The effect of gonadal ablation on transplacentally induced neurogenic tumors in hamsters.

The effects of gonadectomy on tumors induced transplancentally by the ethylnitrosourea precursors, ethylurea and sodium nitrite, were investigated in hamsters. The pregnant hamsters were exposed to four daily doses of ethylurea (100 mg/kg) and sodium nitrite (50 mg/kg) administered from Day 12 to 15 of pregnancy. Weaned offspring were gonadectomized when they reached the age of 5 weeks. Orchiectomized male progeny showed a multiplicity and greater frequency of peripheral nervous system tumors and of any other tumor types than did intact males or their ovariectomized and intact female siblings. The possible inhibitory effects of endogenous androgens on the development and growth of neurogenic tumors in the peripheral nervous system and the influence of an induced endocrinal imbalance on prenatally induced neoplasms are discussed.     

Effect of tocopherol, phenformin and thymus and pineal polypeptide factors on the transplacental carcinogenic effect of N-nitroso-N-ethylurea in rats

The study was concerned with the influence of postnatal treatment with antioxidant tocopherol, antidiabetic drug phenformin and low-molecular polypeptide factors of the thymus (thymalin) and pineal gland (epithalamin) on transplacental carcinogenicity of low-dose (7.5 mg/kg body weight, 3.2% of LD 50) N-ethyl-N-nitrosourea (ENU) in rats. Transplacental exposure to ENU was followed mainly by the development of brain tumors. Tumors of the spinal cord, peripheral nervous system and kidney were observed much more rarely. Treatment with tocopherol, thymalin or epithalamin did not significantly influence the transplacental carcinogenicity of ENU, whereas application of phenformin was followed by a decreased incidence of brain tumors.     

The effect of tocopherol and ascorbic acid on the development of experimental esophageal tumors

The study was concerned with the influence of tocopherol and ascorbic acid on induction of tumors by N-nitrososarcosine ethyl ester (NSEE) in rats. In the first series of experiments, NSEE was given orally in the daily dose of 100 mg/kg body weight during 8 weeks while alpha-tocopherol acetate was administered in the dose of 600 mg/kg food during the following 32 weeks. In the second series, NSEE was given intragastrically in the dose of 50 mg/kg body weight daily during 16 weeks whereas for the following 16 weeks, the animals received 20 g/kg food ascorbic acid. The rats were sacrificed at 40 (series 1) and 32 weeks (series 2) of the experiment. NSEE induced tumors of the esophagus and forestomach in more than 90% of cases, mainly papillomas and--less frequently--carcinomas, five tumors per rat, on the average. Treatment with tocopherol was followed by a 37% decrease in the incidence of esophageal and forestomach tumors, an approximately two-fold drop in their multiplicity as well as by lowered incidence of carcinomas. Ascorbic acid did not affect tumor induction.     

Influence of five different postnatal lifelong treatments on the transplacental carcinogenicity of ethylnitrosourea in sprague-dawley rats

Sprague-Dawley rats received in 10 mg/kg body weight (group I) or 30 mg/kg body weight (group II) ethylnitrosourea (ENU) orally on the 19th day of pregnancy. Their offspring were treated with Bacille Calmette-Guerin, human albumin, hydrocortisone, cyclophosphamide or nicotine starting on the 6th day of life. The ENU treatment significantly reduced the life expectancy of all offspring. Treatment of the offspring did not influence tumor frequency, induction time or localization of neurogenic malignant tumors. Cyclophosphamide treatment of group II offspring increased the number of females bearing mammary carcinomas.     

Effect of long-term administration of retinoids on rats exposed transplacentally to ethylnitrosourea

A neurogenic cancer model, involving transplacental administration of ethylnitrosourea (ENU) to Sprague-Dawley rats, was employed to evaluate the efficacy of retinyl acetate, 13-cis-retinoic acid, and all-trans-retinoic acid in prevention of nervous system tumors in the offspring. Supplementation of the diet with either of these retinoids did not alter the incidence, number, or latency period of the induced neurogenic tumors. Long-term administration of high doses of 13-cis-retinoic acid (240 mg/kg of diet) or all-trans-retinoic acid (65 mg/kg of diet) produced lethal toxicity in this strain of rats, possibly due to interference with vitamin K absorption and the resulting internal hemorrhages associated with hypoprothrombinemia. Prolonged feeding of retinyl acetate increased the retinyl palmitate level in the liver. The concentration reached was not dose-dependent; a maximum level (approximately 10-fold that of controls) was observed after six months of feeding. An unexpected observation was the decrease in liver retinyl palmitate concentration in the livers of rats fed 13-cis-or all-transretinoic acid.     

