Weanling Hershberger Bioassay in Rats: A Short-term Screening Assay for (Anti)Androgenic Properties

1. The OECD initiated a high-priority activity in 1998 to revise existing guidelines and to develop new guidelines for the screening and testing of potential endocrine disrupters (1). One element of the activity was to develop a Test Guideline for the rat Hershberger Bioassay. The Hershberger Bioassay is a short-term in vivo screening test using accessory tissues of the male reproductive tract. The assay originated in the 1930’s and was modified in the 1940’s to include androgen-responsive muscles in the male reproductive tract (2)(9-15). In the 1960s, over 700 possible androgens were evaluated using a standardized version of the protocol (2)(14), and use of the assay for both androgens and antiandrogens was considered a standard method in the 1960s (2)(15). After several decades of use by the pharmaceutical industry, this assay was first standardized by an official expert committee in 1962 as a screening tool for androgenic chemicals (2). In 2001-2007, the rat Hershberger Bioassay has undergone an extensive validation programme including the generation of a Background Review Document (25), compilation of a detailed methods paper (3), development of a dissection guide and the conduct of extensive intraand interlaboratory studies to show the reliability and reproducibility of the bioassay. These validation studies were conducted with a potent reference androgen (testosterone propionate (TP)), two potent synthetic androgens (trenbolone acetate and methyl testosterone), a potent antiandrogenic pharmaceutical (flutamide), a potent inhibitor of the synthesis (finasteride) of the natural androgen (dihydrotestosterone-DHT), several weakly antiandrogenic pesticides (linuron, vinclozolin, procymidone, p,p’ DDE), a potent 5α reductase inhibitor (finasteride) and two known negative chemicals (dinitrophenol and nonylphenol) (4)(5)(6)(7)(8)(26). Test Guideline 441 and this Guidance Document are the outcome of the long historical experience with the bioassay and the experience gained during the validation test programme and the results obtained therein.