Influence of caffeine consumption on 7,12-dimethylbenz(a)anthracene-induced mammary gland tumorigenesis in female rats fed a chemically defined diet containing standard and high levels of unsaturated fat

The effect of caffeine (430-500 mg/liter of drinking water) on the initiation and promotion phases of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary gland tumorigenesis in female Sprague-Dawley rats fed a chemically defined diet containing standard (5%) or high (20%) levels of fat (corn oil) was examined. In the initiation studies, caffeine and the standard or high fat diet treatments were provided for 34 days, from 24-29 days of age to 58-63 days of age. Three days prior to termination of caffeine-fat diet treatments, each rat received a single dose of DMBA. In the promotion studies, caffeine and the standard or high fat diets were provided commencing 3 days after a single dose of DMBA (at 56-61 days of age) and until termination of the study. Caffeine consumption, during the initiation phase significantly (P less than 0.05) reduced mammary carcinoma multiplicity (number of tumors/rat), in rats fed either a standard or high fat diet. In the promotion studies, prolonged consumption of caffeine in rats fed either a standard or high fat diet did not significantly effect mammary carcinoma multiplicity. In the early stages of promotion, an apparent increase in mammary carcinoma multiplicity was observed; this increase in mammary carcinoma multiplicity did not, however, reach the 5% level of statistical probability. When caffeine was administered during both the initiation and promotion phases, no significant effect on mammary carcinoma multiplicity was observed. Treatment of rats during the initiation or promotion phases with caffeinated coffee (via drinking water) mimicked the mammary tumor modulating activities of caffeine. Decaffeinated coffee consumption did not effect either the initiation or promotion phases of this tumorigenic process. In both the initiation and promotion studies, caffeine and/or coffee consumption did not significantly affect the incidence of mammary carcinomas (percentage of rats bearing mammary carcinomas) or the mean latency period of mammary tumor appearance. Thus, in female rats fed a chemically defined standard or high fat diet, caffeine consumption can significantly influence chemical carcinogenesis of the mammary gland; an effect that is dependent upon the duration and time-span of caffeine administration.     

Influence of caffeine and/or coffee consumption on the initiation and promotion phases of 7,12-dimethylbenz(a)anthracene-induced rat mammary gland tumorigenesis

The effect of caffeine and/or coffee consumption (via the drinking water) during the initiation phase and promotion phase of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary gland tumorigenesis in female Sprague-Dawley rats fed a commercial laboratory animal chow was examined. In the initiation studies, DMBA was administered once at 53-55 days of age; caffeine (100-860 mg/liter of drinking water) and/or coffee (moderate or high dose, sole source of drinking water) treatments were for 32 consecutive days, commencing 29 days prior to DMBA treatment and terminating 3 days after DMBA treatment. In the promotion studies, DMBA was administered once at 54-55 days of age; caffeine and/or coffee treatments were daily from 57-58 days of age to termination of experiments (12-21 weeks after carcinogen treatment). In the initiation studies, either moderate (100-400 mg) or high (860 mg) dose levels of caffeine or moderate to high dose levels of caffeinated coffee significantly (P less than 0.05) reduced mammary carcinoma multiplicity (number of tumors/rat). Consumption of high or moderate dose levels of decaffeinated coffee did not significantly alter mammary carcinoma multiplicity. The addition of caffeine to the moderate dose level of decaffeinated coffee resulted in a significant (P less than 0.05) reduction in mammary carcinoma multiplicity. In the promotion studies, prolonged consumption of moderated dose levels of caffeine or moderate or high dose levels of caffeinated coffee or decaffeinated coffee did not significantly effect mammary carcinoma multiplicity. In the early stages of promotion, however, a significant (p less than 0.05) stimulatory effect of caffeine on mammary carcinoma multiplicity was observed; an effect that was temperate and transitory. In both the initiation and promotion studies caffeine and/or coffee consumption did not significantly affect the incidence of mammary carcinomas (percentage of rats bearing mammary carcinomas) or the mean latency period of mammary tumor appearance. These results provide evidence that caffeine and/or caffeinated coffee consumption can significantly influence mammary carcinoma multiplicity in female rats treated with DMBA, an effect that is dependent upon the dose level, duration, and time-span of caffeine administration.     

