Postpartum Persistence of Maternal Uterine Vascular Gestational Adaptation in Rodents

Although pregnancy has long-lasting consequences for maternal vascular health, little is known about vascular changes postpartum (PP). Focusing on the uterine circulation, which undergoes unique structural and functional adaptation during gestation, we hypothesized that most pregnancy-induced changes would return to baseline PP, with minimal hysteresis. Large (main; MUA) and small (segmental; SUA) uterine arteries from adult Sprague Dawley rats (n = 42) were evaluated 1 and 4 weeks PP (1PP, 4PP) and compared with those of late-pregnant (LP, day 21) and age-matched non-pregnant (NP) animals. Some comparisons were extended to mesenteric arteries to evaluate differences between reproductive and systemic vessels. Pregnancy-induced axial elongation regressed > 80% 1PP in MUAs and SUAs, although some minimal hysteresis remained 4PP. Circumferential growth was slower to regress, with no reductions in lumen diameter or media thickness 1PP; values returned to (MUA) or approached (SUA) NP values by 4PP. Changes in vascular smooth muscle cell cross-sectional area-a measure of hypertrophy-paralleled those in lumen diameter. Mesenteric and uterine artery compliance diverged during gestation, and continued to do so PP. Decreased MUA compliance 4PP was supported by an increased collagen:elastin ratio. Adrenergic sensitivity increased in uterine, and decreased in mesenteric arteries during pregnancy, and returned to NP values 4PP in both types of vessels. MUA α-1 adrenoceptor expression tracked along with sensitivity. Thus, postpartum adaptation varies by both parameter and vessel type. While many parameters regressed postpartum, alterations in compliance did not, suggesting that matrix changes may have long-term consequences for maternal vascular function and health.