Equine chorionic gonadotropin increases estradiol levels in the bovine oviduct and drives the transcription of genes related to fertilization in superstimulated cows

Abstract

In the bovine oviduct, estradiol (E2) stimulates secretion and cell proliferation, whereas progesterone (P4) suppresses them. In this study, we have evaluated the effect of two superstimulatory protocols (follicle‐stimulating hormone [FSH] or FSH combined with equine chorionic gonadotropin [eCG]) on the oviductal levels of E2 and P4 and its outcome on oviductal cells. Compared with the control group (a single pre‐ovulatory follicle), we have observed that the cows submitted to FSH/eCG treatment showed a higher concentration of E2 in the oviduct tissue, together with a higher abundance of messenger RNA encoding steroid receptors (ESR1 and progesterone receptor), and genes linked to gamete interactions and regulation of polyspermy (oviduct‐specific glycoprotein 1, heat‐shock protein family A member 5, α‐l‐fucosidase 1 [FUCA1], and FUCA2) in the infundibulum and ampulla segments of the oviduct. However, we did not observe any modulation of gene expression in the isthmus segment. Even though the FSH protocol upregulated some of the genes analyzed, we may infer that the steady effect of FSH combined with eCG on oviduct regulation might benefit fertilization and may potentially increase pregnancy rates.

The incompletely fulfilled promise of embryo transfer in cattle—why aren’t pregnancy rates greater and what can we do about it?

“…Yet, there is reason to suppose that the MOET embryo is also abnormal when compared with an embryo recovered from a non-stimulated female. Superovulation can cause changes in the follicle and follicular fluid ( Dias et al, 2013a ; Santos et al, 2018 ; Fontes et al, 2019 ), oocyte ( Chu et al, 2012 ), oviduct ( Fontes et al, 2019 ), and endometrium ( Forde et al, 2012 ). The effects of superovulation on the reproductive tract could reflect the elevation in circulating concentrations of progesterone associated with the procedure ( Forde et al, 2012 ; O’Hara et al, 2012 ).…”

“…The effects of superovulation on the reproductive tract could reflect the elevation in circulating concentrations of progesterone associated with the procedure ( Forde et al, 2012 ; O’Hara et al, 2012 ). Elevated concentrations of estradiol in the oviduct ( Fontes et al, 2019 ) and blood plasma ( Santos et al, 2018 ) can also occur for cows superovulated with combined treatment with FSH and equine chorionic gonadotropin. Possibly, there are direct effects of FSH on the reproductive tract because the oviduct and uterus express gonadotropin receptors and can be modified by luteinizing hormone and human chorionic gonadotropin ( Ziecik et al, 2005 ).…”