Effect of dietary butylated hydroxytoluene on the in vivo distribution, metabolism and DNA-binding of 7,12-dimethylbenz[a]anthracene

The effect of dietary intake of butylated hydroxytoluene (BHT) (0.6%) on the in vivo distribution, metabolism and DNA-binding of intragastrically administered 7,12-dimethylbenz[a]anthracene (DMBA) was evaluated. Urinary excretion of DMBA increased, blood content of metabolized DMBA increased and blood content of non-metabolized DMBA decreased for rats fed the diet containing BHT as compared to rats fed the control diet. The binding of DMBA to both liver and mammary DNA decreased for rats fed the diet containing BHT as compared to controls. The liver activities of glutathione-S-transferase (GST), epoxide hydrolase (EH) and NAD(P)H-quinone reductase (QR) increased in response to BHT feeding. However, no increase in the mammary tissue activities of these enzymes was observed. These results suggest that the ability of dietary BHT to inhibit the initiation of DMBA-induced mammary carcinogenesis partly may be due to decreased binding of DMBA to mammary DNA. This effect of BHT is not due to an increase in mammary tissue activities of GST, EH and QR, enzymes involved in carcinogen detoxification, but may involve increased liver metabolism of DMBA to products that do not bind to DNA.     

Effect of dehydroepiandrosterone (DHEA) on the metabolism of 7,12-dimethylbenz[a]anthracene (DMBA) in rats

The influence of dehydroepiandrosterone (DHEA), an adrenal steroid, on the biotransformation of the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) in rats has been investigated. Male Sprague-Dawley rats (2-3 months old) were fed DHEA for 14 days at a dietary level of 0.8%. There was an increase in liver weights with increases per whole liver, in total protein, microsomal and cytosolic protein and cytochrome P-450, and cytosolic glutathione transferase activity in DHEA fed rats. DNA content of the liver, however, remained constant. Forty-eight hours after a single i.p. dose of [3H]DMBA (133 mumol/kg body weight, 102 muCi/rat) binding of DMBA derived metabolites to DNA decreased significantly both per unit of DNA (605 versus 194 pmol/mg DNA) as well as per whole liver DNA (25.4 versus 8.5 nmol) in DHEA fed rats. However, a significantly higher amount of DMBA-derived metabolites were bound to total hepatic protein (455 versus 288 nmol) in the steroid fed rats. Microsome mediated binding of DMBA to DNA was 3-fold higher in DHEA fed rats. Excretion of DMBA-derived metabolites in urine was 2-fold higher in DHEA fed rats. The results of this study demonstrate that DHEA inhibits binding of DMBA to hepatic DNA in vivo in spite of the increased metabolic activation of the carcinogen perhaps due to increased detoxification and competitive binding of its active species to proteins.     

Inhibition of mammary tumorigenesis by a reduction of fat intake after carcinogen treatment in young versus adult rats

The present study demonstrates that a reduction of fat intake after dimethylbenz[alpha]anthracene (DMBA) administration to female Sprague--Dawley rats leads to an inhibition of mammary tumorigenesis. Animals were fed a 20% fat diet from weaning and were transferred to a 0.5% fat diet 0, 2, 4, and 6 weeks after carcinogen treatment. In rats given DMBA at 50 days of age, the following observations were obtained: (a) tumor incidence, as well as tumor yield, was decreased when the transfer to a low fat diet was initiated up to 4 weeks after DMBA; (b) regardless of fat intake, over 90% of tumors developed in all dietary groups were adenocarcinomas. This was in contrast to rats given DMBA at 150 days of age. In this case (a) a 50% reduction in tumor incidence was apparent when the low fat diet was introduced even 6 weeks after DMBA intubation; and (b) more benign lesions were found and an association between a reduced risk of carcinogenesis and a lower ratio of adenocarcinoma to fibroadenoma seems to exist. Thus, the data demonstrate that the rats were less vulnerable to delays in reduction of fat intake on subsequent inhibition of mammary tumorigenesis than if they were exposed to the carcinogen at an older age.     

