Inhibition of Mammary Tumors by Pretreatment with 17β-Estradiol in F344 Rats Induced with N-Methyl-N-nitrosourea

The influence of 17β-estradiol (E2) and prolactin was studied on N-methyl-N-nitrosourea (MNU)-induced mammary carcinomas (MCAs) in rats. MNU was intravenously injected once into seven-week-old female F344 rats at a dose of 50 mg/kg body weight. Groups of rats also received either 2.5 mg of E2 or a continuous supply of prolactin and/or growth hormone via transplanted MtT/F84 (mammo-somatotropic pituitary tumor). Rats were observed for up to 36 weeks after MNU administration. Although simultaneous administration of MNU and E2 did not much affect the occurrence of MCAs as compared to administration of MNU alone, rats treated with 2.5 mg of E2 for two weeks before MNU administration had significantly reduced occurrence of MCAs compared to those given MNU alone. In contrast, rats with MNU plus MtT/F84 showed high incidence and shortened latency of MCAs and they also had a high incidence of clitorial gland hyperplasias. Average pituitary weights and serum prolactin levels in E2-treated rats were greatly increased compared to those of MNU-alone rats. Average serum E2 levels were about 100 ng/ml in E2-treated rats and 0.05 ng/ml in rats without E2 treatment. Serum prolactin levels were greatly increased in rats with MtT/F84. The results indicated that pretreatment with E2 before MNU administration was inhibitory while increased prolactin caused by grafting MtT/F84 after MNU injection was promotive for the occurrence of MCAs in female F344 rats.     

Stimulatory effects of retinoic acid on tumor growth and serum insulin-like growth factor-1 in rats bearing estrogen-responsive pituitary tumor MtT/Se

MtT/Se is one of 4 cell lines derived from an estrogen-dependent pituitary tumor, MtT/F84. The main difference between these tumor types is that MtT/F84 secretes both growth hormone (GH) and prolactin (PRL) whereas MtT/Se secretes only GH. MtT/Se grew slowly in ovariectomized (ovex) rats, but tumor growth was much faster in estrogen-treated ovex rats. Effects of dietary retinoic acid (RA) on tumor growth, serum GH and insulin-like growth factor-1 (IGF-1) levels were examined in ovex rats. Latency of tumor growth was shortened, and tumor take and weight were promoted by all-trans RA both in the presence and absence of exogenous estrogen. Serum GH and IGF-1 levels became increased in tumor-bearing rats whereas PRL levels remained unchanged. Serum IGF-1 levels exhibited a good correlation with tumor weights (r = 0.84). Our results suggest a close relationship between increase of tumor weight and stimulation of serum IGF-1 level by RA in tumor-bearing rats.     

Stimulatory Effects of Retinoic Acid on Tumor Growth and Serum Insulin-like Growth Factor-1 in Rats Bearing Estrogen-responsive Pituitary Tumor MtT/Se

MtT/Se is one of 4 cell lines derived from an estrogen-dependent pituitary tumor, MtT/F84. The main difference between these tumor types is that MtT/F84 secretes both growth hormone (GH) and prolactin (PRL) whereas MtT/Se secretes only GH. MtT/Se grew slowly in ovariectomized (ovex) rats, but tumor growth was much faster in estrogen-treated ovex rats. Effects of dietary retinoic acid (RA) on tumor growth, serum GH and insulin-like growth factor-1 (IGF-1) levels were examined in ovex rats. Latency of tumor growth was shortened, and tumor take and weight were promoted by all- trans RA both in the presence and absence of exogenous estrogen. Serum GH and IGF-1 levels became increased in tumor-hearing rats whereas PRL levels remained unchanged. Serum IGF-1 levels exhibited a good correlation with tumor weights ( r =0.84). Our results suggest a close relationship between increase of tumor weight and stimulation of serum IGF-1 level by RA in tumor-bearing rats.     

