Uterine endometrial vascularization during ovarian follicular growth in llamas: The effect of estradiol plasma concentration.

The aim of this study was to evaluated changes in endometrial vascularization area (EVA) between the left and right uterine horn: a) during the ovarian follicular growth in intact llamas, and b) after exogenous estradiol administration of estradiol benzoate in ovariectomized (OVX) llamas. In experiment 1 follicle wave emergence was synchronized (n = 5 llamas) by follicle ablation (Day 0). Females were examined every other day from Day 1 to Day 27, using B mode ultrasonography to evaluate dominant follicle growth profile. Also, EVA was evaluated in each horn using Color-Power Doppler. Blood samples were taken every other day from Day 1 to Day 27 to measure estradiol (E2) plasma concentration by RIA. In experiment 2 OVX llamas (n = 4 llamas/group) were given a single im administration of: a) 1 mg of estradiol benzoate (EB) or b) 1 mL of saline. Females were subjected to ultrasound examinations every 48 h from Day -4 until treatment (Day 0), every 12 h from Day 0 to Day 4, and again every 48 h from Day 5 to Day 11. Evaluation of EVA in both uterine horns was performed as described for experiment 1. Blood sampling for the measurement of E2 was carried out at the same time points indicated for the ultrasound examinations. Serial data were analyzed by one way ANOVA for repeated measures using the MIXED Procedure in SAS. Also, Pearson's correlation was used to determine the relationship between variables. In intact llamas there was an effect of day on the dominant follicle growing profile (P < 0.01) and estradiol plasma concentration (P < 0.05). Dominant follicle diameter positively correlated (r = 0.4; P < 0.017) with estradiol plasma concentration. Also, EVA of right and left uterine horn did not differ (P = 0.89) during the evaluation period; however, it was affected by time (P < 0.05). In ovariectomized llamas estradiol concentration was significantly (P < 0.001) affected by treatment, time and their interaction. Accordingly, treatment with EB (P < 0.0001), time (P < 0.05) and their interaction (P < 0.01) affected EVA of both uterine horns; however, this variable did not differ between horns (P = 0.98). In conclusion, circulating concentrations of estradiol determined an increase in uterine vascularization, during the phase of follicular growth in intact llamas and after the exogenous administration of EB to ovariectomized females; however, no differential effect in endometrial vascularization area between right and left uterine horn was observed.