Calcium-dependent somatostatin secretion from rat neurohypophysis in vitro

Abstract

THE tetradecapeptide somatostatin originally identified in hypothalamic extracts, has been subsequently shown by bioassay, radioimmunoassay and immunohistochemical techniques to be extensively distributed throughout the central nervous system, in the gastrointestinal tract, and in the pancreas^1–5. Within the central nervous system, immunoreactive somatostatin has been localised to fibres in the external zone of the median eminence, to neuronal cell bodies in the anterior hypothalamus, to axons in the posterior pituitary lobe, as well as in spinal ganglia and in fibres in the dorsal zone of the spinal cord^2,6. Although strong indirect evidence exists for the release of somatostatin from the hypothalamus into the portal vessels in physiological conditions⁷ there are no direct studies of somatostatin secretion from nerve cells. Since the neurohypophysis contains a high concentration of somatostatin⁸, and can be readily isolated, we used it as a model for studying the in vitro release of the peptide from nerve terminals. We report that secretion is markedly increased following potassium stimulation, provided calcium is present in the incubation medium.