Male Dunkin-Hartley Guinea Pigs Research Articles

Removal of the infrapatellar fat pad and associated synovium benefits female guinea pigs in the Dunkin Hartley model of idiopathic osteoarthritis.

Several tissues contribute to the onset and advancement of knee osteoarthritis (OA). One tissue type that is worthy of closer evaluation, particularly in the context of sex, is the infrapatellar fat pad (IFP). We previously demonstrated that removal of the IFP had short-term beneficial effects for a cohort of male Dunkin-Hartley guinea pigs. The present project was designed to elucidate the influence of IFP removal in females of this OA-prone strain. It was hypothesized that resection of the IFP would reduce the development of OA in knees of a rodent model predisposed to the disease. Female guinea pigs (n=16) were acquired at an age of 2.5 months. Surgical removal of the IFP and associated synovium complex (IFP/SC) was executed at 3 months of age. One knee had the IFP/SC resected; a comparable sham surgery was performed on the contralateral knee. All animals were subjected to voluntary enclosure monitoring and dynamic weight-bearing, as well as compulsory treadmill-based gait analysis monthly; baseline data was collected prior to surgery. Guinea pigs were euthanized at 7 months. Knees from eight animals were evaluated via histology, mRNA expression, and immunohistochemistry (IHC); knees from the remaining eight animals were allocated to microcomputed tomography (microCT), biomechanical analyses (whole joint testing and indentation relaxation testing), and atomic absorption spectroscopy (AAS). Fibrous connective tissue (FCT) replaced the IFP/SC. Mobility/gait data indicated that unilateral IFP/SC removal did not affect bilateral hindlimb movement. MicroCT demonstrated that osteophytes were not a significant feature of OA in this sex; however, trabecular thickness (TbTh) in medial femorae decreased in knees containing the FCT. Histopathology scores were predominantly influenced by changes in the lateral tibia, which demonstrated that histologic signs of OA were increased in knees containing the native IFP/SC versus those with the FCT. Similarly, indentation testing demonstrated higher instantaneous and equilibrium moduli in the lateral tibial articular cartilage of control knees with native IFPs. AAS of multiple tissue types associated with the knee revealed that zinc was the major trace element influenced by removal of the IFP/SC. Our data suggest that the IFP/SC is a significant component driving knee OA in female guinea pigs and that resection of this tissue prior to disease has short-term benefits. Specifically, the formation of the FCT in place of the native tissue resulted in decreased cartilage-related OA changes, as demonstrated by reduced Osteoarthritis Research Society International (OARSI) histology scores, as well as changes in transcript, protein, and cartilage indentation analyses. Importantly, this model provides evidence that sex needs to be considered when investigating responses and associated mechanisms seen with this intervention.

Experimental evaluation of the nonselective and selective TMEM16 family calcium-activated chloride channel blockers in the airways

Abstract Background The family of calcium-activated chloride channels, TMEM16, plays a significant role in contributing to the pathogenesis of airway inflammatory diseases. Targeting these ion channels and aiming to modulate them may provide an interesting new approach to the therapy of these potentially fatal diseases. Methods We tested this hypothesis in both healthy and ovalbumin (OVA)-sensitized male Dunkin-Hartley guinea pigs. The ion channel activity was modulated by TMEM16A-nonselective (benzbromarone) and TMEM16A-selective blockers (CaCCinh-A01). In vivo airway reactivity, induced by histamine and methacholine, was expressed as specific airway resistance (sRaw) values. The number of citric acid-induced coughs was counted using a double-chambered body plethysmograph, and the frequency of ciliary beating (CBF) was assessed in vitro by brushing method. For comparison, salbutamol and codeine were tested under the same conditions. Results The results showed significant differences in the responses of unsensitized and sensitized airways to both TMEM16 blockers administered. CaCCinh-A01 and benzbromarone significantly reduced the number of cough efforts in the group of OVA-sensitized guinea pigs. Significant improvement in sRaw values could be observed in OVA-sensitized TMEM16 blocker–treated animals compared to salbutamol when challenged with inhalational histamine, and the outcome was similar to salbutamol when challenged with methacholine. CBF was significantly inhibited in animals sensitized to OVA treated with selective inhibition of TMEM16A. Conclusions The results demonstrated that treatment with blockers of TMEM16 can reduce both cough effort and sRaw, and the difference between TMEM16A-selective and TMEM16A-nonselective blocking is only negligibly in favor of CaCCinh-A01. It is also worthwhile to note the impairment of CBF in OVA-sensitized animals treated with CaCCinh-A01.