Effect of short-term feeding of sodium selenite on 7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis in the rat

The inhibitory activity of short-term feeding of one of four concentrations of dietary selenium against the induction of mammary gland carcinomas by 7,12-dimethylbenz(a)anthracene (DMBA) was studied in female Sprague-Dawley rats. When 28 days old, the animals were placed on a Torula yeast diet formulation which contained, by analysis, either 0.05, 0.15, 1.05, or 2.06 microgram of selenium, as sodium selenite, per g of diet. Mammary cancer was induced by a single p.o. administration of either 7.5 or 15.0 mg DMBA at 50 days of age. The animals were maintained on the above diets until 14 days after carcinogen treatment at which time all animals were transferred to a chow diet containing 0.21 microgram of selenium per g of diet. The study was terminated 120 days after DMBA administration. The concentrations of selenium in the liver and mammary tissue measured at the time of DMBA treatment increased with increasing levels of dietary selenium (p less than 0.05). At the low dose of DMBA, there was a trend towards reduction in the number of cancers with increased amounts of selenium, but the only significant difference occurred between groups fed the next to lowest and the highest level of selenium. At the high dose of DMBA, the number of observed cancers showed a strong dose effect (p less than 0.05). In addition, tumor load was significantly reduced in selenium-supplemented rats (p less than 0.05), and there was a significant delay (p less than 0.05) in the time to appearance of the cancers of animals receiving the highest level of selenium when compared with those receiving the lowest level. The dietary concentrations of selenium shown to inhibit the early stage(s) of cancer induction in this system were both significantly lower and fed for a shorter time interval than that which was previously reported.     

Relationship between the anticarcinogenic effect of N6,O2'-dibutyryl cyclic adenosine 3',5'-monophosphate and modulation of gene expression and inhibition of binding of 7,12-dimethylbenz(alpha)anthracene to DNA of mammary cells

Carcinogenic doses of 7,12-dimethylbenz(alpha)anthracene (DMBA) failed to induce mammary carcinoma in the rats that have received N6,O2'-dibutyryl cyclic adenosine 3',5'-monophosphate (DBcAMP) (Cancer Res., 43: 2736, 1983). We now report that the anticarcinogenic effect of DBcAMP correlates with its effect on DNA binding of the carcinogen and on gene expression. Cultured mammary epithelial cells in exponential phase of growth were used to determine the effect of DBcAMP on DMBA binding to DNA. DBcAMP inhibited the DMBA binding in carcinogen-susceptible mammary cells of 50-day-old rats, but it had no effect on the binding in the DMBA-resistant mammary cells of 35- and 110-day-old rats. The inhibitory effect of DBcAMP was appreciable at the concentration of 10(-7) M, one tenth the concentration of [3H]DMBA. DBcAMP at 10(-6) M concentration exhibited the maximal inhibition of DMBA binding; i.e., binding in DMBA-susceptible mammary cells was reduced to the level of binding observed in DMBA-resistant mammary cells. Polyadenylate-containing RNAs isolated from mammary glands of DMBA-susceptible rats (50-day-old) yielded translation products in vitro which bear a greater resemblance to translation products of growing DMBA-induced tumors than they do to products of messenger RNAs from regressing tumors or DMBA-resistant mammary glands of 110-day-old rats. DBcAMP administered to the susceptible rats resulted in changes in the translation products of the mammary glands; the translation products of the glands became similar to those of DMBA-resistant mammary glands or regressing tumors. DMBA feeding 1 day after DBcAMP treatment could not reverse this effect of DBcAMP. These data suggest that the role of cyclic adenosine 3',5'-monophosphate at the genomic level is responsible for the anticarcinogenesis of mammary cells.     

