Adaptation of the uterine arcade in rats to pregnancy.

In order to study the adaptation of the uterine arterial system to pregnancy we measured vascular dimensions and other growth related data (DNA content and [3H]thymidine incorporation rate) on excised uterine arcades, pressurized to 100 mmHg, of rats before and during pregnancy (day 8, 18 and 21 of gestation). The vascular conductance of the arcade was calculated using a numerical method. In order to investigate the response of the arcade to flow impairment during early pregnancy, the same measurements were repeated on uterine arcades from pregnant animals (day 21 of gestation), where the left uterine artery had been ligated on day 8 of pregnancy. In adult virgin rats, the uterine arcade was 0.3 +/- 0.05 mm wide and 50 +/- 5 mm long. With these vascular dimensions the vascular conductance of the arcade (2.5 microliters/(s x mmHg] was calculated to be inadequate for the blood supply to the pregnant uterus at term. During the course of pregnancy modest changes were seen: The arcade increased 80% in length, 30% and 80% in internal diameter at the ovarian and cervical origin respectively and 6 times in conductance. Weight of the arcades increased 2-3-fold, [3H]thymidine incorporation rate 7-fold whereas the DNA mass remained constant. Ligation of the uterine artery on day 8 caused a 2 times increase in internal diameter of the ovarian (open) origin of the arcade without change in weight, whilst the cervical (ligated) origin of the arcade had the same internal diameter as that of the control group. The calculated vascular conductance of the ligated arcade was the same as for controls.(ABSTRACT TRUNCATED AT 250 WORDS)