Studies on the effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on the rodent forestomach

A novel class of hypocholesterolaemic agents, HMG CoA reductase inhibitors, was shown to cause mucosal thickening in the rodent (mouse and rat) forestomach after subacute/subchronic oral administration. These changes were characterized histologically by acanthosis and hyperkeratosis of the squamous epithelium with submucosal oedema and occasionally cellular infiltration. This drug-induced hyperplastic response was both dose and time dependent, did not occur after subcutaneous administration, and was confined entirely to the rodent forestomach (not observed in any other area of the gastro-intestinal tract). The forestomach hyperplastic response correlated with the pharmacological potency of HMG CoA reductase inhibitors of similar structure (observed to varying degrees with all HMG CoA reductase inhibitors examined to date).     

Methylbromide: carcinogenic effects in the rat forestomach

Methylbromide (MB) administered by oral gavage as a solution in arachis oil was carcinogenic to rats in a 90-day experiment. In 13 of 20 animals of the highest dose group, 50 mg MB/kg body wt squamous cell carcinomas of the forestomach developed. All animals of this group showed a marked diffuse hyperplasia of the epithelium of the forestomach. A less pronounced hyperplasia was observed in high and lower incidence with respectively 10 and 2 mg MB/kg body wt. The lowest dose, 0.4 mg MB/kg body wt was without effects.     

Regression of methyl bromide-induced forestomach lesions in the rat

There is continuing concern about the role of irritation in cancer development. Methyl bromide, a widely used fumigant and known irritant reported to cause forestomach carcinomas in rats, was dissolved in peanut oil and given by gavage at 50 mg/kg body wt to Wistar rats five times per week for 13 to 25 weeks. Starting at Week 13, methyl bromide administration was discontinued for half of the methyl bromide-treated rats (stop treatment group). After that, rats from both the continuous treatment and stop treatment groups were terminated at 4-week intervals to follow the progression of the stomach lesions. Forestomach lesions were not found in control rats receiving peanut oil and killed at 13 or 25 weeks. At 13 weeks the forestomachs from rats receiving methyl bromide were contracted and adherent to the liver and spleen. Inflammation, acanthosis, fibrosis, and a high incidence of pseudoepitheliomatous hyperplasia were found microscopically in treated animals. At 25 weeks, 100% of the rats receiving methyl bromide continuously had hyperplastic lesions of the forestomach which were more severe than those at 13 weeks. Evidence of malignancy was seen in one rat and the lesion was considered a very early carcinoma. In the stop treatment group that received methyl bromide for 13 weeks, there was regression of the stomach lesions, but at the 12-week final sacrifice, adhesions, fibrosis, and mild acanthosis remained. This study illustrates the need for regression experiments for complex forestomach lesions in rodents, especially when an irritating chemical is given by gavage.     

Effects of BHA and related phenols on the forestomach of rats

To determine the pathogenesis of BHA-induced forestomach lesions, the nature and time course of the early lesions in the forestomach of Wistar rats were studied. The rats were given BHA at a dose level of 2% in a powdered diet or by oral intubation of 1 g BHA/kg body weight/day in arachis oil. The hyperplastic changes in the mucosa were visible 1 day after the second application. The localization was dependent on the mode of application. Dietary exposure yielded changes in the area of the limiting ridge; oral intubation of BHA produced lesions in the apex of the forestomach. In a subchronic 90-day feeding study in rats, no recognizable effect was observed when 0.125% BHA was incorporated into the diet as a solution in arachis oil. In reversibility studies, severe forestomach lesions observed after feeding 2% BHA for 6, 12 or 15 months regressed almost completely following withdrawal of the BHA for a period of 7 months. BHA induced similar forestomach damage in NMRI mice and Syrian golden hamsters, whereas guinea-pigs, a species having no forestomach, did not show comparable lesions. Substances with similar chemical structure were tested in short-term feeding studies (tert-butylhydroquinone, 4-methoxyphenol, 1,4-dimethoxybenzene, hydroquinone, 3-methoxyphenol, 2-methoxyphenol, anisole, p-cresol, phenol and BHT). Only 4-methoxyphenol strongly affected the forestomach mucosa in a manner similar to that associated with BHA. The methoxy group in the para position seems to be important for the hyperplasiogenic activity.     

