Iprodione delays male rat pubertal development, reduces serum testosterone levels, and decreases ex vivo testicular testosterone production

Iprodione (IPRO) is a dichlorophenyl dicarboximide fungicide similar to procymidone and vinclozolin. All three of these fungicides induce Leydig cell tumors in the rat testis in long-term studies and an endocrine mode of action has been hypothesized to mediate this effect. Although both procymidone and vinclozolin antagonize the Androgen Receptor (AR) in vitro and in vivo, IPRO does not appear to be an AR antagonist. We proposed that pubertal exposure to IPRO would delay male rat pubertal development and reduce testosterone production within the testis. Sprague-Dawley weanling rats were dosed by gavage with 0, 50, 100, or 200mg/kg/day of IPRO from post-natal day (PND) 23 to 51/52. The onset of puberty (progression of preputial separation (PPS)) was measured starting on PND 37. Organ weights, serum Hormones, and ex vivo testis steroid hormone production under stimulated (+human chorionic gonadotropin (hCG)) and unstimulated (-hCG) conditions were measured at necropsy. IPRO delayed PPS at 100 and 200mg/kg/day and decreased androgen sensitive seminal vesicle and epididymides weights at 200mg/kg/day. Furthermore, IPRO increased adrenal and liver weights at 200mg/kg/day, presumably by different mechanism(s) of action. Serum testosterone levels were decreased along with serum 17alpha-hydroxyprogesterone and androstenedione whereas serum LH was unaffected. IPRO reduced ex vivo testis production of testosterone and progesterone. Taken together, these results suggest that IPRO affects steroidogenesis within the testis, not through disruption of LH signaling, but possibly through Enzyme inhibition of the steroidogenic pathway before CYP17. These data, along with the reported failure of IPRO to elicit an AR antagonism in vitro, provide evidence that IPRO differs from the dicarboximides procymidone and vinclozolin in that the effects on male rat pubertal development result from an inhibition of steroidogenesis and not AR antagonism.