Involvement of tubular complexes in pancreatic regeneration after acute necrohemorrhagic pancreatitis.

Localized acute necrohemorrhagic pancreatitis was induced in rats by multiple trypsin injections. Morphological alterations were monitored by light and electron microscopy until complete recovery. In the acute phase, typical pictures of focal acute necrohemorrhagic pancreatitis were observed. In the postacute phase, fibrosis and tubular complexes are characteristic of damaged areas. Tubular complexes appear from the dedifferentiation of acinar cells. They are characterized by duct-like cells bordering wide, empty luminae. In the recovery phase, cellular proliferation was accompanied by differentiation, with progressive acquisition of the morphological characteristics of acinar cells at the periphery of the tubular complexes. In that instance, cellular proliferation was concomitant with the development of collagen septa in tubular complexes. In these structures both duct-like and acinar-like cells presented mitoses. Cell division persisted in the dedifferentiated cells until tubular complexes disappeared. A very similar process was observed in the embryonic pancreas, where organized parenchyma originated from proliferation and differentiation of protodifferentiated cells. We concluded that pancreatic repair following necrohemorrhagic pancreatitis involves proliferation of cells from intact acini and from tubular complexes, at variance with edematous pancreatitis, where regeneration is exclusively due to acinar cell proliferation.