Changes of pancreatic beta cell population during larval development of Rana pipiens.

The morphology and population size of immunohistochemically stained insulin-containing pancreatic beta cells are studied in Rana pipiens during larval development. These beta cells appear as single cells or form small clusters at early stages and gradually develop into large clusters arranged in cords surrounding the blood sinusoids in midlarval stages. The total quantity of these cells increases from stage II through midlarval stages, reaching maximum at stages XVIII and XIX. A significant decrease of total beta cell quantity is observed between stages XIX and XX. This decrease occurs slightly later than the onset of degeneration of exocrine tissue. Morphological indication of beta cell breakdown is also observed during this period. Although the population size of beta cells stays relatively constant from stages XXI to XXV, a further maturational change is observed in beta cell morphology between stages XXIV and XXV. During these stages, the polarization of stained immunoreactivity toward sinusoids is more obvious and there is a general decrease of staining intensity in the cytoplasm.