Normal but not carcinomatous primary rat mammary epithelium: readily transplanted to and maintained in the athymic nude mouse

Transplantation success rates of primary 7,12-dimethylbenz(a)anthracene [(DMBA) CAS: 57-97-6]-induced rat mammary carcinomas and normal rat mammary glandular epithelium into female athymic mice were compared. The rat mammary carcinomas obtained from female Sprague-Dawley rats were transplanted into host athymic mice (6-8 wk of age) as 1 x 1-cm slices xenografted sc (2 slices/mouse) or as enzymatically dissociated cells inoculated into the gland-free mammary fat pad. Normal rat mammary glands (No. 4 glands and 3- to 5-mo-old virgin rats) were transplanted into host athymic mice as whole, intact mammary glands sc (1 gland/mouse) or as enzymatically dissociated cells inoculated into the gland-free mammary fat pad. All (100%) of the normal rat mammary glands were readily accepted and maintained in the athymic mice when transplanted either sc as whole glands or as dispersed cells inoculated into the gland-free fat pad. In contrast, only 13-14% of the DMBA-induced rat mammary carcinomas were accepted and maintained in the athymic mice (transplanted as slices sc or as dispersed cells inoculated into the gland-free fat pad). Treatment of host athymic nude mice with an intense mammotropic hormonal stimulus (prolactin and/or ovarian steroids) markedly enhanced the developmental growth of the transplanted normal rat mammae (subcutaneous slices and fat-pad inoculates); such a hormonal stimulus did not influence the transplantation success rate of the DMBA-induced rat mammary carcinomas. Thus female athymic nude mice can readily accept and maintain transplants of normal rat mammae but not carcinogen-induced carcinomatous rat mammae; the meager acceptance rate of the carcinomatous rat mammae by the athymic nude mouse was not enhanced by providing the host mice with a potent mammotropic hormonal growth stimulant.     

Influence of caffeine on development of benign and carcinomatous mammary gland tumors in female rats treated with the carcinogens 7,12-dimethylbenz(a)anthracene and N-methyl-N-nitrosourea

The effect of chronic caffeine consumption (500 mg/liter of drinking water) on the initiation and promotion stages of 7,12-dimethylbenz(a)anthracene (DMBA) (a low dose, 0.5 mg/100 g body weight, i.v.) and N-methyl-N-nitrosourea (MNU) (a standard dose, 2.5 mg/100 g body weight, i.v.) induced mammary gland tumorigenesis in female Sprague-Dawley rats was determined. In the initiation studies, caffeine was administered for 30 days prior to and for 3-4 days after carcinogen treatment (carcinogens administered at 55-57 days of age); in the promotion studies, caffeine was administered beginning 3-4 days after carcinogen treatment and until experiment termination (DMBA study and MNU study, 48 and 26 weeks after carcinogen treatment, respectively). In the DMBA study, there were 62-73 rats/group, in the MNU study, 40 rats/group. Eighty-nine % of the mammary tumors induced by DMBA were benign (adenomas, fibroadenomas, often with cystic secretory activity), 11% were carcinomas (intraductal and invasive); virtually all of the MNU-induced mammary tumors were carcinomas (approximately 99%). Caffeine consumption during the initiation stage in the DMBA-treated rats resulted in a significant decrease in the mean number of mammary carcinomas per rat (50% reduction, P less than 0.01) and mean number of benign mammary tumors per rat (28% reduction, P less than 0.05); caffeine consumption during the promotion stage significantly decreased the mean number of benign mammary tumors per rat (57% reduction, P less than 0.001) while not significantly influencing mammary carcinoma number. In contrast, caffeine consumption during either the initiation or promotion stages of MNU-treated rats did not significantly influence this tumorigenic process. The influence of caffeine on urinary and fecal excretion of tritiated DMBA and on rat mammary gland development at the time of carcinogen treatment also was determined. Slightly reduced levels of tritium in 24-h urinary samples were observed in caffeine-treated animals (P = 0.06). No significant effect of caffeine on 24- to 96-h fecal or 48- to 96-h urinary excretion of the isotope was observed. No apparent effect of caffeine on rat mammary gland development (number of ducts, degree of lobuloalveolar development) was observed. That caffeine significantly suppresses the initiation stage of DMBA-induced rat mammary gland tumorigenesis, while not influencing this stage when MNU is used as a carcinogen, suggests that caffeine acts via an alteration in carcinogen (DMBA) activation. The lack of a pronounced effect of caffeine on tritiated DMBA excretion, however, does cast some doubt on this mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)     

Inhibition by caffeine of ovarian hormone-induced mammary gland tumorigenesis in female GR mice

The purpose of this study was to determine whether or not caffeine could influence the development of ovarian hormone dependent mammary tumors in GR mice. Virgin female GR mice were treated daily for 24 weeks with 17 beta-estradiol and progesterone, commencing at 8-10 weeks of age. One week after the onset of hormone treatment, caffeine (500 mg/l drinking water) was administered daily until experiment termination to one-half of the hormone-treated mice. Hormone treatment induced mammary tumors in 95-100% of the mice. Caffeine treatment significantly (P less than 0.05) reduced the mean number of mammary tumors per mouse and significantly (P less than 0.05) increased the mean latency period of mammary tumor appearance.     