Study of post-natal effect of chemopreventive agents on ethylnitrosourea-induced transplacental carcinogenesis in rats. III. Inhibitory action of indomethacin, voltaren, theophylline and {varepsilon}-aminocaproic acid

The influence of the arachidonic acid metabolism inhibitors,indomethacin and voltaren; an inhibitor of phosphodiester-aseactivity, theophylline and the protease inhibitor -aminocaproicacid (EACA) on N-ethyl-N-nitrosourea (ENU)-induced transplacentalcarcinogenesis was studied in rats. ENU was given to pregnantrats as a single i.v. exposure at a dose of 75 mg/kg body weighton the 21st day after conception. Indomethacin and voltaren(20 p.p.m. in drinking water), theophylline (0.01% in diet)and EACA (1000 p.p.m. in drinking water) were given to the offspringthroughout their post-natal life until all survivors were killedat 12 months. In the ENU-only control groups, 100% of the offspringdeveloped tumors of brain, spinal cord, peripheral nervous systemor kidneys, with a total average number of 3.1 tumors per ratThe most marked inhibitory effect was exerted by theophylline,which significantly decreased the incidence and multiplicityof total tumors, and at all main sites selectively (brain, spinalcord, peripheral nerves and kidneys). It also prolonged averagesurvival time of the offspring. Indomethacin and voltaren significantlydecreased total tumor incidence and multiplicity, and braintumor incidence and multiplicity. Indomethacin also decreasedkidney tumor multiplicity and voltaren diminished spinal cordtumor multiplicity. EACA decreased multiplicities of total,brain, peripheral nerve and kidney tumors, and diminished theincidence of brain tumors. These chemopreventive agents decreasedtumor incidences 20–33% and tumor multiplicities 1.4–2.7times, compared with the ENU-only controls.     

Transplacental carcinogenic effects of nickel(II) acetate in the renal cortex, renal pelvis and adenohypophysis in F344/NCr rats.

Nickel(II) acetate (NiAcet), a soluble nickel salt known to be an effective initiator of renal epithelial tumors in adult rats, was studied for possible transplacental carcinogenicity. Pregnant F344/NCr rats were given NiAcet i.p. either once a day on day 17 (90 mumol/kg body wt; group 1) or twice on days 16 and 18 of gestation (45 mumol/kg body wt/day; group 2). Offspring of these rats were further subdivided into groups 1A and B and 2A and B, respectively. Groups 1A and 2A received ordinary tap water while groups 1B and 2B received drinking water containing 500 p.p.m. sodium barbital (NaBB) during weeks 4-85 of age. Renal cortical epithelial and renal pelvic transitional epithelial tumors occurred in male offspring given NiAcet prenatally followed by NaBB postnatally (group 1B, 15 tumors in 8/15 rats; group 2B, 10 tumors in 7/15), but not in male offspring given NiAcet only (0/32) or in controls given prenatal sodium acetate (NaAcet) only (0/15) and rarely in males given NaAcet followed by the promoter NaBB (1/15). No renal tumors occurred in females. Pituitary tumor incidence was significantly higher in offspring of both sexes given NiAcet prenatally (NaAcet controls, 4/31, both sexes combined; group 1A, 14/33, P = 0.012; group 2A, 14/31, P = 0.008). Pituitary tumors appeared much earlier in rats given NiAcet prenatally, with or without postnatal NaBB, and often were malignant by cytologic and histologic criteria including pleomorphism and invasion of adjacent structures, unlike the well-differentiated adenomas that occurred less frequently in untreated rats. These results are the first evidence that Ni(II) is a potent transplacental initiator of epithelial tumors in fetal rat kidney and a complete transplacental carcinogen for rat pituitary.     

