Aquatic Toxicology 163 (2015) 97–101 Contents lists available at ScienceDirect Aquatic Toxicology journal homepage: www.elsevier.com/locate/aquatox Short communication Nortestosterone-derived synthetic progestogens do not activate the progestogen receptor of Murray–Darling rainbowfish (Melanotaenia fluviatilis) but are potent agonists of androgen receptors alpha and beta Peter A. Bain a,∗ , Anu Kumar a , Yukiko Ogino b , Taisen Iguchi b a Commonwealth Scientific and Industrial Research Organisation, Land and Water Flagship, PMB2, Glen Osmond, 5064 South Australia, Australia b Division of Molecular Environmental Endocrinology, National Institute for Basic Biology, Nishigonaka-38 Myodaijicho, Okazaki, Aichi Prefecture 444-0867, Japan article info Article history: Received 4 February 2015 Received in revised form 26 March 2015 Accepted 29 March 2015 Available online 31 March 2015 Keywords: Fish Progestins Androgen receptors Progestogen receptors Endocrine disruption abstract Synthetic progestogens derived from 19-nortestosterone can elicit a number of adverse effects in fish including decreased fecundity, altered hormone levels, disruption of normal breeding cycles, expression in females of male-specific biomarkers, development of male secondary sexual characteristics in females, and changes in the expression of steroidogenic genes. A recent in vitro study showed that a number of rep- resentatives from this class of progestins were potent agonists of fathead minnow androgen receptor (AR) and only weak agonists of progesterone receptor (PR) from the same species. This confirms that synthetic progestogens derived from 19-nortestosterone function as AR agonists in otomorphs, which express a single AR subtype. However, numerous perciformes are known to express two AR subtypes. We have recently shown that AR and AR from Murray–Darling rainbowfish (Melanotaenia fluviatilis) respond differently to certain androgens and anti-androgens. The goal of the present study was to determine concentration–response profiles for selected progestins in transactivation assays driven by rainbowfish AR, AR and PR in order to ascertain the relative potency of progestins against these receptors. As a means of confirming the expected activity of the progestins and reference compounds used in the study against human-derived receptors, we also established concentration–response relationships using transactivation assays driven by human PR and AR. We found that all five 19-nortestosterone-derived progestins tested were highly potent agonists of rainbowfish AR, but that only four of the five progestins were potent agonists of rainbowfish AR, with norgestimate exhibiting only weak activity against rain- bowfish AR. The spironolactone-derived progestin, drospirenone, was not an agonist of rainbowfish AR or AR but was a weak agonist of rainbowfish PR. None of the 19-nortestosterone-progestins activated rainbowfish PR. These findings confirm that the majority of 19-nortestosterone-derived progestins are likely to elicit strong androgenic activity in teleosts, but that PR-mediated effects would be minimal. In species that express two AR subtypes similar to rainbowfish AR and AR, biological processes mediated by a specific subtype may be affected differently by progestins such as norgestimate. © 2015 Elsevier B.V. All rights reserved. Synthetic progestogens (also known as ‘synthetic gestagens’, ‘synthetic progestins’ or simply ‘progestins’) are designed to mimic the effects of progesterone (P4) and are the active pharmaceutical ingredient in many contraceptives and hormone replacement ther- apies. Since most progestins are derived from steroid hormones, they can be classified according to the structure of the parent ∗ Corresponding author at: CSIRO Land and Water Flagship, PMB2, Glen Osmond, South Australia 5064, Australia. Tel.: +61 8 8303 8598. E-mail address: peter.bain@csiro.au (P.A. Bain). compound, and include P4 derivatives (dydrogestrone, medroge- stone), pregnane derivatives (chlormadinone acetate, cyproterone acetate, medroxyprogesterone acetate), norpregnane derivatives (progmegestone, nomegestrol acetate), the spironolactone deriva- tive, drospirenone (DPN), and 19-nortestosterone derivatives, which are subdivided into estranes (19-norethindrone [19-NE], lynestrenol, tibolone), ethinylated gonanes (levonorgestrel [LNG], norgestimate [NGM], etonogestrel [ETG], gestodene [GSD]) and non-ethinylated gonanes (dienogest). Like other pharmaceuticals with endocrine receptor-mediated modes of action, progestins are considered as aquatic contaminants of increasing concern http://dx.doi.org/10.1016/j.aquatox.2015.03.021 0166-445X/© 2015 Elsevier B.V. All rights reserved.