Small intestinal and pancreatic microstructures are modified by an intraduodenal CCK-A receptor antagonist administration in neonatal calves

The aim of the present study was to investigate the role of CCK on the upper gut and pancreas microstructure and on pancreatic juice secretion in neonatal calves assessed by a repetitive intraduodenal administration of FK480, a CCK-A receptor antagonist, during the first 6 days of life. The experiment was performed on 10 neonatal calves surgically fitted with a pancreatic accessory duct catheter and duodenal cannulas. Calves were sacrificed on day 7 for tissue sampling. Treatment with FK480 resulted in: reduction of preprandial pancreatic juice secretion at days 1-3, smaller size of pancreatic acini and number of cells per acinus, reduction in intestinal crypt depth (except in the duodenal bulb), numerous modifications of intestinal villi length and width, lower mitotic index of crypt cells, and increased number and size of enterocytes with 'empty vacuoles'. In conclusion, the blockade of CCK-A receptors during early life both reduced pancreatic exocrine secretion and induced complex changes in pancreatic microstructure. The influence of CCK on the upper gut microstructure in neonatal calves could be either direct via activation of CCK-A receptors located in the mucosa of the upper gut or indirect by modulation of the secretion of pancreatic juice.     

Efficiency of Primary Saliva Secretion: An Analysis of Parameter Dependence in Dynamic Single-Cell and Acinus Models,with Application to Aquaporin Knockout Studies

Secretion from the salivary glands is driven by osmosis following the establishment of osmotic gradients between the lumen, the cell and the interstitium by active ion transport. We consider a dynamic model of osmotically driven primary saliva secretion and use singular perturbation approaches and scaling assumptions to reduce the model. Our analysis shows that isosmotic secretion is the most efficient secretion regime and that this holds for single isolated cells and for multiple cells assembled into an acinus. For typical parameter variations, we rule out any significant synergistic effect on total water secretion of an acinar arrangement of cells about a single shared lumen. Conditions for the attainment of isosmotic secretion are considered, and we derive an expression for how the concentration gradient between the interstitium and the lumen scales with water- and chloride-transport parameters. Aquaporin knockout studies are interpreted in the context of our analysis and further investigated using simulations of transport efficiency with different membrane water permeabilities. We conclude that recent claims that aquaporin knockout studies can be interpreted as evidence against a simple osmotic mechanism are not supported by our work. Many of the results that we obtain are independent of specific transporter details, and our analysis can be easily extended to apply to models that use other proposed ionic mechanisms of saliva secretion.     

Cytological effects of urecholine stimulation on the rat pancreas

Summary Stimulation of the exocrine pancreas by the secretagogue urecholine causes degranulation of the acinar cells. Under in vivo conditions, this degranulation is not uniform throughout the tissue. Indeed some of the acini are almost completely depleted of their granules while others display the appearance of resting acini. A noticeable feature is that all the cells of the same acinus display a comparable degree of degranulation. Moreover, groups of neighbouring acini seem to respond simultaneously suggesting that the secretory stimulus is propagated from one acinus to the other. In vitro stimulation of dispersed acini also showed that some of the acini are more responsive than others indicating that this phenomenon can not be attributed to accessibility of the secretagogue to its receptor. These observations lead us to the concept that the response of the pancreatic acinar cell is controlled at the level of the acinus.     

A model for fluid secretion in the exocrine pancreas

Fluid secretion by the isolated rabbit pancreas is strongly dependent on the presence of Na+ in the bathing medium. Substitution of Na+ by another cation such as Li+ or K+ causes an inhibition of fluid secretion rate and a change in the composition of the secreted fluid which is dependent on the nature of the substituent cation. Stimulation of the pancreas by CCK-8 or carbachol increases paracellular ion permeability and, in some cases, also fluid secretion rate. We present a simple, quantitative model for ion and water secretion which accounts for the effects observed upon Na+ substitution and stimulation. The main features are active, Na+-dependent transcellular HCO3- transport and passive, paracellular cation and anion permeation. The activity of the HCO3- pump is dependent on the energy status of the cell and on the Na+ concentration in the bathing medium, and is competitively inhibited by K+. The paracellular ion permeabilities can be modulated by stimulatory agonists. We examine the extent to which, according to the model, fluid secretion is controlled by the various system parameters such as ion permeabilities and ion pump activity, and by external parameters such as the ion concentrations in the bathing medium. In addition, calculation of the effects of changes in these parameters are carried out in order to gain more insight in the mechanisms of secretion.     

