Islet cell response in the neonatal rat after exposure to a high-fat diet during pregnancy.

Although pancreatic beta-cells are capable of adapting their mass in response to insulin requirements, evidence has shown that a dietary insult could compromise this ability. Fetal malnutrition has been linked to low birth weight and the development of type 2 diabetes later in life, while reduced beta-cell mass has been reported in adult rats fed a high-fat diet (HFD). Reported here are the effects of exposure to a HFD, during different periods of gestation, on neonatal rat weight and beta- and alpha-cell development. The experimental groups were composed of neonatal offspring obtained from Wistar rats fed a high-fat (40% as energy) diet for either the first (HF1), second (HF2), or third (HF3) week, or all three (HF1-3) weeks of gestation. Neonatal weights and circulating glucose and insulin concentrations were measured on postnatal day 1, after which the pancreata were excised and processed for histological immunocytochemical examination and image analysis. HF1 and HF2 neonates were hypoglycemic, whereas HF1-3 neonates were hyperglycemic. Low birth weights were observed only in HF1 neonates. No significant differences were detected in the circulating insulin concentrations in the neonates, although beta-cell volume and numbers were reduced in HF1-3 neonates. beta-cell numbers also declined in HF1 and HF3 neonates. alpha-cell volume, number and size were, however, increased in HF1-3 neonates. alpha-cell size was also increased in HF1 and HF3 neonates. In neonates, exposure to a maternal HFD throughout gestation was found to have the most adverse effect on beta-cell development and resulted in hyperglycemia.

Transcription factors, pancreatic development, and beta-cell maintenance.

Transcription factors play an important role during pancreatic development ensuring normal differentiation of the islet endocrine cells. In mature beta-cells, expression of specific transcription factors is essential in maintaining normal beta-cell function.

Brief occlusion of the main pancreatic duct rapidly initiates signals which lead to increased duct cell proliferation in the rat.

In the course of investigating the signals associated with pancreas regeneration, we have developed a method to initiate pancreatic duct cell proliferation by brief occlusion of the main pancreatic duct. The resulting duct cell proliferation, induced by temporary partial main duct occlusion, was compared to that induced by firmly tying a cellophane strip around the head of the pancreas for longer periods of time. Both methods stimulated a biphasic increase in duct cell proliferation, with proliferation maxima at 3 and 14 days post operation. The short duration of temporary main duct occlusion (60 s) that was needed to stimulate duct cell proliferation, and the similar duct cell proliferation profiles that were observed after both the temporary and the longer term main duct occlusion, led us to conclude that the signals which initiate proliferation occur rapidly at the beginning of each procedure.

Induction of cell proliferation and differentiation in the pancreas of the adult Vervet monkey (Cercopithecus aethiops): preliminary results.

Cellophane wrapping of the adult Syrian golden hamster pancreas has been found to result in ductular cell proliferation leading to islet regeneration. Injection of cytosol from a cellophane-wrapped pancreas into normal or diabetic hamsters evoked a similar response. In view of the therapeutic potential of the active substance in this cytosol, it was decided to investigate whether a similar response could be achieved in a primate. In normal adult Vervet monkey (Cercopithecus aethiops) pancreas, proliferation is seen only rarely in islet cells and occasionally in duct and acinar cells. Immunohistochemical investigation of normal Vervet monkey pancreas (n = 4) and 14 days (n = 2) and 56 days (n = 1) after cellophane wrapping of the Vervet monkey pancreas revealed a slight increase in proliferation of islet and acinar cells and a larger increase in proliferation of duct cells and in total endocrine cell volume. The results suggest that there is a latent developmental capability in the adult primate pancreas.

Distribution of endocrine cells displaying immunoreactivity for one or more peptides in the pancreas of the adult vervet monkey (Cercopithecus aethiops).

BACKGROUND: Our previous studies on the Chacma baboon revealed that the most striking difference between islets of the ventral and dorsal regions of the pancreas was their content of A and pancreatic polypeptide (PP) cells with A cells predominating in the tail and PP cells in the uncinate and head. Cells displaying dual immunoreactivity for both glucagon and PP were also observed. The objective of this study was to establish baseline parameters of the adult Vervet monkey (Cercopithecus aethiops) pancreas so that it could be used as a primate model to investigate possible therapies for diabetes. METHODS: Vervet-monkey pancreas was divided into uncinate, head, and tail regions, and the tissue processed for immunolabelling for pancreatic peptides using avidin-biotin-peroxidase as marker. Dot-blotting and absorption controls for antibody specificity were included because of the shared amino acid sequences in pancreatic polypeptide (PP), neuropeptide Y (NPY), and peptide YY (PYY). Endocrine cell distributions and the percentages of each cell type per region were calculated for each monkey. RESULTS: A significant difference in the percentages of PP cells (P = 0.02) was observed between uncinate and tail regions, the distribution of NPY cells was similar to that of the PP cells, and all other distributions were similar to those reported in the literature for most animals studied. Cells displaying dual immunoreactivity for glucagon and PP or NPY, PYY and NPY, or PP, PP and somatostatin and glucagon and insulin were identified and mapped throughout the pancreas. Most co-localizations occurred in the uncinate region. Co-localization of glucagon and insulin has not, to our knowledge, been reported previously in the adult pancreas. CONCLUSIONS: Pancreatic endocrine cell distribution in the adult Vervet monkey was found to be very similar to most other animals studied. The occurrence of cells displaying dual immunoreactivity for a number of different combinations of pancreatic peptides suggests an interesting plasticity of endocrine cells even in the adult animal.

