body temperatures in all groups were elevated by day 9, but returned to normal by day 19 postinfection in the majority of ST-193-treated animals. ST-193 treatment mediated a 2-3-log reduction in viremia relative to vehicle-treated controls. The overall survival rate for the ST-193-treated guinea pigs was 62.5% (10/16) compared with 0% in the ribavirin (0/8) and vehicle (0/7) groups. These data suggest that ST-193 may serve as an improved candidate for the treatment of Lassa fever.     

Evaluation of bioactive glass for mastoid obliteration: a guinea pig model

BACKGROUND: Mastoid obliteration seeks to replace an open mastoid cavity with material that will become viable and free of infection and cholesteatoma. The purpose of this study was to evaluate the efficacy of bioactive glass ceramic particles for mastoid obliteration using a guinea pig animal model. MATERIALS AND METHODS: Ten male guinea pigs (weighing 250-300 g) with normal eardrums and Preyer reflexes were used. Bulla obliteration using bioactive glass was performed on the left side in all guinea pigs. The implanted bioactive glass ceramic particles were examined clinically and radiologically by computed tomography (CT) and histologically. RESULTS: Clinically, there were no signs of inflammation, infection or implant exposure in all guinea pigs. The CT scans showed hyperintense areas that represented new bone formation. Histological evidence of new bone formation was observed in the implant specimens that included: active osteoblasts, osteocytes, chondrocytes and osteoid tissue. There was a definite bond between the implant and the bone interface at the areas of new bone formation. No inflammatory or foreign body reactions, caused by the bioactive glass ceramic particle implantation, were observed in the surrounding tissue. CONCLUSION: Our results suggest that bioactive glass ceramic particles are an ideal implant material. Further studies on bioactive glass ceramic particles should include a larger animal trial to lay the groundwork for human studies.     

Acute and subacute effects of doxorubicin on postextrasystolic potentiation in guinea pig papillary muscles.

To investigate the effects of doxorubicin on postextrasystolic potentiation (PESP), isolated guinea pig papillary muscles were field-stimulated and the resulting isometric force was recorded. Postextrasystolic contraction was evoked following trains of 37 regular stimulations. The effects of acute doses of doxorubicin (0.2 mM) on regular contractions and postextrasystolic contractions were examined for 2 hr. The effects of subacute doses of doxorubicin (total dose 5 mg/kg intraperitoneally) on the relationship between %PESP (postextrasystolic/regular contraction) and both the extra-stimulus coupling interval and the postextrasystolic interval were examined. Acute administration of doxorubicin decreased the amplitude of postextrasystolic contractions more than that of regular contractions. Thus, %PESP in the doxorubicin-treated group decreased significantly over time. There was no similar decrease in the control papillary muscles. Both the extra-stimulus coupling interval and the postextrasystolic interval had less of an effect on %PESP in doxorubicin-treated animals than in control animals. Since PESP depends upon sarcoplasmic reticulum activity, our results indicate that acute and subacute exposure to doxorubicin impairs the activity of the sarcoplasmic reticulum of guinea pig papillary muscles.     

Airway remodeling in the smoke exposed guinea pig model

Although small airway remodeling (SAR) leading to airflow obstruction is a common consequence of human cigarette smoking, the airways have been largely ignored in animal models of chronic obstructive pulmonary disease (COPD). We examined lung structure in a guinea pig model of chronic cigarette smoke exposure to ascertain whether smoke induced SAR, and to evaluate how these anatomic lesions correlate with physiologic changes. We used tissue from guinea pigs exposed to cigarette smoke or air for 6 mo. Pulmonary function tests were performed, and histologic sections were prepared. Airspace size (Lm) and changes in the structure of the small airways were evaluated by morphometric analysis. Chronic smoke exposure was associated with increased airway wall thickness and increased amounts of thick collagen fibers in the walls of the small airways, as well as with increased Lm. The increase in thick collagen fibers related negatively to peak expiratory volume (PEF) and the ratio of forced expiratory volume in 1 s to forced ventilatory capacity (FEV(0.1)/FVC), and positively to airway resistance. Physiologic lung volumes were predicted by airspace size, but residual volume (RV) and total lung capacity (TLC) also were related to airway wall thickness. Amounts of smooth muscle were not changed and did not predict any physiologic abnormalities. We conclude that cigarette smoke exposure results in SAR in the guinea pig, alterations that are reflected in increased airways resistance with diminished airflow and air trapping, mimicking human disease. This model should prove useful in further investigations into the mechanisms of airway remodeling.     

The guinea pig as an animal model for asthma

Experimental guinea pig asthma is a reliable and clinically relevant facsimile of human disease. The guinea pig is the preferred choice for use as a model of allergic bronchial asthma in the evaluation of anti-asthmatic drugs, since the airway anatomy and the response to inflammatory mediators is similar to humans. Further, the great strength of this model is the direct anaphylactic bronchoconstriction upon antigen challenge. Under certain conditions a late asthmatic response can be measured and airway hyperresponsiveness is observed in vitro and in vivo. Moreover, the inflammatory response is comparable with the human situation. More recent studies describe a chronic model for asthma in which airway remodeling is induced as can be observed in the asthmatic patients. The focus here is to demonstrate that guinea pig asthma models are useful for testing novel therapeutics.     

