Effects of Vascular Insufficiency on Placental Ribonuclease Activity in the Rat

Abstract

Intrauterine growth retardation was produced in pregnant albino rats by ligating the uterine artery supplying one horn of the bicornate uterus at 16 days of gestation. The opposite uterine horn was left untouched and served as control. The animals were killed 24, 48, 72 hours after ligation and placentas were divided into three groups: proximal, intermediate and distal to the ligation. In all parameters studied, the degree of abnormality was inversely proportional to the distance of the placental sample from the site of ligation. The fetuses and placentas were smaller on the ligated side. Total RNase activity was higher in placentas of the growth-retarded fetuses per gram of tissue and per milligram of RNA as early as 24 hours after ligation and reached a peak at 48 hours. This elevation of enzyme activity was associated with a reduction in total RNA content and in the RNA/DNA ratio. These data further support the hypothesis that RNase may indeed play a role in regulating the tissue levels of RNA. In addition they suggest the possibility of using placental RNase activity as a marker for fetal growth retardation.