Systemic administration of a pharmacologic iron chelator reduces cartilage lesion development in the Dunkin-Hartley model of primary osteoarthritis

Iron has been emerging as a key contributor to aging-associated, chronic disorders due to the propensity for generating reactive oxygen species. To date, there are a limited number of publications exploring the role of iron in the pathogenesis of primary/age-related osteoarthritis (OA). The objective of this study was to determine whether reduced iron via pharmacologic iron chelation with deferoxamine (DFO) affected the development and/or severity of cartilage lesions in a primary OA model. At 12-weeks-of-age, 15 male Dunkin-Hartley guinea pigs received either 46 mg/kg DFO (n = 8) or vehicle control (n = 7) injected subcutaneously twice daily for five days each week. Movement changes, captured via overhead enclosure monitoring, were also determined. Termination occurred at 30-weeks-of-age. Iron was quantified in serum, urine, liver, and femoral head articular cartilage. Left knees were evaluated for: structural changes using histopathology guidelines; and immunohistochemistry. Gene expression analysis was conducted on right knee articular cartilage. DFO reduced iron levels in femoral head articular cartilage (p = 0.0006) and liver (p = 0.02), and increased iron within urine (p = 0.04) and serum (p = 0.0009). Mobility of control animals declined, while the DFO group maintained activity levels similar to the first month of treatment (p = 0.05). OA-associated cartilage lesions were reduced in knees of DFO animals (p = 0.0001), with chondrocyte hypocellularity a key histologic difference between groups (p < 0.0001). DFO-receiving animals had increased immunostaining for phosphorylated adenosine monophosphate activated protein kinase alpha within knee articular cartilage; lower transcript counts of several proapoptotic genes (p = 0.04–0.0004) and matrix-degrading enzymes (p = 0.02-<0.0001), and increased expression of the anti-apoptotic gene Bcl-2 (p < 0.0001) and a tissue inhibitor of matrix-metalloproteinases (p = 0.03) were also observed. These results suggest that iron chelation delayed the progression of primary OA in an animal model and could hold potential as a translational intervention. These findings provide expanded insight into factors that may contribute to the pathogenesis of primary OA.

Defining matrix Gla protein expression in the Dunkin-Hartley guinea pig model of spontaneous osteoarthritis

BackgroundMatrix Gla (γ-carboxyglutamate) protein (MGP) is considered a strong inhibitor of ectopic calcification, and it has been associated with OA severity, although not conclusively. We utilized male Dunkin-Hartley (DH) guinea pigs to investigate the expression of MGP throughout aging and disease pathogenesis in a spontaneous model.MethodTwenty-five male DH guinea pigs were obtained and nurtured to several timepoints, and then randomly and equally divided by age into five subgroups (1-, 3-, 6-, 9-, and 12-months, with the 1-month group as the reference group). DH guinea pigs in each group were euthanized at the designated month-age and the left or right medial tibial plateaus cartilages were randomly excised. OA severity was described by modified Mankin Score (MMS) at microscopy (Safranin O/Fast Green stain). Proteomic evaluation using isobaric tags for relative and absolute quantification (iTRAQ) was performed to validate the age-related changes in the MGP profiles, and immunohistochemistry (IHC) methods were applied for semi-quantitative determination of MGP expression in articular cartilage.ResultsThe histopathologic findings validated the increasing severity of cartilage degeneration with age in the DH guinea pigs. The MMS showed significant, stepwise (every adjacent comparison P < 0.05) disease progression with month-age. The iTRAQ indicated that MGP levels increased significantly with advancing age (P < 0.05), as supported by the IHC result (P < 0.05).ConclusionIncreased expression of MGP in male DH guinea pigs was present throughout aging and disease progression and may be link to increased OA severity. Further studies are needed to investigate and confirm the association between MGP levels and OA severity.

Antitussive Activity of Herbal Cough Medicine on Guinea Pigs (Cavia porvellus)

This study aims to investigate the antitussive activity of herbal cough medicine containing combined herbal extracts of Echinacea purpurea, Sambucus nigra (Black Elderberry), Glycyrrhiza glabra (licorice), Vitex trifolia (Indian wild pepper), and Zingiber officinale (ginger). Antitussive assays were conducted on male Dunkin-Hartley albino guinea pigs (Cavia cobaya), which are divided into 5 groups, each with 8 individuals. These 5 groups were assigned for negative control group (treated with CMC-Na 0.5%), a positive control group (treated with Dextromethorphan 20 mg/kg BW), and three groups receiving herbal medicine with 3 different doses (Group I: 145 mg/kg BW, Group II: 290 mg/kg BW; Group III: 580 mg/kg BW, respectively). The antitussive activity was evaluated by using a citric acid-induced cough assay. For baseline level, 20 % m/v liquid citric acid was exposed using a nebulizer for 10 min, then the number of coughs in 15 min was counted. Sixty (60) minutes after oral administration of the tested herbal cough medicine, the number of citric acid-induced coughs was counted again to see the effect of herbal cough medicine to reduce cough. The number of coughs before and after herbal administration was calculated to obtain antitussive activity, represented by the percentage of cough suppression (PCS). Average PCS for each treatment group is then compared to control positive Dextromethorphan 20 mg/kg BW and control negative CMC-Na 0.5%. Data are analyzed by applying the one-way ANOVA method, which is followed by conducting a Tukey’s Test to discover differences between groups at 95% level of confidence. In terms of the percentage of cough suppression (PCS), treatment doses at 145mg/kg BW, 290 mg/kg BW and 580 mg/kg BW result in 58.48% ± 8.60% (Group I); 58.69% ± 7.96% (Group II); 59.21% ± 8.79% (Group III) PCS, respectively, which insignificantly differ to treatment with Dextromethorphan dose (66.99% ± 9.63 with p &gt; 0.05, implicating that the herbal cough medicine has comparable effect with dextromethorphan in the doses used in this study.

