Baroreflex regulation and plasma volume in hypertensive pregnant rats with reduced uterine perfusion

Abstract

Abnormal control of blood pressure has potentially lethal consequences in human preeclampsia. Blunted reflex responses to increased blood pressure have also been demonstrated in a hypertensive pregnant rat model. We sought to further characterize alterations in baroreflex control in this model and to investigate whether blood volume is decreased as it is in the human disease. Reduced uterine perfusion pressure (RUPP) was induced on gestational Day 14 by placing clips on the uterine arteries and abdominal aorta. On gestational Day 20, RUPP, SHAM-operated pregnant and VIRGIN rats were anesthetized, cannulated for drug infusions and blood pressure measurement, and the renal sympathetic nerve was prepared for recording. Plasma volume was assessed using dye dilution. RSNA and arterial pressure were measured during increases (methoxamine 100ug/kg/min) and decreases (sodium nitroprusside 10ug/kg/min) in blood pressure, and data fit to a 4-parameter logistic curve. Parameters were compared among groups by ANOVA. Curve midpoint was significantly higher in RUPP (128.9±7.7mmHg) vs. SHAM rats (117.2±11.1mmHg), and maximum slope was blunted in both RUPP (−2.2±.0.7NA/mmHg) and SHAM (−2.0±0.NA/mmHg) vs. VIRGIN (−3.0±1.NA/mmHg) rats. Plasma volume was significantly decreased in RUPP (14.8±4ml) vs. SHAM pregnant rats (20.0±2.9ml), changes similar to those in preeclamptic compared with normal pregnant women. These results demonstrate that plasma volume is reduced in the RUPP rat relative to the normal pregnant rat. In addition, hypertensive RUPP pregnant rats have a diminished ability to reduce sympathetic outflow in response to an increase in blood pressure. NR004184.