Effect of retinyl acetate on the occurrence of ovarian hormone-responsive and -nonresponsive mammary cancers in the rat

The inhibitory activity of retinyl acetate against the induction of ovarian hormone-responsive and -nonresponsive mammary gland adenocarcinomas was studied in intact and castrated female Sprague-Dawley rats. Three experiments were conducted. Mammary cancer was induced by a single p.o. administration of 7,12-dimethylbenz(a)anthracene (DMBA) at 50 days of age. Animals in Experiments 1 and 2 each received 20 mg DMBA, whereas those in Experiment 3 received 15 mg. In all experiments, animals were fed a chow diet supplemented per kg with either a placebo or 328 mg retinyl acetate starting 7 days after carcinogen treatment. In Experiment 1, rats were castrated at either 7, 60, or 90 days postcarcinogen and were killed 120 days after DMBA was given. In Experiment 2, rats were castrated 30 days after DMBA and were killed 240 days after carcinogen treatment. In Experiment 3, rats were castrated when a detected tumor attained a measurable diameter, and the hormone responsiveness of their tumors was subsequently determined. The experiment was terminated 279 days after DMBA treatment. In both intact and castrated rats, mammary tumor occurrence was inhibited by treatment with retinyl acetate. However, there were no differences in the latency to appearance time of hormone-responsive and -nonresponsive cancers in intact animals receiving either placebo or retinyl acetate. The data indicate that retinyl acetate inhibits DMBA-induced mammary tumorigenesis in either the presence or the absence of the ovaries. It appears that retinyl acetate is effective in inhibiting both ovarian hormone-responsive and -nonresponsive mammary tumors.     

Protective effect of chorionic gonadotropin on DMBA-induced mammary carcinogenesis.

The effect of the placental hormone chorionic gonadotropin (hCG) on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumours was studied in young virgin Sprague-Dawley rats. This hormone when administered at a dose of 100 IU day-1 does not induce toxic effects, measured as alterations in body weight or weight of endocrine organs, and has a reversible effect on oestrous cycle. The lack of toxicity and the fact that hCG treatment terminated prior to administration of the chemical carcinogen DMBA protects the mammary gland from malignant transformation, led us to test the effect of hCG treatment on DMBA-initiated mammary tumours. Fifty day-old virgin Sprague-Dawley rats received intragastrically 8 mg DMBA per 100 g body weight and were divided into two groups: group I animals were treated with DMBA only and group II received DMBA at age 50 and in addition, a daily intraperitoneal injection of 100 IU hCG for days 21-81 post carcinogen administration. Tumorigenic response was evaluated by biweekly palpation of all animals and by complete autopsy 24 weeks after DMBA treatment. Group I animals developed an incidence of 100% of both tumours and adenocarcinomas. Group II animals developed a significantly lower incidence of tumours and adenocarcinomas, 51.5% and 45.5% respectively. In both groups lesions developed more frequently in thoracic than in abdominal mammary glands. It is postulated that hCG treatment, probably through stimulation of ovarian oestrogen and progesterone synthesis, induces differentiation of mammary epithelium that although affected by the carcinogen can still be rescued from malignant transformation.     

Comparative study of the influence of pregnancy and hormonal treatment on mammary carcinogenesis

