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

Abstract

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.

Vasoconstrictor reserve in neurally mediated syncope

“…At syncope, much of the vasodilatation can be accounted for by withdrawal of sympathetic vasoconstrictor activity [19][20][21]. The increase in plasma epinephrine, the putative direct beta-adrenergic vasodilator, occurs only at syncope but not before [22][23][24]. However, local beta-adrenergic blockade does not affect forearm vasodilatation at syncope [25,26].…”

Norepinephrine and Epinephrine Responses during Orthostatic Intolerance in Healthy Elderly Men

“…Previous investigators [9][10][11][12][13] have reported significant increases in EPI during orthostatic intolerance in young individuals. Indeed, plasma EPI concentrations at the termination of orthostatic stress have been reported to be two-to eight-fold greater in young subjects experiencing symptomatic hypotension [9][10][11][12][13].…”

“…Indeed, plasma EPI concentrations at the termination of orthostatic stress have been reported to be two-to eight-fold greater in young subjects experiencing symptomatic hypotension [9][10][11][12][13]. Due to its ability to cause peripheral vasodilation and stimulate cardiac vagal fibres, EPI has been implicated as a possible mechanism responsible for orthostatic intolerance [3,11,[13][14][15][16].…”

“…In young men and women undergoing head-up tilt (HUT), marked reductions in MAP, from 94 to 50 mmHg, were associated with attenuated NE concentrations [9]. Additionally, previous investigators [9][10][11][12][13] have reported significant increases in plasma EPI concentrations during orthostatic intolerance in young individuals. During orthostatic intolerance in young men and women, marked reductions of 37 and 44 mmHg in MAP have been associated with a two-to eight-fold increase in plasma EPI concentrations [9,[11][12][13].…”

“…However, while marked reductions in AP resulting in orthostatic intolerance are associated with characteristic changes in EPI and NE in young individuals [8][9][10][11][12][13], the sympathoadrenal responses of elderly individuals during orthostatic intolerance have been inadequately addressed. When elderly individuals experience moderate reductions in MAP, from 100 to 87 mmHg, during orthostatic stress, the increase in NE concentration is not significantly different from normotensive control subjects [19].…”