Pharmacologic iron chelation reduces markers of chondrocyte hypertrophy and osteoarthritis-associated cartilage lesions in an animal model of idiopathic disease

Purpose: It has previously been documented that chondrocytes from joints afflicted with osteoarthritis (OA) undergo improper dedifferentiation into hypertrophic chondrocytes; thus, it is postulated that this process may contribute to the progression of OA. Relative to unaffected adult chondrocytes, hypertrophic chondrocytes mimic cellular processes for endochondral ossification observed during initial development of long bones. In particular, they express markers of hypertrophic differentiation such as runx family transcription factor 2 (runx2), collagen type x, and the matrix degrading enzyme matrix metalloproteinase-13 (MMP-13). In addition to these markers, hypertrophic chondrocytes exhibit increased apoptosis, decreased autophagy, and promote cartilage vascularization and mineralization of the extracellular matrix. One theory for why this hypertrophic state occurs is that oxidative stress from reactive oxygen species (ROS) contributes to this shift in chondrocyte phenotype. We had previously demonstrated the ability of systemic iron reduction, achieved by an iron deficient diet, to reduce ROS production and thereby decrease structural changes of OA in an animal model of idiopathic/spontaneous disease. Given the success of this study, we hypothesized that systemic iron chelation - achieved by administration of the pharmacologic iron chelator deferoxamine (DFO) - would reduce markers of chondrocyte hypertrophy and decrease the development of knee OA in this animal model. Methods: All procedures received University approval and were performed in accordance with the NIH Guide for the Care and Use of Laboratory Animals. Three-month-old male Dunkin-Hartley guinea pigs were randomly assigned to receive either DFO or vehicle control (n=8 per group). Animals within the DFO group received 46 mg/kg of DFO injected subcutaneously twice daily while animals within the control group received an equivalent dose of saline. Animals were subjected to 10-minute sessions of open field behavior monitoring once per month for the duration of the study, with baseline activity levels collected prior to initiating treatment. The study was terminated when animals were 8-months-old, at which time body weights were recorded. Hind limbs were removed and the right tibia was measured using calipers. Articular cartilage was collected from the right knee joint for gene expression analysis using Nanostring nCounter technology. Femoral head cartilage and liver tissue were collected for iron quantification by atomic absorption spectroscopy. Left knee joints were formalin-fixed, paraffin-embedded, and stained with toluidine blue. For histologic analysis, all joint compartments were blindly scored by two assessors using OARSI published guidelines. Data were compared using non-parametric Mann-Whitney U tests, Welch’s t-tests, or unpaired student’s t-tests as appropriate given the normality and heteroscedasticity of the data. All statistical analyses were performed with Prism 8.0; statistical significance was set at P≤0.05. Results: No significant differences in body weight (p=0.576) or tibia length (p=0.628) were present between groups. As anticipated, animals treated with DFO had lower levels of iron within the liver (p=0.0218) and articular cartilage (p=0.0005) tissue than control animals. Histologic grading of knee joints confirmed that animals treated with DFO had lower total joint OA scores than control animals (p<0.0001). Gene transcript analysis demonstrated that, relative to controls, animals treated with DFO had lower expression of runx2 (p=0.0010), MMP-13 (p=0.0151), vascular endothelial growth factor (VEGF; p=0.0140), β- catenin (p<0.0001), wnt (p=0.0008), mammalian target of rapamycin (mTOR; p=0.0018), and the serine/threonine protein kinase AKT (p=0.0041). Animals treated with DFO also had increased expression of b cell lymphoma 2 (BCL-2; p<0.0001), a prototypical anti-apoptotic marker. There was no significant difference in the gene expression of collagen type x between groups (p=0.3163). Open field behavior monitoring indicated that DFO treated animals maintained their baseline activity level throughout the study, while the movement of control animals declined throughout the study. Conclusions: Administration of a pharmacologic iron chelator was successful in reducing iron levels both systemically and within articular cartilage tissue, which was associated with a reduced development of OA-associated cartilage lesions and maintained mobility in these animals. Gene transcript analysis of cartilage tissue revealed that DFO treated animals had a decreased expression of: select markers of chondrocyte hypertrophy (runx2 and MMP-13), negative regulators of autophagy (AKT and mTOR), the angiogenesis promoter VEGF, and genes associated with chondrocyte dedifferentiation (β- catenin and wnt); while displaying increased expression of the anti-apoptotic protein BCL-2. These results indicate that removal of excess iron may help prevent chondrocyte hypertrophy and development of OA-related changes within the cartilage of knee joints.

