Transplacental effect of diethylstilbestrol in female rats.

The effect of diethylstilbestrol propionate (DES; 1 mg/kg body wt. was studied in the female offspring of rats exposed subcutaneously on the 19th day of gestation. Examination of vaginal smears showed persistent estrus in adult rats treated prenatally with DES. Compensatory ovarian hypertrophy (COH) induced by hemicastration of these rats was not suppressed by estrogens. A per oral test for glucose-tolerance revealed decreased utilization of glucose in the offspring of DES-treated rats. Preliminary observations demonstrated that tumors developed in 14 of 18 (77.8%) progeny transplacentally expoed to DES and in 9 of 34 (26.5%) intact control rats. Tumors of the ovary and the endometrium were found only in the rats treated prenatally with DES; no tumors of the uterine cervix or vagina were observed in either experimental or control groups. It is suggested that a transplacental effect of DES in the female is impairment of the sex differentiation of the hypothalamus. The resulting hormonal and metabolic shifts might promote tumorigenesis.     

Retinyl acetate inhibits estrogen-induced mammary carcinogenesis in female ACI rats

Two groups of female ACI rats were placed on powdered AIN-76diets containing retinyl acetate (412000 i.u. per kg diet) andtwo groups of rats were placed on placebo diets. Two weeks laterone group from each diet was subcutaneously implanted with a20 mg pellet containing 1 mg of 17-ethinylestradiol (EE2) mixedwith cholesterol, and the remaining groups received 20 mg cholesterolpellet implants. The four groups of animals were maintainedon their respective diet for 24 weeks after pellet implantation.The EE2-treated rats were hyperphagic and weighed less thanthe cholesterol-treated rats. Retinyl acetate had no effecton food consumption or body wt changes. None of the rats thatreceived pellets composed of cholesterol only exhibited mammarycarcinomas (MC) or pituitary tumors. All rats with an EE2 implanthad pituitary tumors: 88% of the rats on the placebo diet hadone or more MC; 70% of the rats on the retinyl acetate diethad one or more MC. The difference between the two EE2-treatedgroups for incidence of animals with at least one MC was notsignificant (x²). However, the EE2-treated rats on the placebodiet had approximately twice as many MC as the EE2-treated ratson the retinyl acetate diet. Thus, retinyl acetate inhibitedestrogen-induced mammary carcinogenesis in female ACI rats,without evidence of gross toxicity.     

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.     

Preventive effects of antioestrogen on mammary and pituitary tumorigenesis in rats

Six groups of inbred male Wistar/Furth (WF) rats were castrated at 40 days of age and group I received no further treatment. Groups 3 and 5 received 5.0 mg diethylstilboestrol (DES) pellets. Groups 4 and 6 were given both DES and 5.0 mg anti-oestrogen (antiE) clomiphene citrate pellets. At 50-55 days of age groups 2, 5, and 6 were exposed daily to drinking water containing 5.0 mg N-nitrosobutylurea (NBU), for 30 days. None of the castrated rats given NBU alone developed mammary or pituitary tumours (MT, PT). When antiE was administered, both MT and PT incidences were reduced in rats given DES alone or in combination with NBU. Furthermore, in antiE-treated rats receiving DES and NBU the mean number of MT per rat was also significantly decreased. Similarly a marked reduction in the mean pituitary weight was observed in antiE-treated groups. These results indicate that antiE treatment was effective in the prevention of both mammary and pituitary tumorigenesis in rats receiving DES alone or receiving a combination of DES and NBU, and its inhibitory effect on mammary tumorigenesis may be mainly due to competitive antagonism for DES-induced pituitary tumorigenesis by antiE.     

