The nonsteroidal mycoestrogen zearalenone and its five metabolites suppress LH secretion from the bovine anterior pituitary cells via the estradiol receptor GPR30 in vitro.

ABSTRACT

Picomolar concentrations of estradiol produce nongenomic suppression of GnRH-induced LH secretion from the anterior pituitary (AP) of cattle via G-protein-coupled receptor 30 (GPR30). Zearalenone (ZEN) is the nonsteroidal mycoestrogen produced by Fusarium fungi and has been detected in cereal grains, animal feed, and ruminant urine worldwide. Zearalenone has a prolonged blood half-life that results from enterohepatic cycling. There are five metabolites of ZEN α-zearalanol (α-ZAL), ß-zearalanol (ß-ZAL), α-zearalenol (α-ZOL), ß-zearalenol (ß-ZOL), and zearalanone, which may persist for long periods in animals and humans after consumption of ZEN-contaminated feed. We recently reported that GPR30 bound with α-ZAL decreases cytoplasmic cAMP but not gene expression of LHα and LHß subunits, and GPR30 bound with α-ZAL suppresses GnRH-induced LH release in bovine AP cells in vitro. We tested the hypothesis that GPR30 bound with ZEN or one of the four previously untested metabolites suppresses GnRH-induced LH release from the bovine AP cells in vitro. Anterior pituitary cells were cultured for 3 days under steroid-free conditions and were then incubated with various concentrations (0.001-10 nM) of estradiol or one of the ZEN analogs for 5 minutes before GnRH stimulation. Gonadotropin-releasing hormone-stimulated LH secretion from AP cells was inhibited by all of the test concentrations of ZEN, 0.001 to 1 nM of α-ZAL, and 0.001 to 0.1 nM of the remaining four analogs. Pretreatment for 5 minutes with a GPR30-specific antagonist, G36, inhibited estradiol- and the ZEN analog-induced suppression of LH secretion from cultured AP cells. G36 alone had no significant effect on LH secretion. The estimated order of the nongenomic inhibiting effect was ZEN, α-ZAL, zearalanone, α-ZOL, ß-ZOL, and ß-ZAL, which is quite different from the reported order for their genomic effects. Therefore, ZEN and all of its metabolites suppress LH secretion from the bovine AP cells via GPR30 in vitro.