Caffeine inhibits development of benign mammary gland tumors in carcinogen-treated female Sprague-Dawley rats

Summary The purpose of this study was to assess the influence of caffeine on the incidence of benign mammary tumors in carcinogen (DMBA) treated female Sprague-Dawley rats. Four different animal models were used in these studies, i.e., the administration of DMBA to: [1] 55 day old virgin rats; [2] 53 day old ovariectomized, estrogen treated virgin rats; [3] 135 day old virgin rats and [4] 135 day old parous rats. A high incidence of benign mammary fibroadenomas was observed in each of the four animal models. In addition, in the estrogen treated ovariectomized animals, a high incidence of secretory mammary gland cysts was observed. Caffeine (500 mg/L drinking water) was administered daily throughout the study commencing 3–31 days after carcinogen treatment. Caffeine treatment significantly (P<0.05 to P<0.001) reduced the incidence of benign mammary fibroadenomas in the 55 day old virgin rat model (P<0.01), in the 53 day old estrogen treated ovariectomized virgin rat model (P<0.05 to P<0.001) and in the 135 day old virgin rat model (P<0.05). The number of benign mammary fibroadenomas was reduced by caffeine in the 135 day old parous rat model but this reduction was not significant (P<0.10). In addition, in the estrogen treated ovariectomized virgin rat model, caffeine significantly (P<0.05 to P<0.001) reduced the incidence of mammary gland cysts. Caffeine treatment either increased or had no significant effect on body weight gains, depending upon the animal model. Thus, caffeine consumption can influence the development of benign mammary tumors (fibroadenomas and cysts) in carcinogen treated female Sprague-Dawley rats, an influence that was shown to be consistently inhibitory.     

Caffeine (1,3,7-trimethylxanthine), a temperate promoter of DMBA-induced rat mammary gland carcinogenesis

The administration of caffeine to the drinking water (250 mg/l and 500 mg/l) of female Sprague-Dawley rats after treatment with 7,12-dimethylbenzanthracene (DMBA) (5 mg i.g.) resulted in an increase in mammary carcinoma incidence. The confidence levels of statistical significance for the groups of rats receiving the 250-mg and 500-mg doses of caffeine were >0.70 and >0.99, respectively. This increase in mammary carcinoma incidence was observed when caffeine treatment was initiated commencing 3 days after DMBA treatment and continued for 21 weeks. This effect was also observed when caffeine treatment was initiated commencing 20 weeks after DMBA treatment and continued for 6 weeks in rats relatively refractory to carcinogen treatment (mammary tumor-free at onset of treatment) and in rats relatively sensitive to the carcinogen (mammary tumor bearing at onset of caffeine treatment). Caffeine treatment of rats prior to and during carcinogen treatment did not significantly affect mammary carcinoma incidence. Thus caffeine consumption has been shown to significantly enhance the promoting phase but is without effect on the initiating phase of this carcinogenic process.     

Mode of action of selenium inhibition of 7,12-dimethylbenz[a]anthracene-induced mouse mammary tumorigenesis

Possible mechanisms for the inhibitory effect of selenium on mouse mammary gland tumorigenesis were evaluated in two different mouse models, in 7,12-dimethylbenz[a]anthracene [(DMBA) CAS:57-97-6]treated and hormonally stimulated mammary glands with two dietary levels of Se (0.2 and 2.0 ppm). In (C57BL X DBA/2f)F1 (BD2F1) and BALB/c strains of female mice, Se at 2.0 ppm decreased mammary tumor incidences by 36 and 68%, respectively. Selenium-dependent glutathione peroxidase (GSH-Px) activity in the mammary glands of BD2F1 female mice decreased at 6 months of age and then increased to the highest levels at 9 months of age. Mammary glands from DMBA-treated mice had lower GSH-Px activity than those from control mice. The increase of dietary Se to 2.0 ppm did not overcome this DMBA effect. These results indicate that GSH-Px activity does not correlate with the tumorigenic inhibitory effects of Se. In the hormonally stimulated mammary gland, increasing dietary Se to 2.0 ppm increased GSH-Px activity threefold and decreased mammary-gland-membrane-localized lipid peroxidation by 16%. In vitro peroxidation of hormonally stimulated mammary glands was inversely proportional to the level of GSH present in the incubation mixture. The marginal decrease in lipid peroxidation found in the mammary glands exposed to 2.0 ppm Se could not explain the inhibitory effect of Se on tumorigenesis.     