Studies on the mechanism of clonidine-induced mydriasis in the rat

Intravenous administration of clonidine hydrochloride (3-100 micrograms/kg) produced a dose-dependent pupillary dilation in anaesthetized rats. All experiments were carried out in rats in which vagosympathetic nerve trunks were sectioned bilaterally at the cervical level. Clonidine-induced mydriasis was present only in those preparations having intact parasympathetic neural tone to the iris. Depletion of CNS monoamines by more than 95% with reserpine (5 mg/kg) and alpha-methyl-para-tyrosine (2 X 300 mg/kg) failed to alter the dose-response relation to clonidine. Pretreatment with the alpha-2-adrenoceptor antagonist, yohimbine hydrochloride (1.5 mg/kg), produced about a 10-fold shift to the right in the pupillary dose-response curve to clonidine. Yohimbine administered after the highest dose of clonidine also antagonized the mydriatic response. The above results suggest that clonidine acts on CNS post-synaptic alpha-2-adrenoceptors to produce mydriasis by withdrawal of parasympathetic neural tone to the iris. In an attempt to assess the physiological substrate(s) involved, mydriatic responses, due to parasympatho-inhibition, were evoked by electrical stimulation of ascending (sciatic nerve and medullary) and descending (hypothalamic) pathways. Yohimbine (0.3 and 1.0 mg/kg) produced a dose-dependent inhibition of the pupillary dilation evoked by stimulation of the sciatic nerve and medullary loci, whereas these doses of yohimbine failed to alter the dilation in response to hypothalamic stimulation. Similarly, monoamine depletion greatly antagonized the pupillary dilation elicited by sciatic nerve and medullary stimulation without significantly affecting mydriasis due to hypothalamic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

On the histopathogenesis of rat forestomach carcinoma caused by aristolochic acid

The histopathogenesis of rat forestomach carcinoma induced experimentally with aristolochic acid was investigated. The intragastric administration of 10 mg/kg/day caused extensive necrosis of the squamous epithelium, followed by regeneration and hyperplasia, papilloma formation and ultimately by invasive squamous cell carcinoma.     

The effect of lead on cholinergic contractile function in the rat forestomach

Previous studies have demonstrated that subchronic exposure to lead in rats slows gastric emptying. Therefore, the isometric contractile response of the forestomach from lead-treated rats was examined in vitro. Male Wistar rats were fed 4% lead acetate in their diet (NIH-07); controls were pair-fed. After 7 weeks, blood lead levels reached 180-389 micrograms/dl. The forestomach was dissected and suspended in buffer which for lead-treated rats contained 1.2 X 10(-5) M lead acetate. Subchronic lead exposure had no effect on the maximum tonic contraction induced by KCl, methacholine or serotonin. However, lead-treated tissue showed enhanced sensitivity to methacholine with a reduction in EC50 to 59.7% of control. This effect was not observed in control tissue exposed to lead (1.2 X 10(-5) M) only in vitro. Higher in vitro concentrations of lead (16 X 10(-5) M) produced an increase in methacholine EC50. Physostigmine-induced increase in tension was also significantly greater in tissue from lead-treated rats. Electric field stimulation, which produced a contraction attributable to postganglionic acetylcholine release, was unaltered in lead-treated tissue. These results indicate that lead intoxication did not impair the contractile apparatus of the forestomach smooth muscle. The lack of net effect on activation of intramural cholinergic neurons, despite the enhanced sensitivity to a cholinergic agonist, may indicate reduction in acetylcholine release in lead-treated tissue.     

苯并(a)芘诱导小鼠前胃癌模型的建立及共轭亚油酸对其预防作用

目的　用苯并 (a)芘〔B(a)P〕建立小鼠前胃癌模型 ,观察不同构成的共轭亚油酸 (CLA)对前胃癌的抑制作用以及与脂质过氧化的关系。方法　通过灌胃方式给予昆明种小鼠B(a)P ,建立前胃癌模型。用光学显微镜作病理组织检查 ,用比色法测定丙二醛(MDA)含量。结果　利用B(a)P成功地在昆明种小鼠体内建立了前胃癌模型 ,病理结果分析表明所建立的前胃癌为鳞状细胞癌 ;小鼠前胃肿瘤的计数结果表明 ,B (a)P组 ,75 %c9,t11 CLA组 ,98%c9,t11 CLA组 ,98%t10 ,c12 CLA组的肿瘤发生率分别为 10 0 %,75 .0 %,6 9.2 %和 5 3.8%;并且 75 %c9,t11 CLA ,98%c9 ,t11 CLA ,98%t10 ,c12 CLA明显降低前胃肿瘤的直径 ,但对荷瘤小鼠的平均荷瘤数没有影响 ;与阴性对照组和B(a)P对照组相比 ,CLA处理能提高小鼠体内MDA含量。结论　B(a)P诱导昆明种小鼠的前胃组织形成鳞状细胞癌 ;不同构成CLA对B(a)P诱导小鼠前胃癌均具有抑制作用 ,并且MDA可能是CLA发挥预防肿瘤作用的可能机理之一。     

