The effect of a synthetic steroidal antiandrogen, chlormadinone acetate (CMA), on spontaneous benign prostatic hyperplasia (BPH) in dogs was investigated. Male beagle dogs (5-8 years old) were divided into four experimental groups. Group 1 consisted of untreated controls. Groups 2 to 4 received CMA 0.03, 0.1, and 0.3 mg/kg/day, p.o., respectively, for 6 months. In group 1, glandular hyperplasia of the prostate was clearly detected. In groups 2 to 4, CMA produced marked atrophy of the glandular epithelium. In addition, a histopathological study showed that CMA medication for 6 months exerted no effect on the testes except group 4 or on immunoreactive positive cells to LH antibody (pituitary LH cells). Therefore, it is suggested that CMA (0.03 and 0.1 mg/kg) causes regression of spontaneous canine BPH without any histopathological effects on the testes or pituitary LH cells. However, atrophy of seminiferous tubules in testes was found in CMA 0.3 mg/kg/day-treated animals, due apparently to a direct and/or indirect effect on the testes. It is suggested that a marginal antigonadotrophic effect can not be excluded.

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Post-initiation modifying effects of concurrent administration of fish meal and sodium nitrite on the development of glandular stomach tumors after treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in a total of 120 male 6-week-old Wistar rats, divided into 6 groups. Groups 1-3 (30 animals each) were given 100 ppm MNNG in their drinking water and 10% NaCl in diet for 8 weeks as an initiation treatment for gastric cancer induction and thereafter respectively fed diets containing 64%, 32%, and 8% (original concentration in the basal diet) fish meal, and simultaneously given 0.12% sodium nitrite in the drinking water for 52 weeks. Groups 4-6 (10 animals each) were similarly treated without the application of MNNG and NaCl. At the end of the 60th experimental week, all surviving animals were autopsied and examined histopathologically for the existence of gastric proliferative lesions. The incidences and multiplicity of atypical hyperplasias or adenocarcinomas were comparable among groups 1-3. No gastric proliferative lesions were found in groups 4-6. Interestingly, the incidence of adenocarcinomas of the small intestine was significantly (p<0.05) decreased in groups 1 and 2, and that of intrahepatic cholangiomas was significantly (p<0.05) increased in group 1 as compared to the group 3 values. Our results suggest that concurrent administration of fish meal and sodium nitrite does not affect the post-initiation phase of MNNG-initiated glandular stomach carcinogenesis in the rat, but rather modulates development of proliferative lesions in other organs such as the small intestine and liver.

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In order to assess a combined carcinogen and hormone protocol for selective induction of uterine adenocarcinomas in mice, 79 illumination-induced persistent estrous CD-1 mice, divided into four groups, were treated with N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) and/or 17β-estradiol (E₂). Groups 1 and 3 were given a single intra-uterine administration of polyethylene glycol (PEG) at 10 weeks of age, while Groups 2 and 4 received ENNG (12.5 mg/kg), dissolved in PEG. Mice of Groups 3 and 4 were also implanted with E₂ pellets s.c. one week earlier and the pellets were once renewed after 8 weeks. At 15 weeks after the ENNG treatment, the mice were killed for histopathological and endocrinological examination. All groups demonstrated endometrial proliferative lesions, although no severe hyperplasias or adenocarcinomas were found in the control group (Group 1). The incidences of adenocarcinomas in Groups 2, 3, and 4 were 6 (1/19), 25 (5/20), and 55% (11/20), respectively, those for Groups 3 and 4 being significant as compared to the lack in Group 1. The E₂: progesterone (E₂: P) ratios in Groups 3 and 4 were also significantly increased. These results indicate that an increased E₂: P ratio is important for endometrial adenocarcinoma development in CD-1 mice, acting with or without chemical carcinogen initiation to cause uterine cancer development. The relatively short duration, and specifically high yield mean that the present protocol has advantages for two-stage uterine carcinogenicity studies in mice.

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Growth hormone (GH) plays an important role in longitudinal bone growth, and hypophysectomized rats or mutant rats exhibiting dwarfism have generally been used as a GH-deficient model for humans. There also has been a GH deficient model produced by subcutaneous administration to neonatal rats with monosodium glutamate (MSG), followed by destroying GH releasing hormone (GHRH) neurons in the hypothalamic arcuate nucleus, leading to a reduction of GHRH release and a resultant reduction of GH. Recently, Mini rats, a Wistar-derived transgenic rat strain harboring a rat GH antisense gene and showing 40% lower plasma GH levels than Wistar rats, have been developed. In a previous study, Mini rats showed a smaller femur size with lower mineral density and a reduction of the metaphyseal and diaphyseal bone mass. In the present study, neonates of Wistar rats were treated subcutaneously with MSG to obtain GH-deficient rats (MSG rats), and their bones were examined and compared with age-matched MSG-untreated Wistar rats and Mini rats. Compared with the Wistar rats, body weights of the MSG rats were comparable, whereas those of the Mini rats were significantly lower. Bone size, bone mineral content and mineral density were significantly lower in the MSG rats and Mini rats than those in the Wistar rats. Histologically, the amounts of the metaphyseal cancellous bone mass and diaphyseal cortical bone mass were less in the MSG rats and much less in the Mini rats. Compared with the Wistar rats, the growth plate width and longitudinal growth rate were similarly lower. However, there were no differences in bone surface-referent parameters in the secondary spongiosa for histomorphometry among the MSG rats, Wistar rats, and Mini rats, indicating that GH may not influence bone remodeling. Thus, Mini rats are considered to be a useful model for clarifying features of GH-deficiency and examining the effects of various treatments on the bone without any specific surgery or drug administration.