Since it has been shown that pregnancy protects the mammary gland from chemically induced carcinogenesis, this study was designed with the dual purpose of determining whether treatment of young virgin rats with the placental hormone chorionic gonadotropin (hCG) mimics pregnancy-induced changes in the tumourigenic response of the mammary gland and also whether the effect induced by both pregnancy and hormonal treatments was transitory, or a more permanent one, exerting the same effect when the period of time between delivery or termination of treatment and exposure to the carcinogen is lengthened. Virgin Sprague-Dawley rats were utilised in two experimental protocols. For protocol I, 50 day-old rats were either mated (Group II), or started receiving a daily intraperitoneal injection of 100 IU hCG (Group III) at age 50. Age-matched untreated virgin rats were used as controls (Group I). Twenty-one days after either delivery or termination of treatment all the animals received an intragastric dose of 8 mg DMBA/100 gbw. For the second protocol, 50 day-old virgin rats were also mated (Group V) or were treated with hCG for 21 days (Group VI); the resting period between delivery or termination of treatment was lengthened to 63 days, at which time they received a dose of DMBA. Age-matched controls (Group IV) received DMBA only. Tumourigenesis was evaluated 24 weeks post-carcinogen administration in all the groups. Pregnancy and hCG followed by the 21-day resting period significantly depressed mammary carcinogenesis to 11% and 6% respectively, compared with 63% in control animals. When the resting period was prolonged to 63 days there was also a significant depression in adenocarcinoma incidence to 9% in pregnancy (Group IV) in which it was observed that tumour incidence was also reduced as a consequence of aging at the time of exposure to the carcinogen. These results clearly indicate that hCG is as efficient as pregnancy and significantly reduces mammary carcinogenesis, and that the protective effect of both pregnancy and hCG treatment is long-lasting and both are more efficient than aging in reducing mammary carcinogenesis.     

Effects of selenium on 7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis and DNA adduct formation

The purpose of the present investigation was to determine the effects of dietary selenium deficiency or excess on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary neoplasia in rats and to delineate whether selenium-mediated modification of mammary carcinogenesis was associated with changes in carcinogen:DNA adduct formation and activities of liver microsomal enzymes that are involved in xenobiotic metabolism. Female Sprague-Dawley rats were divided into three groups from weaning and were maintained on one of three synthetic diets designated as follows: selenium deficient (less than 0.02 ppm); selenium adequate (0.2 ppm); or selenium excess (2.5 ppm). For the DMBA binding and DNA adduct studies, rats were given a dose of [3H]DMBA p.o. after 1 month on their respective diets. Results from the liver and the mammary gland indicated that neither selenium deficiency nor excess had any significant effect on the binding levels, which were calculated on the basis of total radioactivity isolated with the purified DNA. Furthermore, it was found that dietary selenium intake did not seem to affect quantitatively or qualitatively the formation of DMBA:DNA adducts in the liver. Similarly, in a parallel group of rats that did not receive DMBA, the activities of aniline hydroxylase, aminopyrine N-demethylase, and cytochrome c reductase were not significantly altered by dietary selenium levels. Concurrent with the above experiments, the effect of dietary selenium intake on carcinogenesis was also monitored. Results of this experiment indicated that selenium deficiency enhanced mammary carcinogenesis only when this nutritional condition was maintained in the postinitiation phase. Likewise, an excess of selenium intake inhibited neoplastic development only when this regimen was continued after DMBA administration. In either case, deficient or excess selenium at the time of carcinogenic insult failed to produce a significant effect on subsequent tumor yield, if selenium intake was returned to normal during the proliferative phase of tumor growth. Based on the results of these studies, it is suggested that selenium-mediated modification of mammary tumorigenesis is not exerted via alterations in carcinogenic initiation (i.e., metabolism or DNA adduct formation).     

Effect of age and parity upon the uptake of 9,10-dimethyl-1,2-benzanthracene-9-14C by mammary parenchymal cells of the rat.

The radioactivity of the parenchymal cell intracellular lipid obtained from 200-day old multiparous animals was significantly less than that of both 50- and 200-day old virgin rats at all time intervals. Furthermore, the parenchymal cell dry, fat-free tissue of the multiparous animals ocntained significantly less DMBA-9-14C than this fraction obtained from young or old virgin rats. Since there was a decrease in both the uptake and binding of DMBA-9-14C by the mammary parenchymal cells of multiparous animals, it would appear that factors associated with pregnancy and/or lactation result in an altered susceptibility of the parenchymal cell to this carcinogen. Binding of DMBA-9-14C by parenchymal cells of old virgin rats was significantly less than that of younger animals at 3 and 6 h post feeding but did not differ statistically at the later time intervals. The possibility exists that neoplastic transformation may require the interaction between high levels of DMBA and the constitutents of the mammary parenchymal cells for extended periods of time. Therefore, the decreased exposure of the cellular constituents to DMBA could account for the decrease in mammary cancer incidence observed in older rats.     

