Association between components of the IGF system in blood and in the oocyte microenvironment (follicular fluid) in dairy cows

The somatotropic axis (endocrine) as well as the local IGF system in the follicle (paracrine/autocrine) is known to be important for fertility in dairy cows. In the present study, IGF-1 and respective binding proteins (IGFBP) were analysed in plasma and parallel in the follicular fluid (FF) obtained from the ovulatory follicle to study the hypothesis that a transfer of endocrine IGF-1 to the oocyte mi-croenvironment is possible. It is hypothesized that a correlation be-tween IGF-1 and IGFBPs in plasma and FF can be interpreted as a transfer. Blood samples were taken from 78 dairy cows 30 ± 2 and 50 ± 3 days post-partum (p.p.) and 17 of these animals were cho-sen for OPU (aspiration of 27 follicles) after cycle synchronization (2xPGF2α, detailed ultrasound). In addition, plasma and pooled FF from a cohort of 25 other animals obtained during a project by the Clinic of Reproductive Medicine, Vetsuisse Faculty, University of Zurich, Switzerland were also analysed. BHB in serum and IGF-1, IGFBP-2, -3, -4, -5 and an IGFBP fragment (IGFBP-F) in plasma and FF were determined. In granulosa cells (n = 6), the mRNA expression for IGFBP-2, -4, IGFBP-protease PAPP-A and IGF1R was measured. IGF-1 and IGFBP-2 showed a significant correlation between plasma and FF (IGF-1: r = .57; r2 = .32; p < .001; IGFBP-2: r = −.57; p < .05). In conclusion, the association between IGF-1 and IGFBP-2 between plasma and FF underlines the hypothesis of an existing transfer be-tween the endocrine IGF-1 and the local IGF system. This might rely on a causal association between metabolic disturbances in dairy cows and subsequent fertility.