Cellular processes underlying ontogenesis and regression of streptozotocin (STZ)-induced diabetes in newborn rats were investigated at the most severe stage of diabetes at day 3 and after recovery of normoglycemia at day 8 by immunocytochemistry and quantitative analysis. A previously unknown endocrine cell type subpopulation (PEPS) was identified. It was characterized by granule polymorphism, coexpression of insulin and glucagon immunoreactivity, and a proliferative capacity transiently higher than in B cells. In STZ-treated rats at day 3, B cell mass decreased 14-fold, whereas PEPS cells were unaffected. The islet mass was restored to 55.7% by day 8, with a concomitant appearance of numerous small islets contiguous to small ducts. B cell mass increased by 6.9-fold compared with 1.8-fold in control rats, although proliferative capacities remained similar. Proliferation dropped considerably by day 8, preventing complete B cell mass recovery in STZ-treated rats. STZ-induced neonatal diabetes thus stimulates neogenesis of islets close to ducts and proliferation of PEPS cells. Those partially differentiated islet cells appear to be on the differentiation pathway of stem cells to fully differentiated B cells.

We have determined the cellular distribution of different alpha subtypes of G proteins and adenylyl cyclase (AC) isoforms in endocrine, exocrine, and established pancreatic cell lines. VIP, PACAP, and tGLP-1 receptor proteins are expressed to varying extents in A and B cells, whereas the expression of G alpha subunits is cell specific. Thus, G(olf) alpha is detected in normal rodent B cells and immortalized pancreatic B cell lines, whereas Gs alpha is more ubiquitously expressed. The cellular density of AC isoforms labeling (I, II, III, IV, V/VI) is also islet cell-specific and their distribution is age- and species-dependent. The identification of numerous signaling molecule subtypes, together with the discovery of their specific subcellular distribution, will help the functional characterization of their intraregulatory pathways, leading to the extrusion of insulin or glucagon secretory granules, and those leading to differentiation and apoptosis of islet cells.

We perfused the pancreas with 125I-labeled vasoactive intestinal peptide (VIP) to follow the concomitant distribution of radioactivity in beta- and acinar cells as a function of time. This distribution was quantitated by computer-assisted analysis of high-resolution video autoradiographs. Density labeling was expressed as normalized specific activity (disintegration density per volume density). Immediately after a 4-min perfusion of 125I-VIP, labeling in beta-cells was mainly concentrated on the cell surface and peripheral tubules and vesicles. After three 30-s pulses of 125I-VIP, separated by intervals of 3.5 min of buffer perfusion, lysosome-like structures were heavily labeled. When VIP internalization was prolonged, labeling was similar to that observed with the 4-min perfusion, indicating a high VIP disposal rate in the lysosome-like structures. In acinar cells, labeling persisted on the surface and the early vacuolar system. We conclude the following: 1) an active endocytotic system, linked to the transport and sorting of a neuromediator, is present in beta-cells; and 2) the differences between the distribution of labeling in acinar and beta-cells suggest that the regulation of VIP internalization is tissue specific.