Biochemical, cytochemical and electron microscopic observations on the enhancement of the pancreatic acinar cell secretory activity in the rat during early postnatal growth.

During the first two postnatal weeks the amount of RNA of the pancreatic cells evaluated biochemically is about 3 times lower than that of the cells in the adult rat. Accordingly, in the acinar cells the amount of rough membranes of endoplasmic reticulum and the fraction of the cell volume occupied by the RNAase removable basophilic substance are visibly lower than those of the adult. Radioautography indicated that during this initial period the acinar cell's capacity to synthesize digestive enzymes rises somewhat. At 10-15 days the cellular amount of digestive enzyme is the lowest observed during postnatal life. From day 15 until about the end of the first month there is a marked cytoplasmic accumulation of digestive enzymes, of RNA and of rough endoplasmic reticulum. Concomitantly, the cell efficiency to synthesize, condense and discharge digestive enzymes is enhanced. The proliferative activity of the acinar cells is depressed during the latter period. From the 30-40th day onwards the cells exhibit a more developed and stable morpho-functional pattern.