Effects of COX inhibitors on responsiveness of the tracheal tract to acetylcholine and histamine and their relationship with LTC4 and PGE2 levels of bronchoalveolar lavage fluid in allergic Guinea pigs

Introduction: Nonsteroidal anti-inflammatory drugs (NSAIDs) intervene in the COX (cyclooxygenase) pathways which generate two important inflammation mediators, prostaglandins (PGs) and leukotriene (LTs). Contradictory claims regarding the effect of NSAIDs in asthmatic patients continues to be an issue. The present study investigated the effects of COX inhibitors on the responsiveness of the tracheal tract and on the levels of LTC4 and PGE2 in cells of the bronchoalveolar lavage fluid in an allergic guinea pig model.Materials and Methods: Adult male Dunkin-Hartley guinea pigs (250 − 300 g) were divided into seven groups of six animals each. Four COX inhibitors, aspirin (200 mg/kg and 20 mg/kg), indomethacin (10 mg/kg), ketoprofen (10 mg/kg), and celecoxib (25 mg/kg), were given orally on day 17 to allergy induced guinea pigs at 0, 12, and 24 h before ovalbumin challenge on day 18. PGF2 and LT4 were measured in the bronchoalveolar lavage fluid as well as inflammatory cell count and total protein. Tracheal responsiveness to acetylcholine (Ach) and histamine (His) also was evaluated.Results: An augment in the response of the trachea to Ach and His, as well as overt allergenic signs including short breath, wheezing and sneezing, was observed. The most significant increase in tracheal hyper-responsiveness was observed in the ketoprofen-treated group with similar but less pronounced changes observed in the indomethacin-treated group. Although some variables increased with the aspirin and celecoxib treatments, overall the tracheal sensitivity was reduced. Inflammatory cells including eosinophils and neutrophils corresponded to the changes observed for each treatment group.Conclusion: Ketoprofen and indomethacin increased the tracheal sensibility to Ach and His; therefore, their administration is not recommended in patients susceptible to allergy.

PHARMACOKINETIC COMPARISON OF MONTELUKAST SODIUM FORMULATIONS AFTER A SINGLE ORAL DOSE IN HEALTHY GUINEA PIGS

Objective: Pharmacokinetic evaluation of montelukast sodium chronomodulated capsules (sustained-release solid dispersion of drug enclosed in pH-sensitive film-coated hard gelatin shell) and marketed tablets has been carried out in this study.&#x0D; Methods: A single oral dose of prepared capsules and marketed conventional tablets was administered in healthy male Dunkin-Hartley albino guinea pigs. Blood samples were collected at different time intervals and plasma concentration of drug was determined by reversed-phase high-performance liquid chromatography. Different pharmacokinetic parameters were assessed from plasma drug concentration-time profile by one-compartment model, first-order kinetics.&#x0D; Results: Pharmacokinetic parameters such as time to reach maximum concentration, elimination rate constant, elimination half-life, and mean residence time data indicates that drug release from chronomodulated capsules is significantly prolonged with initial release lag time of 3.5–4 h in comparison with marketed conventional tablets. However, maximum drug plasma concentration, area under the concentration-time curve, and apparent volume of distribution values show non-significant difference between capsules and marketed tablets.&#x0D; Conclusion: The findings specified that capsules were providing time controlled delivery of drug at a desired rate for prolonged time, which may be helpful for the prevention of episodic attack of asthma in early morning hours.