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)     

Effect of constant light on DMBA mammary tumorigenesis in rats

A study of light, and mammary tumorigenesis was conducted in rats. One-hundred female Sprague-Dawley rats were divided by weight into two groups. One group was exposed to constant light (LL) from 26 days of age, and the second group was exposed to 8 h light and 16 h dark per day (LD). Both groups received an 8 mg dose of a chemical carcinogen, dimethylben-zanthracene (DMBA) at 52 days of age. At 13 weeks post-DMBA, there were significantly fewer mammary tumors in the LL group compared with the LD group. Constant light was clearly demonstrated to have a profound effect on mammary tissue development. Although virgin, the majority of the LL rats (29/50) had gross evidence of lactation at 141 days of age. None of the LD rats (0/50) showed evidence of milk production. These results suggest that constant light not only substantially accelerated mammary gland development, but pushed development of the tissue past the stage normally observed in virgin animals (to the lactation stage).     

Effect of human chorionic gonadotropin on mammary gland differentiation and carcinogenesis

The observation that mammary carcinogenesis is inhibited in rats which completed a pregnancy prior to exposure to the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) led us to determine whether the protective effect of pregnancy could be mimicked by treatment with the placental hormone chorionic gonadotropin (hCG). We also studied the effect of this treatment on mammary gland structure and differentiation, and determined whether hCG exerts toxic or collateral effects on body weight and endocrine organs. The systemic effect of hCG on body wt and endocrine organs and mammary gland was studied in outbred virgin Sprague-Dawley rats which at the age of 50 days started receiving 100 IU hCG i.p. daily for 21 days. The animals were subdivided into nine groups of five animals each; one group was killed on the first day of and the others at 5, 10, 15 and 21 days of injection and 5, 10, 15 and 21 days post injection. The effect of the hormonal treatment on the estrous cycle was determined by studying the vaginal smears taken during and after the injection period. The following parameters were determined: body wt, weight and morphology of pituitary gland, adrenals, ovaries and uterine horns. Mammary glands were processed for histology, autoradiography for determination of DNA labeling index (DNA-LI) and whole mount preparation for morphometric studies. The effect of hCG on mammary carcinogenesis was studied in two groups of virgin rats; group I, which at the age of 50 days started receiving a daily i.p. injection of 100 IU hCG for 21 days; 21 days after the last injection they were given 8 mg DMBA/100 g body wt. Group II animals received DMBA only. hCG treated animals gained weight as a function of age at the same rate as controls. Treatment did not modify the weight of adrenal glands. The weight of ovaries, uterus and pituitary gland were transitorily increased by the 15th day of treatment, but had returned to the same values of controls by the time of DMBA administration. Treatment stimulated mammary gland differentiation, measured as a progressive reduction in number of terminal end buds and increase in the number of alveolar buds and lobules. The DNA-LI was significantly depressed in all terminal structures in the glands of treated animals. In group I animals hCG treatment decreased incidence of adenocarcinomas to 6.15 from 43.8% in group II animals.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of carcinogen dose and age at administration on induction of mammary carcinogenesis by 1-methyl-1-nitrosourea.

