Objective: The combined use of Pregnant Mare Serum Gonadotropin (PMSG) and hGC in high doses induces ovarian hyperstimulation syndrome (OHSS) in the rat animal model, characterized by increased vascular permeability related to the simultaneous overexpression of vascular endothelial growth factor (VEGF) and its receptor 2 in ovarian cells. hCG has longer half-life than LH and is believed to have a higher biological activity (approximately 6-fold), including the incidence of complications such as OHSS. Similarly, FSH may also be related to the ovulatory changes within the follicle because there is a simultaneous surge in spontaneous cycles. The aim of this study was to compare the ability of hCG, FSH, and LH in inducing ovulation, and simultaneously prevent OHSS in the animal model. Design: Immature female rats, weighing 42–48 g at the beginning of the experiments were treated daily with 10 IU PMSG injections for 4 consecutive days, and the fifth day 10 IU hCG (hCG group), 10 IU FSH (FSH group), 10 IU LH (LH-10 group), 60 IU LH (LH-60), or saline (control group), to induce ovulation. A total of 30 animals per group were employed in three sets of experiments. In each set and group, half of the animals were sacrificed 12 hours after ovulation triggering to ascertain the number of ovulated oocytes. The remaining rats were employed to measure vascular permeability (VP) 48 hrs after administration of the drugs inducing ovulation. The ovaries were removed and frozen at −80 °C for VEGF mRNA analysis. Materials and Methods: The cumulus complexes obtained 12 hours after ovulation were disolved with hyaluronidase (1%) to ascertain the number of oocytes. To measure VP, 0.2 ml 5mM Evans blue(EB) were injected via the femoral vein. After 30 min, the peritoneal cavity was irrigated with saline. Light absorption was measured in the recovered fluid at 595 nm and the VP expressed as μg EB/100 g body weight. To analyze VEGF expression, RNA was extracted from 4 ovaries in each group and reverse transcribed. B-actin and VEGF primers were used under universal conditions to perform a QF-PCR with an ABIPRISM 7700 thermocycler. A six-point calibration curve was run in parallel to quantify VEGF expression as the VEGF/B-actin ratio. Results: hCG (27.2±2.5), LH-60 (26.7±4.1), FSH (30.4±3.2), and LH-10 (20.0±1.8) had significantly (p < 0.05) higher number of oocytes ovulated than the control group (0.7±0.1). The level of extravasated EB was 30.7±4.1μg EB/100 g body weight in the hCG group, similar to that of FSH (28.2±3.0) and LH-60 (21.1±3.7), and significantly higher than in the LH-10 (12.5±2.3, p = 0.006) and the control (10.8±1.9, p = 0.03) groups. VEGF expression was associated with increased VP, showing similar values in the hCG (1.9±0.2), LH-60 (1.4±0.3), and FSH (1.7±0.3) groups, whereas it was significantly reduced in the LH-10 (1.2±0.2, p = 0.02) and control (1.1±0.3, p = 0.03) groups. Conclusions: FSH and hCG, as well as a 6-fold increase in LH administration, have similar biological activities, including increased VP due to excessive VEGF expression. The use of lower LH doses reaches similar rates of ovulation while preventing the undesired changes in permeability. Thus, these experiments should encourage clinicians to find the optimal dose of LH to be employed in women to trigger ovulation and simultaneously avoid the risk of OHSS.