Effects of Preovulatory hCG Administration on Follicular Dynamics, Reproductive Hemodynamics, Nitric Oxide, and VEGF Levels in Mares

This study aimed to determine the action of a single dose of human chorionic gonadotropin (hCG) on follicular dynamics, CL functionality, ovarian (OV.A) and uterine arteries (MUA) blood flow, hormones (estradiol [E2] and luteinizing hormone [LH]), nitric oxide (NO), and vascular endothelial growth factor (VEGF) levels in Thoroughbred mares. Animals were subjected to ultrasonography scanning, when the dominant follicle (F1) reached 35 mm in diameter, mares were injected with hCG (hCG group; n = 7) at hour 0, while others were injected with saline (control; n = 7). The examination was performed a those points at hours −24 h, −12 h, 0 h, 12 h, 24 h, 36 h, 48 h, 72 h, and 96 h. Blood sampling, ultrasound scanning, hormone assaying, and statistical analysis were performed. F1 was ruptured at 12 h after injection compared to 24 h in the control, with an elevation in its diameter (p ≤ 0.05) and a colored area surrounding F1. The amount of color Doppler area around CL and its diameter were increased (p ≤ 0.05) at 24 and 48 h after injection with an increase (p ≤ 0.05) in the ipsilateral uterine horn colored area from 6 to 36 h after injection. OV.A and MUA Doppler velocity parameters were elevated (p ≤ 0.05) at 24 h. Both NO and VEGF levels were elevated at 24 h after injection, with the elevation (p ≤ 0.05) of E2 occurring only before injection and then declining. hCG and LH levels were increased after injection at 12 and 24 h, respectively, with an interaction (p ≤ 0.05) effect. hCG may speed up and hasten the ovulation process by elevating follicular color amount and CL morphometry via elevating ovarian flow and uterine body total coloration via elevating uterine blood flow (declining Doppler indices) in mares.