Adrenal regulation of mammary tumorigenesis in female Sprague-Dawley rats: histopathology of mammary tumors

Mammary tumors induced in female Sprague-Dawley rats by feeding 7,12-dimethylbenz(a)anthracene (DMBA; 20 mg/100 g body weight) were classified according to histological criteria of tissue differentiation, cellular atypia, and evidence of invasion. The 549 tumors could be placed in three categories, nodular hyperplasia, nodular hyperplasia with atypia, and carcinoma, and combinations of all three. Although tumors classified histologically as carcinomas did not metastasize, upon transplantation to the kidney capsule, a tumor classified as a carcinoma grew for eight generations and metastasized. Tumor heterogeneity was a common finding in DMBA-initiated tumors. Carcinomas were an early lesion. As the length of time between DMBA treatment and sacrifice increased, more tumors with areas of carcinoma were found. Therefore, DMBA-initiated tumors progressed to carcinomas either soon after initiation or later by development within nodular hyperplasias. In 4 separate groups of animals (74 adrenalectomized rats and 90 intact rats), postinitiation adrenalectomy increased the numbers of carcinomas compared to intact animals. This effect was consistently seen in the cervical and thoracic mammary glands. We propose that the mechanism for enhancement of progression to greater malignancy by adrenalectomy may be inhibition of differentiation of initiated cells in the absence of glucocorticoids.     

Dose-response effects of dietary fiber on NMU-induced mammary tumorigenesis, estrogen levels and estrogen excretion in female rats

The publisher wishes to apologise for the inclusion of a duplicateTable IX, and for the omission of Table VIII on page 50 of theabove mentioned paper. The correct Table is shown below. Thetitle of Table V was also incorrect and should have read serumestrogen concentrations^a,b     

Dose-response effects of dietary fiber on NMU-induced mammary tumorigenesis, estrogen levels and estrogen excretion in female rats

The does-related effects of the fiber-rich isolate, soft whitewheat bran (SWWB), and the pure fiber, cellulose, on N-nitrosomethylurea(NMU)-induced mammary tumorigen-esis was assessed in F344 femalerats. SWWB (45% total dietary fiber, TDF) was added to the AIN-76Ahigh-fat diet at 9, 12, 15 and 18% cellulose (98% TDF) was addedto the same diet at 4.5, 6, 7.5 and 9% to give equivalent amountsof TDF. The experimental diets were fed 3 days post-NMU andcontinued for a period of 25 weeks, at which time the experimentwas terminated and tumors enumerated. It was found that significantinhibition of mammary carcinoma occurred only at 9% SWWB, nonsignificantinhibition occurred at 12% SWWB, and no inhibition was seenat higher doses. Cellulose-fed animals exhibited consistentlyhigher tumor yields regardless of dose. The difference in tumoryields between the 9% SWWB group and the remaining seven groupswas attributable to an increased incidence in tumors characterizedhistologic-ally as intraductal proliferation and ductal carcinomain situ in the latter. Analysis of blood, urine and fecal estrogenswas conducted to test whether dietary fiber exerted its tumor-inhibitingeffect by altering the entero-hepatic recycling of estrogens.Although SWWB, in general, lowered urinary estrogen excretion,increased fecal estrogen excretion and lowered blood estrogens,there was no consistent correlation between the amount of SWWBconsumed, estrogen status and tumor yields. These results suggestthat (i) wheat bran fiber at 9% or minor constituents associatedwith it, contain anti-promoting properties that cellulose lacks;(ii) SWWB appears to exert its effects by suppressing the clonalexpansion phase of mammary carcinogenesis; (iii) there is anupper limit (12–15% w/w) to the protective effects ofSWWB; and (iv) the effects of SWWB on mammary tumorigenesismay not be attributed to alterations in the enterohepatic recyclingof estrogens.     

Synergism of diethylstilbestrol and radiation in mammary carcinogenesis in female F344 rats.

One compressed 20-mg pellet containing cholesterol only or cholesterol mixed with 0.98, 1.6, 2.6, or 3.9 mg of diethylstilbestrol (DES) was implanted into each of 203 female F344 rats. Two days later, half the animals in each group were exposed to 150 R of X-rays, and the other half were sham irradiated. The rats were maintained until 350 days post implantation. Mortality increased with the higher doses of DES, with or without X-rays. DES at all dose levels, with or without X-rays, produced pituitary tumors and pyometritis. Only rats that received both DES and X-rays had mammary adenocarcinomas (AC). A synergistic AC response was found in the group that received 2.6 mg DES plus X-rays. Synergism was defined as a significantly greater incidence of rats with mammary neoplasia resulting from DES plus X-ray treatment when compared to the summed incidence from comparable individual treatments. For all other groups of rats that received both treatments, synergism was detected only when their data were combined. Synergism was not detected among rats that had fibroadenomas (FA). Both types of neoplasms were independent phenomena because no significant relationship was found between the incidences of FA and AC.     

