Progesterone Priming Modulates Ovarian and Early Embryonic Responses to Intensified Gonadotropin Stimulation in Rats

Background: The present study investigated the effects of progesterone priming and gonadotropin stimulation intensity on ovarian response and early embryo development during in vitro embryo production (IVEP) in rats. Methods: Sixty adult female Wistar rats were allocated to four treatment groups (n = 15 per group), with five females from each group included in each of three independent experimental replicates. The groups received either standard or intensified gonadotropin stimulation, with or without progesterone priming. Oocyte recovery, two-cell embryo production and two-cell embryo yield were evaluated. Result: Intensified gonadotropin stimulation did not significantly alter oocyte recovery in non-primed females, whereas progesterone-primed females subjected to intensified stimulation exhibited the highest oocyte recovery (25.00±5.66 oocytes; P less than 0.05). This treatment combination also produced the highest number of two-cell embryos (17.60±4.61; P less than 0.05). Among progesterone-primed females, intensified stimulation significantly increased two-cell embryo yield compared with standard stimulation (70.50±7.63% vs. 47.25±2.91%; P less than 0.05). These findings indicate that ovarian and early embryonic responses to intensified gonadotropin stimulation may vary according to the endocrine conditions preceding stimulation. Progesterone priming combined with intensified gonadotropin stimulation was associated with increased oocyte recovery and two-cell embryo production, highlighting the importance of optimizing endocrine pretreatment and stimulation intensity during rat IVEP.