Sex hormone modulation of flow velocity in the parametrial artery of the pregnant rat.

The objective of the study was to correlate the disparate distal/proximal state of maturation of uterine segments in the rat with the hemodynamics of the parametrial uterine artery. Flow velocity was determined by the methylene blue photometric analysis. In nonpregnant animals, the velocity in the distal (VD-->P) and proximal (VP-->D) portions of the parametrial artery were similar, but in late pregnancy, VD-->P was higher than VP-->D. The difference was associated with an increased width of the distal part of the parametrial artery. In addition, the distance from the proximal end of the parametrial artery where the D-->P and P-->D streams collided decreased in animals in late pregnancy, compared with nonpregnant animals. Treatment with estradiol and RU-486 reversed the pregnancy-related hemodynamic changes. The pregnancy-related shift in flow velocity in the parametrial artery is crucial to rat fetal survival in utero and may be a mechanism in vivo for promoting maturation of distal, compared with proximal, segments of the uterine horn.