Impact of ovulation inducers on ovarian artery in mares: pulsatility and resistivity indexes

Abstract

A failure of vascular development in reproductive organs may be the cause of several dysfunctions during the estrous cycle and gestation. Therefore, it is important to evaluate the in vivo influences of ovarian vaso- irrigation on ovulation. The ovarian follicles need an adequate blood supply for oxygen, nutrients, and hormones, besides eliminating CO2 and other metabolites (Bruno et al. Animal Reproduction. 2009; 6, 2:371-379). Transrectal ultrasonography (US) with color, power, and spectral Doppler US has been used to study blood flow and ovarian perfusion in mares (Acosta et al. Biology of Reproduction. 2004b; 71, 2: 502-507). Studies have shown a daily increase in vascularization of the wall of the dominant follicle as it approaches the day of ovulation (Gastal et al. Animal Reproduction Science. 2007; 102, 3-4: 314-321); However, a few hours before ovulation, an abrupt decrease in blood perfusion of the follicular wall has been detected (Ginther et al. Journal of Equine Veterinary Science. 2007a; 27, 1: 20-27). The drugs most used as ovulation inducers in horses are human chorionic gonadotropin (hCG) and analogues of gonadotropin-releasing hormone (GnRH), such as deslorelin (Chavatte & Palmer Equine Veterinary Education. 1998; 10, 26-30). Using different ovulation inducers, this study aimed to evaluate changes in ovarian arteryblood flow after induction of ovulation in mares with follicles ≥ 35mm diameter. Twenty-eight estrous cycles were followed, randomly and equally distributed: GI: control mares without treatment; GII: 1000 IU IV of hCG; GIII: 750µl IV of deslorelin; GIV: 250µg IM of hysterelin. The ovarian artery pulsatility and resistivity indexes (PI and RI) were measured. Thereafter, estrous cycles were followed every 12 hours from time 0 (induction) until ovulation using B-mode US and spectral mode Doppler US of ovarian arteries. Statistical analysis was performed with ANOVA, a p-value of <0.05 was considered significant. No statistical difference was found in PI between groups (p=0.1297) of at the different evaluation times. When the times of analysis were compared separately between the groups, no statistical difference was found between 0h (p= 0.7092), 12h (p= 0.5148), 24h (p=0.2642), and 36h (p=0.582). Similarly, the RI did not differ between the groups analyzed (p= 0.1397), regardless of the time of evaluation, nor between the timepoints analyzed separately between 0h (p= 0.5049), 12h (p= 0.7334), 24h (p=0.3589) and 36h (p=0.1621). It can be concluded that although an increase in vascularization of the wall of the dominant follicle occurred, the PI and RI of the ovarian artery were not influenced by any ovulation inducer of the pre-ovulatory follicles.