Studies on the antinociception effect of melatonin and its mechanism in the rat

The antinociception effect of melatonin（Mel） and its mechanisms were studied on the trauma- pain model in the rat. A trauma - pain model was established in Wistar rats by combining right - hind limb amputation with 50℃ tail - flick test. The effects of Mel on central sensitization were studied through measuring the changes of the expression of c - fos （ an indicator of nociceptive transmission at the spinal level ） , subtance P（SP） and brain - derived neurotrophic factor （BDNF） in the spinal cord using immunohistochemistry. In addition, the contents of nitric oxide （NO） in brain and spinal tissues were also observed. The results showed that the immunoreactivity of BDNF and c - fos in spinal dorsal horn in injuried rats began to increase at the first day,     

Studies on the mechanism of drug-binding to melanin.

The binding to melanin of chlorpromazine, chloroquine, paraquat and Ni²⁺ has been studied in vitro with pigment from beef eyes. The results showed a marked influence of the ionic environment on the ability of the organic substances to bind to melanin, indicating that electrostatic forces between the cationic forms of the substances and anionic sites on the melanin polymer (presumably carboxyl groups) are important for the complex formation. An analysis of the binding by the method of Scatchard showed that more than one binding class must be implicated in the binding of both the organic substances and Nr²⁺ to melanin. Several concordances were found for the data of the paraquat- and Ni²⁺-binding, indicating a dominant influence of electrostatic forces for the melanin-binding of paraquat. However, several indications were found that non-electrostatic contributions must be added to form the binding-sites for chlorpromazine and chloroquine. It is possible that such contributions may be provided by van der Waals forces occurring at the conjunctions of the aromatic rings in the substances and the aromatic indole-nuclei of the melanin. Experiments with chlorpromazine indicated that the positive ion radical of the substance had a very high melanin-affinity. It is suggested that melanin may be able to oxidize chlorpromazine to a positive ion radical, explaining the firm binding of the substance to melanin and the evidence in the literature favouring this possibility are discussed.     

基因重组促红细胞生成素导致高血压的机制研究

目的：探讨基因重组促红细胞生成素（ｒ－ＨｕＥＰＯ）在治疗慢性肾衰（ＣＲＦ）贫血中导致高血压的机制及防治对策。方法：对ｒ－ＨｕＥＰＯ治疗中出现高血压的ＣＲＦ血液透析贫血患者１５例及对照组１５例，应用分光光度法及放免法观察治疗前后血浆一氧化氮代谢产物（ＮＯ２－／ＮＯ３－）及内皮素－１（ＥＴ－１）的变化。同时用大鼠进行对照试验。结果：１．ＣＲＦ贫血患者及贫血鼠用ｒ－ＨｕＥＰＯ１６周后，红细胞压积（Ｈｃｔ）升高、血压升高，ＥＴ－１增加（Ｐ＜０．０１），血浆ＮＯ２－／ＮＯ３－下降（Ｐ＜０．０５），而对照组用药前后无明显变化（Ｐ＞０．０５）。２．在用药１６周后，ＲＴＰＣＲ测得实验组大鼠肾皮质及髓质ｉＮＯＳｍＲＮＡ比对照组明显减少（Ｐ＜０．０５）。结论：研究表明ｒ－ＨｕＥＰＯ导致高血压与ｉＮＯＳｍＲＮＡ减少，合成的ＮＯ减少及ＥＴ－１增加有着重要的关系     

Studies on the mechanism of carbon monoxide-induced vasodilation in the isolated perfused rat heart

We investigated the effects of dissolved CO on isolated potassium-arrested (K+) perfused rat hearts. Hearts from male Sprague-Dawley rats were perfused via the aorta with oxygenated Krebs-Henseleit solution containing 20 mM K+. Coronary flow (Qt) averaged 48.8 +/- 1.6 (SE), 48.1 +/- 1.7, and 55.6 +/- 1.7 ml/min/g dry wt when the perfusate was equilibrated with 95% O2-5% CO2, 5% N2-90% O2-5% CO2, and 5% CO-90% O2-5% CO2, respectively. The change in Qt was statistically significant when CO was present in the perfusion medium, but was not significant when N2 was present. Furthermore, the effect was reversible because coronary flow returned to control levels when CO was removed. Myocardial oxygen consumption (MVO2) did not change significantly when hearts were perfused with either N2 or CO. The magnitude of CO-induced vasodilation was not affected significantly by the addition of either 5 microM propranolol, 2 microM phentolamine, 1 unit of adenosine deaminase, or 0.1 mM indomethacin to the perfusate. In addition, CO reversed the vasoconstrictive effects of the alpha-agonist methoxamine. These results indicate that CO exerts a vasodilatory effect on coronary vasculature that is not the result of decreased O2 content in the perfusate and is not mediated by adrenergic influences, adenosine, or prostaglandins.     

