The role of endothelial cells in the pathogenesis of ovarian hyperstimulation syndrome

Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic complication of treatment with fertility drugs. Using human lung microvascular endothelial cells (HUMEC-L) as an in-vitro model of OHSS, we have tested the hypothesis that the endothelium is a target of HCG in the pathogenesis of OHSS. Since OHSS is characterized by increased capillary permeability, we have investigated the production and action of vasoactive agents. When HUMEC-L were cultured with high doses of estradiol (E-2) no significant changes were observed in the secretion of vascular endothelial growth factor (VEGF), interleukin (IL)-6 or IL-1beta. However, the addition of HCG resulted in a significant increase in the secretion of VEGF and IL-6. Time-course experiments showed that VEGF was secreted within minutes of HCG addition, whereas IL-6 was significantly increased only after 48 h in culture. The secretion of IL-1beta was unchanged by these hormonal conditions. The presence of HCG receptors was demonstrated in HUMEC-L in basal conditions as well as after the addition of E-2. The expression of VEGF receptors was also investigated. High doses of E-2 were unable to increase the expression of KDR, flt-1 and sfl-t, but the addition of HCG significantly upregulated the KDR concentration in endothelial cells, while no change was observed for fit. Permeability assays demonstrated that while E-2 alone did not change the arrangement of HUMEC-L in vitro, the presence of HCG caused changes in the actin fibres corresponding to increased capillary permeability. Anti-human VEGF antibodies were able to overcome these changes. In conclusion, these experiments show that the endothelium may be a primary target of HCG, causing an acute release of VEGF and a significant increase in IL-6 and resulting in an autocrine-paracrine action that may increase vascular permeability.