Comparing effect levels of regulatory studies with endpoints derived in targeted anti-androgenic studies: example prochloraz

Prochloraz is an imidazole fungicide, and its regulatory toxicological data package has been primarily generated in the 1990s. More recently, studies have been published demonstrating an interaction with hormone receptors/steroidogenesis and effects with an endocrine mode of action. In the present study, prochloraz has been investigated in a comprehensive in vivo study including relevant elements of current regulatory reproduction toxicity studies and additional mechanistic parameters. Prochloraz was administered per gavage in oil from GD 6 to PND 83 to pregnant and lactating Wistar rats and their respective offspring, at doses of 0.01 mg/kg bw/day (acceptable daily intake of prochloraz), 5 mg/kg bw/day [expected no-observed-effect-level (NOEL)] and 30 mg/kg bw/day. At 30 mg/kg bw/day maternal and offspring effects (decreased viability, lower number of live offspring) were seen including a delayed entry into male puberty (+1 day) accompanied by lower male offspring body weights, increased anogenital distance/index in females and transiently retained nipples in males at PND 12 (not seen at PND 20). The only finding at the expected NOEL was increased incidences of transiently retained nipples in males which are not considered adverse. No effects were seen in the low-dose group. There was no evidence for a non-monotonic dose-response curve or effects at low levels.