Plasma norepinephrine in essential hypertension. A study of the studies.

Abstract

SUMMARY Of 32 studies comparing plasma norepinephrine concentrations in hypertensive and normotensive groups, 28 (88%) reported higher levels in the hypertensive group. However, only 13 (41%) of the studies reported statistically significant hypertensive-nonnotensive differences in norepinephrine, leading the present attempt to identify factors differentiating "positive" studies (those reporting significant hypertensivenormotensive differences) from "negative" studies (those reporting nonsignificant differences). Hypertensive norepinephrine levels were similar in positive and negative studies (281 vs 288 pg/ml), but normotensive levels were lower in the positive studies (177 vs 269 pg/ml). When compared with the fluorimetric technique, the radioenzymatic type of assay was associated both with a lower frequency of positive results (25% vs 100%) and greater intrastudy standard deviations (152 vs 72 pg/ml). Hypertensive-normotensive differences varied inversely with age (> = -0.37). Resolution of the persisting controversy about norepinephrine levels in essential hypertension will require more attention to the causes of variability associated with the assay technique, to the sources, characteristics, and treatment of the normotensive controls, and to the age of the patient population. (Hypertension 3: 48-52, 1981) KEY WORDS • norepinephrine • catecholamines • hypertensionT HE introduction about a decade ago of sensitive techniques for measuring plasma norepinephrine,'• a and indications that those levels reflect sympathetic neural activity,' promised to help answer a perennial question in hypertension research: Does sympathetic hyperactivity cause essential hypertension? Despite the subsequent publication of more than 30 comparative studies in hypertensives and normotensive controls,*"" controversy persists about whether patients with hypertension exhibit elevated levels of norepinephrine. This report reexamines these studies in an attempt to identify the causes of the inconsistencies in results. MethodsThe studies considered in this review satisfied the following criteria: 1) they were published since 1973, in English; 2) they were not merely abstracts, but were

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