Action of secretin on exocrine pancreatic secretion in vitro

Summary Basal pancreatic fluid and electrolyte secretion by the isolated rabbit pancreas was studied. The hormone secretin stimulated pancreatic fluid secretion, with a maximal flow stimulation of 35 (S.E.: 1.4)% occurring after addition of 480 units/liter bathing fluid. The same dose of secretin also stimulated the²²Na secretion by the rabbit pancreas in vitro. An average stimulation of 39 (S.E.: 2.1)% was observed, which is equal to the stimulation of fluid secretion. These results indicate that secretin stimulates pancreatic fluid production through increasing the active sodium secretion by the pancreas.     

Histamine secretion in leukocyte incubates of patients with allergic hyperreactivity induced by somatostatin-14 and somatostatin-28

Somatostatin is a potent histamine secretagogue found not only in rat mast cells but also in human leukocyte preparations. In concentrations 5 mol/l, somatostatin-14 induces histamine release, which correlates with the basophilic blood cell count, as shown in samples from allergic patients suffering from slight basophilia. Somatostatin-14 is twice as effective as somatostatin-28 on a molar basis, and acylating the tetradecapeptide withN-hydroxysuccinimidyl-p-hydroxy-phenyl-propionate decreases significantly the potency of histamine release.     

What's new in in vitro studies of exocrine pancreatic cell injury?

Exocrine pancreas in vitro models are useful for the study of pancreatic differentiation, secretion mechanisms, cell injury, and lysosomal processing of secretory product. Syrian hamster pancreas in explant organ culture undergoes a series of morphologic changes which parallel in vitro acinar cell injury, differentiation, and phenotypic alteration. Within 48 hours, the cultured acinar cells show morphologic evidence of sublethal cell injury. Autophagy and crinophagy are particularly striking. The autophagic processes can be inhibited by the addition of the protein synthesis inhibitor cycloheximide or by culture at lowered temperatures (20 degrees C). Acinar cells lethally damaged show pyknotic nuclei, high amplitude swelling, and necrosis. Approximately 25% of each explant is viable after 72 hr in culture and the viability remains constant at 25-35% for up to 60 days of culture. The morphological changes of the explants are consistent with many of the features of pancreatitis and carcinoma of the exocrine pancreas. There is an increase in the ductal elements and a decrease in acini over time in culture. This may be due to: (a) an increased replication of ductal epithelial cells concomitant with necrosis of acinar epithelial cells and/or (b) phenotypic alteration of acinar cells to ductal cells. Acinar cell necrosis and phenotypic alterations may in part be due to the activation of lysosomal degradation pathways. Processes which inhibit lysosomal activation proved protective against these alterations, while processes which promote zymogen activation were deleterious.     

Bimodal regulation of adrenal opiate peptides by cholinergic mechanisms

Physiologic stressors increase trans-synaptic impulse activity and result in adrenal catecholamine release and biosynthesis. To determine the effects of stress on the co-localized opiate peptide system, rats were cold stressed at 4 degrees C. While cold stress slightly decreased enkephalin levels, a more severe stress (wetting and cold) increased enkephalin levels by 95%. Examining trans-synaptic-cholinergic mechanisms, treatment with either nicotinic or muscarinic agonists alone resulted in no change in adrenal enkephalin content. However, treatment with both nicotinic and muscarinic agonists together resulted in a three-fold rise in enkephalin levels. To further examine cellular mechanisms, medullae were explanted in the presence of agents that increase second messenger cyclic nucleotide levels. Treatments that increase the levels of cAMP, the cyclic nucleotide associated with nicotinic receptor activation, prevented the rise in medullary enkephalin relative to control explants. In contrast, treatments that increased cGMP levels, the cyclic nucleotide associated with muscarinic receptor activation, had no effect on enkephalin content compared to control explants. However, in the presence of both forskolin (10 microM) plus db-cGMP (5 mM), enkephalin content rose three-fold over control explants. These data suggest that, distinct from catecholamine pathways, enkephalin levels can be positively or negatively regulated by the severity of a stressful stimulus, by cholinergic receptor mechanisms and by an interaction of cyclic nucleotide second-messenger pathways.     