Effect of metabolic inhibitors, methylxanthines, antioxidants, alkali metals, and corn oil on 1,2-dimethylhydrazine carcinogenicity in rats.

The effect of the oral administration of 10 compounds on 1,2-dimethylhydrazine (DMH) carcinogenesis was investigated in 180 male Wistar rats and 510 male BD6 rats. DMH, administered s.c. once per week for 20 consecutive weeks (20 mg/kg body wt/dose), produced intestinal (mainly colon) tumors of various histological type in 100% of both rat strains and, in addition, caused Zymbal gland carcinomas in 79.7% of Wistar rats. Pretreatment with disulfiram (DSF, 500 mg/kg), a known inhibitor of DMH metabolism, totally prevented intestinal and Zymbal gland tumors in Wistar rats. When DSF treatment started after the first DMH injection, the protective effect was not total, the incidence and multiplicity of both types of tumors being comparable to those observed following a single injection of the carcinogen alone. This confirms the involvement of DSF in the initiation stage only of DMH carcinogenesis. A complete prevention of intestinal tumors in BD6 rats was also produced not only by the DSF metabolite carbon disulfide (250 mg/kg) but also by the hepatotoxic agent carbon tetrachloride (1.5 ml/kg), which suggests that the block of DMH metabolism in rat liver is not an exclusive property of thiono-sulfur compounds. Butylated hydroxytoluene (BHT) decreased the multiplicity of intestinal tumors, but not to a significant extent. BHT and the aforementioned metabolic inhibitors were administered by gavage in corn oil, which per se did not significantly decrease intestinal or Zymbal gland tumors. All remaining modulators were administered with drinking water. Two additional antioxidants triggered opposite effects on the multiplicity of intestinal tumors. In fact, sodium selenite (10 mg/l) significantly decreased the number of tumors, whereas ascorbic acid (10 g/l), irrespective of its combination with CaCl2, produced a marked enhancement. The alkali metal salts CaCl2 and KCl (both at 5 g/l) as well as the methylxanthines caffeine and theophylline (both at 600 mg/l) were devoid of significant effects. Neither treatment with DMH alone nor its association with test modulators was accompanied by significant changes in body weight gain or survival of animals. On the whole, depending on the mechanisms involved, the comparative study of test compounds led to a broad array of effects on DMH carcinogenesis, ranging from complete inhibition to significant enhancement. The resulting picture can be visualized at a glance in Figure 1 of this article.     

Dose-response studies of the effect of dietary butylated hydroxyanisole on colon carcinogenesis induced by methylazoxymethanol acetate in female CF1 mice

The effect of dietary butylated hydroxyanisole (BHA) on methylazoxymethanol acetate [(MAM AC) CAS: 592-62-1; methyl-ONN-azoxy)methanol acetate]-induced intestinal carcinogenesis was studied in female CF1 mice. BHA was added at levels of 0, 0.03, 0.1, 0.3, and 0.6% to the NIH-07 open-formula diet and at 0 and 0.6% to the AIN-76 semipurified diet and fed to mice, starting at 5 weeks of age until termination of the experiment. At 7 weeks of age, all animals except the vehicle-treated controls were given ip injections of MAM AC (15 mg/kg body wt for four times in 11 days for the low-dose group: total dose, 60 mg/kg body; 15 mg/kg body wt for eight times in 22 days for the high-dose group: total dose, 120 mg/kg body wt). With a low dose of carcinogen, the lung tumor incidence was inhibited in mice fed the NIH-07 diet containing 0.03-0.6% BHA and the AIN-76 diet containing 0.6% BHA compared to lung tumor incidence in those fed the diets without BHA; with a high dose of carcinogen, the inhibition was observed in mice fed the NIH-07 diet containing 0.1-0.6% BHA. Colon tumor incidence and colon tumor multiplicity (number of tumors per animal and number of tumors per tumor-bearing animal, respectively) were lower in mice fed the NIH-07 diets with 0.03-0.6% BHA or fed the AIN-76 diet with 0.6% BHA, as well as treated with a low dose of carcinogen, than in animals fed no BHA; with a high dose of carcinogen, colon tumor multiplicity and colon tumor incidence were inhibited in animals fed the NIH-07 diet containing 0.1-0.6% BHA. Consumption of the NIH-07 diets containing 0.03-0.6% BHA resulted in increased glutathione transferase activity of liver and small intestinal and colon mucosae in a dose-related manner.     