应用麻醉豚鼠对药物引起的QT间期延长的评价

目的为应用麻醉豚鼠评价药物引起的QT间期延长提供方法学验证。方法豚鼠分为5组:阳性对照索他洛尔(2,4和8mg·kg-1)、奎尼丁(3,10和30mg·kg-1)和西沙必利(0.3,1和3mg·kg-1)组;阴性对照维拉帕米(0.3,1和3mg·kg-1)和普萘洛尔(0.3,1和3mg·kg-1)组。豚鼠ip给予乌拉坦1.5g·kg-1麻醉后,各组按生理盐水→低→中→高剂量药物的顺序静脉滴注,滴注持续10min,每个剂量给药前留有30min的平衡时间;于给生理盐水前及静脉滴注各剂量药物后10min记录心电图。根据31只豚鼠给生理盐水前实际记录的QT及RR间期分别采用Bazzet公式、Fridericia公式和Van de Water公式进行校正QT(QTc)间期的计算,选择一个合适的校正公式,计算QTc,评价药物对QT和QTc间期的影响。结果分别使用3个公式计算31只豚鼠给药前的QTc与RR间期进行线性回归评价,Bazett公式为最佳校正公式。阳性对照药索他洛尔、奎尼丁和西沙必利剂量依赖性延长QT及QTc间期;而阴性对照药维拉帕米和普萘洛尔对QTc间期无明显影响。结论麻醉豚鼠可以作为一种评价受试物引起QT间期延长的动物模型。     

Chlordecone potentiation of CCl4 hepatotoxicity in ovariectomized rats

Previous reports from this laboratory have established the propensity of chlordecone to potentiate the hepatotoxicity and lethality in male and female rats. The present study was designed to investigate the hepatotoxicity of CCl4 in chlordecone (CD) pretreated, ovariectomized rats. Ten days after bilateral ovariectomy, the rats were maintained on a dietary protocol of either 0 or 10 ppm chlordecone and on the day 15, they received a single i.p. injection of either corn oil (1 ml/kg) or 25 microliter CCl4/kg in corn oil. Hepatic function, serum enzyme levels and histopathological changes were assessed 24 h after CCl4 challenge as functional biochemical, and morphological parameters of hepatotoxicity. Hepatobiliary function was markedly impaired and serum enzyme levels were elevated in ovariectomized rats receiving the same treatment but not significantly different from normal females receiving the chlordecone and CCl4 combination. Histological findings indicated a greater degree of centrilobular hepatic necrosis accompanied by extensive fatty infiltration. This study suggests that chlordecone sensitizes the liver in ovariectomized rats as well to amplify the toxic effects of CCl4.     

Isolated paced guinea pig left atrium: a new ouabain-induced arrhythmia model.

Ouabain (1.0 x 10(-6) M) produced a uniform, consistent and reproducible arrhythmia on paced guinea pig left atrium bathed in Ringer-Locke solution. A second spell of arrhythmia of similar intensity and pattern, which had the same latency to onset, was reproduced 60 min after the first spell of arrhythmia. Lignocaine (3.46 x 10(-5) M) and propranolol (1.69 x 10(-5) M) gave full protection against the second spell of arrhythmia, whereas lower doses of these drugs were able to delay the onset and reduce the duration. Clonidine (3.75 x 10(-5) M), however, was found to be ineffective. This model can be used for the detection and assessment of directly acting antiarrhythmics in very low concentrations, since this is a sensitive and reliable method.     

Therapeutic efficacy of a topical tolnaftate preparation in guinea pig model of tinea pedis

The therapeutic efficacy of a topical antifungal ointment containing 2% tolnaftate was studied in a guinea pig model of tinea pedis using the following four topical antifungal preparations commercially available as reference drugs: variotin (3,000 U/g ointment); phenyl-11-iodo-10-undecynoate (0.5% ointment); siccanin (1% ointment); and clotrimazole (1% cream). After the infection fully developed, the infected animals were treated twice daily with the testing drug or reference drug for consecutive four weeks. Therapeutic efficacy was mainly evaluated on the basis of the extent of the yield of fungal cultures from the infected skin tissues (infection intensity) at the end of the treatment period. In animal groups treated with tolnaftate as well as with three reference drugs, siccanin, phenyl-11-iodo-10-undecynoate and clotrimazole, the average infection intensity was significantly lower than that for untreated control group (P < 0.05-0.005) although no culture-negative animal was seen in any treated animal group. Comparing with all the reference drugs, tolnaftate was the most highly effective and there was significant difference in the average infection intensity between a tolnaftate treated and each reference drug-treated groups (P < 0.01-0.005). These results confirm the clinical usefulness of the current tolnaftate preparation in the treatment of patients with tinea pedis and probably other clinical forms of dermatophytoses.     

Antifungal effect of eugenol and nerolidol against Microsporum gypseum in a guinea pig model

Essential oils have been widely used in anti-infectious application. In the present study, we elucidated the antifungal activities of eugenol and nerolidol isolated from Japanese cypress oil in a guinea pig model infected by Microsporum gypseum (M. gypseum). A minimal inhibitory concentration (MIC), skin lesion scoring, hair culture and histopathologic examination of skin tissues were performed to evaluate the antifungal effect of these oils. The MICs of eugenol, nerolidol and econazole (positive control) were 0.01-0.03% and 0.5-2% and 4-16 microg/ml, respectively. Based on these MICs, eugenol and nerolidol were adjusted to 10% concentration with a base of Vaseline petroleum jelly and were applied topically to the skin lesion infected with M. gypseum daily for 3 weeks. Both eugenol and nerolidol were clinically effective at improving the lesion during the first week of application, as determined by skin lesion scoring. Nerolidol improved the skin lesions infected by M. gypseum, but eugenol did not, as determined in the hair culture test. Histopathologic examination revealed that the eugenol- and nerolidol-treated groups had a lower degree of hyperkeratosis and inflammatory cell infiltration than the positive control. Taken together, these results suggest that eugenol and nerolidol could apply supplementary antifungal agents.