Abstract
1) Catecholamine (CA) release from isolated bovine adrenal medullary granules suspended in isotonic KCl medium was stimulated by Ca++ or ATP·Mg.++ Low concentration of Ca++ may participate in the action of ATP·Mg.++ 2) The activity of Mg++-ATPase and DA-βS-hydroxylase in the granules was increased under the conditions which caused the release of CA from the graules by Ca++ or ATP·Mg.++ There appears to be close correlation between these enzyme activities and the rate of release of CA from the granules. 3) CA release from adrenal medullary slices was stimulated by serotonin, histamine and tyramine. However the stimulatory effects of these amines on CA release from the slices was observed both in the presence or absence of Ca++ in the incubation medium. 4) Cyc lic AMP and dibutyryl cyclic AMP have also stimulatory effects on the release of CA from the slices. However, the release of CA from the granules was not stimulated by these agents. Cyclic AMP was found to increase the rate of release of CA from the granules by ATP·Mg.++ Therefore it was suggested that cyclic AMP also play a role in the CA release from adrenal medulla by serotonin, histamine and tyramine. 5) Basing on these results, a working hypothesis of CA release from isolated adrenal medullary granules was represented.
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