丁酸钠、激活素A和地塞米松诱导小鼠胚胎干细胞分化为胰腺外分泌细胞

目的： 探讨丁酸钠、激活素A （activin A）和地塞米松诱导小鼠胚胎干细胞（ES细胞）分化为胰腺外分泌细胞的可行性,并对诱导作用进行比较。方法： 小鼠 ES细胞悬浮培养为拟胚体后,以不同浓度的丁酸钠（1 mmol/L,2 mmol/L,3 mmol/L）诱导分化,通过RT-PCR检测不同时点胰腺特异性外分泌基因的表达水平,确定丁酸钠诱导ES细胞向胰腺外分泌细胞分化的最佳浓度和作用时间。进一步单独或联合应用丁酸钠、activin A、地塞米松诱导ES细胞分化,并通过细胞形态学变化、RT-PCR和免疫荧光检测观察不同诱导方案对胰腺外分泌基因和蛋白表达的影响,确定最佳诱导方案。结果：1 mmol/L丁酸钠能明显促进胰腺外分泌基因amylase、chymotrypsinogen、elastase1、elastase2和carboxypeptidase的表达,随着丁酸钠浓度的增加,丁酸钠的诱导作用逐渐减弱;1 mmol/L丁酸钠诱导第3 d后可检测到amylase、chymotrypsinogen、elastase1、elastase2和carboxypeptidase的表达,在第5 d外分泌基因mRNA表达水平达到高峰,随后逐渐下降。与自发对照组相比,单独应用丁酸钠、activin A、地塞米松诱导ES细胞分化,均能提高amylase、chymotrypsinogen、elastase1、elastase2和carboxypeptidase的表达水平。但联合应用丁酸钠、activin A、地塞米松诱导后,ES细胞形态更为均一,上述胰腺外分泌基因的表达进一步增强;免疫荧光结果显示amylase表达为阳性。结论： 低浓度的丁酸钠、activin A以及地塞米松均可以诱导小鼠ES细胞胰腺外分泌基因的表达,多种诱导因子的联合作用能明显提高胰腺外分泌细胞的诱导效率。     

Classification of pancreatic exocrine tumours

Current international histologic classification of exocrine pancreatic tumours is presented. Macro- and microscopic characteristics of benign and malignant tumors are described. The role of immunohistochemistry in differential diagnosis is shown.     

Endocrine-paracrine cells in pancreatic exocrine carcinomas

Eleven cases of primary pancreatic adenocarcinomas have been investigated histochemically, immunohistochemically and with electron-microscopy. Endocrine-paracrine (EP) cells were present in six of these tumours. In one case numerous 5HT-enterochromaffin cells (EC) of the intestinal type and a few somatostatin immunoreactive D cells were found. Two cases contained insulin-immunoreactive cells and another case displayed glucagon-IR elements. In the remaining two cases argyrophilic cells were present. These findings demonstrate that polypeptide hormone or amine production is not restricted to islet cell tumours. It is suggested that both endocrine and exocrine components of the tumours studied might have derived from a common precursor.     

Properties of Ca2+ currents in acutely dissociated neurons of the chick ciliary ganglion: inhibition by somatostatin-14 and somatostatin-28.

Whole-cell voltage-clamp recordings were made from acutely dissociated neurons obtained from the embryonic chick ciliary ganglion. Recording pipettes were filled with salines containing 120 mM CsCl or 120 mM tetraethylammonium-Cl. Application of depolarizing voltage commands evoked L-type Ca2+ currents and, at voltages positive to 0 mV, an unidentified cationic conductance. The unidentified cationic conductances made the Ca2+ currents appear to undergo voltage-dependent inactivation and made a large contribution to tail currents present during repolarizing voltage steps. Ca2+ Ca2+ currents showed little or no sign of inactivation and did not reverse at voltages up to +60 mV. Application of somatostatin-14 or somatostatin-28 produced a reversible inhibition of Ca2+ currents in virtually all cells, regardless of size. Somatostatin-28 (1-14) was inactive. The effects of somatostatin-14 and somatostatin-28 were attenuated by pretreatment with pertussis toxin, suggesting a role for G-proteins in mediating the response. Somatostatin-14 and somatostatin-28 had no effect on voltage-dependent K+ currents. The results suggest that somatostatin peptides modulate the motor output of the chick ciliary ganglion.     