Development and characterization of the BALB/cNIV mouse strain

The strain BALB/cNIV/Crgl was developed by infecting BALB/c/Crgl mice with mouse mammary tumor virus from C3Hf mice. A BALB/c normal mammary duct was transplanted into the gland-free fat pad of a hormone-stimulated female C3Hf X BALB/c F1 mouse. A hyperplastic alveolar nodule was found in the BALB/c ductal outgrowth and was transplanted into another hybrid gland-free fat pad. The resultant hyperplastic alveolar outgrowth was finally transplanted to female BALB/c mice. The hyperplastic alveolar outgrowth contained an exogenous, infectious mouse mammary tumor virus named the nodule-inducing virus, which was thought to be derived from the endogenous low oncogenic mouse mammary tumor virus found in C3Hf mice. The hyperplastic alveolar outgrowth-bearing BALB/c mice were inbred for four generations, and one family was selected as the strain BALB/cNIV/Crgl. It was found that (a) the mouse mammary tumor virus found in the BALB/cNIV strain was milk transmitted, but not transmitted by infected males; (b) the BALB/cNIV breeding females had a low tumor incidence (40%) and a longer latent period (14 months) than did female BALB/cfC3H mice (92% at 8 months); (c) the BALB/cNIV nodule outgrowths had low tumor-producing capabilities (50%) and longer latent periods (13.4 months) than did nodule outgrowths derived from female BALB/cfC3H mice (100% at 7.7 months).     

Effect of wheat bran fiber on the development of mammary tumors in female intact and ovariectomized rats treated with 7,12-dimethylbenz(a)anthracene and in mice with spontaneously developing mammary tumors

We examined the effect of consumption of graded increases of dietary fiber (soft white wheat bran) on the development of mammary gland carcinomas in intact female Sprague-Dawley rats during the promotion stage of carcinogenesis, induced with 7,12-dimethylbenz(a)anthracene (DMBA). The percent of rats with mammary carcinomas, the total number of mammary carcinomas and the mean number of mammary carcinomas per rat were reduced significantly at all fiber levels examined compared to rats fed a control diet. Inclusion of 9.6% fiber in the diets of ovariectomized rats that had been treated with a single i.v. dose of 2.5 mg DMBA/100 g body weight 2 weeks prior to removal of the ovaries resulted in a significant decrease of carcinomatous and benign mammary tumors compared to ovariectomized rats fed a control diet. Development of spontaneous mammary carcinomas in virgin C₃H/HeOuJ female mice and growth of a transplantable mammary gland tumor in such mice were reduced by inclusion of 9.6% fiber in the diet, a reduction that was significant or just barely missed significance, depending on the source of the fiber. Our observations provide evidence that inclusion of soft white wheat bran in the diet is effective in the suppression of mammary gland tumorigenesis in an array of experimental animal models. Int. J. Cancer 75:439–443, 1998. © 1998 Wiley-Liss, Inc.     

Bioactivity of male (sperm transmitted) mouse mammary tumor virus as influenced by donor, recipient and age at treatment.

The sperm collected from mammary tumor virus (MTV)-carrying mice (C3H, BALB/cfC3H, BALB/cfRIII and RIII) was separately tested for mammary tumor-inducing activity in (BALB/c x C3Hf)F1, (BALB/c x RIIIf) F1, and BALB/c female recipients by i.p., injection of 0.1 ml of the sperm at 1-2 weeks or at 3 months of age. A total of 551 recipents was observed, including control mice. The results may be summarized as follow: 1) mammary tumor incidence in experiments with or without histocompatibility between sperm donor and recipient is the same; 2) bioactivity is related to the type of MTV (C3H, RIII) and to the type of recipient, not to the sperm donor; 3) the activity of RIII MTV released in the sperm appears to be less influenced by the age of recipients than is that of C3H MTV; 4) BALB/c recipients are more susceptible to C3H than to RIII sperm-released MTV; 5) (BALB/c x RIIIf) F1 hybrids are resistant to sperm-released MTV, especially to C3H MTV infection, and show a 34% incidence of late spontneous lymphomas inherited by the RIIf male parent; 6) (BALB/c x C3Hf) F1 hybrids are susceptible to both C3H and RIII sperm-released MTV and show a 30% incidence of late spontaneous mammary tumors due to genetic transmission of MTV by the C3H male parent.     