Transplacental genotoxicity of diethylstilbestrol

Diethylstilbestrol (DES) is a transplacental carcinogen in humans and in rodents. As part of an attempt to examine the mechanism of transplacental carcinogenesis, the transplacental genotoxity of this stilbene estrogen has been investigated. Pregnant hamsters received single injections of 200 mg/kg DES on the 10th day of gestation and were killed 5 or 24 h after treatment. The maternal organs were found to contain the same DES-DNA adduct patterns observed previously by 32P-postlabeling analysis in female hamsters. These adduct patterns, generated by the genotoxic metabolite diethylstilbestrol-4',4h'-quinone (DES Q), were also observed in fetal heart and kidney DNA. In fetal liver DNA, this modified nucleotide, generated by the quinone, was only the minor adduct. The major DNA adduct in this organ was not observed previously and may have been generated by an unknown DES metabolite. The data demonstrate that DES is a transplacentally active genotoxic agent. They also provide evidence for fetal metabolism of DES to DES Q and to other unknown genotoxic intermediates.     

Relationship between stages of mammary development and sensitivity to gamma-ray irradiation in mammary tumorigenesis in rats

Mature Wistar-MS rats were ovariectomized and treated with estradiol benzoate and/or progesterone. Control animals were treated with olive oil. The rats were then exposed to γ-rays and implanted with a pellet of diethylstilbestrol. The incidence of mammary tumors in rats treated with estradiol benzoate or with progesterone was significantly higher than in rats in the non-treated control group, whereas, in rats treated with both estradiol benzoate and progesterone, the incidence was not significantly different from that in the controls. Histological examination of the mammary tumors showed 2 types of neoplasm: adenocarcinoma and fibroadenoma. Interestingly, over half of all the tumors in the rats treated with estradiol benzoate were adenocarcinomas, while fibroadenomas were mainly induced in the rats treated with progesterone or with both estradiol benzoate and progesterone. The expression of estrogen and progesterone receptors in the tumor tissues showed some differences according to whether the groups were treated with estradiol benzoate or with progesterone. Morphologically, mammary glands at irradiation showed well-developed lobuloalveoli in both the estradiol-benzoate-treated rats and in those rats treated with both estradiol benzoate and progesterone. This was consistent with the higher incorporation of [³H]thymidine into the DNA in the mammary glands of rats in both of these groups. Our findings suggest that a more advanced developmental stage of the mammary glands, dependent upon ovarian hormones, is related to a higher incidence of mammary tumors induced by irradiation. © 1995 Wiley-Liss, Inc.     

Transplacental tumor-preventive effects of polyclonal antibodies generated against the soluble 53 kDa antigen on mammary tumorigenesis in offspring.

This study was designed to determine whether immunizing females with polyclonal antibodies generated against the soluble 53 kDa tumor-associated antigen (s53 TAA) has a tumor-preventive effect on their progeny and whether this effect is manifested in some biochemical characteristics. Rat females were immunized before mating with anti-s53 IgG (50 microg/rat in Freund's complete and incomplete adjuvant, three times during a month) and their 5-week-old offspring was exposed to the carcinogen (dimethylbenz(a)antracene, 10 mg/rat). Results of these experiments were studied 4 months later. Vaccination of mothers decreased the tumorigenic effects of DMBA on their offspring. Blood levels of soluble TAA were analyzed in offspring of different groups. Two TAA were isolated from the blood, with molecular masses of 64 and 53 kDa. Their concentrations differed in offspring obtained from different maternal groups. Vaccination itself resulted in a marked increase in the blood levels of TAA, not only in the mothers but also in their offspring, however, this increase was not significant in tumor-bearing animals. In offspring from non-vaccinated mothers, tumorigenesis resulted in high overexpression of s53. In offspring from vaccinated mothers, a high blood level of s53 was shown even in tumor-free animals, probably due to maternal vaccination. We conclude that maternal vaccination before pregnancy increases immunoreactivity in offspring and can reduce risk of tumors in those progeny.     