Chemopreventive effects of the aromatase inhibitor vorozole (R 83842) in the methylnitrosourea-induced mammary cancer model

The chemopreventive activity of the highly specific nonsteroidal aromatase inhibitor, vorozole, was examined in the methylnitrosourea (MNU)-induced rat model of mammary carcinogenesis. Various doses of vorozole (0.08-1.25 mg/kg body wt/day) were administered daily (by gavage) to female Sprague-Dawley rats starting at 43 days of age. Seven days later, the rats were given a single i.v. dose of MNU (50 mg/kg body wt). Rats were continually treated with vorozole until the end of the experiment (120 days post-MNU). Vorozole caused a dose dependent inhibition of mammary cancer multiplicity. The highest dose of vorozole (1.25 mg/kg body wt/day) decreased cancer multiplicity by approximately 90%, and simultaneously decreased cancer incidence from 100 to 44%. The next two highest doses of vorozole (0.63 and 0.31 mg/kg body wt/day) inhibited MNU-induced mammary cancer multiplicity by 70-80%. Even the two lowest doses of vorozole (0.16 and 0.08 mg/kg body wt/ day) decreased cancer multiplicity -50%. Serum level determinations were performed on a variety of endpoints at either 4 or 24 h following the last dose of vorozole. Insulin-like growth factor (IGF)-1 levels were slightly, but significantly, increased by vorozole treatment. Vorozole induced striking increases in serum testosterone levels at 4 h at all the dose levels employed. Testosterone levels were significantly elevated over controls at 24 h in rats given the lower doses of vorozole (0.08-0.31 mg/kg body wt/day), but were significantly lower than in rats administered the higher doses of vorozole (0.63 or 1.25 mg/kg body wt/ day). This result presumably reflects the limited half- life of vorozole in rats. In a second series of experiments, the effects of limited duration of dosing with vorozole (2.5 mg/kg body wt/day) or intermittent dosing with vorozole were determined. Treatment of rats with vorozole for limited time periods, from 3 days post-MNU administration until 30 or 60 days post-MNU treatment, resulted in significant delays in the time to appearance of palpable cancers. However, these limited treatments did not greatly affect the overall incidence or multiplicity of mammary cancers when compared with the MNU controls at the end of the study (150 days post-MNU). Finally, the effects of intermittent dosing with vorozole (2.5 mg/kg body wt/day) were examined. Rats were administered cycles of vorozole daily for a period of 3 weeks followed by treatment with the vorozole vehicle for the next 3 weeks (total of four cycles). Although this intermittent treatment did inhibit the appearance of new tumors during each of the periods that vorozole was administered, it did not cause regression of palpable cancers.      

Induction of neurogenic tumors in C3HeB-FeJ mice by nitrosourea derivatives: observations by light microscopy, tissue culture, and electron microscopy

Neurogenic tumors were induced in 32.3% of C3HeB/FeJ mice treated transplacentally with ethylnitrosourea (ENU) and in 10.5% of mice treated intravenously (IV) with methylnitrosourea (MNU). Earlier reports on other strains of mice treated with nitrosourea derivatives indicated that non-neural tumors, particularly lymphomas, were readily induced. However, tumors of the nervous system did not develop or occurred only in a low percentage of treated mice. Genetic strain of mice appears to influence susceptibility of mice to nitrosoureas. Two brain tumors, an oligodendroglioma in the diencephalon and a mixed neuroblastoma-glioma of the cerebellum, occurred in 19 adult male mice treated IV every 4 weeks with 25 mg/kg MNU to a total of 175 mg/kg. Neurinomas of cranial nerves developed in 9 of 31 offspring of pregnant mice treated with 20 mg/kg ENU IV on the 19th day of gestation. One MNU-induced oligodendroglioma and 1 ENU-induced neurinoma were propagated in tissue culture. Cells of both tumors produced intracerebral (IC) and subcutaneous (SC) tumors following injection into syngeneic mice. Tissue samples from both IC transplanted tumors contained abundant clusters of C-type RNA viruses in interstitial spaces. Budding virus particles were readily demonstrated on the plasma membranes of tumor cells.     

