The storage of endogenous noradrenaline in sympathetic nerve terminals.

1. The subcellular distribution of noradrenaline in sympathetic nerve terminals of rat vas deferens and cat spleen has been studied by cell fractionation methods combined with fluorescence and electronmicroscopic histochemical methods for noradrenaline.2. Pinched-off axon varicosities (synaptosomes) were isolated and identified by fluorescence and electronmicroscopy in the mitochondrial pellet.3. The proportion of large to small dense-cored vesicles in electronmicrographs of sympathetic nerve terminals varies in different organs. In rat vas deferens 4% and in cat spleen 20% are large vesicles.4. Density gradients of rat vas deferens have a single low density peak of noradrenaline at 0.6 M sucrose, whereas those of cat spleen have an additional peak of noradrenaline at 1.1 M sucrose.5. Small dense-cored vesicles were identified electronmicroscopically in the low density fractions and large dense-cored vesicles in the high density fractions from density gradients.6. We conclude that both small and large dense-cored vesicles store noradrenaline.