Ezetimibe reverses the inhibitory effects of dietary cholesterol on mammary tumorigenesis in rats

There are concerns regarding increased cancer incidence in patients treated with ezetimibe, an inhibitor of the absorption of dietary cholesterol. Here we tested the hypothesis that ezetimibe will accelerate mammary tumorigenesis in rats. The drug was administered at a dose of 1 ppm in an AIN‐93G diet that contained 0.3% cholesterol. This experimental diet and control diets that contained either no additions or cholesterol or ezetimibe only, were fed to groups of 30 Sprague‐Dawley rats 3 days after they were treated with 50 mg/kg methylnitrosourea (MNU). All rats were euthanized 22 weeks after MNU administration. Tumor multiplicity was significantly smaller in rats fed cholesterol than those fed no cholesterol (1.84 ± 0.42 vs. 3.86 ± 0.86 respectively, P < 0.05), but was significantly greater in the cholesterol/ezetimibe group than the group fed only cholesterol (3.48 ± 0.59 vs. 1.84 ± 0.42 respectively, P < 0.04). The average weight of tumors/rat was also significantly larger in the cholesterol/ezetimibe group than those fed cholesterol alone (5.67 ± 1.15 vs. 2.56 ± 0.71 respectively, P < 0.04). As expected, ezetimibe prevented the cholesterol raising effect of the dietary cholesterol. These results show that ezetimibe reverses the inhibitory effect of dietary cholesterol on the development of rat mammary tumors.     

Effect of age and strain on N-methyl-N'-nitro-N-nitrosoguanidine tumorigenesis in ACI and Wistar Furth rats

N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) dissolved indistilledwater (5 g/1) was administered orally once by gastrictube ata dose of 0.25 ml/10 g body weight to 5-day-old or 28-day-oldWistar Furth (W/Fu) or ACI rats. Gastric tumorsin the glandularstomach were found in 58% of 5-day-old ACI rats, but none werefound in the rest of the groups. Forestomach tumors were foundin both strains of rats at bothage groups with incidences of68–100%. Lung tumors wereinduced in 64% of 5-day-old and6% of 28-day-old W/Fu rats,but not in ACI rats. Besides thetumors, a high frequency of hepatic cysts was also noted inACI rats. Intestinal metaplastic foci with alkaline phosphataseactivity were foundin the group of 5-day-old ACI rats and nonein the rest ofthe groups. The results showed that the incidencesand thelocations of tumors in rats induced by MNNG are greatlyinfluencedby both strain and age.     

Adrenal regulation of mammary tumorigenesis in female Sprague-Dawley rats: incidence, latency, and yield of mammary tumors

Huggins and Morii (J. Exp. Med., 114: 741, 1961) reported that massive adrenal necrosis occurs in 79 and 100% of female Sprague-Dawley rats receiving 20 and 30 mg, respectively, of the mammary carcinogen 7,12-dimethylbenz(a)anthracene (DMBA). Here, adrenal necrosis and regeneration were studied in 158 rats for up to 21 days post-DMBA by radioautography of the adrenals of animals given 50 microCi [3H]thymidine 30 min before sacrifice. Adrenal cell proliferation was markedly inhibited 21 days post-DMBA. Regenerated adrenals were more susceptible to this adrenocorticolytic effect. To investigate if alterations in adrenal function modify tumorigenesis, animals underwent adrenalectomies (ADX), hypophysectomies, ovariectomies, and pituitary transplants alone or in combination 6 days after receiving DMBA (20 mg/100 g intragastrically) at 50 days of age. To prevent adrenal necrosis, 24 animals were pretreated with metyrapone. Methylprednisolone acetate, 1 mg i.m., was given to 40 animals every 5 days beginning 6 days post-DMBA. There were 50 non-DMBA-treated intact and surgical controls. DMBA was necessary but not sufficient to induce mammary tumors. No tumors developed in controls or in 46 animals hypophysectomized 6 days after DMBA. Metyrapone reduced tumor incidence and yield. ADX after DMBA treatment increased the tumorigenic response and eliminated resistance to tumorigenesis in older rats. Only three tumors developed in DMBA-treated rats receiving methylprednisolone acetate. Mammary tumorigenesis was increased by pituitary transplant 6 days after DMBA to intact and ADX animals. Ovariectomy 6 days after DMBA was as effective as methylprednisolone acetate in preventing tumorigenesis; ADX did not overcome either inhibition. We conclude that adrenal hormones inhibit proliferation of initiated mammary cells.     

