[The influence of increased uterine resting tonus on renal sympathetic nerve activity in pregnant rabbit].

ABSTRACT

We have shown that an increase in uterine resting tonus causes an increase in maternal blood pressure and a decrease in renal blood flow, and a neural factor may control this phenomenon through a Utero-Renal Reflex in pregnant rabbits. To explore this possible neural factor, we examined the changes in renal sympathetic nerve activity (R-SNA) in late pregnant rabbits under urethane anesthesia. SNA was measured with a bipolar electrode and renal cortical blood flow (RBF) was measured by a thermocouple method. An increase in uterine resting tonus was made by inserting a small balloon into the uterine cavity on the ovarian or cervical side. An increase in resting tonus on the ovarian side caused an increase in maternal blood pressure, increases in R-SNA and renal vascular resistance (RVR), and a decrease in RBF. However, an increase in resting tonus on the cervical side resulted in an increase in maternal blood pressure, slight increases in R-SNA and RVR, and an increase in RBF. These data indicate that an increase in uterine resting tonus can stimulate R-SNA, which in turn causes the deterioration of renal circulation.