Does equine chorionic gonadotropin (ECG) bind to FSH and LH receptors in follicles of cows?

Abstract

Aiming to improve reproductive efficiency in cattle, various hormonal protocols have been developed to synchronize the emergence of a new follicular wave, estrus and ovulation, thus allowing fixed time artificial insemination (FTAI). However, despite the use of these protocols, suboptimal conception rates remain a problem and the use of gonadotropins such as equine chorionic gonadotropin (eCG) is being included in FTAI protocols with the purpose of increasing follicular growth, ovulation and consequently conception rate. However, it is not completely understood the biological effect of eCG on the follicles of cattle. Thus, the present study aims to evaluate if eCG is able to bind to FSH and LH receptors in granulosa cells from follicles with different sizes and developmental stages. In Experiment 1, ovaries from Holstein cows will be collected immediately after slaughter and the follicles will be measured by ultrasound and separated into four groups: G1) follicles from 6.0 to 7.9 mm; G2) follicles from 8.0 mm to 9.9; G3) follicles from 10.0 to 11.9 mm; G4) follicles larger than 12 mm. After measurement the follicles will be aspirated individually to collect follicular fluid and granulosa cells that will be used to perform a binding assay for FSH and LH receptors after exposure to eCG by a radioreceptor technique described by Diekman et al. (1978) and best described in material and methods. In Experiment 2, the methodology will be similar with the same four groups, however, cows will be submitted to synchronization of the follicular wave and the follicles will be aspirated in vivo to obtain the granulosa cells and further binding assay for FSH and LH. The statistical analysis of the variables related to the number of granulosa cells and the binding assay for FSH and LH receptors will be made through the GLIMMIX procedure of SAS. (AU)