(1) Background: Cortisol and melatonin (MT) act in regulating follicular development. We hypothesized that abnormal levels of cortisol, MT, and steroids in theca interna cells might be involved in the development of follicular cysts in sows. (2) Methods: To test this hypothesis, we measured the mRNA levels of enzymes involved in steroid hormone synthesis, the glucocorticoid receptor (GR), and melatonin receptors (MTRs) in theca interna cells of cystic and normal porcine follicles. (3) Results: The concentrations of estradiol, progesterone, and cortisol were greater in cystic follicles than in control ones (p = 0.034, p = 0.020, p = 0.000), but the concentration of MT was significantly lower (p = 0.045). The levels of GR, 11β-HSD1, and 11β-HSD2 were higher in cystic follicles than in control l follicles. MT types 1 and 2 were significantly lower in cystic follicles (p < 0.05). The mRNA expression levels of genes encoding the steroid hormone synthesis enzymes, steroidogenic acute regulatory protein (StAR), recombinant cytochrome P45011A1 (CYP11A1), and 3β-hydroxysteroid dehydrogenase (3β-HSD) in theca interna cells of cystic follicles were significantly higher than in control follicles. Thus, there was disruption of hormone secretion in the fluid of cystic follicles in sows. (4) Conclusions: The levels of steroid hormones, cortisol and MT are disrupted in porcine cystic follicles.
Keywords: cortisol; follicular cyst; melatonin; pig; steroid hormones.