Abstract
The aim of the study was the description of the prenatal development of rabbit pancreas, cell modifications, and changes in their volume and mitotic activity. Immunohistochemical, light and electron microscopic procedures were employed.
Stereological methods were used for estimation of cellular and nuclear volumes. hits on epithelial cells, tubular lumens, and endocrine progenitor cells were counted by systematic field sampling using test grid. Number of mitoses was registered in various cellular types after colchicine treatment.
Data obtained were converted to 1 mm3 tissue. First granules were observed in cells on day 10 and 18 hours, however two different granular types are distinguishable by electron microscopy only on day 15, when insulin and glucagon can be detected immunohistochemically.
Cellular volume increased remarkably in harmony with findings of granules in serous cells. Number of epithelial cells increased also exponentially.
The increase was more rapid between days 13 and 15, later it appeared exponential. Value of mitotic index and length of cell cycle did not change considerably between days 15 and 24.
Mitoses were observed in ductal, exocrine, as well as endocrine cells. The dividing endocrine cells were those that contained fine dense granules (progenitor cells).
The sub-population of progenitor cells is able to divide, however, this source of cells appears insufficient for exponential growth. Results after colchicine treatment show the increase of cell population but the life-span and a period necessary for volume multiplication vary.
Mitoses decrease in both sub-populations during the prenatal period. The progenitor cells arise probably by differentiation from the ducts, because their number increases proportionally to the main cell population.