Adverse influence of coumestrol on secretory function of bovine luteal cells in the first trimester of pregnancy.

Coumestrol is one of a few biologically active substances present in leguminous plants, which are widely used as fodder for ruminants. Depending on the doses, coumestrol acts on the reproductive processes as an estrogen-like factor or antiestrogen to evoke a decrease in ovulation frequency, elongation of estrous cycle duration. The aim of the current investigations was to study the influence of coumestrol on secretory function of luteal cells obtained from first trimester of pregnant cows. Luteal cells (2.5 × 10(5) /mL) from 3rd to 5th, 6th to 8th, and 9th to 12th week of pregnancy were preincubated for 24 h and incubated with coumestrol (1 × 10(-6) M) for successive 48 h and the medium concentrations of progesterone (P4), oxytocin (OT), prostaglandin (PG) E2 and F2α were determined. Moreover, the expression of mRNA for neurophysin-I/oxytocin (NP-I/OT; precursor of OT) and peptidyl-glycine-α-amidating mono-oxygenase (PGA, an enzyme responsible for post-translational OT synthesis) was determined after 8 h of treatment. Coumestrol did not affect P4 secretion but increased the secretion of OT from the cells collected at all stages of gestation studied. Hence, the ratio of P4 to OT was markedly decreased. Simultaneously, coumestrol increased the expression of NP-I/OT mRNA during 9th to 12th weeks of pregnancy, and mRNA for PGA during 3rd to 5th and 9th to 12th weeks of gestation. Furthermore, coumestrol decreased PGE2 secretion from luteal cells in all studied stages of pregnancy, while it affected PGF2α metabolite (PGFM) concentration only from week 3 to 5 of pregnancy. Obtained results suggest that coumestrol impairs secretory function of the corpus luteum (CL) and this way it can affect the maintenance of pregnancy in the cow.

The adverse effect of phytoestrogens on the synthesis and secretion of ovarian oxytocin in cattle.

The current investigations were undertaken to study the mechanism of the adverse effect of phytoestrogens on the function of bovine granulosa (follicles >1< cm in diameter) and luteal cells from day 1-5, 6-10, 11-15, 16-19 of the oestrous cycle. The cells were incubated with genistein, daidzein or coumestrol (each at the dose of 1 × 10(-6) m). The viability and secretion of estradiol (E2), progesterone (P4) and oxytocin (OT) were measured after 72 h of incubation. Moreover, the expression of mRNA for neurophysin-I/OT (NP-I/OT; precursor of OT) and peptidyl-glycine-α-amidating monooxygenase (PGA, an enzyme responsible for post-translational OT synthesis) was determined after 8 h of treatment. None of the phytoestrogens used affected the viability of cells except for coumestrol. The increased secretion of E2 and P4 was only obtained by coumestrol (p<0.05) from granulosa cells from follicles <1cm in diameter and decreased from luteal cells on days 11-15 of the oestrous cycle, respectively. All three phytoestrogens stimulated (p<0.05) OT secretion from granulosa and luteal cells in all stages of the oestrous cycle and the expression of NP-I/OT mRNA in the both types of cells. The expression of mRNA for PGA was stimulated (p<0.05) by daidzein and coumestrol in granulosa cells, and by genistein and coumestrol in luteal cells. In conclusion, our results demonstrate that these phytoestrogens can impair the ovary function in cattle by adversely affecting the synthesis of OT in follicles and in corpus luteum. However, their influence on the ovarian steroids secretion was less evident.