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At least 19 recordsLinked to original sources
PubMed2001

Lineage commitment and cellular differentiation in exocrine pancreas.

Exocrine pancreatic cell types comprise greater than 90% of parenchymal cell mass in the adult pancreas. However, the factors regulating differentiation of acinar and ductal epithelial cells remain incompletely characterized. Like pancreatic islet cells, acinar and ductal cells arise from pluripotent precursors within embryonic pancreatic epithelium. Recent studies have suggested that a common pool of pluripotent stem cells is responsible for generating both endocrine and exocrine cell types, and that specific signaling pathways regulate a critical balance between endocrine and exocrine lineage commitment.

Animals↗
PubMedDate not supplied

Cytosolic Ca2+ gradients triggering unidirectional fluid secretion from exocrine pancreas.

Exocrine gland cells secrete Cl(-)-rich fluid when stimulated by neurotransmitters or hormones. This is generally ascribed to a rise in cytosolic Ca2+ concentration ([Ca2+]i), which leads to activation of Ca2(+)-dependent ion channels. A precise understanding of Cl- secretion from these cells has been hampered by a lack of knowledge about the spatial distribution of the Ca2+ signal and of the Ca2(+)-dependent ion channels in the secreting epithelial cells. We have now used the whole-cell patch-clamp method and digital imaging of [Ca2+]i to examine the response of rat pancreatic acinar cells to acetylcholine. We found a polarization of [Ca2+]i elevation and ion channel activation, and suggest that this comprises a novel 'push-pull' mechanism for unidirectional Cl- secretion. This mechanism would represent a role for cytosolic Ca2+ gradients in cellular function. The cytosolic [Ca2+]i gradients and oscillations of many other cells could have similar roles.

Acetylcholine↗
PubMedDate not supplied

Morphologic sites for regulating blood flow in the exocrine pancreas.

The exocrine pancreas has a lobular structure and an intricate capillary network supplies the lobules. Casts of these capillaries are either straight and of constant width, provided with many shallow crests, or undulating and of varying diameter, provided with bulges and deeper constrictions. The mean capillary cast diameter is 6.32 microns (SD 0.53) and 3.91 microns (SD 0.84) at constriction sites. The first type corresponds to non-fenestrated capillaries, makes 24% of capillaries and is more frequently provided with pericytes (2.7 +/- 0.9 pericytes per capillary profile). The second type corresponds to fenestrated capillaries, comprises 76% of the capillaries and is less frequently provided with pericytes (1.5 +/- 0.6 pericytes per capillary profile). The endothelial cells of capillaries regularly form intermediate junctions and microvilli and contain microtubuli and cytoplasmic filaments. Intravital observations show that capillaries are capable of contracting and narrowing the capillary lumen. This contractility is accomplished by endothelial cells both at and apart from their nuclear regions while pericytes never contracted spontaneously during our in vivo observations. The capillary diameters estimated by intravital measurements, 3.53 microns (SD 1.05), are similar to cast measurements but differ at constricted segments from cast measurements. Flow reduction shows more variability in smaller capillaries and the flow is more reduced in capillaries of 5 microns diameter to about 40% of open capillaries vs. 68% in capillaries with 7.5 microns diameter. Veins are either provided with smooth muscle sphincters or with valves. These results indicate that corrosion casting accurately shows the geometry of capillaries. However, where the capillaries are drastically constricted, they might not be filled and therefore may be underestimated during measurements. Since none of the intravital luminal constrictions are small enough to reduce flow (smaller than 1 micron luminal diameter) and because many constrictions are effective to reduce flow, we conclude that capillaries of the exocrine pancreas are always capable of maintaining continuous blood flow yet can influence blood perfusion. The presence of venous valves in association with venous sphincters constitutes a new situation concerning blood drainage regulation in the exocrine pancreas.

Animals↗
PubMed1989

Type of dietary lipids exerts a major influence on the secretory activity of the exocrine pancreas: medium-term studies.

A possible influence of the type of dietary lipids on the pancreas exocrine function was tested on rats. For this purpose, four groups of rats were fed on different diets comprising 5% of different types of lipids: fish oil, evening primose oil, hydrogenated beef tallow, and a mixture of fish oil and evening primose oil. After a 6 week feeding period, the secretory activity of the pancreas was measured. Under resting conditions, rats fed hydrogenated beef tallow release different proportions of amylase, lipase, and serine proteases as compared to rats fed unsaturated lipids. In stimulated conditions, there was no significant difference in the relative proportions of enzymes secreted by the pancreas among the different groups of rats but the secretory response to cerulein stimulation from rats fed saturated lipids was increased by more than 40%. These results demonstrate that the type of dietary lipids exerts a major influence on the secretory activity of the pancreas.

