Influence of the increased uterine tonus on maternal hemodynamics

In an experiment using 103 late pregnant rabbits, the resting uterine tonus was increased by inserting a balloon into the amniotic cavity on the cervical side (n = 71) or the ovarian side (n = 52) and the effects of this increase on the maternal blood pressure, renal cortical blood flow (measured by a thermocouple method), renal arterial and carotid arterial blood flow (measured with an electromagnetic flowmeter) were studied. The findings are briefly described, as follows: The maternal blood pressure was slightly increased on both sides (by 12.0 +/- 3.5% on the cervical and by 12.0 +/- 3.8% on the ovarian side). However, there was a hemodynamic difference between the renal cortical and renal arterial blood flow on the cervical side and those on the ovarian side: They were slightly increased on the cervical side and slightly decreased on the ovarian side. On the basis of these findings, the following may be proposed: An increase in resting uterine tonus causes a rise in maternal blood pressure associated with blood redistribution from the uteroplacental vascular bed. However, the fact that the renal blood flow was decreased consequently upon the increase in resting uterine tonus raised a possibility of neurotransmission via the ovarian plexus as well as utero-renal reflex.