Kvetnansky, R., Mikulaj, L. 1970. Adrenal and urinary catecholamines in rats during adaption to repeated immobilization stress. Endocrinology 87, 738-743.

Rats subjected to daily immobilization for up to one year still excreted greater amounts of epinephrine than did control animals or animals after their first immobilization. These increases levels of urinary ephinephrine were not accompanied by a decrease in adrenal epinephrine. This suggests that the 'adaptation' of the adrenal medulla to repeated stress .. was the result of an enhanced ability to replace the catecholamines which were released, rather than to a diminished release of catecholamines in response to the repetition of immobilization.