Bimodal regulation of T cell-mediated immune responses by TIM-4

T cell Ig and mucin domain (TIM)-4 is preferentially expressedon antigen-presenting cells, and its counter-ligand, TIM-1,is thought to deliver co-stimulating signals to T cells. However,the physiological functions of TIM-4 remain unclear. Here, wedemonstrate that TIM-4 inhibits naive T cell activation througha ligand other than TIM-1. The inhibitory effect of TIM-4 wasspecific to naive T cells which do not express TIM-1, and theeffect disappeared in pre-activated T cells. Conversely, antibody-mediatedblockade of TIM-4 in vivo substantially suppressed T cell-mediatedinflammatory responses despite enhanced generation of antigen-specificT cells. Furthermore, treatment with anti-TIM-4 reduced theinflammatory responses developed in mice that were adoptivelytransferred with antigen-primed T cells. These results suggestthat TIM-4 exerts bimodal functions depending on the activationstatus of T cells.     

Histogenetic classification of exocrine pancreatic carcinomas

The structures of normal ductal and ductular epithelium were compared with cytological peculiarities of pancreas carcinoma. This provided the basis on which to propose histogenetic classification of exocrine pancreas carcinoma. Most of the pancreas carcinomas are adenocarcinomas and originate from small lateral ductules. Preneoplastic ductal alterations, such as proliferation of ductal epithelium, adenomatous dysplasia, and light-cell transformation, may be topographically distinguished from ductular changes, including centroacinic hyperplasia, oncocytic transformation, microglandular metaplasia, ductulo-acinic metaplasia, hepatocellular metaplasia, and peri-insular metaplasia. The close correlations that exist between ductular and acinic cells may be summarised under the cover term of terminal ductulo-acinic intercalated duct complex. Dysplasia is generally accompanied by decline in neutral glycosaminoglycans and occurrence of unsubstituted sialomucin of the embryonic type.     

Duct-oriented classification of exocrine pancreatic carcinoma

Histogenetic classification was applied to 416 cases of human exocrine pancreas carcinoma. Fundamental importance was attributed, in that context, to duct-associated histogenesis. A distinction was, therefore, made between ductal and ductular pancreas carcinomas. Invasive ductal carcinomas were subdivided by three categories: highly stromatous classical adenocarcinoma with poor prognosis, invasive ductal carcinoma with further differentiation (myxoma, squamous carcinoma, pleomorphous macrocellular and parvicellular types), and variations with specific differentiation (serous, mucinous tumours) with good prognosis. Invasive ductular carcinomas were subdivided by terminal non-papillary adenocarcinoma with protracted illness, ciliary adenocarcinoma, microglandular adenocarcinoma, ductulo-acinous tumour with excellent prognosis, and oncocytic carcinoma. These should be distinguished from intermediary cells with cellular transformation and neoplastic differentiation, such as adenocarcinoma with hepatocellular differentiation and mixed tumours (exocrine and endocrine) with alternatingly predominant cell spectra. Determination of prognostically differentiated tumours types is considered to be an indispensable prerequisite for adequately adjusted effective therapy. This appears to be the only approach which promises progress for the future.     

Effect of food restriction on plasma cholecystokinin levels and exocrine pancreatic function in rats.