The effect of diet on the Vervet monkey endocrine pancreas.

Vervet monkeys (Cercopithecus aethiops) used for pancreatic endocrine cell distribution studies were found to have been maintained on different diets. Although the effect of dietary changes on the exocrine pancreas has been described in several animals, little, apart from the effect of malnutrition, has been reported for the endocrine pancreas. Reported here are pancreatic endocrine cell distributions in monkeys on a standard diet (n = 3) compared with monkeys on an atherogenic diet (n = 3). Quantitation of immunolabelled pancreatic endocrine cell types revealed a significant 80% increase in A (glucagon) cell volume in monkeys on an atherogenic diet concomitant with a significant reduction in B (insulin) cell volume to approximately 60% of normal. This reflects a pattern of events that occurs in non-insulin dependent diabetes. An accompanying reduction in PP (pancreatic polypeptide) cell volumes supports our hypothesis that altering A and PP cell volumes could reflect differential gene expression in those cells in the adult in which glucagon and PP are co-localized.

Do the pancreatic primordial buds in embryogenesis have the potential to produce all pancreatic endocrine cells?

A heterogeneity in the cellular composition of the endocrine pancreas, with a preponderance of pancreatic polypeptide cells in the lower head region, has been linked to the dual origin of the organ. The pancreas develops from a ventral bud thought to contain potential pancreatic polypeptide cells and a dorsal bud contributing the non pancreatic polypeptide cells. This does not explain, however, several anomalies including the results reported here of a homogenous distribution of non insulin cells in the foetal baboon whilst the adult pancreas exhibits a heterogenous distribution with the pancreatic polypeptide-rich area in the lower head of the pancreas. If this heterogeneity is associated with the dual origin of the pancreas, it would be expected to be more pronounced in the foetus. The anomalies could be explained if both primordial buds contained progenitor cells of all endocrine cell types which could be expressed to meet the requirements of the body at any particular time.

Preliminary observations on the co-existence of regulatory peptides in cells of the baboon endocrine pancreas.

Immunocytochemical procedures at ultrastructural and light microscopy level revealed, in the Chacma baboon endocrine pancreas, cells which were immunoreactive for glucagon and pancreatic polypeptide (PP). Some D cells were observed to contain secretory granules with both the appearance and immunoreactivity of A cell secretory granules.

Morphology and endocrine production of cells in the islets of Langerhans of the Chacma baboon.

Biopsies of the pancreas head, tail, and uncinate regions of 6 Chacma baboons (Papio ursinus) were processed for ultrastructural and immunocytochemical (ICC) studies using avidin-biotin peroxidase label for light microscopy (LM) and immunogold for electron microscopy (EM). Survey 0.5 micron sections of Spurrs resin embedded tissue revealed areas of suitable islets. Thin 100-nm sections were then cut and stained from the osmicated blocks for ultrastructural studies. For ICC investigations, 1 micron sections were immunolabeled for LM before areas were selected for thin sectioning for ultrastructural immunolabeling. The baboon endocrine pancreas ultrastructure was found to be similar to that of other mammals with minor differences in islet and secretory granule size and shape and in electron opacity of the secretory granule cores. Insulin glucagon, somatostatin and pancreatic polypeptide (PP) producing cells were described. A small number of cells were seen to contain both glucagon and PP and some D cells were observed to contain a few granules with both the appearance and immunoreactivity of A cell secretory granules. Statistical analysis of 100 secretory granule diameters of each of the 4 cell types in 6 baboons revealed significant differences (p less than 0.001) in size between all but those of the A and D cells. The insulin precursor subunit, C-peptide, and the glucagon precursor, glicentin, were each found together with the final hormone product in their respective secretory granules. The precursors were often located toward the periphery of the secretory granule, suggesting that the conversion of precursor to active hormone may be membrane associated. A nonrandom topographical association was observed between A and D cells, suggesting a strong functional implication.

Distribution of cell types of the islets of Langerhans throughout the pancreas of the Chacma baboon.

Biopsies of the pancreas head, tail, and uncinate regions of four baboons were processed for immunocytochemical (ICC) studies by using avidin-biotin-peroxidase label for light microscopy (LM). Toluidine-blue- or methylene-blue-stained 0.5-micron sections of nonosmicated resin-embedded tissue were viewed to locate areas of suitable islets. For ICC investigations, batches 10 microns apart of ten consecutive 1-micron sections throughout ten islets from each of the three regions were immunolabelled for LM. Four slides in each batch were immunolabelled consecutively for insulin, glucagon, somatostatin, and pancreatic polypeptide, the fifth acting as one of the range of controls in each batch. The number of each of the four cell types was counted in at least ten immunolabelled islets from each of the pancreas heads, uncinate portions, and tails. The uncinate region and not the head, as in most mammals, was found to contain significantly higher numbers of pancreatic polypeptide (PP) cells and lower numbers of A (glucagon) and D (somatostatin) cells (P less than .001). The PP cells occurred in clumps and not as described in other mammals as part of the mantle of A, D, and PP cells. PP and A cell numbers were significantly different for each region (P less than .001), being lowest in the head for PP and in the uncinate process for A cells. D cell distribution was similar to that of the A cells whilst a significantly smaller number of B (insulin) cells was found in the tail compared with other regions (P less than .001).