Progesterone is actively metabolized to 5α-pregnane-3,20-dione and 3β-hydroxy-5α-pregnan-20-one by the marine mussel Mytilus galloprovincialis

Progesterone (P4) and synthetic progestins enter the aquatic environment through wastewater treatment plant effluents and agricultural run-off, posing potential risks to aquatic organisms due to their biological activity. P4 is a precursor of a number of steroids in vertebrates, including estrogens and androgens. Mussels Mytilus galloprovincialis were exposed to P4 at the ng to low mu g/L range (0.02-10 mu g/L) for 7 days with the aim of (a) assessing potential alterations on endogenous steroids as a consequence of exposure, and (b) describing the enzymatic pathways involved in P4 metabolism in mussels. No significant alteration of the levels of testosterone (T) and estradiol (E2) was observed in mantle/gonad tissue of exposed mussels, in spite of a 5.6-fold increase in immunoreactive Tin those exposed to 10 mu g P4/L, which was attributed to cross-reactivity. P4 was actively metabolized to 5 alpha-pregnane-3,20-dione (5 alpha-DHP) and 3 beta-hydroxy-5 alpha-pregnan-20-one (3 beta,20-one) in digestive gland, with no evidence for the synthesis of 17 alpha-hydroxyprogesterone or androstenedione. The metabolism of P4 to 5 alpha-DHP was not altered by exposure. Histological examination of the gonads suggested that exposure to 10 mu g/L P4 induced gamete maturation and release in mussels. Nonetheless, environmental concentrations of P4 are unlikely to have an endocrine action in mussels. (C) 2015 Elsevier B.V. All rights reserved.