The objective of the work reported in this paper was to determine if the tumorigenic response to 1-methyl-1-nitrosourea (MNU) in the mammary gland varied with age of administration and was dose dependent when the carcinogen was injected prior to 50 days of age. Using a recently developed method for mammary tumor induction, MNU was injected i.p. at doses ranging from 25 to 75 mg/kg at 35 days of age or 50 mg/kg at 28, 35 or 42 days of age. Treatment with MNU resulted in induction of both benign and malignant mammary tumors. The incidence of mammary gland adenocarcinomas was 100% at and above the 50 mg/kg dose of MNU, irrespective of the age at which carcinogen was administered. The number of cancers increased in proportion to carcinogen dose, whereas cancer latency decreased as the MNU dose increased. In rats injected with 50 mg MNU/kg body weight at 28, 35 or 42 days of age, differences among groups in cancer incidence, number or latency were not statistically significant. Metastases of mammary neoplasms to lung, liver and spleen were observed in rats injected with MNU at 35 or 42 days of age. These data indicate (i) the dose responsiveness of MNU-induced mammary carcinogenesis in rats initiated prior to 50 days of age; (ii) the lack of effect of age at initiation if prior to 50 days on final tumor outcome; and (iii) that the age at which MNU is injected may affect the metastatic potential of the mammary carcinomas that are induced.     

Progression of rat mammary development with age and its relationship to carcinogenesis by a chemical carcinogen

The progression of mammary gland development in Sprague-Dawley rats between 5 and 440 days of age was studied. Tumorigenesis of the mammary gland after administration of 7,12-dimethylbenz(a)anthracene (DMBA) was also investigated during different prepubertal and postpubertal stages. The mammary gland starts as a single primary duct on day 5 and with age branches and grows into a complete gland. The growth of the gland was observed to start from the nipple area and progress into the empty fat pad. This growth was in the form of club-shaped end-buds which, after the onset of puberty, became gradually transformed into alveolar buds. [³H]-thy-midine labelling index (LI.) was high (19%) in prepubertal glands, but it eventually declined to 8% at 60-65 days. The postpubertal gland at the age of 150 days was determined to be practically mitotically static, but at 440 days, there was another increase in LI. There was a direct relationship between mammary tumorigenesis by DMBA and LI. in the mammary gland at the time of treatment with the carcinogen. Up to 55 days of age, tumorigenesis was 90-100%, and LI. was also high during this period. The carcinogen was practically ineffective at 150 days, when the mammary gland was non-proliferative. Though the total tumor induction was high in the prepubertal rats, the majority of the tumors (up to 84%) were benign fibro-adenomas, while almost all the tumors in postpubertal rats were adenocarcinomas. Thus, a relationship was observed between the presence of ovarian hormones and the induction of malignant tumors. It was concluded that cell proliferation index at the time of carcinogen treatment is important for tumor induction, but whether or not the tumor is malignant is determined by the presence or absence of ovarian hormones.     

Transplacental action of diethylstilbestrol on mammary carcinogenesis in female rats given one or two doses of 7,12-dimethylbenz(a)anthracene

Aspects of the development, morphology, and estrogen binding capacity of mammary tumors in rats exposed prenatally to the synthetic estrogen, diethylstilbestrol (DES), and treated postnatally with 7,12-dimethylbenz(a)anthracene (DMBA) were analyzed as part of a project aimed at understanding the effects of transplacental exposure to DES on estrogen-sensitive tissues. Pregnant Sprague-Dawley rats were given injections of DES (total dose, 1.2 micrograms) or vehicle alone on Days 15 and 18 of gestation. All female offspring were given gastric intubations of DMBA, either a single 10-mg dose on Day 50 or two doses (10 mg each) on Days 50 and 57. Among rats treated postnatally with 10 mg of DMBA, the DES-exposed group had a significantly greater incidence of palpable mammary tumors than did the vehicle-exposed controls. In addition, there was an earlier time of appearance of palpable tumors in the DES-exposed group. When the data from rats treated postnatally with two 10-mg doses of DMBA were analyzed, there were no significant differences in palpable mammary tumor incidence or tumor latency between the DES-exposed and vehicle-exposed groups. When the pathology of the mammary tumors produced in rats treated with 10 mg of DMBA was analyzed, the DES-exposed group had a significantly higher proportion of benign tumors (fibroadenoma, adenoma, lobular hyperplasia) than adenocarcinomata compared to vehicle-exposed controls. Both exposure groups had similar numbers of nonpalpable mammary lesions discovered at necropsy. Estrogen binding capacities of representative adenocarcinomata did not differ significantly between the two prenatal exposure groups treated postnatally with 10 mg of DMBA. These results demonstrate the importance of the dose of the challenge carcinogen in revealing the effects of transplacental drug exposure and may have special significance for women who were exposed to DES in utero.     

