Increased expression of cyclooxygenase-2 in rat lung tumors induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanone: the impact of a high-fat diet.
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Aberrant or excessive expression of cyclooxygenase (COX)-2 has been implicated in the pathogenesis of many disease processes, including carcinogenesis. COX-2 expression was immunohistochemically examined in archival samples (D. Hoffmann et al., Cancer Res., 53: 2758-2761, 1993) of lung neoplasms (adenomas, adenocarcinomas, and adenosquamous carcinomas) induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in male F344 rats that had been fed either a semipurified AIN-76A diet with high-fat (HF; 23.5% corn oil) or low-fat (LF; 5% corn oil) content. The intensity and extent of COX-2 positivity was graded from 0 (undetectable or negligible expression) to grades 1 (<30% expression), 2 (30-60% expression), 3 (60-90% expression), and 4 (>90% expression). The scoring criteria were similar to those used with specimens from human lung cancers (T. Hida et al., Cancer Res., 58: 3761-3764, 1998). In group 1 (NNK plus HF diet), adenomas, adenocarcinomas, and adenosquamous carcinomas were of mean grades 2, 3, and 4, respectively; in group 2 (NNK plus LF diet), the corresponding mean grades were 1, 1, and 3. Although control rats, given HF (group 3) or LF (group 4) diets but no NNK, developed spontaneous lung tumors, the expression of COX-2 was either negligible (one adenoma of grade 0 in group 3) or of a very low grade (one adenocarcinoma of grade 1 in group 4). In addition, the latency of the tumors in the peripheral lung in assays with NNK is significantly shorter in rats maintained on the HF diet than in those on LF diet. COX-2 expression was not evident in normal lung tissues. We report here for the first time that NNK induces increasingly higher levels of COX-2 expression with progressive stages of lung tumorigenesis when rats are fed the HF diet. The increase in COX-2 expression may be associated with the development of lung tumors induced by NNK. This well-defined animal model is valuable for studying modulation of COX-2 expression in lung carcinogenesis by various factors, including dietary components. (+info)
Effect of calorie restriction on in vivo glucose metabolism by individual tissues in rats.
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We evaluated the effects of 8 mo of calorie restriction [CR: 60% of ad libitum (AL) food intake] on glucose uptake by 14 tissues in unanesthetized, adult (12 mo) F344xBN rats. Glucose metabolism was assessed by the 2-[3H]deoxyglucose tracer technique at 1500 or 2100. Despite an approximately 60% decline in insulinemia with CR, plasma 2-[3H]deoxyglucose clearance for CR was greater than for AL at both times. A small, CR-related decrease in glucose metabolic index (R'g) occurred only at 1500 in the spleen and heart, and this decrease was reversed at 2100. In some tissues (cerebellum, lung, kidney, soleus, and diaphragm), R'g was unaffected by diet, regardless of time. In the other tissues (brown fat, 3 white fat pads, epitrochlearis, plantaris, and gastrocnemius), R'g was higher or tended to be higher for CR vs. AL at one or both times. These findings indicate that 8 mo of CR did not cause a continuous reduction in in vivo glucose uptake by any tissue studied, and, in several insulin-sensitive tissues, glucose uptake was at times greater for CR vs. AL rats. (+info)
Susceptibility of Lewis and Fischer rats to stress-induced worsening of TNB-colitis: protective role of brain CRF.
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We assessed the role of central corticotropin-releasing factor (CRF) in stress-induced worsening of colitis in inbred rat strains with hypo (Lewis/N) and hyper (Fischer344/N) CRF responses to stress. Intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid (TNB) induced colitis of similar severity in both strains as assessed on day 7 by macroscopic scoring, histological evaluation, tissue myeloperoxidase (MPO) activity, and decrease in food intake and body weight. Colitis was inhibited by daily intracerebroventricular injections of CRF in both strains. Chronic stress (3 h/day, water avoidance or wrap restraint on alternate days for 6 days) aggravated colitis more in Lewis than Fischer rats (71 and 22% further increase in MPO activity, respectively). The CRF antagonist astressin injected intracerebroventricularly enhanced the colitis response to stress and caused mortality in both strains. Fischer rats had higher plasma corticosterone levels 20 min after stress alone on day 1 and after TNB plus stress on days 1 and 3 compared with Lewis. These data show that central CRF restrains the proinflammatory action of stress in experimental colitis. (+info)
Organic cation transport in rat choroid plexus cells studied by fluorescence microscopy.
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Quinacrine uptake and distribution were studied in a primary culture of rat choroid plexus epithelial cells using conventional and confocal fluorescence microscopy and image analysis. Quinacrine rapidly accumulated in cells, with steady-state levels being achieved after 10-20 min. Uptake was reduced by other organic cations, e.g., tetraethylammonium (TEA), and by KCN. Quinacrine fluorescence was distributed in two cytoplasmic compartments, one diffuse and the other punctate. TEA efflux experiments indicated that more than one-half of intracellular organic cation was in a slowly emptying compartment. The protonophore monensin both emptied that TEA compartment and abolished punctate quinacrine fluorescence, suggesting that a large fraction of total intracellular organic cation was sequestered in acidic vesicles, e.g., endosomes. Finally, quinacrine-loaded vesicles were seen to move within the cytoplasm and to abruptly release their contents at the blood side of the cell; the rate of release was greatly reduced by the microtubule disrupter nocodazole. (+info)
Estradiol modulates vascular response to melatonin in rat caudal artery.
