CYP19A1 and polycystic ovary syndrome: The effects of KH on Cyp19a1 mRNA expression are shown in Figure 5A. Letrozole induction significantly downregulated the Cyp19a1 mRNA expression in untreated PCOS rats compared with the normal control group (0.094 ± 0.01 vs. 1.00 ± 0, p < 0.05).