The salivary glands of Hyalomma anatolicum anatolicum: structural changes during attachment and feeding

The histology and ultrastructure of the salivary glands of male and female H.a. anatolicum ticks have been examined m unfed and feeding ticks with special emphasis on aspects related to the feeding process. The salivary glands of H.a. anatolicum consisted of three types of acinus (acinus I, II and III) in females and an additional type IV acinus in males. The type I acinus was agranular and showed slight morphologic changes during feeding. The presence of cells with ultrastructural features characteristic of epithelia involved in the secretion of hyperosmotic fluids supports the hypothesis that these acini secrete hygroscopic saliva during questing stages to absorb water from an unsaturated atmosphere. There were five granular cell types (a, b, c₁–c₃) in type II acinus, three granular cell types (d, e, and f) in type III acinus, and one granular cell type (g) in type IV acinus. The cells a, d and e secreted most of their granules early in feeding and are considered to be cement precursors. The b and c cells appeared to synthesise and secrete their products throughout feeding and so are likely to secrete anticoagulants, enzymes and other pharmacologically active agents required during feeding. The interstitial cells, which were insignificant in acinar types II, III and IV of unfed ticks, became more distinct during feeding. The type III acinus in females showed remarkable cell transformations, during the course of feeding. The ablumenal interstitial cells of type III acinus, in females formed a basal labyrinth of extraordinary complexity by interdigitating with the basolateral membranes of transformed f cells to form a network of extracellular channels to excrete fluid during feeding. There was an enormous increase in the secretory granules of g cells as the feeding advanced. The secretory granules were released by a process of exocytosis, by direct fusion with the apical membranes and through channels connecting several granules.     

Cholecystokinin/pancreozymin induces the parallel discharge of digestive enzymes from the in vitro rabbit pancreas.

Considerable controversy has surrounded the question of whether the exocrine pancreas discharges digestive enzymes in a parallel or nonparallel fashion. A recent report (Rothman, S.S., and Wilking, H. (1978) J. Biol. Chem. 253, 3543-3549) claimed that the in vitro rabbit pancreas demonstrated nonparallel enzyme discharge after stimulation with cholecystokinin/pancreozymin, but that parallel discharge followed stimulation with the COOH-terminal octapeptide of cholecystokinin/pancreozymin. It was suggested that the full hormone acted to inhibit chymotrypsinogen secretion while stimulating trypsinogen secretion. Because of the fundamental importance of this question to our understanding of the exocrine secretion of exportable proteins, we have repeated these experiments using the same preparation and stimulant but have observed only parallel enzyme discharge. We conclude that it is unlikely that cholecystokinin/pancreozymin causes the selective inhibition of chymotrypsinogen secretion.     

凹耳臭蛙消化系统解剖学及组织学观察

对凹耳臭蛙Odorrana tormota消化系统进行了解剖学及组织学观察。消化道可以分为口腔、咽、食道、胃、十二指肠、回肠和直肠,末端开口于泄殖腔。肝脏和胰腺为消化腺。消化道管壁的组织结构均为4层结构,由管腔向外依次为黏膜层、黏膜下层、肌层和浆膜。胃黏膜层中含有许多胃腺,可明显分为腺颈部和腺体部。小肠含有十二指肠腺,直肠含有直肠腺。肝脏发达,分为左、中、右3叶,肝小叶界限不明显。胰腺中的腺泡由腺细胞围成。凹耳臭蛙肠全长与头体长之比为0.44～0.91,是迄今为止报道的无尾两栖类中最小的。     

Dynamics of pancreatic tissue cells in the rat exposed to long-term caerulein treatment: 1. Biochemical, morphological and morphometrical evaluations

This study was undertaken to evaluate whether hypertrophy and hyperplasia of the pancreatic acinar cells induced by caerulein remained after termination of the hormonal treatment. Rats received subcutaneous injections of saline or caerulein for 4 days and were killed immediately after termination of treatment or 2, 15 and 50 days later. Caerulein treatment induced significant increases in pancreatic weight and contents of DNA, RNA, protein, amylase and chymotrypsinogen along with an increased number of acinar cells per acinus and zymogen granules per acinar cells. During the post-treatment period, the caerulein-treated pancreas reverted to control values for their contents in proteins, enzymes and RNA and number of zymogen granules per acinar cell while the number of pancreatic cells remained constant as indicated by the absence of modification in total DNA content and acinar cells per acinus. During that same period, saline-treated pancreas exhibited constant growth. These morphological and biochemical data indicate that the already present and newly formed acinar cells can remain in place once the trophic stimulus is withdrawn and that they can adjust their cellular components and thus their digestive capacity to the circulating levels of endogenous cholecystokinin released in response to normal meals.     

