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We compared the effects of infused norepinephrine (NE) to another alpha-adrenergic agonist, phenylephrine, in order to understand better the influence of circulating NE on plasma renin activity (PRA) in man. In matched groups of normotensive men, NE (80 ng/min/kg) or phenylephrine (800 ng/min/kg) raised blood pressure by 15 to 20 mm Hg and caused reflex decreases in heart rate of 8 to 10 beats per minute. Infused phenylephrine suppressed PRA by about 15%, whereas NE increased PRA by about 40% (P less than .02). This differential effect of alpha-agonists on PRA defines an important humoral effect of NE, which should be considered to be a "cardiovascular hormone."
Licht et al. (1989) studied this question.