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.     

Leiomyomas and leiomyosarcomas of the kidney in 4-day-old BUF rats given methylazoxymethanol acetate intraperitoneally.

The effect of age and sex on the development of renal tumors was studied in inbred BUF male and female rats 4 days, 5, 8, 12, 24, or 52 weeks old. Methylazoxymethanol (MAM) acetate was injected ip (20 mg/kg body wt) once weekly for 9 weeks. Animals 52 weeks old died from hepatic and/or renal necrosis; however, animals of other ages survived 24-42 weeks. Female rats 4 days old were susceptible to the development of leiomyomas and leiomyosarcomas of the kidney, whereas 4-day-old male rats had a few leiomyomas. Adenomas and carcinomas of the kidney and nephroblastomas were not observed. It was concluded that the aglycone of cycasin, MAM, is important in the induction of leiomyosarcomas of the kidneys in 4-day-old rats.     

The stimulating effect of acetic acid, alcohol and thermal burn injury on esophagus and forestomach carcinogenesis induced by N-nitrososarcosin ethyl ester in rats

Five groups of outbred white male rats were given N-nitrososarcosin ethyl ester (NSEE) i.g. for 4 or 6 months at a daily dose of 50 mg/kg of body wt. 5 days/week. Some groups of animals were given a 3% water solution of acetic acid or a 40% solution of ethanol i.g. for 8 months from the beginning of the experiment. The remaining groups of these rats received controlled local thermal burn injury of the esophageal mucosa 15 days before the beginning of the experiment. Acetic acid solution increased the multiplicity of benign and malignant tumors as well as carcinoma incidence in the esophagus. Ethanol in combination with NSEE did not influence carcinogenesis in the esophagus but increased the incidence of leukokeratosis and the multiplicity of forestomach papillomas. In rats treated with NSEE after thermal burn injury, a significant increase in the frequency and multiplicity of papillomas was found in the burn zone.     

The inhibiting activity of meadowsweet extract on neurocarcinogenesis induced transplacentally in rats by ethylnitrosourea

Inhibitory activity of a decoction of meadowsweet, given postnatally, was studied in rats at risk for neurogenic and renal tumors initiated by transplacental exposure to ethylnitrosourea (ENU). Chemical analysis of ethanol and aqueous extracts of meadowsweet has shown high content of biologically active flavonoids and tannins. Pregnant rats of LIO strain were given a single i.v. injection of ENU, 75 mg/kg, оn the 21st day of gestation. After weaning at 3 weeks after birth, the offspring were divided into two groups: the first was a positive control (ENU), while rats in the second group (ENU?+?meadowsweet) were given daily a decoction of meadowsweet as drinking water throughout their lifetime. All rats of the first group (ENU) developed multiple malignant tumors, which occurred in brain (86%), spinal cord (43%), peripheral and cranial nerves (29%) and in kidney (31%). More than one-third of CNS tumors were oligodendrogliomas. Mixed gliomas (oligoastrocytomas) occurred less frequently. All other types including astrocytomas, glioblastomas, and ependymomas were rare. All PNS tumors were neurinomas (schwannomas). The spectrum of tumors was similar in rats of the second group. Postnatal consumption of meadowsweet significantly reduced number of tumor-bearing rats (by 1.2 times), the incidence and multiplicity of CNS tumors (brain—by 2.0 and 2.1 times, respectively; spinal cord—by 3.1 and 3.0 times, respectively) and significantly increased latency period, compared to rats of the first group. No significant reduction in PNS or renal tumors was seen in rats given meadowsweet. Meadowsweet extract can be considered an effective cancer preventive agent especially as a neurocarcinogenesis inhibitor.     

N-ethyl-N-nitrosourea-induced spinal tumors in an inbred strain of W albino rats.

