On the mechanism of release of norepinephrine from cat spleen slices by sodium deprivation and calcium pretreatment.

Endogenous norepinephrine (NE) content of cat spleen slices was markedly depleted by incubating them in a sodium-free solution for 2 hours at 37 degrees C. Dopamine beta-hydroxylase (DBH) activity was not changed by this treatment. During incubation of the slices in sodium-free solution for 30 minutes at 37 degrees C, there was a marked release of NE into the medium without a concomitant release of DBH. Incubation of the slices in a potassium-rich solution (140 mM) resulted in the release of both NE and DBH into the medium. In control slices, the soluble form of DBH accounted for nearly 30 percent of the total DBH activity. The proportion of soluble DBH was not appreciably affected when slices were incubated in sodium-free medium for 2 hours at 37 degrees C. It is concluded that release of NE from sympathetic nerves by sodium deprivation probably occurs by a process other than exocytosis. Additional information is presented concerning the DBH levels in spleen slices which were depleted by their endogenous NE content by preincubation in calcium-rich solution and then in normal Krebs' solution or by a simultaneous inhibition of both glycolytic and oxidative metabolism.