Differentiation*

Putatively preneoplastic, pancreatic atypical acinar cell foci (AACF) and nodules (AACN), collectively termed atypical acinar cell lesions (AACL), were induced in male Lewis rats by L-azaserine (300 mg/kg body weight [bw] in divided doses). Rats given carcinogen and then fed a lipotrope deficient (LD) diet developed a significantly greater number of larger lesions than animals fed complete diet throughout the experiment. It is suggested that lipotrope deficiency plays a promoting role in this model of pancreatocarcinogenesis. Ultrastructural morphometric studies of AACF, when compared to control tissues, revealed the following significant results: 1) a decrease in surface area of cell cytoplasm with no change in nuclear area, and hence increased nucleus/cytoplasm (N/C) ratio; 2) a reduction in size and uniformity of zymogen granules; and 3) an increase in number of granules per,um2 of cell. The results suggest that arrested development of the AACF cells is associated with reduced cytoplasm and zymogen production per cell. AACL may be eosinophilic due to an overall increased concentration of zymogen in these hyperplastic lesions and not because individual acinar cells in the AACL contain an increased amount of zymogen or are "zymogen-rich, " as has been reported. Keywords. Atypical acinar cell foci (AACF); carcinogenesis; electron microscopy; neoplasia; promotion; exocrine pancrea