Exposure to nitrate and nitrite disrupts cardiovascular development through estrogen receptor in zebrafish embryos and larvae.

Increasing nitrate concentration on surface and groundwater due to anthropogenic activities is an environmental concern. In this study, Tg(fli1: EGFP) zebrafish embryos were exposed to nitrate (NO₃^-) and nitrite (NO₂^-), and their cardiovascular development were investigated. Exposure to 10 mg/L NO₃-N and 1 and 10 mg/L NO₂-N decreased heart rate at 48-96-h post-fertilization (hpf), ventricular volume, and red blood cell flow rate at 96 hpf. Similar concentrations increased the number of embryos and larvae with pericardial edema and missing intersegmental and parachordal vessels in the caudal region at 48-96 hpf. Addition of ICI 182,720 (ICI) reversed the effects of nitrate and nitrite, suggesting estrogen receptors (ER) are involved. 10 mg/L NO₃-N and 1 mg/L NO₂-N decreased cardiovascular-related genes, gata4,5,6, hand2, nkx2.5, nkx2.7, tbx2a, tbx2b, and fgf1a. Gene expressions of ovarian aromatase and brain aromatase (cyp19a1a and cyp19a1b, respectively) decreased in the exposed groups, whereas ERs (esr1, esr2a, and esr2b) and nitric oxide synthase 2a (nos2a) increased. The effects on gene expression were also reversed by addition of ICI. Taken together, nitrate and nitrite disrupt cardiovascular system through ER in developing zebrafish, implying that environmental nitrate and nitrite contamination may be harmful to aquatic organisms.