Short-term effects of various phenols and acids on the Fischer 344 male rat forestomach epithelium

A series of phenols and acids was fed to rats for 9 days to determine effects on the [methyl-3H]thymidine labelling index and the histological appearance of the forestomach. A variety of proliferative effects in the rat forestomach were observed which paralleled changes in the [methyl-3H] thymidine labelling index. The 3-tert-butyl isomer of butylated hydroxyanisole (BHA) was as effective as the food grade mixture. In the 4-hydroxybenzoic acid ester series, activity was not found either with the free acid or the methyl ester. With the ethyl, n-propyl and n-butyl esters activity in the perfundic region of the forestomach increased with alkyl chain length, the n-butyl ester being nearly as effective as BHA. In contrast, 4-methoxyyphenol and propionic acid demonstrated their greatest effects in the midregion of the forestomach, the action of propionic acid not being apparent until 21 or 27 days of treatment. It was also found that after a 9-day treatment involving coadministration of BHA and acetylsalicyclic acid, the overall effect of the antioxidant on the forestomach was greatly reduced.     

Studies of the mechanism of chloroquine binding to synthetic DOPA-melanin

In order to elucidate the mechanism of drugs binding to melanin, effects of pH, ionic strength and organic solvent on the interaction of chloroquine with synthetic dopa-melanin were studied. The results indicate that electrostatic, hydrophobic and van der Waals' forces participate in the formation of the chloroquine-melanin complex. Binding analysis by the Scatchard method showed that two classes of binding sites take part in the complex formation: strong binding sites with the association constant k1 approximately to 10(5) and weak binding sites with K2 approximately 10(4). Experiments with chemically modified melanin yielded some information about binding sites of this biopolymer. The obtained results suggest that strong binding involves both hydrophobic interaction and electrostatic attraction between the protonated ring system of chloroquine and the ortho-semiquinone groups of melanin. However, the weakly reacting sites can be identified as ionic bonds between protonated aliphatic nitrogen of chloroquine molecule and carboxyl groups of melanin. Van der Waals' forces occurring at the conjunctions of the aromatic rings of the drug and the aromatic indole-nuclei of the melanin probably take part in the weak binding too.     

化浊解毒汤对慢性肾功能衰竭大鼠的实验研究

目的对化浊解毒汤治疗慢性肾功能衰竭大鼠的作用机理进行探讨。方法用腺嘌呤诱发肾衰模型 ,再用化浊解毒汤灌胃治疗 4周 ,以包醛氧化淀粉作阳性对照药。结果化浊解毒汤能降低大鼠血清肌酐 (Scr)、尿素氮 (BUN)水平 ,改善肾功能 ,并且具有抗氧化作用 (P <0 0 5 )。肾小管及间质内结晶沉积物明显减少 ,部分肾小管形态结构接近正常 ,光镜下肾脏病理明显改善。结论化浊解毒汤能明显改善肾功能 ,抑制慢性肾衰的发展     

雄激素非依赖性前列腺癌发生机制相关的信号传导通路研究进展

几乎所有经过内分泌治疗的前列腺癌(prostate cancer,PCa)患者都会发展为雄激素非依赖性前列腺癌(androgen-independent prostate cancer,AIPC),而目前对AIP(尚无有效的治疗手段,因此,探索AIPC可能的发生机制成为基础与临床研究的重点,本文就与AIPC相关的信号传导通路研究进展做一综述.     

Studies on 3-hydroxykynureninase from rat liver.

Kynureninase (L-kynurenine hydrolase E.C. 3.7.1.3.) was purified about 200 times from rat liver. The purified enzyme catalyzes the L-3-hydroxykynurenine leads to 3-hydroxyanthranilate reaction more favorably than the L-kynurenine leads to anthranilate reaction, with Km values of 1.67 x 10(-6) M for L-3-hydroxykynurenine and of 1.67 x 10(-4) M for L-kynurenine. Besides, this enzyme did not produce 5-hydroxyanthranilate from D,L-5-hydroxykynurenine. Therefore we think it is mainly a 3-hydroxykynureninase regulating the tryptophan degradation towards the formation of nicotinic acid necessary to NAD synthesis, rather than towards the accumulation of anthranilate.