Cytochemical demonstration of somatostatin 28-(1-14)-like immunoreactivity in the rat hypothalamus and gastro-entero-pancreatic endocrine system.

Somatostatin-28 (SS 28) is a NH2-terminally extended form of somatostatin-14 (SS 14). Using an antiserum whose antigenic determinant is contained in segment 1-14 of SS 28, the cellular localization of a SS 28-(1-14)-like immunoreactivity was examined in the hypothalamus and gastro-enteropancreatic endocrine system of the rat. Immunoreactivity for SS 28-(1-14) was recognized in the SS 14-immunoreactive nerve cells of the hypothalamus and their axons terminating in the median eminence. Electron microscopic immunocytochemistry revealed that SS 28-(1-14)-like immunoreactivity in the median eminence was localized in the secretory granules of a type of nerve terminal. The immunoreactive cells in the gastro-enteropancreatic endocrine system also corresponded to the SS 14-immunoreactive D cells. Only in the pyloric antrum, however, did SS 14-immunoreactive D cells show no or very weak reactivity to the anti-SS 28-(1-14) serum. The wide distribution of SS 28-(1-14)-like immunoreactivity in the same cellular elements as those containing SS 14 supports the view that SS 28 is a precursor of SS 14.