Morphometrical and immunocytochemical studies on rat pancreatic acinar cells under control and experimental conditions

Process of amylase and chymotrypsinogen secretion by acinar cells has been studied applying morphological and biochemical approaches. Three conditions were investigated; resting (fed control), cholinergic stimulation and fasting. Morphometrical evaluations have shown that under stimulation, the volume density of zymogen granules decreases drastically while that of the Golgi apparatus increases. This may result from the enhancement in protein processing and the rapid discharge. Quantitation of amylase and chymotrypsinogen immunolabelings present over the cellular compartments has shown that there is no difference in the intensities between tissues from control and stimulated animals. These results imply that total amounts of protein processed by the Golgi apparatus are markedly enhanced primarily because of the increase in size of the organelle, the amounts of protein processed per unit surface remaining unchanged. Under starvation where reduction of secretion occurs, there is a significant decrease in the volume density of the Golgi apparatus but no variation in that of the zymogen granules. However, the morphological aspect of these was markedly altered since many of them present an electron luscent periphery which was devoid of immunolabeling for amylase and chymotrypsinogen. Quantitation of amylase and chymotrypsinogen immunolabelings has shown significant diminution for both enzymes. In both experimental conditions, the volume density of lysosomes was enhanced, however in none of these conditions evidence of crinophagy was observed. The morphometrical and immunocytochemical results were consistent with those obtained from biochemical determination of amylase and chymotrypsinogen contents in tissues. Correlations between results obtained from morphometric and immunocytochemical studies were made leading to a better understanding of the cellular secretory activity during experimental conditions.