Progestins are shown to alter the expression of steroidogenic
enzymes in zebrafish and fathead minnows (Overturf et al., 2014;
Fent, 2015). Transcriptional changes were generally more sensitive
than changes on steroid levels and revealed a number of
affected pathways, including steroid hormone receptor activities
and steroid hormone mediated signaling pathways, cellular
response to steroid hormone stimulus and thyroid hormone receptor
activity (Zucchi et al., 2014). More recently, Zhao et al. (2015)
reported significant and dose-dependent alterations of the circadian
rhythm network in the brain of zebra fish exposed to progesterone
and DRO.