Description of the Follicular Fluid Cytokine and Hormone Profiles in Human Physiological Natural Cycles

Cytokines seem to play a pivotal role in reproductive success, creating an immune-permissive and embryotrophic environment that supports fertilization, early embryo development, blastocyst implantation, and fetal growth. Accordingly, cytokines found in follicular fluid influence embryo quality, implantation and pregnancy rate. In IVF/ICSI cycles, the stimulation with exogenous gonadotrophins significantly interferes with local follicular regulatory system, which in turn influences oocyte quality. The fact that follicular fluid cytokine profile of stimulated IVF cycles differs from natural modified cycles supports the hypothesis that conventional ovarian stimulation indirectly and heterogeneously influences the intrafollicular milieu, and therefore affects the oocyte quality and the IVF/ICSI outcome. The studies dealing with IVF/ICSI natural cycle, actually report about modified natural cycles, in which ovulation is induced by the exogenous administration of hCG able to modulate follicular fluid cytokine content. Therefore, these IVF/ICSI natural cycles are not fully equivalent to a physiological context. Studies on physiological natural cycles are crucial to understand the role of follicular fluid cytokines and follicular fluid hormones on the follicle development and to improve stimulation protocols. Our study is the first that tries to define in physiological natural cycles the cytokine and hormone profiles in individual follicular fluids gently aspirated from antral follicles of normal ovaries resected before Ovarian Tissue Cryopreservation. It is also the first study which analyzes 27 cytokines/chemokines and growth factors (IL-1β, IL-1Ra, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL-12, IL-13, IL-15, IL-17, IFN-γ, TNFα, G-CSF, GM-CSF, VEGF, PDGF, FGF, IP-10, MCP-1, RANTES, EOTAXIN, MIP-1α, and MIP-1β ) and 5 hormones (P, A, T , E1 and E2) in the follicular fluids of physiological natural cycles trying to define the relationship between follicular fluid hormones and cytokines and to correlate these data with age, menstrual cycle phases and follicular size. Our results suggest that in physiological natural cycles there is a compelling relationship between follicular fluid cytokine profile and follicular fluid hormone profile, which are both age-dependent and both influence the follicle size. Follicular fluid hormone and cytokine levels are not different in the different phases of the menstrual cycle. The absence of correlation between the levels of the follicular fluid hormones and the follicular and luteal phase seems to indicate that hormones found in the follicular fluid of physiological natural cycles could be regulated independently of the endogenous gonadotropins, but could also be explained by the fact that 74% of the punctured follicles are ≤ 6mm and could therefore develop independently of cyclic gonadotrophin secretion. Follicular fluid cytokine and hormone profiles which are different in stimulated IVF/ICSI cycles and in physiological natural cycles, suggest that conventional ovarian stimulation could influence heterogeneously the intrafollicular milieu. Our findings could help to refine stimulation protocols in the context of optimizing the intrafollicular environment during oocyte maturation.