A repeated 28-day oral dose toxicity study of 17α-methyltestosterone in rats, based on the 'Enhanced OECD Test Guideline 407' for screening the endocrine-disrupting chemicals

Abstract

As part of the international validation project to establish the Enhanced OECD Test Guideline 407, we performed a 28-day repeated-dose toxicity study of 17alpha-methyltestosterone, an exogenous androgen agonist. Special attention was paid to the sensitivity of additional parameters for detecting endocrine-related effects of endocrine-disrupting chemicals, based on the existing Test Guideline 407. Seven-week-old Crj:CD(SD)IGS rats were allocated to one of four groups, each consisting of ten males and ten females, and 17alpha-methyltestosterone was administered daily by gavage at doses of 0 (control), 5, 20 and 80 mg/kg body weight per day. Male rats were killed on the day after the 28th administration and females on the day of the diestrus stage during the 4 day period after the 28th administration. Male rats receiving 80 mg/kg 17alpha-methyltestosterone demonstrated decreases in testis and epididymis weights, atrophy of seminiferous tubules and Leydig cells, and degenerated pachytene spermatocytes in the testes and degenerated germ cells in the epididymides as major alterations. Female rats showed abnormal estrous cycles, decreases in ovary and adrenal weights, increase in immature follicles with decreased corpus lutea in the ovaries at doses of 5 mg/kg and higher, as well as atrophy of zona reticularis in the adrenals and increase in mammary gland secretion at 20 mg/kg and above. Dilatation of the lumina and apoptosis of endometrial cells in the uterus, mucinification in the vagina and increase in serum follicle-stimulating hormone were seen with 80 mg/kg. Among the parameters examined in the present experimental system, effects of 17alpha-methyltestosterone on endocrine-related organs were detected in organ weights and histopathological examination of both sexes, and in serum hormones and estrous cycle of females. Based on these results, the no-observed-adverse-effect level (NOAEL) in the present study was estimated to be below 5 mg/kg per day. In particular, effects were most sensitively detected by organ weights and histopathological examination of sexual organs.

A repeated 28-day oral dose toxicity study of genistein in rats, based on the 'Enhanced OECD Test Guideline 407' for screening endocrine-disrupting chemicals

“…The incidences of the lesions were very low, but were nevertheless judged to be genistein-induced. Histopathological changes in the vagina observed using the same protocol with methoxychlor included severe thickening of mucosal epithelium with mucinification (Okazaki et al 2001), and were also seen with 17a-methyltestosterone (Okazaki et al 2002) and ethinylestradiol (Andrews et al 2002;Yamasaki et al 2002), greatly resembling those generated by 17b-estradiol administered in the diet for 90 days in rats (Biegel et al 1998). The lesions of the vagina in the present study might represent early or very slight effects within the range in the above studies.…”

“…These reports suggest that our test system, the 28-day oral toxicity study based on the existing TG 407, with intact adult rats might have lower sensitivity than assays on ovariectomized or immature animals. Our previous studies revealed that assessment of histopathological features, the weights of endocrine-linked organs, serum hormone levels and the estrous cycle allow detection of endocrine-related effects with flutamide (Toyoda et al 2000), 17a-methyltestosterone (Okazaki et al 2002) and methoxychlor (Okazaki et al 2001), all these being relatively strong agonists or antagonists. However, in the case of a weak agonist or antagonist like genistein, it might be difficult to obtain unequivocal data with our test system alone and results of other tests such as uterotrophic assays, Hershberger assays and in vitro assays might be needed to identify any endocrine-related effects.…”

“…We have already examined the effects of 17a-methyltestosterone (Okazaki et al 2002) as an androgen agonist, flutamide (Toyoda et al 2000) as an androgen antagonist, and methoxychlor (Okazaki et al 2001) as an estrogen agonist using this approach. The results obtained suggest that the weights of endocrine-linked organs and their histopathological assessment, serum hormone levels, and estrous cycle best allow the detection of endocrine-related effects.…”

Tamoxifen: 28-day oral toxicity study in the rat based on the Enhanced OECD Test Guideline 407 to detect endocrine effects

“…The potential value of this enhanced protocol is presently being investigated in a worldwide effort by 13 laboratories using 10 chemicals known to interact with the endocrine system through different mechanisms (Andrews et al 2001(Andrews et al , 2002Okazaki et al 2001Okazaki et al , 2002aOkazaki et al , 2002bToyoda et al 2000;Yamasaki et al 2002aYamasaki et al , 2002b. Our laboratory was assigned to conduct a study with a strong antiestrogen (tamoxifen).…”

Relation between statistics and treatment-related changes obtained from toxicity studies in rats: if detected a significant difference in low or middle dose for quantitative values, this change is considered as incidental change?

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