Phytoestrogens and Their Metabolites Inhibit the Sensitivity of the Bovine Corpus Luteum to Luteotropic Factors

Abstract

The aim of this study was to examine whether active metabolites of phytoestrogens (equol and para-ethyl-phenol) inhibit sensitivity of bovine corpus luteum (CL) to luteinizing hormone (LH) and to auto/paracrine luteotropic factors (prostaglandin E₂-PGE₂ and prostaglandin F_2α-PGF_2α), and whether they influence pulsatile progesterone (P₄) secretion by the bovine CL. In in vivo experiments, high levels of equol and para-ethyl-phenol were found in plasma and in the CL tissue of heifers and cows fed a soy bean diet (2.5 kg/animal/day), along with lower concentrations of P₄ (P<0.05). Both Prostaglandins (PG) and LH strongly stimulated P₄ secretion in cultured pieces of CL that were collected from cows fed a standard diet (P<0.01). There was no effect of PGs and LH on P₄ stimulation in CLs obtained from cows fed a diet rich in soy bean. Finally, we examined whether active metabolites of phytoestrogens participated in regulation of pulsatile P₄ secretion and LH-stimulated P₄ secretion in vitro using a microdialysis system. Equol and para-ethyl-phenol had no effect on basic and pulsatile P₄ secretion in CLs during 240 min of perfusion when compared to the control (P<0.05). However, they inhibited LH-stimulated P₄ secretion (P<0.05). Phytoestrogens and their metabolites may disrupt CL function by inhibiting PG- and LH-stimulated P₄ secretion.