Role of progesterone in capillary permeability in hyperstimulated rats

The role of progesterone in capillary permeability, which may be causally related to the pathophysiology of ovarian hyperstimulation syndrome (OHSS), was investigated in immature rats. A total of 96 female Wistar rats aged 22 days were given 10 IU of equine chorionic gonadotrophin daily for 4 consecutive days, and given 30 IU of human chorionic gonadotrophin on the fifth day to produce hyperstimulated manifestations. On the sixth day, groups of 12 rats each received RU486 at a dose of 0, 1, 2.5, 5, 10, 15 or 20 mg/kg (groups 1-7), or RU486 at 5 mg/kg combined with 6alpha-methyl-17alpha-hydroxy-progesterone acetate at 10 mg/kg (group 8). On the 7th day, the ovarian weight and capillary permeability of all rats were determined. Capillary permeability was evaluated from the Evans blue dye (EB) content in the ovaries and the EB level in peritoneal irrigated fluid at 30 min after the intravenous injection of EB. The peritoneal fluid EB level was significantly lower in groups 3, 4, and 5 than in the vehicle group. However, the peritoneal EB level in group 7 was higher than in the vehicle group, although not significantly. These findings demonstrated that RU486 has two divergent effects on capillary permeability, depending on the dose administered. In group 8, on the other hand, the peritoneal EB level and ovarian EB content were significantly higher than the corresponding values in group 4, respectively, suggesting that progesterone has a role in capillary permeability and ovarian enlargement. These results imply that progesterone may contribute, at least in part, to the pathophysiology of OHSS in this experimental model.