Neoplastic response of F344 rats and B6C3F1 mice to the polymer and dyestuff intermediates 4,4'-methylenebis(N,N-dimethyl)-benzenamine, 4,4'-oxydianiline, and 4,4'-methylenedianiline

Feeding 4,4'-methylenebis(N,N-dimethyl)benzenamine [CAS: 101-61-1; 4,4'-methylenebis(N,N-dimethylaniline)] to inbred F344 rats increased the incidence of thyroid lesions (hyperplasia, adenomas, and carcinomas) in both sexes, especially in the female rats. 4,4'- Oxydianiline (CAS: 101-80-4) in the diet increased adenomas and carcinomas in the thyroid gland and neoplastic nodules and carcinomas in the liver of male and female F344 rats. In addition to increasing thyroid adenomas in females and hepatocellular adenomas or carcinomas in male and female B6C3F1 mice, 4,4'- oxydianiline increased adenomas of the harderian gland in male and female mice. 4,4'- Methylenedianiline (CAS: 101-77-9) in the drinking water increased neoplasms of the thyroid gland and liver in F344 rats and B6C3F1 mice.     

Effect of phenobarbital on the development of liver tumors in juvenile and adult mice

The effect of long-term exposure to phenobarbital (CAS: 50-06-6) subsequent to tumor initiation on the development of liver tumors in BALB/c and (C57BL/6 X C3H/Anf)F1 (B6C3F1) mice was determined. In male B6C3F1 mice that received either 15 or 45 ppm diethylnitrosamine [(DENA) CAS: 55-18-5] between 6 and 10 weeks of age, subsequent treatment with 500 ppm sodium phenobarbital in the drinking water resulted in the promotion of liver tumors. However, in male B6C3F1 mice initiated on day 15 of age with 25 mg DENA/kg, beginning long-term treatment of 500 ppm sodium phenobarbital at 4 weeks of age inhibited the development of liver tumors, whereas in male BALB/c mice initiated with 25 mg DENA/kg on day 15 of age, beginning the long-term treatment with 500 ppm sodium phenobarbital at 4 weeks of age promoted the development of liver tumors. Hence phenobarbital can either enhance or inhibit the formation of liver tumors, depending both on the mouse strain used and the animal's age at the start of exposure.     

17beta-oestradiol and Enovid mammary tumorigenesis in C3H/HeJ female mice: counteraction by concurrent 2-bromo-alpha-ergocryptine

Chronic administration of 17beta-oestradiol (via drinking water) or the oral contraceptive Enovid (norethynodrel and mestranol) (0-1 mg injected s.c. twice weekly) to nulliparous C3H/HeJ female mice, beginning at one month of age and terminating at 20 months (17beta-oestradiol) or 22 months (Enovid), significantly increased the incidence of mammary tumours over solvent-treated controls. Concurrent treatment of the steroid-treated mice with 2-bromo-alpha-ergocryptine (CB-154) (0-1 mg s.c. injected daily) significantly reduced mammary tumour incidence and mammary hyperplastic nodule development to the control level. CB-154 is an efficacious inhibitor of pituitary prolactin secretion. These results demonstrate that steroid-induced mammary gland dysplasias can be sharply reduced by chronic CB-154 treatment, and suggest that some of the mammary tumorigenic activities of oestrogenic steroids in C3H mice are mediated via an increased secretion of pituitary prolactin.     

Effect of dietary selenium levels on 7,12-dimethylbenzanthracene-induced mouse mammary tumorigenesis

