The magnitude of sympathetic hyperactivity in pregnancy-induced hypertension and preeclampsia

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Background It is unclear whether pregnancy-induced hypertension (PIH) and preeclampsia (PE) are separate conditions or represent opposite ends of a spectrum of a single disease entity. Sympathetic hyperactivity exists in both PIH and PE; however, only the latter is characterized by multiorgan involvement, particularly renal impairment. As there is evidence in hypertension that target organ damage is associated with increased sympathetic drive, this study was designed to test the hypothesis that the magnitude of sympathetic hyperactivity in PE is greater than that in PIH. Methods Microneurography was used to compare peripheral sympathetic neural discharge, its reflex control and end-organ effect (plethysmographic measurement of calf blood flow) in 33 women with PIH, PE, and normal pregnancy (NP) who were matched for age, body weight, and gestation. Results As expected, patients with PIH and PE had higher levels of mean arterial pressure than those with NP. The frequency of sympathetic neural discharge was greater in the hypertensive disorders of pregnancy compared with NP; however, it was not increased in PE compared with PIH as might be expected. Conclusions Based on the study results, PE is not associated with greater sympathetic hyperactivity than PIH, suggesting that any renal impairment in PE involves mechanisms that are not solely dependent on sympathetic hyperactivity.