Transplantable argyrophilic gastric carcinoid of Mastomys natalensis secreting both histamine and serotonin.

A transplantable strain of gastric carcinoids of Mastomys (Praomys) natalensis secreted not only histamine but also serotonin [5-hydroxytryptamine (5-HT)]. Mastomys bearing growing transplants excreted 11.3 times more histamine and 4.4 times more 5-hydroxyindole-3-acetic acid (5-HIAA) in the urine than did Mastomys in which transplanted tumors did not grow. Mastomys that developed primary gastric carcinoids also excreted 3.9 times more histamine than did those free from primary tumors, but the difference in urinary excretion of 5-HIAA was not significant in both groups. All transplantable carcinoids contained definite amounts of both histamine and serotonin, whereas the primary gastric carcinoids contained only histamine. We also confirmed that the histamine and 5-HIAA excreted in urine increased as the size of transplanted tumors enlarged. 5-HT was histochemically demonstrated in a small number of carcinoid cells of the transplanted tumors but not in primary carcinoids.