Localization of Immunoreactive Somatostatin in Tumor Tissues Derived from Various Organs

Abstract

A sensitive and specific radioimmunoassay system has been developed for measuring somatostatin in tissues. Immunization of rabbit with somatostatin yielded the specific anti-somatostatin antibody that did not cross-react with various hormones tested. The radioimmunoassay system could detect as little as 6 pg of somatostatin. The recovery of somatostatin added to tissues was 67.8 ± 3.7%. Inhibition curves of the extracts obtained from a normal pancreas and two gastric carcinomas were parallel to those obtained with synthetic somatostatin. Immunoreactive(IR) somatostatin was not detectable in normal and tumor tissues of the lung and kidney, except in two out of seven lung carcinomas. However, variable amounts of IR-somatostatin (0.3–13.6 ng/g wet wt.) were detected in carcinomas of the pancreas and stomach, although the values were lower than those in respective control tissues. A case of medullary carcinoma of the thyroid showed relatively high levels of serum calcitonin and tissue IR-somatostatin in both primary and metastatic carcinoma. These data suggest that some malignant tumors could produce somatostatin-like substance, but its significance remains to be elucidated.