Pregnancy-induced changes in sheep uterine and carotid arteries

To characterize the effects of pregnancy on vascular tissue, intact segments of the uterine and carotid arteries were removed from nonpregnant and near-term pregnant sheep. Pressure-diameter relations were measured on isolated segments under activated (122 mM K+, 10(-4) M phenylephrine) and passive (0.1 mM Ca2+, 10(-5) M iodoacetic acid) conditions. DNA and RNA were determined spectrophotometrically. Collagen, elastin, and water contents were also measured. Pregnancy had no effect on either the mechanics or the biochemical properties of the carotid artery. However, there was a marked increase in internal radius in the uterine artery with pregnancy (0.060 +/- 0.016 vs. 0.198 +/- 0.019 cm). Active tangential stress increased, as did passive stiffness of the uterine artery. The collagen fraction decreased during pregnancy (57.2 +/- 2.4 vs. 45.7 +/- 2.2%), while elastin and RNA remained unchanged. A small decrease in DNA produced a significant increase in the RNA-to-DNA ratio. These data suggest that, in pregnancy, the uterine artery selectively undergoes a characteristic hypertrophy of its vascular smooth muscle.