Animals↗
PubMed1996

Immunocytochemical and cytochemical demonstration of a novel selective lysosomal pathway (SLP) of secretion in the exocrine pancreas.

The intracellular distributions of lysosomal and zymogen granule (ZG) membrane proteins were analyzed in the pancreas exocrine acinar cell by cytochemical and immunocytochemical approaches. A strong signal was observed with acid phosphatase (AcPase) in the trans-Golgi network and condensing vacuoles, whereas mature ZG and acinar lumina were devoid of any detectable reaction. The enzyme appears to exit from the regulated pathway by a shedding process during conversion of condensing vacuoles to mature granules. Trimetaphosphatase (TMPase) shows no reaction in the Golgi apparatus and condensing vacuole but is present in immature granules. The exit from the regulated pathway appears to occur at a later stage of the ZG maturation process. A third lysosomal enzyme, nicotinamide adenine dinucleotide phosphohydrolase (NADPase), was found in the median cisterna of the Golgi stack, was undetectable in condensing vacuoles and ZG, but produced a strong signal in the acinar lumen. Our observations show that only one type of intermediate organelle can explain the transport of that enzyme from the Golgi apparatus to the acinar lumen, and it is represented by a subpopulation of lysosomal bodies (LBs) highly reactive for this enzyme. In parallel, immunocytochemical observations with specific antibodies to GP2, a major protein component of the ZG membrane, have confirmed that most of the GP2 molecules in the acinar lumen do not derive from the ZG compartment but rather are from a subpopulation of highly reactive lysosomal structures. Because both NADPase and GP2 co-localize in specific lysosomal structures, and because these LBs are extruded in the acinar lumen, we conclude that this subpopulation of LBs is involved in selective transport of some lysosomal enzymes from the Golgi apparatus to the acinar lumen. This selective lysosomal pathway of secretion can explain the kinetics of GP2 transport and release from the acinar cell that cannot be explained either by the constitutive or the regulated pathway of secretion.

Acid Anhydride Hydrolases↗
PubMed2001

[Effect of continuous enteral feeding on pancreas exocrin function in rats].

The aim of this study was to examine the effects of continuous enteral feeding (CEF) on the exocrine pancreas in rats. Eight male Wistar rats were intrajejunally cannulated and CEF was started on postoperative day 6. In 10 control animals, laparotomy was followed by intragastric feeding (GF) with the same nutriment (Osmolite, Abbott, 254 mosm/l) from postoperative day 6. The daily discharge was 24 kcal in both groups. After five days of feeding, the pancreas was removed, its weight and its protein, DNA, trypsin and lipase contents were determined. The results revealed no significant difference in body weight loss between the two groups of animals, whereas the pancreas weight/body weight ratio was lower (p < 0.01) in the CEF group. The pancreatic protein, DNA, trypsin and lipase contents were decreased (p < 0.01) after CEF as compared with the values for the GF group.

Animals↗
PubMed2001

Neurohormonal control of exocrine pancreas.

The exocrine pancreas is regulated by various hormonal factors derived from the gut through hormone-hormonal and neurohormonal interactions. Physiologic stimuli entering the upper small intestine elicit the release of intestinal hormones and activate sensory reflex mechanisms from the intestinal mucosa to stimulate or inhibit exocrine pancreatic secretion. In addition, the endocrine pancreas, intrapancreatic nerves, and some extrapancreatic neural pathways, with or without mediation by the vagus nerve, are known to participate in regulation of exocrine pancreatic secretion. It has been established that two key intestinal hormones, secretin and cholecystokinin (CCK), in physiologic doses, act through the vagal afferent pathway and interact with each other as well as with other gut hormones. The releases of these two hormones are mediated through the corresponding releasing peptides. In the past few years, the roles of secretin- and CCK-releasing peptides have become more clearly defined. The participation of several neurotransmitters and regulatory peptides in the regulation of exocrine pancreatic secretion has also been established. In addition, neurotransmitters and neuropeptides released from the central nervous system may participate in the regulation of pancreatic secretion. It is conceivable that a few neurotransmitters and neuropeptides are involved in each neural regulatory pathway. However, their roles and sites of action in each pathway remain to be determined.

