Elsevier

Developmental Biology

Volume 25, Issue 2, June 1971, Pages 248-279
Developmental Biology

Morphologic and biochemical observations on the development of the rat parotid gland

https://doi.org/10.1016/0012-1606(71)90030-3Get rights and content

Abstract

Litters of rats were sacrificed at 2–5-day intervals from 18 days in utero to 40 days postnatally, and their parotid glands were subjected to biochemical and light and electron microscopic analyses. Biochemical assays were employed in homogenates of the glands for DNA, RNA, protein, and the secretory digestive enzymes α-amylase, alkaline RNase, and DNase I.

The results revealed that acinar differentiation in the rat parotid gland is primarily postnatal. Prior to and at birth, the parenchyma of the gland is rudimentary in regard to the enzymes and structures which are characteristic of the acini of the mature gland. One day after birth, the secretory digestive enzymes begin to increase above the levels found in adjacent, nonparenchymal tissues. At the same time, secretory granules appear in the clusters of cells at the terminal ends of the tubular apparatus. The appearance of PAS-positive material in the ductal lumens suggests that functional (secretory) activity begins at this time. There are two periods of rapid growth and differentiation, from about birth to 12 and 15–25 days. The proportional increases of the enzymes in the gland are much higher in the first period, but the absolute amounts gained are higher in the second. Cell size, as indicated by the concentration of DNA per unit of tissue, appears to decrease slightly during the first period, and increase markedly in the second, while the number of cells (DNA per gland) increases rapidly in both periods. At 25 days, the gland has nearly achieved the adult (100-day) levels of all parameters measured except weight. Increases in the amounts of secretory granules and rough endoplasmic reticulum and the development of active Golgi complexes appear to be well correlated with increases in the secretory enzymes and in RNA. The secretory digestive enzymes assayed increase in a noncoordinate manner, suggesting that the control of their synthesis may be asynchronous during the course of acinar differentiation. The onsets of the first and second periods of rapid differentiation coincide respectively with the onsets of suckling and weaning. This suggests that substrates in the food and secretory stimulation may have inductive significance in the differentiation of the gland.

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    Present address: Division of Oral Biology, School of Dentistry, University of Minnesota, Minneapolis, Minnesota 55455.

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