Environmental glucocorticoids corticosterone, betamethasone and flumethasone induce more potent physiological than transcriptional effects in zebrafish embryos.

Many glucocorticoids occur in the aquatic environments but their adverse effects to fish are poorly known. Here we investigate effects of the natural glucocorticoid corticosterone and the synthetic glucocorticoids betamethasone and flumethasone in zebrafish embryos. Besides studying the effects of each steroid, we compared effects of natural with synthetic glucocorticoids, used as drugs. Exposure at concentrations of 1 µg/L and higher led to concentration-related decrease in spontaneous muscle contractions at 24 h post fertilization (hpf) and increase in heart rate at 48 hpf. Betamethasone showed a significant increase at 0.11 µg/L in heart rate. Corticosterone also accelerated hatching at 60 hpf at 0.085 µg/L. Transcription of up to 24 genes associated with different pathways showed alterations at 96 and 120 hpf for all glucocorticoids, although with low potency. Corticosterone caused transcriptional induction of interleukin-17, while betamethasone caused transcriptional down-regulation of the androgen receptor, aromatase and hsd11b2, indicating an effect on the sex hormone system. Furthermore, transcripts encoding proteins related to immune system regulation (irg1l, gilz) and fkbp5 were differentially expressed by corticosterone and betamethasone, while flumethasone caused only little effects, mainly alteration of the irg1l transcript. Our study shows that these glucocorticoids caused more potent physiological effects in early embryos than transcriptional alterations in hatched embryos, likely due to increased metabolism in later developmental stages. Thus, these glucocorticoids may be of concern for early stages of fish embryos in contaminated aquatic environments.