Exposure to N-ethyl-N-nitrosourea (ENU) either transplacentally via the maternal bloodstream or postnatally by direct injection into the cerebellum or the cisterna magna resulted in a high incidence of spinal tumors in an inbred strain of W albino rats. After prenatal exposure to 60 mg ENU/kg maternal body weight, as many as 92% of the offspring developed 1 or more tumors in the spinal cord, whereas after postnatal exposure to 0.2 mg ENU/animal, 50% of the animals eventually developed spinal tumors. These tumors included relatively pure oligodendrogllomas, astrocytomas, and the usual mixed gllomas. Obvious clinical symptoms of paralysis of the limbs and weight loss accompanying the high incidence of tumors in the spinal cord make this system pertinent to the study of carcinogenesis in the central nervous system as well as to the study of related problems to the incidence of these tumors are discussed.     

Induction of tumors of the sympathetic nervous system in rats

Benign (ganglioneuromas in 6 rats) and malignant (ganglioneuroblastomas--4) tumors and neuroblastomas (7) were induced in 17 animals by a single dose of 80 mg/kg ethylnitrosourea injected on days 18-19 of gestation. The animals were exposed to continuous lighting during gestation and lactation. Tumors of the sympathetic nervous system were at different stages of maturity. Since most tumors were located along the sympathetic trunk of the mediastinum and retroperitoneal cavity and because of their certain morphological features, such neoplasms may be regarded as an adequate model of similar tumors in children.     

Study of the post-natal effects of chemopreventive agents on ethylnitrosourea-induced transplacental carcinogenesis in rats. II. Influence of low-molecular-weight polypeptide factors from the thymus, pineal gland, bone marrow, anterior hypothalamus, brain cortex and brain white substance

The influence of the polypeptide factors extracted from thymus,pineal gland, bone marrow, anterior hypothalamus, brain cortexor brain white substance on N-ethyl-N-nitrosourea (ENU)-inducedtransplacental carcinogenesis was studied in rats. ENU was givento pregnant rats as a single i.v. exposure at a dose of 75 mg/kgbody weight on the 21st day of gestation. The polypeptide factorswere given to the offspring as a series of s.c. injections,at a dose of 0.5 mg/rat/day, starting at one or 2.5 months ofage and continuing throughout the whole of post-natal life.ENU induced tumors of the brain, spinal cord, peripheral nervesand kidneys in 94-98% of the offspring exposed to the carcinogen,with an average number of 2.3-2.6 tumors per rat, and an averagesurvival time of 294 days. Post-natal thymus factor or pinealgland factor administration was followed by an increase in meanlifespan of 2 months and a significant decrease (P < 0.05)in the total tumor number per tumor-bearing rat, as well asthe incidence and multiplicity of spinal cord tumors. Pinealgland factor also decreased the incidence of peripheral nerveand kidney tumors and their number per tumor-bearing rat. Braincortex factor and brain white substance factor treatment wasfollowed by a decrease in total tumor multiplicity of 1.2- to3.3-fold, and a decrease in incidence of brain tumors of 10to 33% per rat in comparison to the controls. Brain cortex factoralso decreased the total tumor incidence. At the same time,brain white substance factor administration increased the incidenceof peripheral nerve tumors and decreased the mean lifespan.Both bone marrow factor and anterior hypothalamus factor didnot have any modifying effects on any of the ENU-induced tumorsand mean lifespan. Thus, our results show the possibility ofattenuation of transplacental ENU-induced carcinogenesis withpost-natal administration of some polypeptide substances.     

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.     

Colon carcinogenesis in germ-free rats with intrarectal 1,2-dimethylhydrazine and subcutaneous azoxymethane.

The effect of intestinal microflora on colon carcinogenesis by 1,2-dimethylhydrazine and azoxymethane was studied, with the use of germ-free and conventional female Fischer rats. At 7 weeks of age, germ-free and conventional rats were treated with 20 weekly intrarectal 1,2-dimethylhydrazine (20 mg per kg body weight per week) or subcutaneous azoxymethane (10 mg per kg body weight per week) doses and were autopsied 15 weeks later. Tumors were induced in the small intestine and colon of germ-free and conventional rats treated with intrarectal 1,2-dimethylhydrazine; the number of rats with colon tumors and the multiplicity of tumors were decreased in germ-free rats, compared with conventional animals. Azoxymethane given subcutaneously increased the incidence and multiplicity of colon tumors in germ-free rats, compared with conventional controls. It is concluded that the intestinal microflora alter the carcinogenic and/or cocarcinogenic effect of different compounds in the large intestine.