Induction of invasive carcinomas in the accessory sex organs other than the ventral prostate of rats given 3,2'-dimethyl-4-aminobiphenyl and testosterone propionate

The promotion effects of testosterone propionate (TP) on prostate carcinogenesis were investigated in F344 rats given the prostatic carcinogen, 3,2'-dimethyl-4-aminobiphenyl (DMAB). One group of animals received s.c. DMAB injections at a dose of 50 mg/kg body weight at 2-week intervals for a total of 10 injections along with s.c. implantations of TP-containing Silastic tubes. A second experimental group of rats was given DMAB at the same dose and intervals but each injection of DMAB was combined with 3 prior consecutive daily 100-mg/kg body weight s.c. injections of TP. After cessation of carcinogen administration, animals in these two groups received TP implants from week 21 to the end of the experiment. All surviving animals were killed at week 56 and accessory sex gland tumor incidences were compared to those in DMAB alone and other appropriate control groups. The groups given TP plus DMAB and subsequent long term administration of TP developed lesions of the dorsolateral prostate, seminal vesicles, and coagulating glands which were all invasive adenocarcinomas. Incidences were 84.2% (16 of 19 rats) and 66.7% (12 of 18 rats), respectively. Macroscopic large tumors were induced in 13 animals among which 8 demonstrated metastasis to the abdominal cavity, liver, or lung. None of the control groups except for the group given TP injections plus DMAB had equivalent tumors. Development of carcinomas of the ventral prostate, which were all of in situ type, were not increased by subsequent treatment with TP. These data thus clearly showed that TP can exert strong enhancing effects on tumor development in the dorsolateral prostate, seminal vesicles, and coagulating glands but not in the ventral prostate.     

Estrogen receptor levels and tumor growth in a series of pituitary clonal cell lines in rats.

Four kinds of in vitro clonal pituitary tumor cell lines named MtT/Se, MtT/SM, MtT/S and MtT/E, each of which shows different sensitivity to estrogen on proliferation, were inoculated into fat pad of ovariectomized rats and estrogen-loaded ovariectomized rats at 10(5) and 10(6) cells/site. They formed tumor with average latency ranging from 30 to 71 in ovariectomized rats and 13 to 63 days in estrogenized rats inoculated with 10(6) cells. MtT/Se was highly sensitive to estrogen for growth, and MtT/SM also grew well in estrogenized rats. With MtT/S and MtT/E, there was no significant shortening of average tumor latency in estrogenized rats. In vivo, the cytosolic estrogen receptor (ER) levels of MtT/Se, SM, S and E were measured to be 452 +/- 66, 370 +/- 115, 260 +/- 16 and 83 +/- 8 fmol/mg protein, respectively. In vitro, however, the lowest ER level was noted in MtT/Se. Histologically, all four tumors grown in rats were composed of homogeneous round cells, and MtT/Se contained particularly large nucleated cells. In MtT/E, the cells appeared to be changing into fibromatous cells. Three cell lines except MtT/E maintained the function of hormonal secretion in vivo as well as in vitro. Serum GH level was increased in rats with MtT/Se and MtT/S. Increased levels of both prolactin and growth hormone were measured in sera of rats with MtT/SM. Increases of hormones as well as tumor sizes were promoted by the estrogen.     

Estrogen Receptor Levels and Tumor Growth in a Series of Pituitary Clonal Cell Lines in Rats

Four kinds of in vitro clonal pituitary tumor cell lines named MtT/Se, MtT/SM, MtT/S and MtT/ E, each of which shows different sensitivity to estrogen on proliferation, were inoculated into fat pad of ovariectomized rats and estrogen-loaded ovariectomized rats at 10⁵ and 10⁶ cells/site. They formed tumor with average latency ranging from 30 to 71 in ovariectomized rats and 13 to 63 days in estrogenized rats inoculated with 106 cells. MtT/Se was highly sensitive to estrogen for growth, and MtT/SM also grew well in estrogenized rats. With MtT/S and MtT/E, there was no significant shortening of average tumor latency in estrogenized rats. In vivo , the cytosolic estrogen receptor (ER) levels of MtT/Se, SM, S and E were measured to be 452 ±66, 370 ±115, 260 ±16 and 83 ±8 fmol/ mg protein, respectively. In vitro , however, the lowest ER level was noted in MtT/Se. Histologically, all four tumors grown in rats were composed of homogeneous round cells, and MtT/Se contained particularly large nucleated cells. In MtT/E, the cells appeared to be changing into ftbromatous cells. Three cell lines except MtT/E maintained the function of hormonal secretion in vivo as well as in vitro . Serum GH level was increased in rats with MtT/Se and MtT/S. Increased levels of both prolactin and growth hormone were measured in sera of rats with MtT/SM. Increases of hormones as well as tumor sizes were promoted by the estrogen.     

