Etsuo Ikawa

Promotion by ascorbic acid, sodium erythorbate and ethoxyquin of neoplastic lesions in rats initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine

The promoting effects of ascorbic acid, sodium erythorbate and ethoxyquin on two-stage urinary bladder carcinogenesis in F344 rats initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) at a dose of 0.05% in the drinking water were examined. Administration of 5% sodium erythorbate in the diet significantly increased the incidences of preneoplastic lesions, papilloma and cancer of the urinary bladder, whereas administration of 5% ascorbic acid in the diet did not. Administration of 0.8% ethoxyquin also increased the incidence of neoplastic lesions. Administrations of 5% sodium L-ascorbate and 5% sodium erythorbate caused increases in the pH, the sodium content and crystals of MgNH4PO4 in the urine. These results show that sodium erythorbate and ethoxyquin promote urinary bladder carcinogenesis, while ascorbic acid does not.

Compared promoting potential of d-galactosamine, carbon tetrachloride and partial hepatectomy in rapid induction of preneoplastic liver lesions in the rat

Effectiveness of two different chemically induced stimuli for hepatocellular proliferation was compared with regard to that of commonly used partial hepatectomy (PH), for the purpose of developing short-term protocol for the assay of promoting agents of hepatocarcinogenesis. Enhancing effect of D-galactosamine (DGA) and carbon tetrachloride (CCl4) given during the promotion procedure by 2-acetylaminofluorene (2-AAF) was compared along with PH in rats initiated by diethylnitrosamine (DEN), using preneoplastic glutathione S-transferase positive (GST-P+) hepatocyte foci as an end-point marker lesion. The number of GST-P+ foci per cm2 was largest in the group given CCl4 followed by DGA, no treatment (2-AAF alone) and PH. In contrast, the area (mm2) per cm2 and mean diameter of the focus were largest in the PH group then DGA followed by CCl4 and no treatment. The results indicate that the number of GST-P+ foci were not clearly affected by 3 different treatments whereas area and size of foci which represented the result of promoting effect were clearly influenced by those treatments, indicating they caused differential proliferation of initiated cells. In this respect, even though PH is the most potent procedure, DGA is also efficient and preferred to CCl4 for the non-surgical enhancing method.

Enhancement of N-bis(2-hydroxypropyl)nitrosamine-initiated lung tumor development in rats by bleomycin and N-methyl-N-nitrosourethane

Potential modification of N-bis(2-hydroxypropyl)nitrosamine (DHPN)-induced lung carcinogenesis by bleomycin and N-methyl-N-nitrosourethane (MNUT) was investigated in male F344 rats. Rats were given 0.2% DHPN for 1 week followed by a weekly i.p. injection of either bleomycin at 2.0 mg/kg body wt or of MNUT at a dose of 1.0 mg/kg body wt for 35 weeks. Animals given DHPN followed by solvent administration alone, either saline or 0.02% ethanol and animals given bleomycin or MNUT without DHPN pretreatment were served as controls. Bleomycin treatment increased the incidence of cancer, whereas hyperplasia, adenoma and cancer of the lung were all significantly elevated after MNUT administration. MNUT alone induced low incidences of lung tumors. Bleomycin also increased the incidence of papillary or nodular hyperplasia of the urinary bladder while it inhibited the development of thyroid tumors. MNUT, however, did not affect tumor development in other organs.

Modification potentials of ethyl alcohol and acetaldehyde on development of preneoplastic glutathione S-transferase P-form-positive liver cell foci initiated by diethylnitrosamine in the rat

The modification potentials of ethyl alcohol (EA) and acetaldehyde (AA) on development of immunohistochemical glutathione S-transferase (placental type)-positive (GST-P+) liver cell foci were examined in an in vivo short-term assay system. Rats were given a single intraperitoneal injection of diethylnitrosamine (DEN) and then various concentrations of EA (20, 10, 5%) or AA (5, 2.5%) in their drinking water from week 2 till termination in week 6. All rats were subjected to two-thirds partial hepatectomy in week 3. Animals given EA (20% and 10%) or AA showed significant decrease in liver and body weight. However, only EA caused significant dose-related inhibition of development of areas of foci (mm2/cm2), but AA had no effect on their development.

Lesions of the prostate glands and seminal vesicles induced by N-methylnitrosourea in F344 rats pretreated with ethinyl estradiol

In an attempt to induce a high incidence of prostate carcinoma, N-methylnitrosourea (MNU), a multipotential carcinogen, was given during the period of cell proliferation of the prostate gland induced by administration of methyltestosterone (MT) to F344 rats pretreated with ethinyl estradiol (EE). Rats were given diet containing EE for 3 weeks and then diet containing 300 ppm of MT for 5 days. On the 3rd day of MT-treatment, they were given a single intravenous injection of 50 mg/kg body wt. of MNU. Control rats (group 4) were given vehicle only. After treatment with MT for 5 days, the rats were given basal diet (group 1), diet containing MT (group 2) or diet periodically containing EE (groups 3 and 4) until the end of the experiment (week 60). Carcinoma of the prostate was found only in 1 of 17 rats in group 3. Atypical hyperplasia of the prostate was found in 1 of 10 rats in group 1 and 3 of 17 rats in group 2. The incidences of atypical hyperplasia of the seminal vesicles in groups 1-3 were 0%, 41% and 29%, respectively. No tumor promoting effect of MT or EE was observed except promotion by MT on the development of atypical hyperplasia of the seminal vesicles.

Proliferative Response of Rat Accessory Sex Organs to Dietary Sex Hormones After Castration or Initial Dietary Administration of Estrogen

The hormone dependent proliferative response of five accessory sex organs was examined subsequent to castration-induced or estrogen-induced atrophy using male six-week-old F344 rats. Three weeks after castration, rats were treated with dietary methyltestosterone (300 ppm), ethinyl estradiol (0.75 ppm) or methyltestosterone plus ethinyl estradiol for up to 17 days. Cell proliferation was assessed by 3H-thymidine incorporation as determined from labelling indices using autoradiography. The maximum labelling indices which appeared on days 2 or 3 of administration of methyltestosterone were 24.3, 8.4, 9.6, 21.6 and 13.7% for the ventral, lateral and dorsal prostate, seminal vesicle and coagulating glands, respectively. Combined methyltestosterone and ethinyl estradiol induced mild proliferative responses whereas ethinyl estradiol did not. In a further group of non-castrated rats which were pretreated with dietary ethinyl estradiol for three weeks and then given methyltestosterone, the maximum labelling indices were about 70 to 80% of that in castrated rats.