封闭群草原兔尾鼠肝脏和胰腺的组织学观察

首次对封闭群草原兔尾鼠的肝脏、胰腺进行了组织学观察,结果表明：1．草原兔尾鼠的肝脏纤维组织极少,肝小叶间界限不明显;部分中央静脉周围可见少量毛细胆管;门管区较少,分布不均匀,其静脉形状不规则、腔大,胆管及动脉则较小。2．胰腺分叶清晰,腺泡细胞较大,胞浆多呈嗜酸染色;小叶中部腺泡着色较深,外侧腺泡着色较浅;胰岛大小不等,细胞排列呈不规则索状,光镜下未见特殊改变。     

Morphology of the exocrine glands of the frog skin

Frog skin contains three distinct types of exocrine glands: granular (poison), mucous, and seromucous. The granular gland forms a syncytial secretory compartment within the acinus, which is surrounded by smooth muscle cells. The mucous and seromucous glands are easily identifiable as distinct glands. The serous and mucous secretory cells are arranged in a semilunar configuration opposite the ductal end and are filled with granules. Within the acinus, located at the ductal pole of the gland, are distinct groups of cells with few or no granules in the cytoplasm. In both the mucous and seromucous gland there is a cell type with abundant mitochondria; the one in the mucous gland is located in the region adjacent to the secretory cells. The duct of these glands is two-layered, with the individual cells appearing morphologically similar to the layers of the skin epithelium as the duct traverses the skin. The duct appears to be patent throughout its length. The morphological heterogeneity and distinct distribution of the cell types within the gland acinus may be indicative of a functional heterogeneity that allows the production of distinctly different types of secretion from the same gland type, depending on the type of stimulus.     

What are the relevant parameters for the geometrical optimization of an implantable bioartificial pancreas?

A sphere within a cylinder representing the islet encapsulated in a hollow fiber can model an implantable bioartificial pancreas. Based on a finite element model for insulin response to a glucose load in the presence of various oxygen supplies, the present study aimed at pointing out the major parameters influencing this secretion. The computational results treated with the Taguchi method clearly demonstrated that geometrical parameters (fiber length and islet density) should be precisely optimized for an enhanced insulin response. This requires the collection of more relevant experimental data concerning the islet oxygen consumption. Moreover, the relative errors on glucose consumption or insulin secretion by the islets do not seem to affect the whole optimization process, which should focus on the oxygen supply to islets.     

Vasoactive intestinal polypeptide (VIP) in the pig pancreas: role of VIPergic nerves in control of fluid and bicarbonate secretion

Vasoactive intestinal polypeptide (VIP) in the pig pancreas is localized to nerves, many of which travel along the pancreatic ducts. VIP stimulates pancreatic fluid and bicarbonate secretion like secretin. Electrical vagal stimulation in the pig causes an atropine-resistant profuse secretion of bicarbonate-rich pancreatic juice. In an isolated perfused preparation of the pig pancreas with intact vagal nerve supply, electrical vagal stimulation caused an atropine-resistant release of VIP, which accurately parallelled the exocrine secretion of juice and bicarbonate. Perfusion of the pancreas with a potent VIP-antiserum inhibited the effect of vagal stimulation on the exocrine secretion. It is concluded, that VIP is responsible for (at least part of) the neurally controlled fluid and bicarbonate secretion from the pig pancreas.     

利用假型反转录病毒对大部分胰腺切除后再生细胞的世系追踪

胰腺是一个重要的内外分泌混合腺, 胰腺发生损伤后能够再生。为了探讨胰腺活体细胞世系追踪的方法和胰腺损伤后再生细胞的来源,分别通过胰腺伤口涂抹并胰内注射、尾静脉注射及腹腔注射三种方法, 利用假型反转录病毒对成体小鼠大部分切除后胰腺的细胞进行世系追踪。结果发现在活体条件下, 与尾静脉注射及腹腔注射法相比, 胰腺伤口涂抹并胰腺内注射反转录病毒的方法能够更有效的标记胰腺细胞; 而且, 通过对标记细胞的世系追踪研究证明, 在胰腺损伤后, 胰腺腺泡细胞能够接受损伤信号刺激发生再生。为今后进一步利用反转录假病毒对活体胰腺进行细胞命运追踪研究奠定基础, 为利用反转录病毒载体进行胰腺疾病的基因治疗提供线索。     

