Di(n-butyl) phthalate (DBP) has antiandrogenic-like effects on the developing reproductive tract in the male rat and produces regions of interstitial cell
hyperplasia and gonocyte degeneration in the developing fetal testes at maternal doses of 100-500 mg/kg/day. Neither DBP nor its primary metabolites interact with the
androgen receptor in vitro. The present study was performed to examine gene expression in the fetal rat testes following in utero DBP exposure. Pregnant Sprague-Dawley rats received
corn oil, DBP (500 mg/kg/day), or
flutamide (reference
antiandrogen, 50 mg/kg/day) by gavage daily from gestation day (GD) 12 to 21. Dose levels were selected to maximize fetal response with minimal maternal toxicity. Testes were isolated on GD 16, 19, and 21. Global changes in gene expression were determined by microarray analysis. Selected genes were further examined by quantitative RT-PCR. DBP, but not
flutamide, reduced expression of the steroidogenic
enzymes cytochrome P450 side chain cleavage,
cytochrome P450c17, and
steroidogenic acute regulatory protein. Testicular
testosterone and
androstenedione were decreased on GD 19 and 21, while
progesterone was increased on GD 19 in DBP-exposed testes.
Testosterone-repressed prostate message-2 (TRPM-2) was upregulated, while c-kit (
stem cell factor receptor)
mRNA was downregulated following DBP exposure. TRPM-2 and bcl-2
protein staining was elevated in GD 21 DBP-exposed Leydig and Sertoli cells. Results of this study have led to the identification of several possible mechanisms by which DBP can induce its antiandrogenic effects on the developing male reproductive tract without direct interaction with the
androgen receptor. Our results suggest that the antiandrogenic effects of DBP are due to decreased
testosterone synthesis. In addition, enhanced expression of cell survival
proteins such as TRPM-2 and bcl-2 may be involved in DBP-induced Leydig cell
hyperplasia, whereas, downregulation of c-kit may play a role in gonocyte degeneration. Future studies will explore the link between these identified gene expression alterations and ultimate adverse responses.