98 UTERINE INVOLUTION AND VASCULAR PERFUSION DURING EARLY POSTPARTUM IN MARES

Abstract

In horses, a rapid involution of the uterus occurs right after parturition, allowing the reestablishment of a favourable uterine environment for embryo development. However, limited evidence is found regarding the vascular events during puerperal period in mares. We aimed to evaluate the morphological (size of uterus and uterine fluid content) and haemodynamic (endometrial and mesometrial vascular perfusion) characteristics of the uterine involution process. Mares (n = 10) were evaluated by transrectal ultrasonography from the first day postpartum (d1) to the sixteenth day after first ovulation (D0 = ovulation). For ultrasound exams, a duplex B-mode and Doppler ultrasound instrument (M5 VET; Mindray Medical International Limited, China) equipped with a transrectal transducer was used. The previously pregnant (PH) and nonpregnant (NPH) horns were individually evaluated. Data were analysed for the main effects of horns (PH and NPH), day, and their interaction, using the PROC MIXED procedure of SAS software (9.3 version; SAS Institute Inc., Cary, NC, USA). Discrete variables were analysed by ANOVA. A reduction (P < 0.05) in the uterine diameter was observed during the first 7 days postpartum, but the rate of uterine involution (decrease in uterine size) decreased thereafter. The involution was complete around the d21 for the NPH and around d24 for the PH. Presence of uterine luminal fluid (mm) was increased between d1 (no fluid) and d2 (31.41 ± 2.88) postpartum, followed by a decrease between d4 (30.43 ± 4.52) and d7 (10.20 ± 1.76). No fluid was observed after d16 postpartum or after the third day postovulation (D3). For endometrial and mesometrial vascular perfusion, only a day effect (P < 0.05) was observed. An increase in the endometrial and mesometrial vascularization was detected, respectively, between d1 and d4, and between d1 and d2. Vascular perfusion did not differ after d4 for endometrial tissue, whereas it was reduced (P < 0.05) between d2 and d10 for mesometrium. For the vascular perfusion after ovulation, an increase (P < 0.05) from D0 to D5, followed by a decrease (P < 0.05) between D5 and D11 and an increase (P < 0.05) between D11 and D14 was observed in the endometrial and mesometrial tissues. The profile of the vascular perfusion in endometrium and mesometrium after first ovulation postpartum is similar to that observed during oestrous cycles and early pregnancy, indicating a return of the uterus to the pre-pregnant uterine characteristics in mares.Research was supported by FAPESP process no. 2010/10692-9 and CNPq process no. 135954/2011-8.