[New approaches in the evaluation of sympathoadrenal system activity during periods of rest and stress]

The sympathoadrenal system (SAS) activity in mammals has usually been evaluated by measuring plasma and urinary catecholamine (CA) levels. The aim of this work was to explain theoretically and to demonstrate practically in own experiments new methods for evaluation of SAS activity. Nowadays methods are available which estimate not only plasma levels of CA but also CA release, spillover, reuptake, degradation, and also in vivo CA synthesis by determination of plasma dihydroxyphenylalanine (DOPA) levels. In our experiments simultaneous measurements of plasma CA, their precursor DOPA, the deaminated metabolites dihydroxyphenylglycol (DHPG) and dihydroxy phenylacetic acid (DOPAC), and the O-methylated metabolites normetanephrine (NMN), methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were performed in humans and rats during basal and stress conditions. Plasma CA levels are determined by the rate of CA spillover into the bloodstream and by plasma CA clearance. Immobilization stress(IMO) markedly increased plasma noradrenaline (NA) levels but NA spillover was less elevated because the NA clearance was reduced in IMO rats. Dissociation between changes of plasma NA and DHPG levels can indicate changes in neuronal reuptake of NA. We found such a dissociation in humans during bicycle ergometry suggesting a reduced NA reuptake. DOPA circulates in plasma at higher levels than NA. During stress, increased sympathoadrenal outflow stimulates DOPA synthesis and release into the circulation supporting the view that changes in plasma DOPA levels reflect in vivo changes in CA synthesis. Thus, the presented data demonstrate the importance of simultaneous measurement of plasma CA levels, CA synthesis, release, reuptake, and degradation for evaluation of SAS activity in basal and stress conditions of the organism. (Fig. 10, Ref. 56.).