Evaluation of sympathetic nervous system and adrenomedullary activity in normal children.

In 22 healthy children heart rate, blood pressure and plasma levels of epinephrine (E) and norepinephrine (NE) were evaluated under basal conditions and in response to standing (5 min). Basal plasma E and NE levels found in these children were (means +/- S.E.M.) 139 +/- 17.9 pg/ml and 236 +/- 31.0 pg/ml respectively. Ten out of the 22 children reported dizziness and discomfort by the end of the 5 min standing period. These children showed not only a greater decrease in both systolic and diastolic blood pressure but also a lower basal heart rate, a tendency to higher basal NE levels and a blunted plasma NE response (23 +/- 7%) when compared with children not reporting symptoms (60 +/- 9%, P less than 0.01). Plasma E levels also showed an increment although a wide range of individual responses was observed in both groups.