The protective effect of α-hederin, the active constituent of Nigella sativa, on tracheal responsiveness and lung inflammation in ovalbumin-sensitized guinea pigs

Many investigations have demonstrated the prophylactic effect of Nigella sativa on asthma disease. One of its active constituents is α-hederin. In the present study, the preventive effect of two different concentrations of α-hederin on tracheal responsiveness and lung inflammation in ovalbumin-sensitized guinea pigs was examined. Forty male adult Dunkin-Hartley guinea pigs were randomly divided into the control (C), sensitized (S) and sensitized pretreated groups with thymoquinone (3 mg/kg i.p., S + TQ), low-dose α-hederin (0.3 mg/kg i.p., S + LAH) and high-dose α-hederin (3 mg/kg i.p., S + HAH). The responsiveness of tracheal smooth muscle (TR) to methacholine, histamine and ovalbumin was assessed. Moreover, total and differential white blood cell counts in lung lavage fluid were examined. Compared with the S group, the mean EC50 value in the S + LAH group increased significantly (p < 0.05). The mean EC50 value of histamine contraction in the S + LAH and S + HAH groups was significantly higher than in the S group (p < 0.05). In all pretreated groups, the TR to ovalbumin decreased in comparison to the S group (p < 0.001). Both the S + HAH and S + LAH groups showed significantly decreased TR compared to the S + TQ group (p < 0.01-p < 0.01). Total WBC and eosinophil counts in all pretreated groups decreased significantly in comparison with the S group (0.001-0.01). There was a significant increase in neutrophil, lymphocyte and monocyte counts in the pretreated groups compared to the S group (p < 0.001-p < 0.05). The basophil count in the S + TQ and S + HAH groups was significantly lower than in the S group (p < 0.01-p < 0.05). This study suggested that α-hederin has anti-inflammatory and bronchodilatory effects like thymoquinone.

Morphine glucuronidation increases its analgesic effect in guinea pigs

AimsMorphine is extensively metabolized to neurotoxic morphine-3-glucuronide (M3G) and opioid agonist morphine-6-glucuronide (M6G). Due to these different roles, interindividual variability and co-administration of drugs that interfere with metabolism may affect analgesia. The aim of the study was to investigate the repercussions of administration of an inducer (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) and an inhibitor (ranitidine) of glucuronidation in morphine metabolism and consequent analgesia, using the Guinea pig as a suitable model. Main methodsThirty male Dunkin–Hartley guinea pigs were divided in six groups: control, morphine, ranitidine, ranitidine+morphine, TCDD and TCDD+morphine. After previous exposure to TCDD and ranitidine, morphine effect was assessed by an increasing temperature hotplate (35–52.5°C), during 60min after morphine administration. Then, blood was collected and plasma morphine and metabolites were quantified. Key findingsAnimals treated with TCDD presented faster analgesic effect and 75% reached the cut-off temperature of 52.5°C, comparing with only 25% in morphine group. Animals treated with ranitidine presented a significantly lower analgesic effect, compared with morphine group (p<0.05). Moreover, significant differences between groups were found in M3G levels and M3G/morphine ratio (p<0.001 and p<0.0001), with TCDD animals presenting the highest values for M3G, M6G, M3G/morphine and M6G/morphine, and the lowest value for morphine. The opposite was observed in the animals treated with ranitidine. SignificanceOur results indicate that modulation of morphine metabolism may result in variations in metabolite concentrations, leading to different analgesic responses to morphine, in an animal model that may be used to improve morphine effect in clinical practice.

Infusion rate and plasma volume expansion of dextran and albumin in the septic guinea pig

Intravenous fluid treatment of hypovolaemia in states of increased capillary permeability, e.g. sepsis, is often accompanied by adverse oedema formation. A challenge is therefore to achieve and maintain normovolaemia using as little plasma volume substitution as possible to minimise interstitial oedema. In the present study, we evaluated the importance of infusion rate for the plasma volume expanding effects of 6% dextran 70 and 5% human albumin in a guinea pig sepsis model. In this prospective, randomised study, 50 anaesthetised adult male Dunkin-Hartley guinea pigs were used. After laparotomy, sepsis was induced by caecal ligation and incision. Three hours later, an infusion (12 ml/kg) of one of the studied fluids was given either over 15 min (bolus group) or over 3 h (continuous group). A sham group underwent the same surgical procedure but did not receive any fluid. At the end of the experiment 3 h after the start of infusion, plasma volumes in the continuous group and the bolus group, respectively, were: 47.2 ± 5.3 ml/kg and 36.5 ± 3.9 ml/kg (P < 0.001) for 6% dextran 70, and 47.3 ± 7.5 ml/kg and 39.7 ± 2.8 ml/kg (P < 0.01) for 5% albumin. Plasma volume for the sham group at the same time point was 29.9 ± 3.3 ml/kg. The study performed on a guinea pig sepsis model showed that the plasma volume expanding effects of fixed volumes of 6% dextran 70 and 5% albumin were greater when given at a slow than at a fast infusion rate.