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.     

Transplacental effects of a 15% olive-oil diet on chemically-induced tumorigenesis in offspring

We evaluated whether feeding pregnant female rats a diet high in olive-oil, that showed a tumor-preventive effect in adults, has a similar preventive effect on chemically-induced cancer in offspring (i.e. mammary glands and colon cancer in rats). The control group was fed the same 7% corn-oil diet as their mothers. Experimental group I was fed a 7% corn-oil diet while their mothers received a 15% olive-oil diet. Experimental group II was fed the same 15% olive-oil diet as their mothers. Female offspring were twice administered 7,12-dimethylbenz(a)antracene (DMBA) in doses of 10 mg/rat. Male offspring were injected 6 times with 1, 2-dimethylhydrazine (DMH) in doses of 20 mg/kg body weight. Effect of DMBA was manifested in a high rate of tumorigenesis: the number of tumor-bearing rats in control offspring reached 52.0%. This effect increased to 60.6% among offspring of experimental group II and to 67.7% in offspring of experimental group I. The mean tumor size increased significantly in control offspring. Following administration of DMH number of tumor-bearing rats was similar in all groups of offspring: 36.7%, 40.7% and 42.8%. Tumor types differed: the majority of tumors in the control group were benign polyps and adenomas (72.1%) and the number of adenocarcinomas was low (27.9%). The number of malignant tumors increased to 37.5% in offspring of experimental group II and to 45.5% in offspring of experimental group I. In control group offspring, a distinct tendency to increased body weight and a significant increase in spleen weight were seen. The findings indicate that feeding mothers a diet high in fat concentrations, even those with known tumor preventive significance in adults, lose this cancer-inhibiting role in offspring.     

雄激素对雌性小鼠乳腺发育的影响

目的：观察雄激素（睾酮）对雌性小鼠乳腺生长、发育的影响,为研究雄激素与乳腺疾病的关系奠定基础。方法：对小鼠进行睾酮皮下注射和来曲唑灌胃给药,一段时间后,应用整装切片法和HE染色法,观察小鼠乳腺组织的发育情况。结果：高剂量雄激素主要使雌性小鼠正常乳腺组织的导管二、三级分支、末端终蕾数量减少;低剂量雄激素一定程度上可以促进乳腺的发育。结论：高剂量雄激素可能经过AR及其它信号通路或作用间质细胞产生某种信号分子抑制乳腺的生长。     

Transplacental administration of diethylstilbestrol (DES) causes lesions in female reproductive organs of Donryu rats, including endometrial neoplasia.

The effects of transplacental administration of diethylstilbestrol (DES) on female reproductive organs were investigated using Donryu rats. The animals were given subcutaneous injections of DES dissolved in olive oil at doses of 0.01 or 0.1 mg/kg on days 17 and 19 of gestation. In female offspring, clinical signs, body weights and estrous cycles were continuously assessed until all survivors were killed at month 18. A low mean litter size and shortening of period of pregnancy were recognized in the 0.1 mg/kg group. Disorder and/or suspension of the estrous cycle (so called persistent estrus) also appeared very early in the 0.1 mg/kg group. Macroscopically, the incidences of hypoplasia of the oviduct, cystic dilatation of the uterus and small size of the uterine cervix were higher in the 0.1 mg/kg group than those in the control group. Histologically, in the ovary, the incidence and degree of atrophy were increased in both 0.01 and 0.1 mg/kg groups. In the uterus, total incidences of endometrial hyperplasias were about the same in all groups. However, endometrial adenocarcinomas were dose-dependently increased in the treated groups, the incidence in the 0.1 mg/kg group being significant, compared to that in the control. In the vagina, mucification was more prominent in the treated animals, especially at the higher dose, but no tumors were observed. The present results indicate that prenatal exposure to DES can produce uterine adenocarcinomas in rats, as reported earlier for mice, although its carcinogenic activity is not so strong. Increase of endometrial adenocarcinoma incidence might depend on hormonal imbalance resulting from the ovarian atrophy due to transplacental treatment of DES.