Release of immunoreactive somatostatin from hypothalamic cells in culture: inhibition by gamma-aminobutyric acid.

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Abstract
Primary cultures of dispersed hypothalamic cells were prepared from embryonic rats to study the release of immunoreactive somatostatin. The immunoreactive somatostatin content of these cultures increased during the 1st 2 wk after plating and was readily measurable for several weeks thereafter; this material was characterized by gel permeation and reverse-phase chromatography. Depolarization of the cells with 60 mM K+ or with veratridine resulted in a Ca dependent release of immunoreactive somatostatin which cochromatographed with synthetic somatostatin on reverse-phase chromatography. Tetrodotoxin blocked the veratridine-evoked release. Even in the absence of exogenous stimuli, immunoreative somatostatin was released by the cells into the medium. More than 70% of this tonic release was Ca dependent and inhibited by tetrodotoxin, indicating that spontaneous electrical activity in the cultures leads to a release of immunoreactive somatostatin. .gamma.-Aminobutyric acid inhibited the tonic release of immunoreactive somatostain and this was reversed by bicuculline. .gamma.-aminobutyric acid apparently inhibits somatostatin release in vivo.