Animal models of cough: Literature review and presentation of a novel cigarette smoke-enhanced cough model in the guinea-pig

A wealth of literature describes the approaches that investigators have used to develop animal models of cough. The relevance of the models to cough in man and disease is still unknown. Furthermore, the choice of animal model that is used will depend on the purpose of the investigation and what questions are being asked. Cigarette smoke is known to cause COPD and cough is a principle symptom where patients demonstrate an increased cough response to citric acid or capsaicin. This paper describes the development of exacerbated cough to these agents in the guinea-pig following cigarette smoke exposure and pharmacological profiling of these models. Male Dunkin–Hartley guinea-pigs were exposed to air or cigarette smoke (4 or 5 research cigarettes daily for the capsaicin and citric acid studies, respectively) for a 3 s puff every 30 s, for up to 10 days. At selected time points conscious, unrestrained animals were placed in a plethysmograph chamber and challenged with an aerosol of 0.3 M citric acid (10 min) or 10 μM capsaicin (7 min). Cough and Penh area under the curve (AUC) were recorded during the exposure and for a further 10 min (citric acid) or 8 min (capsaicin) after exposure. Compounds were administered on day 3 or 11 for citric acid or capsaicin, respectively. Significant enhancement of citric acid-induced cough was evident 24 h (12±2 to 24±4 * coughs) after a single exposure and further enhanced after 2 days (13±3 to 36±4 * coughs). Enhanced cough to capsaicin was not reliable until after 10 days of cigarette smoke exposure (2±1 to 14±3** coughs). Data are expressed as mean±s.e.mean ( n=10), * p<0.05, ** p<0.01 vs. air-exposed animals (Mann–Whitney rank-sum test). The minimum effective doses to inhibit citric acid-induced cough were 10, 10, 3 and 0.3 mg/kg for codeine (p.o. −30 min), a selective NK 1/NK 2 antagonist, DNK333 (p.o. −2 h), terbutaline (s.c. −1 h) and atropine (s.c. −1 h), respectively. The minimum effective doses to inhibit capsaicin-induced cough were 3, 1, 0.3 and 0.3 mg/kg for codeine, DNK333, terbutaline (p.o. −2 h) and atropine, respectively. The VR1 antagonists capsazepine and iodo-resiniferatoxin (IRTX) did not inhibit cough in either model. Differences in sensitivity between citric acid and capsaicin to pharmacological agents may be partly explained by the difference in magnitude of response to these agents. Clinically used compounds such as codeine and terbutaline have shown activity in both models, however the relevance of the models to cough in man and disease for potential new therapies is unknown.

Age-Related Three-Dimensional Microarchitectural Adaptations of Subchondral Bone Tissues in Guinea Pig Primary Osteoarthrosis

We explored potential mechanisms of the microarchitectural adaptations of subchondral bone tissues in a guinea pig primary osteoarthrosis (OA) model. We harvested proximal tibiae of male Dunkin-Hartley (Charles River strain) guinea pigs at 3, 6, 9, 12, and 24 months of age (10 in each group). These proximal tibiae were scanned by micro-computed tomography to quantify the three-dimensional microarchitecture of the subchondral plate, cancellous bone, and cortical bone. Subsequently, the bones were compression-tested to determine their mechanical properties. Furthermore, bone collagen, bone mineral, and bone density were determined. Mankin's score corresponded to OA grading from absent or minimal cartilage degeneration in 3-month-old to severe degeneration in 24-month-old guinea pigs. In young guinea pigs, the volume fraction and thickness of the subchondral plate markedly increased from 3 to 6 months, whereas the volume fraction of the subchondral cancellous bone displayed an initial decline followed by an increase. With age, the trabeculae increased in thickness, changed from rod-like to plate-like, and became more axially oriented. An increasing ratio of bone collagen to mineral in subchondral bone indicated undermineralized bone tissues. In subchondral cancellous bone, Young's modulus was maximal at 6 months of age, whereas ultimate stress and failure energy showed a gradual increase with age. The findings show pronounced alterations of the microarchitecture and bone matrix composition of the subchondral bone. These alterations did not appear to follow the same pattern as in normal aging and may have different influences on the resulting mechanical properties.

Postnatal growth in male Dunkin–Hartley guinea pigs ( Cavia cutleri f. porcellus)

Summary The aim of the present study was to describe postnatal organ and body weight growth in male Dunkin–Hartley guinea pigs from birth to 250 days of age. The modified JANOSCHEK growth curve was fitted to the age group means for each measurement by nonlinear regression and characteristics of the resulting growth curves were calculated. At birth, brain weight showed the highest percentage of its adult value (59%), followed by eye weight (37%). Lowest percentage birth weights were found for genital organs, adrenals and pancreas, the majority of organs showed values between 4% and 15%. Weights of body, heart, spleen, liver, genital organs, thyroids and adrenals followed a sigmoidal growth course. The remaining, as examined in this study, organs exhibited simple exponential growth without a postnatal point of inflection. Among internal organs, brain weight reaches adult size first (74 days of age). Genital organs with exception of prostate, duodenum, heart and spleen are fast-growing organs, too.