利用假型反转录病毒对大部分胰腺切除后再生细胞的世系追踪

胰腺是一个重要的内外分泌混合腺, 胰腺发生损伤后能够再生。为了探讨胰腺活体细胞世系追踪的方法和胰腺损伤后再生细胞的来源,分别通过胰腺伤口涂抹并胰内注射、尾静脉注射及腹腔注射三种方法, 利用假型反转录病毒对成体小鼠大部分切除后胰腺的细胞进行世系追踪。结果发现在活体条件下, 与尾静脉注射及腹腔注射法相比, 胰腺伤口涂抹并胰腺内注射反转录病毒的方法能够更有效的标记胰腺细胞; 而且, 通过对标记细胞的世系追踪研究证明, 在胰腺损伤后, 胰腺腺泡细胞能够接受损伤信号刺激发生再生。为今后进一步利用反转录假病毒对活体胰腺进行细胞命运追踪研究奠定基础, 为利用反转录病毒载体进行胰腺疾病的基因治疗提供线索。     

Ultrastructure of the accessory glands of gene's organ in the cattle tick, Boophilus

The organization and ultrastructure of the accessory glands of the cattle tick, Boophilus microplus, are described. The glands consist of two groups of acinar cells situated on either side of Gene's organ. A single acinus consists of from eight to 12 cells and each cell is connected via an individual duct to pores on the dorsal surface of the mouthparts. The position of these pores is such that the secretion of the accessory glands is incorporated into the egg wax during oviposition. Each gland cell has striking quantities of smooth endoplasmic reticulum and numerous Golgi dictyosomes and appears to produce a secretion that is lipoidal in nature. Each cell secretes into its own individual lumen and is connected to a cuticular pore by a duct cell.     

A novel model of solute transport in a hollow-fiber bioartificial pancreas based on a finite element method

Extravascular bioartificial pancreas based on hollow fiber seems to be a promising treatment of diabetes mellitus. However, solutes mass-transport limitations in such a device could explain its lack of success. To determine critical device parameters, we have developed a novel tridimensional model based on finite element method for glucose, insulin, and oxygen diffusion around an islet of Langerhans encapsulated in a hollow-fiber section. A glucose ramp stimulation was applied outside the fiber and diffused to the islet. Concomitantly, a stationary oxygen partial pressure was applied outside the fiber, and determined local oxygen partial pressure on the islet environment. An insulin secretion model stimulated by a glucose concentration ramp and corrected by the local oxygen partial pressure was also implemented. Insulin secretion by the islet was thus computed as a response to glucose signal. The model predictions notably showed that the fiber radius had to be small enough to favor a fast response for insulin secretion and to ensure a maximal oxygen partial pressure in the islet environment. Besides the effect of fiber radius, a better islet oxygenation could be achieved by adjustments on the islet density, i.e., on the fiber length dedicated to a single islet. These hints should allow the future proposal of an optimal design for an implantable bioartificial pancreas.     

Effect of electrical field stimulation on insulin and glucagon secretion from the pancreas of normal and diabetic rats.

The effect of electrical field stimulation (EFS) on insulin (INS) and glucagon (GLU) secretion from normal and diabetic rat pancreas is poorly understood. In our study, EFS (5-20Hz, 50 V amplitude and 1.0 ms pulse width), when applied alone, resulted in a significant (p<0.05) increase in INS secretion from the pancreas of both normal and diabetic rats. Atropine (10(-5) M) did not inhibit the EFS (5 Hz)-evoked INS secretion in normal pancreas and failed to alter the effect of EFS (10-20 Hz) on INS secretion from the pancreas of both normal and diabetic rats. Propranolol (Prop) inhibited INS secretion to below basal level in the presence of EFS (5 Hz) but not at EFS (10- 20 Hz). Tetrodotoxin (TTX) also significantly (p = 0.002) inhibited INS secretion from normal pancreas in the presence of EFS (5-20 Hz). The decrease in insulin secretion observed when pancreatic tissue fragments were incubated in Prop and TTX in the presence of EFS was reversed by yohimbine (10(-5) M). In contrast, TTX did not significantly modify INS secretion from diabetic pancreas in the presence of EFS. EFS (5-20 Hz) significantly (p<0.05) increased GLU release from normal and diabetic rat pancreas when applied alone. Neither atropine, Prop nor TTX significantly modified GLU release from the pancreas of either normal or diabetic rats. This suggests that GLU secretion may be controlled through a different pathway. The EFS-evoked INS and GLU secretion is probably executed via different mechanisms. These mechanisms include 1) activation of cholinergic nerves by EFS; 2) EFS of alpha- and beta-adrenergic nerves; 3) activation of non-adrenergic non-cholinergic pathway by EFS; 4) EFS-induced depolarization and subsequent action potential in pancreatic endocrine cells and 5) electroporosity caused by EFS-induced membrane permeability. All of these effects may be summative. In conclusion, EFS (5-20 Hz), when applied alone, can evoke significant increases in INS and GLU secretion from the pancreas of both normal and diabetic rats. Insulin secretion is controlled via alpha-2 adrenergic (inhibition) and beta-adrenergic (stimulation) receptors. Glucagon secretion is enhanced by alpha2 adrenergic stimulation.     