Modulation of DNA damage by vitamin A in developing Sprague-Dawley rats.

Prenatal and neonatal Sprague-Dawley rats were given a diet deficient in or with an excess of Vitamin A and at the age of 55 days female progeny were treated with a single i.g. dose of 80 mg/kg DMBA or 50 mg/kg MNU. Under these experimental conditions it was found that the exposure of perinatal rats to a diet containing an excess of Vitamin A caused a decrease in the amount of DMBA- and MNU-induced DNA damage in the mammary gland and the liver of the female offspring. When diets were deficient in Vitamin A there was a dual effect in terms of DNA damage detected in the same organs, namely DMBA caused an amount of DNA damage comparable to controls, while the extent of DNA damage induced by MNU greatly increased in both organs. These results indicate that Vitamin A can permanently change the sensitivity of adult progeny to chemically induced DNA damage when it is given to pregnant and lactating females.     

7,12-dimethylbenz[a]anthracene-induced DNA binding and repair synthesis in susceptible and nonsusceptible mammary epithelial cells in culture

The effect of age and parity on the binding of 7,12-dimethybenz[a]anthracene (DMBA) to DNA and the repair of DMBA-damaged DNA have been demonstrated in logarithmic phase and confluent mammary epithelial cell cultures from young virgin (YV), old virgin (OV), and parous (P) noninbred and inbred Sprague-Dawley rats. Over a dose range of 0.1-0.4 micrograms DMBA/ml, DNA binding was 1.5-to 2.0-fold higher in YV cells than in OV or P cells. In addition, a steeper slope of the dose-response curve was obtained with YV cells, suggesting a greater susceptibility of YV cells to DMBA. Excision repair was determined by measuring, in the presence of hydroxyurea and 5-bromodeoxyuridine, tritiated thymidine incorporation into DNA during the repair process. At high doses od DMBA (0.5-2.0 micrograms/ml), excision repair in YV cells was 1.5 times higher than in OV cells and 2 times higher than in P cells. However, with lower DMBA doses (less than 0.5 micrograms/ml) similar levels of repair were obtained in all 3 groups of rats. Since binding to DNA is higher in YV cells at these low DMBA doses, ti is apparent that OV and P cells exhibit a greater DNA repair per unit damage. These results, therefore, suggest that age and parity not only lower the binding of DMBA to mammary epithelial cell DNA but also increase the efficiency of DNA repair processes, which may explain the lower susceptibility of OV and P rats to DMBA-induced mammary carcinogenesis.     

Plasma hormone levels and the incidence of carcinogen-induced mammary tumours in two strains of rat.

The incidence of mammary tumours developing after administration of the carcinogen DMBA (at 50 days of age) has been determined in 2 strains of Sprague-Dawley rat. Untreated animals of each strain were exsanguinated in dioestrus at a time corresponding to the early post-carcinogen stage (at 70 days of age) and the plasma concentrations of prolactin, oestradiol-17B and progesterone were measured by radioimmunoassay. In an inbred strain of rats, tumour-induction rate was 6-4% and plasma prolactin concentration was 2-5 x lower than that found in a random-bred strain with a tumour-induction rate of 41-6%. No difference was found between the 2 strains in the level of either ovarian hormone. It is concluded that the difference between these strains in mammary gland susceptibility to DMBA may be related to plasma prolactin concentration, but it is unlikely to be determined by the ovarian hormones.