Male Wistar specific-pathogen-free rats aged 2, 7, 17, 30, 60, 120, 200, 360 and 
600 days, all killed in experiment on the same day, were examined. The body 
weight significantly increased until the 200th day, the weight of adrenals until 
the 120th day and the adrenal protein content until the 30th day of life. The 
adrenaline content of the adrenals increased continuously during the 600 days 
studied. Adrenal noradrenaline content increased rapidly over the first 17 days, 
remained at a stable level until the 120th day, and rose to a higher level after 
200 days. The activity of adrenal catecholamine-synthesizing enzymes also 
increased with age: tyrosine hydroxylase gradually increased until the 360th 
day, dopamine-beta-hydroxylase and phenylethanolamine-N-methyl transferase until 
the 200th day. Our results demonstrate that, in the rat, during development 
there is a gradual increase of adrenal weight, adrenaline content, tyrosine 
hydroxylase and phenylethanolamine-N-methyl transferase activity until 
maturation (120th day), whereas the adrenal noradrenaline content reaches the 
adult values earlier, around the 17th day. During aging, adrenal catecholamines 
significantly increase when compared to young-adult rats (120-day-old), probably 
due to the elevated activity of the adrenal catecholamine-synthesizing enzymes. 
The increased adrenal catecholamine levels in old animals might be connected 
with a higher incidence of cardiovascular diseases in aged.