Changes in Pepsinogen lsozymes in Stomach Cancers Induced in Wistar Rats by N -Methyl- N ′-nitro- N -nitrosoguanidine and in Transplantable Gastric Carcinoma (SG2B) 2

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Abstract
With the use of Wistar rats, changes in pepsinogen (Pg) isozymes, separated by polyacrylamide gel electrophoresis, were studied in 30 well-differentiated adenocarcinomas and 2 adenomas induced by N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), 2 transplantable well-differentiated adenocarcinomas induced by MNNG and 4-nitroquinoline-1-oxide, and 21 nonneoplastic gastric mucosae Irritated by acetyl salicylic acid (ASA). The Pg content was significantly decreased in the gastric adenocarcinomas and adenomas; Pg 1, the fastest moving of the 3 Pg isozymes normally present in the pyloric mucosa, was greatly reduced or not detectable in 28 well-differentiated adenocarcinomas and 2 adenomas in the pylorus. Pg 1 was also not detectable in 2 transplanted well-differentiated adenocarcinomas originally induced in the pylorus and transplanted sc into the backs of newborn rats. Two (Pg 1, 2) of the 4 isozymes of Pg (Pg 1–4) in the fundic mucosa were also decreased or absent in 2 well-differentiated fundic adenocarcinomas; these adenocarcinomas gave the same electrophoretic patterns as did those of well-differentiated pyloric adenocarcinomas. No changes in Pg were found in fundic and pyloric mucosa irritated by ASA. Histochemically and ultrastructurally, adenocarcinomas and adenomas consisted of mixtures of the following three types of cells: cells resembling gastric pit mucous cells, pyloric gland cells, and cells without mucus. Tumors mainly consisting of pyloric glandlike cells showed the least decrease in Pg content, whereas those consisting of cells like gastric pit mucous cells and cells without mucus showed the greatest decrease in Pg content.