Role of prolactin in rat mammary carcinogenesis: detection of carcinogenicity of low-dose carcinogens and of persisting dormant cancer cells.

Rats used were W/Fu strain with a reported incidence of spontaneous mammary tumors (MTs) of 17%. Most of these have been benign fibroadenomas in older females. X-ray or fast neutron irradiations were given in subthreshold doses, some as low as 10 rads. Also, low doses (150 mg) of a chemical carcinogen (N-nitroso-N-butylurea; NBU) prolactin (MtH). The prolactin was provided by grafting a syngeneic mammatropic pituitary tumor (MtT.W95 or MtT.W98). Tumors developing at the implantation site were chormophobe adenomas. The latent period of tumor induction decreased after the 4th generation of animal passage of the tumors. In some rats, ovariectomy was done 1 week before X-irradiation. No MT was found in 18 untreated controls during 1 year of observation. No MT developed in 32 rats having only the grafts for 9-12 months. Total-body-X-irradiation with 25 or 50 rads alone elicited no MT for 1 year. Among 27 rats exposed to 200 rads of X-rays 2 developed MT fibroadenomas after 5 and 7 months. The supplemental administration of prolactin greatly increased and accelerated the occurrence of MTs in irradiated rats. Most of these were adenocarcinomas. Ovariectomized rats had fewer MTs than intact females. A correlation was found between dose and MT incidence. The persistence of chemically transformed MT cells was shown by the addition of prolactin several months after NBU therapy. MTs developed in 8 of 10 rats within 3 months after the MTT graft became palpable. All but 1 of these were adenocarcinomas. Apparently there had been no repair or elimination of damaged cells in the dormant state. It is suggested that progressive growth of MTs may depend on the hormonal milieu of the host.     

Functional and morphological characteristics of transplantable rat pituitary tumors established in nude mice

Two strains of transplantable rat pituitary tumors, MtT SA5 and MtT SA6, have been established in female nude mice from a single original pituitary tumor which had spontaneously occurred in a female Wistar rat at 759 days of age. MtT SA5 tumor produces prolactin (PRL), growth hormone, and adrenocorticotropic hormone, and MtT SA6 tumor secretes PRL and growth hormone. Additionally, both tumors induce severe nephropathy and promote pathogenicity of murine hepatitis virus, resulting in hepatic necrosis. Electron micrographs of MtT SA5 and MtT SA6 tumors revealed three and two types of cells, respectively, in reference to secretory granules. The tumors seem to consist of mixed population, each cell secreting each hormone. Since marked adrenal enlargement and relatively low serum corticosterone levels were found in MtT SA5-bearing rats, it is suggested that MtT SA5 tumor secretes adrenocorticotropic hormone and/or its related peptides which induce adrenal hyperplasia with little or no stimulation of corticoid production. In nude mice bearing MtT SA5 tumor, concentrations of growth hormone in serum and tumor tissue were exceedingly higher than those of PRL, while they were in the same magnitude in MtT SA6-bearing nude mice. We also found that PRL levels in serum and tumor tissue of MtT SA5-bearing nude mice were much higher in males than females, although those of MtT SA5-bearing rats were not significantly different in both sexes.     

Pituitary hormones and the metabolism of N-hydroxy-N-2-fluorenylacetamide in female rats

The transplantable functional pituitary tumor, Furth MtT/F4, enhances hepatoma formation by the carcinogen N-hydroxy-N-2-fluorenylacetamide (N-OH-FAA) in rats. Therefore the metabolism of a single intraperitoneal dose of N-OH-FAA-9-¹⁴C was followed in groups of female Fischer rats which were fed either N-OH-FAA-containing or control diets for 8 weeks, with or without MtT implantation. The MtT markedly increased rectal temperature, food and water intake, urinary volume and body, liver, and kidney weights. The carcinogen-prefeeding alone did not affect the total percentage of radioactivity from labeled N-OH-FAA excreted in 24-hour urine, but the proportion excreted as urinary glucosiduronic acids and as the glucuronide of N-OH-FAA was greater. MtT implantation had no significant effect on the urinary metabolites in the animals on a control diet. However, the combination of carcinogen-prefeeding and MtT transplantation increased the urinary excretion of total radioactivity, the urinary glucosiduronic acids, and especially the glucuronide of N-OH-FAA. Maintenance of higher levels of N-OH-FAA, the altered endocrine situation and the increased metabolic rate may contribute to the enhancement of hepatoma formation in female rats implanted with MtT.     