Electrical coupling and uncoupling of exocrine acinar cells

The electrical communication network in the mouse pancreatic acinar tissue has been investigated using simultaneous intracellular recording with two separate microelectrodes and direct microscopical control of the localizations of the microelectrode tips. All cells within one acinus were electrically coupled, and the coupling coefficient (the electrotonic potential change in a cell neighboring to the cell into which current is injected [V2] divided by the electrotonic potential change in the cell of current injection [V1]) between two cells near each other (less than 50 micron) was always close to 1. Cells farther apart (50-100 micron) were, in some cases, coupled; in other cases, there was no coupling at all. Coupling coefficients varied between 0 and 1. There was rarely electrical coupling over distances of more than 110 micron. Using microiontophoretic acetylcholine (ACh) application, it was possible to evoke almost complete electrical uncoupling of two previously coupled pancreatic or lacrimal acinar cells from different acini or within one acinus. The effects were fully and quickly reversible. While the ACh-evoked uncoupling in the pancreas was associated with membrane depolarization, ACh caused hyperpolarization in the lacrimal acinar cells. The uncoupling was associated with a very marked reduction in electrical time constant, indicating a reduction in input capacitance (effective surface cell membrane area). The concentrations of stimulants needed to evoke reduction in pancreatic cell-to-cell coupling were 1 micron for ACh, 0.14 nM for caerulein, and 3 nM for bombesin. These concentrations are smaller than those required to evoke maximal enzyme secretion.     

Comparison of insulin and glucagon pulsatile secretion between the rat and dog pancreas in-vitro

Sustained pulses of insulin and glucagon were obtained from the isolated perfused in vitro rat pancreas. The respective periodicity of hormone release (peak to peak interval) was calculated by the Pulsar computer algorithm as insulin 5.8 +/- 0.3 min and glucagon 6.5 +/- 0.25 min. Because pulsatile insulin secretion is absent in type II diabetics, pulsatile islet hormone secretion could theoretically be regulated directly by intra-islet hormone interactions or indirectly by hormone sensitive nerve feedback, possibly from a venous hormone sensitive receptor system within the pancreas. To test the possible contributions of these systems in pulse regulation, the direction of perfusion was reversed in both rat and dog pancreata to prevent hormone contact with putative venous hormone receptors. The periodicity of hormone secretion was unchanged by reversed perfusion in both species. As vascular perfusion of islet cells is normally B to A to D, these results suggest that neither intra-islet hormone interactions nor intra-pancreatic insulin or glucagon sensitive nerve feedback systems are responsible, on an acute basis, for the regulation of pulsatile insular secretion from the normal pancreas. Insulin regulates net glucagon secretion but does not acutely influence glucagon pulses. The presence of pulses during retrograde perfusion may be the result of the entrainment of the pacemaker-islet system. These observations are consistent with the presence of an independent pacemaker and neural coordinating system within the dog and rat pancreas which may influence both the A- and B-cell.     

Functional distinction of secreting pools of the pancreas and participation of the pancreatic ductal system in the development of the pancreatic secret properties

Acute experiments on dogs with separate secretion of the pancreatic enzymes, either stimulated or inhibited, from two lobes of pancreas, and investigation into the character of kinetics of the secretion from 5-7 ductal pools of the pancreas showed the functional specifics, with the device of ductal valves and microdepot of a secret of the pancreas ductal system playing an important role. The conclusion is made that the final secret of pancreas removed to the duodenum is a product of a secret-motor activation of non-equipotentional microregions of the gland, being the components of an intervisceral dynamical mosaic.