The differential effect of VIP and PACAP on guinea pig gallbladder in vitro.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a recently identified member of the secretin/glucagon/vasoactive intestinal peptide (VIP) family. Like VIP, PACAP is largely inhibitory in the gastrointestinal tract. The aim of our work was to characterize the effects of PACAP on both contraction and relaxation of guinea pig gallbladder (GPGB) muscle. Gallbladder muscle strips were obtained from male Dunkin-Hartley guinea pigs (250-350 g). Isometric tension was measured in strips suspended in gassed (95% O2, 5% CO2) Krebs' solution at 37 degrees C and equilibrated for 60 min. Cumulative additions of VIP or PACAP (10(-9)-10(-6) mol/l) were performed with strips at basal tone or with strips pre-contracted with cholecystokinin-octapeptide (CCK-8). VIP had no effect on basal tone, in contrast with PACAP which produced concentration-dependent contraction to a maximum of 57.9 +/- 24.3% of control (CCK 3 x 10(-7) mol/l). The highest concentration (10(-6) mol/l) of VIP produced a 32 +/- 6% relaxation of 3 x 10(-9) mol/l CCK-8-contracted GPGB. With 3 x 10(-8) mol/l CCK-contracted GPGB strips, VIP produced a 26.7 +/- 6.6% relaxation. PACAP produced a further concentration-dependent contraction of 3 x 10(-9) mol/l CCK-contracted strips which reached 17.5 +/- 9.9% at the maximal concentration used (10(-6) mol/l). PACAP produced a concentration-dependent relaxation of 3 x 10(-8) mol/l CCK-contracted strips which reached a maximum relaxation of 19 +/- 5% of the control. PACAP has a dual effect on guinea pig gallbladder motility in vitro, producing contraction in the basal state, and both contraction and relaxation in the CCK-contracted state. This is in contrast to the effects of VIP, a closely related peptide.

OZONE-INDUCED DNA STRAND BREAKS IN GUINEA PIG TRACHEOBRONCHIAL EPITHELIAL CELLS

Ozone (O3), the major oxidant of photochemical smog, is thought to be genotoxic and a potential respiratory carcinogen or promoter of carcinogenic processes. Because of oxidative reactions with the mucus in the upper airway, O3 reaction products are able to penetrate into the tracheobronchial epithelial (TE) cells. The carcinogenic effects of O3 on the TE cells are especially of interest since most previous studies have focused on the morphology or permeability changes of tracheas only. Therefore, the objective of this study was to examine the potential O3 genotoxicity in TE cells after an in vivo exposure, using DNA strand breaks as an index. Two-month-old male Dunkin-Hartley guinea pigs, specific pathogen free, 4 in each group, were exposed to 1.0 ppm 03 for 0, 12, 24, 48, 72, or 96 h. Animals exposed to filtered air without 03 exposure were used as controls. After O3 exposure, the trachea with two main bronchi was removed from each animal, and TE cells were isolated and employed for determination of DNA strand breaks by fluorometric analysis of DNA unwinding (FADU). The statistical significance level was set at a=.05. Compared with controls, ozone exposure did not alter the TE cell yield or viability, but caused an increase in protein content in tracheal lavage and an increase in DNA strand breaks. The amount of DNA left in the alkali lysate of TE cells found at 72 h exposure was significantly decreased from controls for 3 different alkali incubation times. An increase of the double-stranded DNA left in the alkali lysate of TE cells was observed at 96 h of exposure and approached the value of 24 h of exposure. The same pattern was seen with all 3 different alkali incubation times at 15°C. One Qd unit was estimated to correspond to 100 strand breaks per cell. The Qd was also used as an indicator for 03 damage. Compared to controls, the Qd increases significantly after 1 ppm 03 exposure for 72 h, regardless of the alkali incubation time at 15°C.

The effects of NK1 receptor antagonists (FK224 and FK888) on agonist- and antigen-induced nasal microvascular leakage in guinea pigs.

To study the inhibitory effects of two NK1 receptor antagonists on substance P (SP) and antigen-induced increase of nasal vascular permeability in ovalbumen (OA)-sensitized guinea pigs. Male Dunkin-Hartley guinea pigs. SP (100 mumol/l), FK224 (1-10 mumol/kg) and FK888 (0.2-2 mumol/kg). The in vivo model of nasal microvascular leakage was used for nasal allergic challenge in ovalbumin (OA)-sensitized guinea pigs, or nasal stimulation with substance P (SP) in non-sensitized animals. Nasal microvascular leakage was measured by the accumulation of Evans Blue dye after intravenous injection. Following nasal stimulation with SP 100 microM, the concentration of dye in the nasal lavage fluid rapidly increased. NK1 receptor antagonists FK224 (10 mumol/kg i.v.) and FK888 (2 mumol/kg i.v.) inhibited SP-induced microvascular leakage. In OA-sensitized guinea pigs, exudation of dye into nasal lavage fluid was observed soon after topical antigenic stimulation and continued for over 60 min. Both NK1 receptor antagonists inhibited the immediate phase of the antigen-induced microvascular leakage. We conclude that the immediate change of vascular permeability during the nasal allergic response is mediated by activation of the NK1 receptor in the guinea-pig.

