[The effect of chronic stress on the activity of the sympathetic-adrenomedullary system].

Plasma levels of adrenaline (ADR) and noradrenaline (NA) belong to the best parameters of activity of the sympatho-adrenomedullary system (SAS). Introduction of a sensitive radioenzymatic method for the determination of catecholamines in small volumes of plasma (0.05 ml) and observing conditions of stressless blood collection by means of an indwelling catheter made in possible to determine basal plasma catecholamine levels and their dynamics during stress. Changes in plasma catecholamines were studied in acute and chronic stress (continual or intermittently repeated) in three stress models: 60-day hypokinesia, immobilization (IMO) repeated over 30 days, and 14-day or one-day handling of the rat for 1 minute. On first exposure to the given stressor the plasma levels of both catecholamines studied were increased. In the course of 60-day hypokinesia as well as during one- or 14-day handling plasma ADR levels returned to virtually resting values, plasma NA levels, however, remained at equally high values as recorded at the first exposure. During 30-day IMO basal values of ADR and NA in plasma were elevated, yet the catecholamine response to the last IMO was reduced compared to the first exposure. Under the effect of mild chronically acting stressors a dissociation was observed in the changes of plasma catecholamine levels: ADR failed to exhibit further increases, whereas NA kept significantly rising all over the period of the activity of the stressor. This differentiated activation of plasma catecholamines suggests the existence of different regulatory regions in the CNS.(ABSTRACT TRUNCATED AT 250 WORDS)