Hyposensitivity of peripheral alpha-adrenoceptors in respirator-dependent amyotrophic lateral sclerosis assessed by intravenous norepinephrine infusion.

Intravenous norepinephrine infusion test was performed in eight patients with amyotrophic lateral sclerosis (ALS) supported by respirators and nine control subjects, to examine alpha-adrenoceptor function of peripheral resistant blood vessels. Baseline plasma norepinephrine concentrations in ALS patients were significantly higher than those in control subjects, indicating basal sympathetic hyperactivity (normal 218.2 +/- 59.7 pg/ml; ALS 450.0 +/- 288.4 pg/ml). The stimulus-response curves in the patients were similar to those in control subjects, and there were no significant differences between mean gains of the stimulus-response curves in both groups (normal 18.7 +/- 5.5; ALS 15.2 +/- 11.2). However, three ALS patients, two of whom had circulatory fluctuation and sympathetic hyperactivity, revealed lower gain levels than the mean minus 2 SD in control subjects (4.7, 1.1 and 3.7). This indicates hyposensitivity or down-regulation of the alpha-adrenoceptor function of peripheral blood vessels in these ALS patients. For early detection of sympathetic hyperactivity and prediction of circulatory collapse, it would be useful to measure the plasma norepinephrine concentration and the gain of the norepinephrine infusion curve in respirator-dependent ALS patients.