Environmental antiandrogens: low doses of the fungicide vinclozolin alter sexual differentiation of the male rat

Abstract

In humans and rodents, exposure to antiandrogenic chemicals during sexual differentiation can produce malformations of the reproductive tract. Perinatal administration of 100 or 200 mg vinclozolin (V) kg⁻¹ day⁻¹ during sexual differentiation in rats induces female-like anogenital distance (AGD), retained nipples, cleft phallus with hypospadias, suprainguinal ectopic scrota/testes, a vaginal pouch, epididymal granulomas, and small to absent sex accessory glands in male offspring. Vinclozolin is metabolized to at least two active forms, M1 and M2, that display antiandrogenic activity by binding the androgen receptor (AR). Here, we present information on the reproductive effects of oral treatment with low dosage levels of V during sexual differentiation of the male rat. Vinclozolin was administered to the dam at 0, 3.125, 6.25, 12.5, 25, 50, or 100 mg kg⁻¹ day⁻¹ from gestational day 14 to postnatal day 3 (the period of fetal/neonatal testicular testosterone synthesis and sexual differentiation). At doses of 3.125 mg V kg⁻¹ and above, AGD was significantly reduced in newborn male offspring and the incidence of areolas was increased. These effects were associated with permanent alterations in other androgen-dependent tissues. Ventral prostate weight in one year old male offspring was reduced in all treatment groups (significant at 6.25, 25, 50, and 100 mg kg⁻¹ day⁻¹), and permanent nipples were detected in males at 3.125 (1.4%), 6.25 (3.6%), 12.5 (3.9%), 25 (8.5%), 50 (91%), and 100 (100%) mg V kg⁻¹ day⁻¹. To date, permanent nipples have not been observed in a control male from any study in our laboratory. Vinclozolin treatment at 50 and 100 mg kg⁻¹ day⁻¹ induced reproductive tract malformations and reduced ejaculated sperm numbers and fertility. Even though all of the effects of V likely result from the same initial event (AR binding), the different endpoints displayed a wide variety of dose-response curves and ED₅₀'s. The dose-response data for several of the functional endpoints failed to display an obvious threshold. These data demonstrate that V produces subtle alterations in sexual differentiation of the external genitalia, ventral prostate, and nipple tissue in male rat offspring at dosage levels below the previously described no-observed-effect-level (NOEL). These effects occur at a dosage level an order of magnitude below that required to induce malformations and reduce fertility. Hence, multigenerational reproduction studies of antiandrogenic chemicals that were not conducted under the Environmental Protection Agency's new Harmonized Multigenerational Test Guidelines, which include endpoints sensitive to antiandrogens at low dosage levels, could yield a NOEL that is at least an order of magnitude too high.