Epinephrine and dopamine β-hydroxylase secretion from bovine adrenal

The perfusate of the isolated, acetylcholine-stimulated bovine adrenal was studied for epinephrine (E) concentration and dopammne β-hydroxylase (DBH) activity. Analysis of single stimuli showed that DBH disappeared from the perfusate with a t 1/2 of 19.1-29.0 min, whereas E disappeared with a t 1/2 of 0.78-1.0 min. Stimulation every 5 min over 105 min caused a gradual decline in E concentration to 36% of its initial value, whereas DBH activity reached a plateau after the second stimulus and thereafter remained unchanged. The decline in E was not influenced by addition of catecholamine precursors and biosynthetic cofactors to the medium and was not accompanied by a shift in the ratios of E and norepinephrine (NE) in the perfusate. Inhibitors of DBH activity were not detected in the perfusate and nonexocytotic leakage of DBH into the perfusate did not occur. These results document the temporal dissociation of the appearance and disappearance of DBH and E after a single stimulus and the progressive dissociation of DBH and E secretion under conditions of prolonged perfusion with rapid and repetitive stimulation. Possible explanations of these observations are offered.