Nitrosamide-induced sarcomas in the gastric pylorus of hamsters. A histological and ultrastructural survey on the histogenesis.

A histological and ultrastructural survey on the histogenesis of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced gastric sarcomas in hamsters was attempted. Within 3 months after the beginning of oral administration of MNNG, simple spindle cell proliferation in the submucosal zone of the pyloric region of the glandular stomach was evident. By 5-6 months, the cells had acquired a sarcomatous appearance. Ultrastructurally, the spindle cells in the early stage, were divided into 3 types, i.e., angiogenic cells, fibroblastic cells, and primitive mesenchymal cells. Similarly, those in the late-appearing sarcomatous tumors were also classified into different types of angiogenic, fibroblastic, histiocytic and miscellaneous cells. Among the cell population of the 2 major groups, angiogenic cells were the most predominant cell type. Some morphological transition appeared to occur between the corresponding cell types at the early and late stages. DNA content of cell nuclei of the representative forms of the nitrosamide-induced sarcomas was higher than that of early appearing spindle cells. Thus, the evidence suggests that the early appearing spindle cells are precursors for the gastric sarcomas.