The conversion of an ovariectomy-nonresponsive to an ovariectomy-responsive mammary tumor strain.

MTW9, a transplantable mammary tumor in Wistar Furth rats, shows little growth unless host serum prolactin is increased. This study compares the response to ovariectomy of MTW9-MtT, a tumor developed in rats bearing the mammosomatotropic tumor MtTW10 (serum prolactin 500 to 7000 ng/ml) with MTW9-P developed in rats given chronic perphenazine treatment (4 mg/kg/day). Serum prolactin concentrations were 150 to 600 ng/ml in MTW9-P bearing rats. MTW9-MtT does not regress after ovariectomy but does regress after surgical removal (resection) of MtT. Ovariectomy plus MtT resection leads to greater tumor regression than MtT resection alone. MTW9-P does not regress when perphenazine administration is stopped but does regress after ovariectomy, whether or not rats are given perphenazine. Administration of estradiol (10 mug/day) to rats with complete ovariectomy-induced regression of MTW9-P results in regrowth of tumor. These data suggest that MTW9-P may represent a clone of MTW9 with a lower requirement for prolactin.     

Variation in tumor yield in the prostate and other target organs of the rat in response to varied dosage and duration of administration of 3,2'-dimethyl-4-aminobiphenyl

The effects of varying dosages of 3,2'-dimethyl-4-aminobiphenyl (DMAB) in combination with cyclic dietary administration of ethinyl estradiol (EE) on induction of prostate carcinoma were investigated in male F344 rats. Animals received repeated treatment with 0.75 ppm of EE for 3 wk with intervals of 2 wk on basal diet. The cycle was repeated 10, 5, and 3 times in Groups 1, 2, and 3, respectively, a single s.c. injection of DMAB being given 2 days after each change to basal diet at a dose of 50 mg/kg of body weight in Group 1, 100 mg/kg of body weight in Group 2, and 167 mg/kg of body weight in Group 3. With this dosing schedule, the total dose of DMAB (500 mg/kg of body weight) per rat was the same in each group. Subsequent to the last treatment with EE, all rats were given basal diet until the end of the experiment (Wk 60) when all surviving animals were sacrificed for histological examination. Carcinoma of the prostate was found in 58.6, 45.0, and 25.9% of rats surviving for 60 wk in Groups 1 to 3, respectively, the incidences of atypical hyperplasia being 86.2, 85.0, and 74.1%. However, tumors of the small and large intestines, preputial gland, and pancreas developed in a dosage-dependent manner, the largest incidences being found in the group given 167 mg of carcinogen 3 times. Thus the present experiment confirmed that administration of DMAB combined with cyclic treatment with EE induces a high incidence of prostate carcinoma in rats and demonstrated that a low dosage of DMAB given over a long period is superior to a high dosage over a short period for specific induction of prostate lesions.     

The prophylaxis of rat and mouse mammary gland tumorigenesis by suppression of prolactin secretion: A reappraisal