The effect of dietary selenium levels on 7,12-dimethylbenz-anthracene(DMBA)-induced mammary tumors was examined in mice fed a semi-purifieddiet (20% casein, 50% sucrose, 5% corn oil). (C57BLxDBA/2f)F₁(BD2F²) female mice were fed diets containing 0.2, 0.5, 1.0and 2.0 p.p.m. selenium starting at 7 weeks of age. The mammarytumor incidence was 56, 30, 25 and 16%, respectively, afterthe mice were on the diet for 9 months. In a second experiment,BALB/cV female mice were fed diets containing 0.2 and 2.0 p.p.m.selenium. After 9 months on the diet, the mammary tumor incidencewas 39 and 7%, respectively. Both strains of mice grew equallywell on the 0.2 and 2.0 p.p.m. selenium diets indicating thatthe highest dietary selenium level was compatible with normalgrowth. The selenium concentration and selenium dependent-glutathioneperoxidase (GSH-Px) activity of mammary glands from controlBD2F, mice fed 0.2, 1.0 and 2.0 p.p.m. dietary selenium wasexamined at 8, 9 and 10 months of age. As in previous experimentsin adult BALB/c mice, the concentration of mammary gland selenium,but not GSH-Px activity, increased with increasing levels ofdietary selenium. These results document that nutritional levelsof dietary selenium (0.5 p.p.m. Se) as well as non-toxic higherlevels (2.0 p.p.m. Se) inhibit DMBA-induced mammary tumorigenesis.     

NTP Toxicity Studies of Sodium Dichromate Dihydrate (CAS No. 7789-12-0) Administered in Drinking Water to Male and Female F344/N Rats and B6C3F1 Mice and Male BALB/c and am3-C57BL/6 Mice

