Norgestrel shows androgenic properties and triggers reproductive neuroendocrine toxicity in the testes of Pacific oysters (Crassostrea gigas).

Norgestrel (NGT), a prevalent progestin in the aquatic environment, can pose risks to vertebrates even at very low concentrations (<1 ng/L). Nevertheless, the understanding of NGT's effects on invertebrates is limited. Therefore, through histology and multi-omics, we explored the toxic effects of NGT (0, 10, and 1000 ng/L) on Pacific oysters Crassostrea gigas testes over 21 days. NGT accumulated in the testes and exhibited androgenic characteristics. Furthermore, transcriptomic sequencing revealed that differentially expressed genes were significantly enriched in the neurotransmitter ligand-receptor signaling pathway. A significant decrease in G protein-coupled receptors (GPCRs) and Calmodulin/ Calmodulin -dependent protein kinase gene expression was identified as the potential mechanism preventing hyperphosphorylation and G protein overactivation. Notably, the 1000 ng/L group showed clear Cytochrome P450/glutathione-s-transferase detoxification characteristics. Metabolomics analysis indicated that small peptides and organic acids were the most abundant differential metabolites, accounting for 26.96 %. The positive correlation between neuroendocrine related metabolites and several important G protein-coupled receptor genes, as revealed by correlation analysis, might play a major role in regulating NGT toxicity. In conclusion, NGT affects the reproductive neuroendocrine system in the C. gigas testis and triggers detoxification mechanisms. These findings provide new targets and a theoretical basis for environmental progestin toxicity and ecological risk assessment.