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The purpose of this study was to determine whether estrogen modulates the function of vascular melatonin receptors. We used the rat caudal artery and found that the contractile effects of melatonin were influenced by the estrous cycle, ovariectomy, and estrogen replacement. In arterial ring segments isolated from female rats, melatonin potentiated, in a concentration-dependent manner, contractions produced either by adrenergic nerve stimulation or by phenylephrine. Constrictor responses to melatonin were smaller in arteries from female rats in proestrus compared with other stages of the estrous cycle and after ovariectomy. Administration of 17beta-estradiol to ovariectomized female rats also resulted in decreased constriction of isolated arteries to melatonin; however, in vitro addition of 17beta-estradiol (10(-7) M) had no effect. In the caudal artery, melatonin appears to act on two receptor subtypes that mediate contraction and relaxation, respectively. The selective melatonin MT2-receptor antagonist 4-phenyl-2-propionamidotetraline (4P-PDOT) enhanced constrictor responses to melatonin in arterial segments from intact female rats, consistent with the inhibition of MT2 receptor-mediated relaxation. In contrast, 4P-PDOT had no significant effect in arteries from ovariectomized female rats. However, when estradiol was replaced in vivo, the effect of 4P-PDOT on melatonin responses was restored. Thus circulating estradiol appears to enhance MT2 melatonin-receptor function in the thermoregulatory caudal artery of the female rat resulting in increased vasodilatation in response to melatonin. (+info)
Cancer chemopreventive mechanisms of tea against heterocyclic amine mutagens from cooked meat.
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Cooking meat and fish under normal conditions produces heterocyclic amine mutagens, several of which have been shown to induce colon tumors in experimental animals. In our search for natural dietary components that might protect against these mutagens, it was found that green tea and black tea inhibit the formation of heterocyclic amine-induced colonic aberrant crypt foci (ACF) in the rat. Since ACF are considered to be putative preneoplastic lesions, we examined the inhibitory mechanisms of tea against the heterocyclic amines. In the initial studies using the Salmonella mutagenicity assay, green tea and black tea inhibited according to the concentration of tea leaves during brewing and the time of brewing; a 2-3-min brew of 5% green tea (w/v) was sufficient for >90% antimutagenic activity. N-hydroxylated heterocyclic amines, which are direct-acting mutagens in Salmonella, were inhibited by complete tea beverage and by individual components of tea, such as epigallocatechin-3-gallate (EGCG). Inhibition did not involve enhanced mutagen degradation, and EGCG and other catechins complexed only weakly with the mutagens, suggesting electrophile scavenging as an alternative mechanism. Enzymes that contribute to the metabolic activation of heterocyclic amines, namely microsomal NADPH-cytochrome P450 reductase and N, O-acetyltransferase, were inhibited by tea in vitro. Studies in vivo established that tea also induces cytochromes P450 and Phase II enzymes in a manner consistent with the rapid metabolism and excretion of heterocyclic amines. Collectively, the results indicate that tea possesses anticarcinogenic activity in the colon, and this most likely involves multiple inhibitory mechanisms. (+info)
Latent Pneumocystis carinii infection in commercial rat colonies: comparison of inductive immunosuppressants plus histopathology, PCR, and serology as detection methods.
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Histopathologic evaluation combined with a period of immunosuppression has been the standard procedure for detection of Pneumocystis carinii in commercial rat colonies. Variation in induction regimens and in the sensitivity of detection methods may result in underreporting of the presence of P. carinii in breeding colonies or delay its detection. In the present study, methylprednisolone and cyclophosphamide were evaluated for the ability to induce P. carinii infection in rats from an enzootically infected commercial barrier colony. The presence of P. carinii was detected by histopathologic methods and by amplification of a targeted region of the P. carinii thymidylate synthase gene by PCR over the 8-week study period. Sera taken from rats prior to either induction regimen were evaluated for the presence of P. carinii-specific antibodies by the immunoblotting technique. Few significant differences in ability to induce organism burden or in histopathology were observed between the two immunosuppressive regimens. However, a dramatic loss of weight over the study period was observed in rats treated with methylprednisolone but not in rats treated with cyclophosphamide. Although histopathologic changes attributable to P. carinii did not appear before 2 weeks with either immunosuppressant, the presence of the organism in these animals was detected by immunoblotting and PCR. Cyst scores and the intensities of the histopathologic lesions increased during the study period, but the number of rats exhibiting evidence of P. carinii infection did not change after week 3. These results suggest that use of the PCR method on postmortem lung tissue of rats without prior induction regimens or identification of anti-P. carinii antibodies in antemortem serum samples is a sufficiently sensitive method for detection of the presence of a P. carinii carrier state in rodent breeding colonies. (+info)
Genetic determination of cardiac mass in normotensive rats: results from an F344xWKY cross.
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Genetic determinants affect adult cardiac mass and the predisposition to develop cardiac hypertrophy. The aim of this study was to identify quantitative trait loci (QTL) that control heart and left ventricular (LV) weight by use of normotensive inbred rat strains that differ in their adult cardiac mass phenotype. We studied 126 male F2 rats derived from a cross of normotensive Wistar-Kyoto and Fischer 344 rats. At 12 weeks of age, total heart weight and LV weight were measured. Genomic DNA from these animals was screened by use of polymorphic microsatellite markers across the whole genome (excluding the sex chromosomes). In this cross, the genetic contribution to total heart weight variation was 56%, and the genetic contribution for LV weight was 55%. Using the Mapmaker/QTL computer package, we identified a significant QTL on chromosome 3 with a log10 likelihood (LOD) score of 4.8, which accounted for 16.5% of the total variance of LV weight. This QTL was centered close to the marker D3Rat29. The QTL was also found to be significantly linked with total heart weight (LOD=4.4). These data provide the first demonstration of a QTL on chromosome 3 that plays a role in determining the difference in LV mass between normotensive Fischer 344 and Wistar- Kyoto inbred rat strains. The prostaglandin synthase 1 gene is located within the QTL. (+info)