Summary The purpose of this study was to evaluate the effect of early and temporal CB-154 induced suppression of prolactin secretion on the genesis of mammary tumors in female Sprague-Dawley rats treated i.g. with 3 doses of 7,12-dimethylbenzanthracene (DMBA); doses which yield a high (20 mg), moderate (5 mg) and low (1.25 mg) mammary carcinoma incidence. In addition, the effect of prolactin suppression on the genesis of mammary tumors in strains of rodents which, when treated with maximally tolerated doses of DMBA, develop a moderate (female Lewis rats) and a low (female Long-Evans rats and female Balb/c mice) mammary carcinoma incidence was also evaluated. Daily suppression of prolactin secretion during DMBA treatment (30 days before, during and 30 days after) (series 1) or commencing 30 days after DMBA treatment (for 60–81 days) (series 2) significantly (P<0.05) reduced the number of mammary carcinomas in Sprague-Dawley rats treated with 20 and 5 mg DMBA and in Lewis rats (series 2); treatment with CB-154 did not significantly lower mammary carcinoma incidence in Sprague-Dawley rats treated with 1.25 mg DMBA, nor in Lewis rats (series 1), Long-Evans rats and Balb/c mice. These results provide evidence that the effectiveness of prolactin suppression in the prophylaxis of chemical carcinogenesis of the rodent mammary gland is enhanced when a moderate or large dose of the carcinogen is used, or a strain of rodent is used which is moderately or highly susceptible to the mammary oncogenic effects of the carcinogen. Low doses of the carcinogen or use of a rodent strain relatively resistent to the carcinogen nullifies the chemopreventive activities of early prolactin suppression. Address for reprints: Clifford W. Welsch, Ph.D., Department of Anatomy, Michigan State University, East Lansing, MI 48824.     

Induction of dorsolateral prostate adenocarcinomas and other accessory sex gland lesions in male Wistar rats by a single administration of N-methyl-N-nitrosourea, 7,12-dimethylbenz(a)anthracene, and 3,2'-dimethyl-4-aminobiphenyl after sequential treatment with cyproterone acetate and testosterone propionate

Groups of 20-25 male Wistar rats (Cpb:WU), nine groups of 4-week-old rats, and nine groups of 8-week-old rats, were given cyproterone acetate (CA) s.c. or by gavage daily for 18 days at a dose of 50 mg/kg/day. Directly following CA treatment, the rats received 3 daily s.c. injections with testosterone propionate (TP) at a dose of 100 mg/kg/day. On the day after the last TP administration, a single dose of one of the following carcinogens was given to 3 groups: N-methyl-N-nitrosourea (MNU), 50 mg/kg i.v.; 7,12-dimethylbenz(a)anthracene, 30 mg/kg i.v.; 3,2'-dimethyl-4-aminobiphenyl, 250 mg/kg s.c. Three other groups received the same carcinogen treatments after 7 days of recovery from the CA administration. The last 3 groups received carcinogen without TP treatment, but immediately after CA pretreatment was stopped. A 25% incidence of invasively growing, metastasizing adenocarcinomas was found in the dorsolateral prostate region of 8-week-old rats that had received MNU after treatment with CA plus TP. In addition, this group had a 5% incidence of carcinoma in situ and a 5% incidence of atypical hyperplasia in the dorsolateral prostate. Lower incidences of adenocarcinoma of the dorsolateral prostate region and of carcinoma in situ and atypical hyperplasia of the dorsolateral prostate were found in other groups that were treated with MNU or 7,12-dimethylbenz(a)anthracene after pretreatment with CA, followed by TP or recovery, but never in rats that had been treated with CA only. In the groups treated with 3,2'-dimethyl-4-aminobiphenyl, which is slowly metabolized, these lesions were also found in groups that were pretreated with only CA. The carcinomas seemed to originate from the dorsolateral prostate and their average latency time was approximately 61 weeks. The 8-week-old rat given a MNU injection after sequential treatment with CA and TP may provide a relevant animal model for human prostatic cancer.     

Analysis of prolactin and growth hormone production in hyperplastic and neoplastic rat pituitary tissues by the hemolytic plaque assay

