Depletion and recovery of catecholamines in the rat adrenal medulla and its relationship with dopamine β-hydroxylase

Abstract

Exposure of rats to a stressing atmosphere containing 20% CO 2 for 5 h did not affect the level of adrenal catecholamines (CA) or dopamine β-hydroxylase (DBH) activity. Rats given reserpine showed a 40% decrease in adrenal CA in 5 h and a 90% decrease in 24 h, whereas rats given reserpine and then exposed to CO 2 for 5 h showed a decrease of 95% in adrenal CA at the end of the 5 h exposure as well as at 24 h. DBH activity was not altered either at 5 or 24 h after treatment with reserpine or reserpine plus CO 2 . Pretreatment with mecamylamine prior to the combined treatment with reserpine plus CO 2 prevented the maximum depleting effect of such treatment on adrenal CA. Following combined treatment with reser­pine plus CO 2 in unilaterally splanchnicotomized rats, levels of CA were unchanged in the adrenal gland with the nerve supply interrupted, while the content of CA in the right contralateral innervated gland was maximally depressed. Exposure of rats to CO 2 for 5 h immediately or 24 h after reserpine resulted in an additional lowering of adrenal CA when compared to the levels of CA in rats treated with reserpine alone. However, exposure to CO 2 48 h or more after reserpine injection resulted in no additional lowering of CA. The pattern of recovery of rat adrenal CA following depletion with reserpine plus CO 2 showed that levels of CA remained depressed from 5 to 48 h, followed by a modest recovery at 72 h and essentially complete recovery in about 6 days. In contrast, the recovery pattern following depletion with reserpine alone showed that levels of CA recovered to about half of normal 48 h and were essentially normal in 4–5 days. After treatment with reserpine alone, DBH activity was unchanged from the control level up to 1 day but it increased on the second day and remained high for 4–5 days, After reserpine + CO 2 , DBH activity was unchanged up to one day but it decreased below the control level on the second and third day.