Electrolyte, Oestradiol and Progesterone Concentrations in Ovarian Cyst Fluid in Guinea Pigs (Cavia porcellus)

Despite their high prevalence, the aetiopathogenesis of ovarian cysts in guinea pigs (Cavia porcellus) is unknown. We examined tissue samples of cystic ovaries from 20 guinea pigs by histopathology and immunohistochemistry for CD10 antigen, and determined the concentrations of Na⁺, K⁺, Cl^-, oestradiol and progesterone in the cyst fluid. Cystic rete ovarii were found in all 20 guinea pigs but no follicular cysts. Concentrations of Na⁺ (142.2 ± 5.04 mmol/l), K⁺ (5.6 ± 0.76 mmol/l) and Cl^- (116.1 ± 5.25 mmol/l) corresponded to extracellular, rather than intracellular, fluid indicating that rete ovarii cysts in guinea pigs are transudative in nature. A positive correlation was found between Na⁺ and Cl^- concentrations (r = 0.7713, P <0.0001). The mean concentrations of oestradiol (61.9 ± 17.44 pg/ml) and progesterone (2.7 ± 5.42 ng/ml) in the cyst fluid were higher than expected because the rete epithelium is not known to have steroidogenic activity. A negative correlation was found between oestradiol and progesterone concentrations in cyst fluid (r = -0.4296, P = 0.0178). Possible pathogenetic mechanisms of cystic rete ovarii in guinea pigs are discussed.