The peripubertal male rat assay as an alternative to the Hershberger castrated male rat assay for the detection of anti-androgens, oestrogens and metabolic modulators

Abstract

A range of chemicals with various levels of activity as actual or potential endocrine disrupters have been evaluated for activity in the peripubertal male rat assay. The chemicals studied included anti‐androgens (vinclozolin), cyproterone acetate, flutamide, 2,2‐bis(4‐chlorophenyl)‐1,1‐dichloroethylene (DDE), metabolic modulators (anastrazole, finasteride, ketoconazole) and oestrogens (butyl benzyl phthalate (BBP), methoxychlor, bisphenol A (BPA), diethylstilboestrol (DES)), the suspected anti‐androgen dibutyl phthalate (DBP) and the non‐oestrogen fenitrothion. Dosing extended over postnatal days (pnd) 22–35, 36–50, 36–55 and 22–35, with recovery to pnd 55 or 22–55. The endpoints studied were changes in the weights of testes, epididymides, seminal vesicles and prostate. Changes in body weight and the weights of the liver and kidney were also monitored. In some experiments changes in the day of prepuce separation (PPS) were also determined. Only BBP and BPA were inactive in all the assays conducted. Changes in the weight of reproductive tissues provided a sensitive indicator of activity for the remaining chemicals with the exception of DDE, for which higher dose levels could have been used. However, none of the curtailed periods of exposure were able to detect all of the agents. Diethyl stilboestrol, and to a lesser extent DBP and DDE, delayed PPS when exposure occurred over the period pnd 22–55. A complex dependence of the day of PPS on the period of exposure and the body weight of the test animals was observed, and caution is recommended when assessing this endpoint in the presence of reductions in body weight. It is concluded that reproductive tissue weight changes in the peripubertal male have shown sensitivity to a range of biochemical modulators, oestrogens and anti‐androgens, and that as such the assay warrants further evaluation. Measurement of delays in PPS may be of value in cases of large delays, but delays of 1–2 days will be difficult to interpret with confidence. The present results are discussed within the context of the sexually mature male rat assay described by O’Connor and the castrated male rat assay described by Hershberger, both of which are the subject of current international study. It is concluded that a decision on the usefulness of the peripubertal male rat assay must await the generation of further data on each of these three assays. There is an urgent need for international agreement on a list of reference endocrine disrupters and their active dose levels, with which to validate individual endocrine disruption assays and batteries of assays. Copyright © 2000 John Wiley & Sons, Ltd.

Antiandrogenic activity and metabolism of the organophosphorus pesticide fenthion and related compounds.

“…Antiandrogenic compounds so far reported include vinclozolin, linuron, iprodione, chlozolinate, procymidone, flutamide, p,p´-DDE, and ketoconazole (Gray et al 1999a(Gray et al , 1999bLambright et al 2000;McIntyre et al 2000;Ostby et al 1999;You et al 1999). In contrast, both positive and negative results on the antiandrogenic activity of fenitrothion, a relative of fenthion, have been reported (Ashby and Lefevre 2000;Curtis 2001;Sohoni et al 2001;Sunami et al 2000;Tamura et al 2001). The significant antiandrogenic activity of fenitrothion found in our study supports previous findings that fenitrothion has antiandrogenic properties.…”

Developmental variations in environmental influences including endocrine disruptors on pubertal timing and neuroendocrine control: Revision of human observations and mechanistic insight from rodents

“…As shown in Table 8, with the exception of early balano-preputial separation after exposure to phthalates (Ge et al, 2007;Saillenfait et al, 2008), EDCs appear to cause either no effect or a delay of sexual maturation in the male rodent. BPA does not show any effect whatever the dose and the window of exposure (Tinwell et al, 2002;Nagao et al, 1999;Tan et al, 2003;Ashby and Lefevre, 2000). As shown in Fig.…”

“…Although both fetal and early postnatal periods of exposure fall into the so-called "programming window", there may be differences in sensitivity to endocrine disruption even within this particular period. The dose of EDC plays a critical role since, when investigated at a given period of life, higher doses appear to be more effective such as shown after prenatal exposure for DDE (Loeffler and Peterson, 1999) and phthalates (Saillenfait et al, 2008;Salazar et al, 2004), or after lactational exposure for DDE, vinclozolin or DES (Yoshimura et al, 2005) or following exposure after weaning for DDE (Ashby and Lefevre, 2000;Yoshimura et al, 2005), vinclozolin (Yoshimura et al, 2005;Monosson et al, 1999), DES (Yoshimura et al, 2005;Shin et al, 2009), phthalates (Ge et al, 2007;Noriega et al, 2009) and PBDE (Stoker et al, 2004). It is noteworthy that in two studies using phthalates, opposing effects are observed since lower doses are associated with early puberty and higher doses with delayed puberty (Ge et al, 2007;Saillenfait et al, 2008).…”

Environmental Factors and Puberty Timing: Expert Panel Research Needs

“…P,pЈ-DDE exposure in "foreign-born" girls was associated with earlier puberty relative to native-born Belgians 99 and, possibly, increasing DDE in utero exposure with earlier puberty in girls 97,98 ; however, no animal studies of DDE exposure and female puberty timing were identified, limiting additional interpretation of the human data. In male rats, peripubertal DDE exposure delays PPS, [116][117][118] although no relation to lower exposures was found in boys after in utero DDE exposure. 97 The weight of animal and human data, although suggestive, remains inconclusive for establishing a causal relation between EDCs and human pubertal disturbances.…”