Sodium dichromate dihydrate is one of a number of inorganic compounds containing hexavalent chromium (CR VI) found in drinking water supplies as a contaminant resulting from various industrial processes including electroplating operations, leather tanning, and textile manufacturing. Because of the lack of adequate experimental data on the toxicity and carcinogenicity of hexavalent chromium ingested orally, and because hexavalent chromium has been found in human drinking water supplies, the California Congressional delegation and the California Environmental Protection Agency nominated hexavalent chromium to the NTP for study. In study 1, male and female F344/N rats and B6C3F1 mice were exposed to sodium dichromate dihydrate (greater than 99% pure) in drinking water for 3 months. In study 2, sodium dichromate dihydrate was administered in drinking water to male B6C3F1, BALB/c, and am3-C57BL/6 mice for 3 months. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and mouse peripheral blood erythrocytes. In study 1, groups of 10 male and 10 female F344/N rats and B6C3F1 mice were given drinking water containing 0, 62.5, 125, 250, 500, or 1,000 mg sodium dichromate dihydrate/L for 3 months (equivalent to average daily doses of approximately 5, 10, 17, 32, or 60 mg sodium dichromate dihydrate/kg body weight to rats and 9, 15, 26, 45, or 80 mg/kg to mice). On a molecular weight basis, these doses are equivalent to approximately 1.7, 3.5, 5.9, 11.2, and 20.9 mg hexavalent chromium/kg body weight per day to rats and 3.1, 5.2, 9.1, 15.7, and 27.9 mg/kg per day to mice. Additional groups of 10 rats per sex were exposed to the same concentrations of sodium dichromate dihydrate for 4 weeks. All rats and mice survived to the end of the study. Reduced body weights occurred in 500 and 1,000 mg/L male rats, 1,000 mg/L female rats, and in male and female mice exposed to 125 mg/L or greater. Water consumption by male and female rats exposed to 250 mg/L or greater and male and female mice exposed to 125 mg/L or greater was generally less than that by the control groups, and decreases in urine volume and increases in urine specific gravity in rats were related to reduced water consumption. Exposure to sodium dichromate dihydrate caused a microcytic hypochromic anemia in rats and mice, but the severity was less in mice. Serum cholesterol and triglyceride concentrations were decreased in rats. Increased bile acid concentrations in exposed groups of rats may have been due to altered hepatic function. The incidences of histiocytic cellular infiltration were generally significantly increased in the duodenum of rats and mice, the liver of female rats, and the mesenteric lymph node of mice exposed to 125 mg/L or greater. Significantly increased nonneoplastic lesions (focal ulceration, regenerative epithelial hyperplasia, and squamous epithelial metaplasia) occurred in the glandular stomach of male and female rats exposed to 1,000 mg/L. Incidences of epithelial hyperplasia of the duodenum were significantly increased in all exposed groups of mice. In study 2, sodium dichromate dihydrate was administered in drinking water to groups of 10 male B6C3F1, 10 male BALB/c, and five male am3-C57BL/6 mice for 3 months at exposure concentrations of 0, 62.5, 125, or 250 mg/L (equivalent to average daily doses of approximately 8, 15, or 25 mg/kg sodium dichromate dihydrate or 2.8, 5.2, or 8.7 mg/kg chromium to B6C3F1, BALB/c, and am3-C57BL/6 mice). All mice in study 2 survived until study termination. Mean body weights of 125 and 250 mg/L B6C3F1 and BALB/c mice and all exposed groups of am3-C57BL/6 mice were less than those of the control groups. Mice exposed to 250 mg/L consumed less water than the control groups. Exposure concentration-related decreases in mean red cell volumes and mean red cell hemoglobin values were observed in all three mouse strains. Erythrocyte counts were increased in exposed B6C3F1 and BALB/c mice but not in am3-C57BL/6 mice. Changes in organ weights were generally consistent with reduced body weights in exposed groups in all mouse strains. No biologically significant differences in reproductive parameters were observed in any strain. Histiocytic cellular infiltration and epithelial hyperplasia of the duodenum occurred in most mice exposed to 125 or 250 mg/L, and the incidences of these lesions were increased in the 62.5 mg/L group compared to controls. Secretory depletion was present in the pancreas of most mice exposed to 125 or 250 mg/L. The incidences of glycogen depletion of the liver were significantly increased in male B6C3F1 mice exposed to 125 or 250 mg/L and in all exposed groups of male am3-C57BL/6 mice. The incidence of histiocytic cellular infiltration in the mesenteric lymph node was significantly increased in the 250 mg/L group of male am3-C57BL/6 mice. Sodium dichromate dihydrate was mutagenic in S. typhimurium strains TA100 and TA98 and in E. coli strain WP2 uvrA pKM101 with and without induced rat liver S9 enzymes. The results of four micronucleus tests conducted in the three strains of mice from studies 1 and 2 were mixed. In study 1, no significant increases were seen in micronucleated normochromatic erythrocytes in peripheral blood samples from male or female B6C3F1 mice; there was a decrease in the percentage of polychromatic erythrocytes among total erythrocytes (an indication of bone marrow toxicity), but the changes were small and not well correlated with exposure concentrations. In study 2, a significant exposure concentration-related increase (P<0.001) in micronucleated normochromatic erythrocytes was seen in am3-C57BL/6 male mice. An equivocal increase in micronucleated erythrocytes was noted in male B6C3F1 mice, based on a small increase in micronucleated normochromatic erythrocytes that did not reach statistical significance. No increase in micronucleated normochromatic erythrocytes was observed in male BALB/c mice. No significant effect of sodium dichromate dihydrate exposure on the percentage of polychromatic erythrocytes was observed in any of the three micronucleus tests conducted in study 2. In summary, administration of sodium dichromate dihydrate in the drinking water to F344/N rats and B6C3F1 mice resulted in focal ulceration, hyperplasia, and metaplasia in the glandular stomach at the limiting ridge in rats in the 1,000 mg/L group and evidence of increased histiocytic infiltration in the liver (female), duodenum of the small intestine, and/or pancreatic lymph nodes at concentrations as low as 62.5 mg/L, the lowest concentration studied. In addition, a microcytic, hypochromic anemia occurred at all exposure concentrations and was considered evidence of a toxic response resulting from absorption of Cr VI following oral ingestion in rats. A similar, but less severe, anemia was evident in mice receiving drinking water containing sodium dichromate dihydrate; histiocytic infiltration was noted in the duodenum of all three strains studied (B6C3F1, BALB/c, and am3-C57BL/6) at all concentrations employed, in the mesenteric lymph nodes at 125 mg/L or greater in the B6C3F1 strain, and at 250 mg/L in the am3-C57BL/6 strain. There was no consistent evidence of hepatocyte injury in mice in any of the strains tested. Variations in glycogen content were considered more likely related to diminished food intake than to the toxicity of sodium dichromate dihydrate. Synonyms: Chromic acid; dichromic acid; disodium salt, dihydrate; disodium dichromate dihydrate; chromium VI.     

Precancerous mammary hyperplastic alveolar nodules in four strains of virgin mice with different mammary tumor potentials: Influence of chronic caffeine ingestion

Based on the stimulating effects of caffeine on the formation of precancerous mammary hyperplastic alveolar nodules (HAN) in mice, the onset time of HAN was estimated by chronic caffeine ingestion in four strains of virgin mice with varying mammary tumor potentials (SHN, SLN, GR/A and C3H/He). Beginning at 21 days of age at weaning, mice were given tap water with (0.05%) or without caffeine and were killed at 40, 60, 90, 120 and/or 150 days of age. In the caffeine-treated groups, HAN appeared at 60, 120, 60 and 90 days of age in SHN, SLN, GR/A and C3H/He, respectively, while no such changes developed in the controls at the respective ages. These are the consequence of stimulation by caffeine of the growth of very early foci of HAN and indicate that HAN appear after 40,90, 40 and 60 days of age in SHN, SLN, GR/A and C3H/He, respectively. The onset time of HAN is associated with mammary tumor potential of virgin mice. Caffeine did not affect estrous cycle, plasma levels of prolactin and growth hormone and endocrine organ weights, suggesting that promotion by caffeine of HAN growth is minimally mediated by the endocrine system.     