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Mini rats have been reported to be a Wistar-derived strain of transgenic rats that harbors a rat growth hormone (GH) antisense gene and shows lower plasma GH levels than Wistar rats. Our previous study has revealed that: 1) Mini rats show smaller hind limbs with lower metaphyseal and diaphyseal bone mass than Wistar rats; 2) that the differences of the diaphyseal cortical bone mass and metaphyseal bone mass between Mini rats and Wistar rats are due largely to the differences in the periosteal bone formation and longitudinal growth rate, respectively, and ; 3) that the bone turnover in the secondary spongiosa, an area were bone remodeling may occur, does not differ between the two strains. In the present study, 8-week-old male Mini rats were treated intraperitoneally with GH at doses of 0, 2, 6 or 20 IU/kg/time twice daily for 14 days. After the dosage period, we measured the size, bone mineral content, and mineral density of the femur and tibia in each group, and we performed cancellous and cortical bone histomorphometry on the tibia to examine the effects of GH on the bone modeling and remodeling. In the GH-treated groups there were increases in the metaphyseal cancellous bone mass, growth plate width, longitudinal growth rate, and periosteal bone formation accompanied by increases in bone size, mineral content, and mineral density in a dose-related fashion. However, bone histomorphometric parameters related to bone turnover in the secondary spongiosa of the metaphysis, where lamellar bone formation took place, did not differ between the control and GH-treated groups. These findings indicated that GH may not influence bone remodeling in the latter groups, and that GH replacement may not influence the number of osteoclasts involved in bone resorption in Mini rats as a whole.

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Potential promotion activity of nasal carcinogenesis by xylazine, an agent commonly used in veterinary medicine as an α₂-adrenergic agonist, was examined using a N-bis(2-hydroxypropyl)nitrosamine (DHPN)-initiated two-stage nasal carcinogenesis model. Male F344 rats received diet containing 1,000 (maximum tolerated dose) or 0 ppm xylazine hydrochloride (XZ) for 52 weeks with or without prior a single subcutaneous injection of 2,400 mg/kg of DHPN as an initiation treatment. Histopathologically, epithelial hyperplasias, dysplastic foci, adenomas, undifferentiated carcinomas, and/or a squamous cell carcinoma in the nasal cavity were observed in the groups initiated with DHPN, but the incidences of these proliferative lesions were not altered by the treatment of XZ. Plasma levels of xylazine and 2, 6-dimethylaniline (DMA), a major metabolite and a known nasal promoter/carcinogen were at or below the detection limit (0.02 μg/ml) except in 2 animals of the DHPN + XZ group (DMA concentrations were 0.04 and 0.06 μg/ml). These results suggest that XZ does not have any tumor promoting effect in the nasal tissues and its conversion to carcinogenic DMA is very low in vivo. The possibility of nasal carcinogenic effects of DMA in consumers via ingestion of edible tissues in food-producing animals treated with xylazine is extremely low.

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The modifying effects of dietary administration of β-cryptoxanthin and hesperidin rich powder (CHRP) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in male F344 rats. The effects of CHRP on glutathione S-transferase (GST) and quinone reductase (QR) activities in liver and colonic mucosa of rats gavaged with CHRP (0, 40, 200, and 400 mg/kg body wt) for 5 days were also examined. CHRP containing 0.67% β-cryptoxanthin and 3.58% hesperidin was prepared from Satsuma mandarin (Citrus unshiu Marc.)juice. Rats were given s.c. injections of AOM (20 mg/kg body weight) once a week for 2 weeks to induce ACF. They also received the experimental diet containing 500 ppm CHRP for 4 weeks, starting one week before the first dosing of AOM and maintained on a basal diet CE-2 for 7 weeks. AOM exposure produced 80 ± 3 ACF/rat at week 4 and 119 ± 5 ACF/rat at week 11. Dietary administration of CHRP caused significant reduction in the frequency of ACF: 64 ± 9 (20% reduction, p<0.01) at week 4 and 97 ± 11 (18% reduction, p<0.005) at week 11. Also, the number of cryptal cells positive for proliferative cell nuclear antigen in ACF and surrounding “normal-appearing” crypts were lowered by feeding of CHRP containing diet. In the liver and colon of rats gavaged with CHRP, the activities of GST and QR were significantly elevated. These findings might suggest possible chemopreventive effects of CHRP, through their modulation of the cryptal cell proliferation activity and/or activities of phase II enzymes GST and QR, on colon tumorigenesis.

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Both long and short forms of Prolactin-receptor (PRL-R) mRNA were detected in a spontaneous mammary adenocarcinoma of an aged female F344 rat, using sensitive techniques, reverse transcriptase-polymerase chain reaction (RT-PCR), and in situ hybridization (ISH). Amplified products of the long form of PRL-R were markedly identified by RT-PCR, and the mRNA was diffusely exhibited in the cytoplasm of neoplastic epithelium by ISH. Additionally, the long form of PRL-R mRNA was exhibited in the normal mammary tissue surrounding the neoplasm. However, amplified products of the short form of PRL-R were weakly detected by RT-PCR, and the mRNA was not detected in either normal tissue or the neoplasm by ISH. PRL-R mRNA was detected in the rat spontaneous malignant mammary neoplasm and the long form of PRL-R was more highly expressed than the short form.

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