Venous plasma adrenaline response to orthostatic syncope during tilting in healthy men.

The effect of transient cerebral ischaemia connected with acute orthostatic hypotension on plasma adrenaline and noradrenaline levels was studied in seven healthy male volunteers during tilt. Sublingual administration of 1 mg nitroglycerin was used to block peripheral vascular reflexes and thus to provoke orthostatic intolerance. A consistent increase in plasma adrenaline concentrations (from 19.2 to 104.3 pg/ml on average, P less than 0.01) was found in six subjects who developed clinical signs of collapse after tilting. Plasma adrenaline never changed after tilting without collapse. Posturally stimulated plasma noradrenaline increases were similar yet irrespective of the presence of collapse.