Calcium-dependent release of somatostatin and neurotensin from rat brain in vitro

Abstract

THE peptides somatostatin and neurotensin were first described in extracts of mammalian hypothalamus^1–3. The recent development of sensitive radioimmunassay techniques and the application of immunohistochemical studies have shown that these peptides are concentrated in nerve terminals in various regions of the central nervous system (CNS)^4–12. Somatostatin-containing nerve terminals are particularly abundant in the median eminence of the hypothalamus, from which somatostatin seems to be released as a hypophysiotropic hormone controlling the secretion of growth hormone from the anterior pituitary⁷. Somatostatin is also present in a variety of glandular tissues, in the gastrointestinal tract^8,9, and in nerve terminals in many areas of the CNS outside the hypothalamus^4–6. Neurotensin is similarly present in high concentration in the hypothalamus, and is also found in other areas of the CNS, in the gastrointestinal tract and in pituitary gland^10–12. Within the CNS, the unique localisation of these peptides in specific systems of neurones suggests that they may be released as neurotransmitters or neuromodulators, as has been proposed for other neuropeptides such as substance P (ref. 13) and the enkephalins¹⁴. So far, however, it has not been shown that somatostatin or neurotensin can be released from CNS neurones, although a calcium-dependent release of somatostatin was recently reported from neurohypophyseal tissue in vitro¹⁵. We describe here the release of both somatostatin and neurotensin from rat brain tissue in vitro by a calcium-dependent mechanism, thus lending further support to the hypothesis that they may normally be released from nerve terminals within the CNS.