Endothelin type A receptor blockade attenuates the hypertension in response to chronic reductions in uterine perfusion pressure

A chronic reduction in uterine perfusion pressure in pregnant rats is associated with a significant elevation in mean arterial pressure (MAP) and reduction in kidney function. The purpose of this study was to examine the role of endothelin in mediating the hypertension in response to chronic reductions in uterine perfusion pressure in conscious, chronically instrumented, pregnant rats. MAP in pregnant rats with chronic reductions in uterine perfusion pressure (123.0+/-1.8 mm HE) was significantly higher than that in control pregnant rats (101.3+/-4.0 mm Hg). Renal expression of preproendothelin mRNA as determined by ribonuclease protection assay was also significantly elevated in the medulla (>45%, P<0.05) and in the cortex (>22%, P<0.05) of the pregnant rats with chronic reductions in uterine perfusion pressure compared with control pregnant rats. Chronic administration of the selective endothelin type A receptor antagonist (ABT-627, 5 mg/kg per day for 10 days) markedly attenuated the increase in MAP observed in the pregnant rats with chronic reductions in uterine perfusion pressure (103.3+/-5.6 mm Hg, plus endothelin antagonist; P<0.05). However, endothelin type A receptor blockade had no significant effect on blood pressure in the normal pregnant animals (96.0+/-2.7 mm Hg, plus endothelin antagonist). These findings suggest that endothelin plays a major role in mediating the hypertension produced by chronic reductions in uterine perfusion pressure in pregnant rats.