Localization of vasopressin in synaptic vesicles of extra-hypothalamic rat brain

The subcellular localization of vasopressin (VP) from extra-hypothalamic areas of rat brain was investigated by measuring its distribution (a) along a continuous sucrose gradient; (b) during the preparation of isolated nerve endings (synaptosomes) and (c) during the preparation of synaptic vesicles. Quite large amounts of vasopressin are isolated in the same fractions as mitochondria, as well as synaptosomes. Osmotic rupture of membrane bound organelles in the homogenate results in the vasopressin being measured largely in the fraction containing synaptic vesicles. These results would suggest that vasopressin could be released by nerve terminals which is consistent with the hypothesis that it may have a neurotransmitter/neuromodulator function in the CNS.