Release of noradrenaline from the rat tail artery induced by inhibition of the sodium pump in calcium-free solution

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Abstract
The release of noradrenaline [norepinephrine, NE] from the isolated rat tail artery into Ca2+- and K-free, 1 mM ouabain-containing solution was measured by means of radioenzymatic method. The rate of NE release increased gradually, reaching a maximum of .apprx. 2.30 nmol .cntdot. g-1 per h after 100 min. The enhancement of NE release could be inhibited by cocaine and phenoxybenzamine, but not by desipramine. The rate of NE release could be approximately doubled by prior inhibition of monoamine oxidase with pargyline. The release was accompanied by a decline in the proportion of storage vesicles containing an electron-dense core. In the absence of external Ca2+, inhibition of the Na pump apparently causes nonexocytotic release of endogenous NE.