The objective of this study was to examine the effects of 10% food restriction on body weight, plasma cholecystokinin (CCK) levels, and exocrine pancreatic function in male Sprague-Dawley rats. A matched group of rats with unrestricted access to food served as controls. After ingesting the diets for 32 da, the rats were killed and blood obtained for plasma cholecystokinin, glucose, and insulin determinations. To evaluate pancreatic function, the pancreases were removed, weighed, and digested with collagenase to isolate pancreatic acini, which were incubated with maximal stimulating dose of CCK. The fraction of amylase that was released into the medium was measured. To explore the role of membrane receptors in exocrine pancreatic secretion, CCK receptor affinity and CCK receptor capacity were determined by radioligand binding assays in isolated, purified membranes from pancreatic acini. Compared to the control group, rats with 10% food restriction showed (a) reduced body weight gain, (b) increased pancreatic weight, (c) increased plasma CCK level, and (d) no significant changes in plasma glucose or insulin levels. The food-restricted group showed a reduction of pancreatic function, assessed by measuring amylase release in response to maximal CCK stimulation; the amylase release was diminished by 35% in the food-restricted group. In isolated acinar cell membranes from food-restricted rats, CCK receptor affinity and capacity were reduced by 23% and 16%, respectively, compared to controls. These results indicate that consumption of less food than normal affects pancreatic function by a mechanism that evidently involves CCK release and downregulation of CCK receptors. The data suggest that CCK plays an important physiological role in the adaptation to eating less food, and thereby to the lowering of body weight in rats and, possibly, in other animals.     

Mapping of somatostatin-28 (1-12) in the alpaca diencephalon

Using an immunocytochemical technique, we report for the first time the distribution of immunoreactive cell bodies and fibers containing somatostatin-28 (1-12) in the alpaca diencephalon. Somatostatin-28 (1-12)-immunoreactive cell bodies were only observed in the hypothalamus (lateral hypothalamic area, arcuate nucleus and ventromedial hypothalamic nucleus). However, immunoreactive fibers were widely distributed throughout the thalamus and hypothalamus. A high density of such fibers was observed in the central medial thalamic nucleus, laterodorsal thalamic nucleus, lateral habenular nucleus, mediodorsal thalamic nucleus, paraventricular thalamic nucleus, reuniens thalamic nucleus, rhomboid thalamic nucleus, subparafascicular thalamic nucleus, anterior hypothalamic area, arcuate nucleus, dorsal hypothalamic area, around the fornix, lateral hypothalamic area, lateral mammilary nucleus, posterior hypothalamic nucleus, paraventricular hypothalamic nucleus, suprachiasmatic nucleus, supraoptic hypothalamic nucleus, and in the ventromedial hypothalamic nucleus. The widespread distribution of somatostatin-28 (1-12) in the thalamus and hypothalamus of the alpaca suggests that the neuropeptide could be involved in many physiological actions.     

Nervous control of pancreatic exocrine secretion in pigs

The pancreatic secretion of fluid, bicarbonate and protein in response to electrical stimulation of the vagus and splanchnic nerves, to exogenous and endogenous secretin and to various pharmacological agents was studied in anesthetized young pigs (21 kg). Vagal stimulation increased flow, bicarbonate output and protein output in a frequency dependent manner; the half maximal effective frequency was 2–4 Hz and the maximal effective frequency 12 Hz. The secretory response to vagal stimulation was potentiated by physiological elevations of the arterial concentration of secretin brought about by injection of secretin or by acidification of the duodenal bulb. Simultaneous stimulation of the splanchnic nerves strongly inhibited the response to vagal stimulation; splanchnic nerve stimulation alone had no demonstrable effect. The flow and bicarbonate response to vagal stimulation was unaffected by atropine, but abolished by hexa-methonium. Protein output was strongly inhibited by both agents. The response to intraarterial infusion of acetylcholine resembled that elicited by vagal stimulation but it was smaller and it was completely abolished by atropine and unaffected by hexamethonium. Alpha- and beta-adrenergic blockade stimulated rather than inhibited the secretory response to vagal stimulation. The portal vein plasma concentration of secretin was not affected by vagal stimulation. The results indicate that the protein response, and the flow and bicarbonate response to vagal stimulation are not brought about by the same mechanism. An increased release of secretin is not involved. Peptidergic (VIP-containing) nerves may contribute.     

Mechanisms of changes in composition of serum protein fractions after disturbance of the pancreatic exocrine function

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