Carcinogenesis Studies of Dichlorvos in Fischer Rats and B6C3F1 Mice

Dichlorvos (dichlorovinyl dimethyl phosphoric acid ester) is a cholinesterase inhibitor used widely as a contact and stomach insecticide for control of internal and external parasites. Carcinogenesis studies were conducted by administering dichlorvos in corn oil by gavage 5 times a week for 103 weeks to groups of 50 male and 50 female Fischer rats at 0, 4, or 8 mg/kg body weight, to groups of 50 male B6C3F1 mice at 0,10, or 20 mg/Ag, and to groups of 50 female B6C3F1 mice at 0, 20, or 40 mg/kg. During the course of the studies, body weights and survival rates of the male and female rats and mice were not different from those of their respective controls; females of both species appeared to gain more weight than controls. Neoplasms induced by dichlorvos included adenomas of the exocrine pancreas (male rats), mononuclear cell leukemia (male rats), and squamous cell papilloma of the forestomach (male and female mice; two other female mice had squamous cell carcinomas). Lesions observed in female rats that may have been due to dichlorvos administration included adenomas of the exocrine pancreas and fibroadenomas of the mammary gland. The results demonstrated that dichlorvos is carcinogenic for Fischer rats and B6C3F1 mice.     

Long-term effects of neonatal steroid exposure on mammary gland development and tumorigenesis in mice.

Newborn female mice of three strains--BALB/cfC3H [mammary tumor virus (MuMTV)-infected], BALB/c, and C57BL (both virus-free)--were given injections of 17beta-estradiol or testosterone, alone or in combination with ovine prolactin, for the first 5 days of life. Half of each group of mice were ovariectomized at 40 days of age, and all mice were killed between 6 and 16 months of age. Mammary glands of BALB/cfC3H mice receiving steroid hormones were better developed than those of mice not receiving steroids. Androgen induced a higher incidence of grossly dilated ducts and secretion-filled alveoli. Mammary nodule and tumor incidences were higher in steroid-treated mice than in controls; androgen resulted in higher incidences than did estrogen. The age of onset of mammary tumors was also earlier after neonatal steroid treatment. In BALB/c mice, neonatal injections of estrogen induced some alveolar development of the mammary gland; neonatal injections of ovine prolactin had a greater effect. The mammary glands of C57BL mice did not show any evidence of stimulation by neonatal hormone treatment, which indicated the probability of strain differences. However, no nodules or tumors occurred in these MuMTV-free strains. Therefore, MuMTV was essential for neoplastic mammary responses to neonatal hormone treatment. Ovariectomy prevented alveolar development and abnormal changes in the mammary glands of all groups, thus indicating that ovary-independent alterations in the mammary gland were not induced by neonatal steroid treatment. We concluded that neonatal steroid exposure resulted in increased mammary tumor risk in mice, but only in the presence of both MuMTV and ovaries.     

Carcinogenesis studies of dichlorvos in Fischer rats and B6C3F1 mice

Dichlorvos (dichlorovinyl dimethyl phosphoric acid ester) is a cholinesterase inhibitor used widely as a contact and stomach insecticide for control of internal and external parasites. Carcinogenesis studies were conducted by administering dichlorvos in corn oil by gavage 5 times a week for 103 weeks to groups of 50 male and 50 female Fischer rats at 0, 4, or 8 mg/kg body weight, to groups of 50 male B6C3F1 mice at 0, 10, or 20 mg/kg, and to groups of 50 female B6C3F1 mice at 0, 20, or 40 mg/kg. During the course of the studies, body weights and survival rates of the male and female rats and mice were not different from those of their respective controls; females of both species appeared to gain more weight than controls. Neoplasms induced by dichlorvos included adenomas of the exocrine pancreas (male rats), mononuclear cell leukemia (male rats), and squamous cell papilloma of the forestomach (male and female mice; two other female mice had squamous cell carcinomas). Lesions observed in female rats that may have been due to dichlorvos administration included adenomas of the exocrine pancreas and fibroadenomas of the mammary gland. The results demonstrated that dichlorvos is carcinogenic for Fischer rats and B6C3F1 mice.