Morphological evidence for the involvement of calcium in neurohypophysial hormone release.

An elevated intracellular Ca2+ concentration in the secretory nerve endings of the rat neurohypophysis was detected histochemically by means of light microscopy concomitant with the vasopressin secretion evoked by hypertonic saline. The electron microscopic and X-ray microanalytical results furnish morphological evidence for the function-dependent Ca2+ storage capacity of the mitochondria, and suggest their role in the regulation of the free Ca2+ level in the neurosecretory axon terminal.