The reverse hemolytic plaque assay (RHPA) was used to detect hormone release from cultured normal, hyperplastic, and neoplastic rat pituitary cells. Hyperplastic pituitary cells were produced by s.c. diethylstilbestrol (DES) treatment (10 mg in Silastic tubes) for 3, 6, and 9 weeks. Neoplastic pituitary cells from rats with MtT/W15 transplantable tumors treated with DES for 3 weeks were also analyzed. Aliquots of the same cells were also analyzed by immunocytochemical staining. DES treatment resulted in an increase in prolactin (PRL)-producing cells in hyperplastic pituitaries compared to untreated pituitaries after 9 weeks of treatment by the RHPA [61.2 +/- 5.2 (SE) versus 32 +/- 3.0] and by immunocytochemical staining [70.9 +/- 2.4 versus 36 +/- 1.4]. The percentage of mammosomatotropic cells decreased from 11.3 +/- 3.8 to 4.2 +/- 2.6% in pituitary cells from these same groups of animals. After 3 weeks of DES treatment in rats with MtT/W15 tumor, there was an increase in growth hormone (GH)-producing cells and a decrease in PRL-producing cells when analyzed by the RHPA (control: percentage of GH, 36.3 +/- 6.2; percentage of PRL, 39.0 +/- 1.6 versus DES-treated tumors: percentage of GH of 68.2 +/- 1.9; and percentage of PRL, 3.2 +/- 1.8%). The percentage of mammosomatotropic cells declined from 12.4 +/- 2.3 to 0.77 +/- 2.4%. A combined procedure of RHPA followed by immunocytochemical staining on the same slides also revealed a decline in mammosomatotropic cells after chronic DES treatment in hyperplastic and neoplastic MtT/W15 tumor cells. These results show that DES has different effects on PRL and GH secretion and storage in hyperplastic pituitary and in the MtT/W15 pituitary tumor cells.     

Growth-promoting Effect of Retinoic Acid in Transplantable Pituitary Tumor of Rat

MtT/F84 grew well in Fischer rats (F344), but tumor growth was promoted in hyperestrogenized rats. Effects of dietary retinoic acid (RA) on tumor growth, estrogen receptor (ER) and serum growth hormone (GH) level were examined. Tumor latency became shortened, and tumor take and weight were promoted by all- trans RA at dosages of 50 and 200 mg/kg basal diet, but not dose-dependently. ER level was elevated in tumor of RA-treated rats, whereas the retinoic acid-binding protein level remained unchanged. RA also elevated incorporation of 5-bromo-2'-deoxyuridine, a thymidine analogue, into DNA of tumor cells. Average serum GH level was increased in tumor-bearing rats treated with RA and was well correlated with tumor weight. RA may directly affect ER level and enhance estrogenic action, resulting in promotion of tumor growth, or it may act independently for tumor growth and elevation of serum GH level.     

Prolactin binding in ovariectomy-responsive and ovariectomy-nonresponsive rat mammary carcinoma.

Growth of the transplantable mammary tumor, MTW9, in W/Fu rats is greatly enhanced by elevated serum prolactin concentrations. This report compares the prolactin binding to tumor membranes in two mammary tumor strains derived from MTW9. Maximum binding to membranes of both tumors occurred at pH 7.6 after incubation for 30 hr at 4 degrees. The binding was inhibited only by polypeptide hormones that possess lactogenic activity. MTW9-P, an ovariectomy-responsive tumor developed in rats maintained on daily perphenazine injections, had 4-fold-higher prolactin binding than had MTW9MtT, an ovariectomy-nonresponsive tumor developed in rats bearing the mammosomatotropic pituitary tumor, MtTW10. Withdrawal of perphenazine from rats bearing MTW9-P caused a fall to normal of plasma prolactin, no tumor regression, and no significant change in prolactin binding. In contrast, resection of MtT resulted in tumor regression, a fall to normal of serum prolactin, and a nearly 3-fold increase in prolactin binding. Scatchard plots of prolactin binding data yield an apparent affinity constant, Ka, of 1.2 X 109 liters/mole for both tumors. The 4-fold-higher prolactin binding in the ovariectomy responsive variant suggests a positive correlation between ovariectomy response and the number of membrane prolactin-binding sites. No correlation between prolactin sensitivity and prolacting binding is apparent.     

3-(Methylnitrosamino)propionitrile: occurrence in saliva of betel quid chewers, carcinogenicity, and DNA methylation in F344 rats

