Pregnancy-induced long-term uterine vascular remodeling in the rat

Despite the available research investigating uterine physiology during and immediately following pregnancy, including at the vascular and muscular levels, knowledge of the potential long-term timeline of such changes is limited. Thus, our study sought to investigate the potential long-term changes in uterine vasculature and horn length in the postpartum rat, following delivery and weaning. Female Long-Evans rats (n = 9-11 rats/group/timepoint) were divided into two groups: a pregnant group and an age-matched virgin control group. Rat weight, food consumption and vaginal impedance measurements were recorded throughout the experiment. Rats in the pregnant group were bred and pregnancy was confirmed using ultrasound imaging. The uterus and its vasculature were collected at various timepoints following weaning: 3 (week of weaning), 8-9 and 13 weeks postpartum, and at age-equivalent timepoints in the virgin group, and the diameters of the main uterine artery and vein, and lengths of the mesometrial segmental vessels (MSV) and uterine horns were recorded. The results indicated a significant difference between the previously-pregnant and virgin rats in both internal and external arterial diameters (but not arterial wall thickness), as well as the uterine horn length, 3 weeks postpartum, but not 8-9 and 13 weeks postpartum. Significant differences were observed in both venous diameter and MSV length at all timepoints measured. Placental scars were also observed in previously-pregnant rats at all timepoints measured. Our study highlights the long-term impact of pregnancy on the uterine vasculature and the necessity for consideration of such changes on subsequent pregnancies, as well as pregnancy-related vascular pathologies.