Vascular endothelial growth factor in serum and in the follicular fluid of patients undergoing hormonal stimulation for in-vitro fertilization

A cross-sectional study regarding endocrine and cytokine parameters in human follicular fluid (FF) as compared to serum values following hormonal stimulation for in-vitro fertilization was conducted. The patients (n = 32) were treated sequentially with the luteinizing hormone-releasing hormone (LHRH) agonist buserelin followed by a combination of buserelin plus highly purified follicle stimulating hormone and finally human chorionic gonadotrophin, in order to induce ovulation. The FF content of pro-inflammatory (IL-1, IL-6), and anti-inflammatory (IL-1ra, IL-10) cytokines, of the immune response-related soluble interleukin-2 receptor (sIL-2R), as well as the mitogens vascular endothelial growth factor (VEGF) and basic fibroblastic growth factor (bFGF) were determined. Routine evaluation included peripheral blood cell counts, morphological data of the ovary and ova, ovarian steroids, prolactin concentrations and thyroid function parameters [free thyroxine (fT4), thyroglobulin]. The concentrations of IL-6, IL1-ra, sIL-2R, VEGF and bFGF in the FF compartment were higher than in serum in the majority of cases. Regression analysis showed a significant association between the serum and FF concentrations of fT4 (P = 0.04; y = 0.37 + 0.34x) and IL-6 (P = 0.002; y = 0.78 + 0.5x). Multiple regression analysis revealed that progesterone played a role in determining VEGF concentrations in the FF (P = 0.07; y = 0.37 + 0.86x). Thyroglobulin concentrations within the FF were extremely low, whereas fT4 concentrations in the FF were similar to those in serum. Patients with a previously diagnosed hypothyroidism tended to have lower serum oestradiol and higher serum progesterone when compared to euthyroids. We conclude that the human FF represents a functional compartment that integrates endocrine, immunological, and mitogenic signalling that is unique for each ovarian follicle. The close association between progesterone and VEGF within the FF suggests a close association of this mitogen to gonadotrophin stimulation, confirming the ovary as a production site of VEGF.