A morphometric study of the 24-hour variations in subcellular structures of rat pancreatic acinar cells during the periweaning period.

Pancreatic acinar cells of rats obtained before (21 days of age) and after (31 and 42 days) weaning were morphometrically examined at six evenly spaced times during 24 h. Morphometric analysis demonstrated clear-cut variations in the average volume of the cell and nucleus, the incidence of binucleate acinar cells, and the volume and numerical densities of various cytoplasmic organelles during 24 h, at each stage. The daily mean values and variation of these parameters at 21 days clearly differed from those at 31 and 42 days. In particular, changes in the volume densities of rER and zymogen granules were bimodal at 21 days, whereas they were unimodal at 31 and 42 days. Moreover, some parameters also differed between 31 and 42 days, the main difference being an 8 h time shift in the variation curves of the volume densities of rER and zymogen granules. These findings indicate that morphometric analysis of the subcellular structures of pancreatic acinar cells during 24 h can be used to determine their developmental stage.