[Changes in circulating catecholamine levels in old rats under basal conditions and during stress].

The aim of the paper was to study the levels of circulating catecholamines in unrestrained cannulated rats under basal resting conditions and after exposure to two stressors. Catecholamines were determined radioenzymatically in 4-, 11-, 12-, 24-, and 28-month-old rats. Immobilization and exposure to ether vapors were used as stress models. The results confirmed a definite trend to increased norepinephrine (NA) levels, concerning partially also epinephrine (ADR) levels in older animals compared to young ones. During immobilization the plasma NA response was markedly increased in 11-month-old rats, whereas in 28-month-old rats the increase was only mild. Plasma ADR concentration was only slightly elevated in 11-month-old rats, whereas in the older animals no changes were recorded compared to 4-month old rats. On comparing the age groups studied after exposure to ether vapors, the oldest age group of 24-month-old rats showed a slower return of the stress-induced higher plasma NA levels to initial values. On balance, the response of circulating catecholamines depends on the age of the animals and on the stressor used.