To the Editor: The study by Lang and colleagues (July 20 issue)1 is provocative but lacks two important control observations. First, as compared with the white subjects, the black subjects had markedly attenuated forearm blood-flow responses to isoproterenol yet similar increases in regional norepinephrine spillover. Hyperresponsiveness to the ÃŽÂ±-adrenergic effects of endogenous norepinephrine is therefore at least as likely an explanation of the findings as hyporesponsiveness to β-adrenergic stimulation by isoproterenol. No mention is made of this possibility; a direct infusion of norepinephrine or phenylephrine would easily settle the issue. Second, since regional norepinephrine spillover is heavily dependent on blood.
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