3-(Methylnitrosamino)propionitrile (MNPN), a potent carcinogen in F344 rats, was detected for the first time in the saliva of betel quid chewers at levels ranging from 0.5 to 11.4 micrograms/liter. The tumorigenic properties of MNPN and its potential to methylate DNA in F344 rats were evaluated. Groups of 21 male and 21 female rats were given 60 s.c. injections over a 20-week period (total doses 0.055 and 0.23 mmol per rat). The experiment was terminated after 106 weeks. MNPN at the higher dose induced 18 (86%) malignant tumors of the nasal cavity in male and 15 (71%) in female rats. The lower dose induced nine (43%) liver tumors. Groups of four or five male F344 rats were treated with a single s.c. or i.v. injection of MNPN (0.4 mmol/kg). MNPN was also administered to rats by swabbing the oral cavity (2.21 mmol/kg). The levels of 7-methylguanine and O6-methylguanine, formed 0.5-36 h after treatment, were measured in the liver, nasal mucosa, esophagus, and oral issues. The highest levels of methylated guanines were detected in the nasal cavity independent of the route of administration. The results of this study demonstrate that MNPN is present in the saliva of betel quid chewers and is a potent carcinogen in F344 rats.     

Growth-promoting effect of retinoic acid in transplantable pituitary tumor of rat

MtT/F84 grew well in Fischer rats (F344), but tumor growth was promoted in hyperestrogenized rats. Effects of dietary retinoic acid (RA) on tumor growth, estrogen receptor (ER) and serum growth hormone (GH) level were examined. Tumor latency became shortened, and tumor take and weight were promoted by all-trans RA at dosages of 50 and 200 mg/kg basal diet, but not dose-dependently. ER level was elevated in tumor of RA-treated rats, whereas the retinoic acid-binding protein level remained unchanged. RA also elevated incorporation of 5-bromo-2'-deoxyuridine, a thymidine analogue, into DNA of tumor cells. Average serum GH level was increased in tumor-bearing rats treated with RA and was well correlated with tumor weight. RA may directly affect ER level and enhance estrogenic action, resulting in promotion of tumor growth, or it may act independently for tumor growth and elevation of serum GH level.     

Lack of modification by naturally occurring antioxidants of 3,2'-dimethyl-4-aminobiphenyl-initiated rat prostate carcinogenesis

The modifying effects of 6 naturally occurring antioxidants on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-initiated rat prostate carcinogenesis were investigated in male F344 rats. Animals were pretreated with DMAB in a 20-week initiation protocol and then administered basal diet containing 0.8% catechol, 0.8% resorcinol, 0.8% hydroquinone, 2 ppm selenium, 2% gamma-orysanol or 1% alpha-tocopherol for 40 weeks. The experiment was terminated at week 60 for histopathological assessment of lesion development. Atypical hyperplasias and carcinomas of the prostate were observed in the ventral lobe in all groups treated with DMAB. However, the incidences of these lesions were not significantly different between carcinogen control and antioxidant-treated groups. There were also no significant increases or decreases in the incidences of tumors in any other organs.     

Mammotropic and somatotropic hormones in sera of normal rats and in rats bearing primary and grafted pituitary tumors

Parallel determinations were made of the concentration of MtH and StH in the sera of rats with spontaneous, estrogen-induced and grafted pituitary tumors and, for a base, in sera of normal rats of both sexes, in various physiologic states, following oophorectomy and treatment with gonadal hormones. The characteristic sharp rise of MtH during proestrus was confirmed. This was not accompanied by a rise in StH. Following oophorectomy the levels of both hormones dropped. After estrogen treatment of normal rats, both hormones rose gradually, reaching very high levels with development of pituitary tumors. Similar increases were found with spontaneous mammotropic tumors (MtH) in rats of both sexes. Seven MtT's, originating in six different strains, were studied in the course of successive transplantations. All exhibited mammary gland stimulation, with very high MtH and StH levels, depending on the tumor size and tumor strain. In general, hormone secretion decreased in the course of successive transplantations. One variant of the originally typical MtT.W5, MtT.W5/H, markedly lost the ability to produce MtH while maintaining the ability to produce StH, as indicated by both radioimmunoassays and biological changes in the tumor hosts. The oldest transplantable tumor of this series (MtT.F4), secreted large quantities of AtH and StH without biological evidence of somatotropic effects. The StH effect became “unmasked” by adrenalectomy. Biological evidence of AtH secretion by the other MtH strains was inconstant and variable. It was often present in the first transplant generation but vanished in the course of successive transplantations with the exception of the F4 strain. The MtH values in normal as well as MtT-bearing hosts were higher in female than in male rats. There was relatively more StH in males than in females.