Journal Article↗
PubMed1989

Heterogeneity of the exocrine pancreas.

The exocrine pancreas is generally considered to be a homogeneous organ at the morphological and functional levels. Recent work, reviewed here, has provided multiple reasons to question this. Morphologically, differences have been found in cell size and digestive enzyme content in "peri-" vs. "teleinsular" acini by methods including acinar separation, enzyme assay, and both light and electron microscopic immunocytochemistry. Detection of several blood group antigens in human acinar tissue showed striking cellular heterogeneity in a mosaic pattern. Stimulation of pancreatic lobules by specific secretagogues and separation of individual zymogen granules with microfluorometric assay of enzyme content also confirmed heterogeneity at the lobular and organellar level. Functionally, evidence that nonparallel digestive enzyme secretion can be taken as direct support for acinar heterogeneity is reviewed, as is the work leading to direct demonstration of secretagogue-specific heterogeneous sequestration and storage of nascent digestive enzyme protein. A general overview of pancreatic acinar cell specificity is presented; the model incorporates temporal changes in secretion from eligible acini, with secretagogue specificity of whole acini containing specific preset mixtures of digestive enzymes.

Animals↗
PubMed1978

Sulphate metabolism in the exocrine pancreas. II. The production of sulphated macromolecules by the mouse exocrine pancreas.

The types of sulphated macromolecules produced by the exocrine pancrease were investigated. To determine whether this tissue utilized inorganic sulphate for protein production, the in-vitro behaviour of material labelled with 35S-sulphate was compared with material labelled with [3H]leucine (secretory proteins). While incubating tissue slices in the presence of cycloheximide resulted in an immediate and nearly complete inhibition of protein synthesis, a similar decrease in production of sulphated material was not observed until after 2 h of incubation in the presence of the drug. Likewise, the kinetics of pilocarpine-induced discharge of radioactive material from pancreatic slices pulse-labelled with either 3H-Leu. or 35S-sulphate was compared. During the first 90 min of stimulation sulphated macromolecules were detected in chase medium 10-15 min prior to the appearance of 3H-labelled secretory proteins. That in-vitro behaviour of sulphated material differed from radioleucine-labelled material is indicative of the fact that the pancreas utilizes inorganic sulphate for the production of macromolecules other than secretory proteins. Lipid and proteoglycan fractions were prepared from pancreatic tissue 4 h after intraperitoneal injection of radiosulphate. The recovery of a significant amount of radioactivity in both fractions deomonstrated the ability of the pancreas to use inorganic sulphate for the production of both sulphated lipids and sulphated proteoglycans. The possible function of sulphated macromolecules in pancreatic secretion is discussed.

Animals↗
PubMed2006

The role of aquaporin water channels in fluid secretion by the exocrine pancreas.

The mammalian exocrine pancreas secretes a near-isosmotic fluid over a wide osmolarity range. The role of aquaporin (AQP) water channels in this process is now becoming clearer. AQP8 water channels, which were initially cloned from rat pancreas, are expressed at the apical membrane of pancreatic acinar cells and contribute to their osmotic permeability. However, the acinar cells secrete relatively little fluid and there is no obvious defect in pancreatic function in AQP8 knockout mice. Most of the fluid secreted by the pancreas is generated by ductal epithelial cells, which comprise only a small fraction of the gland mass. In the human pancreas, secretion occurs mainly in the intercalated ducts, where the epithelial cells express abundant AQP1 and AQP5 at the apical membrane and AQP1 alone at the basolateral membrane. In the rat and mouse, fluid secretion occurs mainly in the interlobular ducts where AQP1 and AQP5 are again co-localized at the apical membrane but appear to be expressed at relatively low levels. Nonetheless, the transepithelial osmotic permeability of rat interlobular ducts is sufficient to support near-isosmotic fluid secretion at observed rates. Furthermore, apical, but not basolateral, application of Hg(2+) significantly reduces the transepithelial osmotic permeability, suggesting that apical AQP1 and AQP5 may contribute significantly to fluid secretion. The apparently normal fluid output of the pancreas in AQP1 knockout mice may reflect the presence of AQP5 at the apical membrane.

Animals↗