Reduced plasma norepinephrine response to standing in autonomic dysfunction.

In five patients having primary autonomic dysfunction with clinical manifestations including postural hypotension, the mean plasma norepinephrine concentrations were significantly lower than those of normal subjects after two and five minutes in the standing position. The mean (+/-SE) increment in the plasma norepinephrine concentration after two minutes standing were 123 +/- 19 pg/ml in the normal subjects and 13 +/- 4 pg/ml (P less than .001) in the patients with primary autonomic dysfunction. After five minutes standing, the mean increment in plasma norepinephrine concentration was 244 +/- 36 pg/ml in the normal subjects and 99 +/- 51 pg/ml (P less than .05) in the patients. There were no statistically significant differences in plasma epinephrine between the two groups.