Monolayer cell culture of neonatal rat pancreas: an ultrastructural and biochemical study of functioning endocrine cells.

Cells obtained by enzymatic dissociation of newborn rat pancreases grown in monolayer culture for periods of 14 hours to 20 days were utilized for ultrastructural and physiological studies. Small clusters of epithelioid cells, first recognized at 14 hours, increased in size with time, frequently merging to form large sheets of cells surrounded by fibroblastoid cells. Endocrine B and A cells were the most numerous elements in the clusters. The integrity of their differentiated ultrastructure was documented by the accumulation of stored immunoreactive insulin and immunoreactive glucagon within the cultures and the ability to regulate their release into the medium by means of normal physiological stimuli. The morphophysiological integrity of the B cells was also demonstrated in a pulse-chase experiment by closely correlating the movement of 3 H-leucine into proinsulin and insulin with sequential labeling by autoradiography of the rough endoplasmic reticulum, Golgi, and secretory granules. Furthermore, the presence of mitotic division among granulated cells provided evidence of B-cell replication. In contrast, surviving pancreatic exocrine cells underwent progressive morphologic simplification, giving rise to a population of dedifferentiated epithelioid cells whose ultimate fate requires further study.