MR protocols for imaging the guinea pig knee

Magnetic resonance images of the femorotibial joints of male Dunkin-Hartley guinea pigs were obtained in two and three dimensions at 2.35 T using a wide range of T 1 - and T 2 -weighted imaging sequences. The effect of slice position on visualisation of articular cartilage, bone and periarticular tissues in sagittal and coronal sections was investigated along with the resolution and signal/noise ratio achievable. Based on that survey, a two-dimensional spin echo sequence (repetition time = 1500 ms, echo time = 40 ms) was found to give optimum visualisation of the normal joint anatomy with in-plane resolution of 75 × 150 μm and a 1 mm slice thickness in an imaging time of 25 min. This protocol was also found to be highly effective in distinguishing many features of the spontaneous, osteoarthritic-like pathology found in the joints of older animals compared to juveniles and therefore provides a means of monitoring disease progression longitudinally. Three-dimensional spin echo imaging methods demonstrated focal changes in signal intensity in the articular cartilage of the medial tibial plateau in older animals. The resulting imaging times of several hours, however, precludes their routine use in vivo.

Cartilage swelling and loss in a spontaneous model of osteoarthritis visualized by magnetic resonance imaging

The objective of this study was to investigate whether the rate of change in cartilage pathology could be effectively monitored by magnetic resonance imaging (MRI) as part of a longitudinal investigation of an osteoarthritis model in vivo, and to define the minimum requirements necessary to establish disease progression. Magnetic resonance images of the knee of eight male Dunkin-Hartley guinea-pigs were obtained at 8, 12, 18, 24, 30, 36 and 52 weeks of age using a two-dimension spin-echo sequence with a TR of 1500 ms and TE of 40 ms. The total thickness of the femoral and tibial cartilage was measured from those images. Over the same time course, sets of spin-spin relaxation-weighted images were acquired from two additional animals of the same age, from which the T2 relaxation times of water in the articular cartilage were estimated and compared with those of muscle and adipose tissue within the same joint. The cartilage thickness of all the animals increased during the first 6 months, then either stayed thicker (4/8) or became progressively thinner (4/8). Up to 18 weeks of age, the cartilage T2 value was between 23-24 ms but became elevated by 30 weeks and the mean value was more than 40 ms at the end of the study, T2 values for the muscle and adipose tissue remained within the range 30-33 ms, or 47 ms, respectively. We concluded that in this model, cartilage thickness measurements from an magnetic resonance image would not provide a reliable marker to stage osteoarthritis progression partly because the cartilage was so thin in a joint of this size, but also because the changes with time were not linear but biphasic. However, quantitation of the T2 relaxation values may provide a more predictable indicator of cartilage pathology for longitudinal studies because the changes were monotonic and independent of cartilage thickness.

Use of Precision-Cut Liver Slices to Evaluate Species Differences in 2-Acetylaminofluorene-Induced Unscheduled DNA Synthesis

Precision-cut liver slices were prepared from male Sprague–Dawley rats (pretreated with or without Aroclor 1254), male Dunkin–Hartley guinea pigs, male cynomolgus monkeys, and humans. Liver slices were cultured for 24 hr using a dynamic organ culture system in medium containing [3H]thymidine and 2-acetylaminofluorene (2-AAF), aflatoxin B1(AFB1), or 6-aminochrysene (6-AC). The liver slices were then harvested and processed for autoradiographic evaluation of unscheduled DNA synthesis (UDS). All three genotoxins induced UDS in liver slices from untreated and Aroclor 1254-treated rats. In human liver slices 2-AAF produced a concentration-dependent induction of UDS and at the highest concentration examined 2-AAF also induced UDS in guinea pig liver slices. However, 2-AAF did not induce UDS in cynomolgus monkey liver slices, although both AFB1and 6-AC induced UDS in liver slices from this species as well as from guinea pigs and humans. The inability of 2-AAF to induce UDS in cynomolgus monkey liver slices appears to be at least partially due to the absence of hepatic CYP1A2 in this species. Precision-cut liver slices appear to be a useful alternative to primary hepatocyte cultures for studies of xenobiotic-induced genotoxicity employing the UDS technique. As shown by this study they may also be employed to evaluate species differences in xenobiotic-induced genotoxicity.