Morphological changes in the rat exocrine pancreas after pancreatic duct ligation

In the present study, morphological changes of the exocrine pancreas in rats after pancreatic duct ligation were examined with light microscopy (hematoxylin-eosin, TUNEL, and PCNA staining) and scanning electron microscopy in order to elucidate the effects of increased pancreatic duct pressure. On the fifth day after pancreatic duct ligation, ductular proliferation, periductal fibrosis, and disappearance of acini were observed. TUNEL and PCNA staining demonstrated many apoptotic acinar cells and proliferating ductal cells immediately after ligation, which reached a maximal number on the 2nd or 3rd day. Tortuous or helical interlobular pancreatic ducts with inner surfaces containing many crater-like depressions and long cilia were found after ligation. These changes were almost identical to those observed in the pancreatic tissue of model chronic pancreatitis rats, WBN/Kob rats, and stroke-prone spontaneously hypertensive (SHRSP) rats. In summary, the morphological changes observed after pancreatic duct ligation were similar to those of chronic pancreatitis, therefore, the characteristic changes of pancreatic ducts observed in chronic pancreatitis may be caused by increased pancreatic duct pressure.     

Disaccharidase activities after jejunoileal bypass in rat

Digestive enzymatic activities (maltase, lactase and sucrase) have been determined in the intestinal mucosa of rats subjected to a jejunoileal bypass of 45 cm. The weight and protein content of the mucosa (mg/cm) were significantly decreased in the bypassed segment and significantly increased in the unbypassed segment, as compared to control rats. Maltase, lactase and sucrase specific (U/g protein) and total activity (U/cm intestine) were significantly decreased in the bypassed jejunum, compared to sham-operated rats. In the ileum, maltase specific and total activities increased in bypassed animals while the lactase and sucrase activities remained unchanged.     

Ultrastructural localization of zinc in rat exocrine pancreas by autoradiography

Summary ⁶⁵Zn was infused at a constant rate for 10 days into a rat. Glutaraldehyde fixed, Epon-araldite embedded ultrathin sections of pancreatic tissue were coated with Ilford L4 emulsion and at 211 days exposure were developed. Silver grains were found over the zymogen granules and over the rough endoplasmic reticulum of exocrine cells. Islet tissue was not observed in these studies. The failure of other zinc localization methods to demonstrate zinc in acinar tissue is discussed as are some of the pitfalls of the autoradiographic method and suggestions for future improvement.Published with the approval of the Director of the Wisconsin Agricultural Experiment Station, Madison. Supported in part by USPHS Research Grant AM-05606 from the Nat. Institute of Arthritis and Metabolic Diseases.Supported by an NIH post-doctoral fellowship.     

Leucine absorption after jejunoileal bypass in rats

Jejunal and ileal absorption of L-leucine has been studied in rats subjected to jejunoileal bypass and in sham-operated rats, for five minute periods, using a perfusion technique. Aminoacid concentrations were: 1, 2.5, 5, 10 and 25 mM. In some experiments methionine was added to determine simple diffusion. The ratio of the active/diffusive components of absorption were calculated at the different luminal aminoacid concentrations in both groups of rats, showing that this ratio was lower in control animals.     

Ultrastructural changes in rat epididymis after vasectomy

Summary Epididymal biopsies from rats that had undergone unilateral or bilateral vasectomies from one to eight months previously were compared with biopsies from their contralateral side or from normal controls to ascertain what ultrastructural changes had occurred. After vasectomy, spermatozoa appeared to dissolve in the lumen of the caput epididymidis and to be absorbed by the principal cells. About 5 weeks after vasectomy, numerous lamellar accumulations became apparent in the supernuclear region. Their resemblance to lysosomes or residual bodies was confirmed by an acid phosphatase reaction. After 10 weeks, similar lamellar and polymorphic accumulations on the contralateral side of animals with unilateral vasectomies indicated that resorption had also increased on the unligated side.Publication No. 627 of the Oregon Regional Primate Research Center. This study was supported by NIH Grants No. RR-00163 and HD-05969.The author wishes to thank Ms. J. Hren for her excellent technical assistance.     

Amino acid transport in the rat exocrine pancreas

Summary Amino acid transport and incorporation have been studied in vitro in rat pancreatic lobules after maximal and supramaximal hormonal stimulation with caerulein. Incorporation into proteins was increased already after 30 and 120 min of maximal stimulation, but was decreased after the infusion of a supramaximal dose. Uptake of neutral amino acids was monitored using labeled leucine and -aminoisobutyric acid (AIB). In the case of leucine the free pool was consistently reduced after maximal stimulation, while supramaximal doses led to an increase which could be potentiated by the addition of 2mM tetracaine. Using AIB, a significant increase in the intracellular pool was observed after maximal stimulation, conversely a decrease after supramaximal stimulation. Release of labeled leucine and AIB from preloaded lobules during incubation in the cold was significantly reduced after maximal secretory stimulation, but was found enhanced by 200 to 300 percent after supramaximal stimulation. No fine structural alterations at junctional complexes or at both the lateral and luminal plasma membranes were observed after maximal stimulation except an increased number of exocytotic figures at the luminal face. However, supramaximal stimulation led to progressive rarefaction of the tight junctional network and disintegration of the gap junctions. Concomitantly, an equal distribution of membrane particles on both faces of the plasma membrane together with a random occurrence of exocytotic figures were observed.Supported by a grant from the Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg (SFB 122, project C 5). Dedicated to Professor Dr. Gerhard Petry, Marburg, on the occasion of his 65th birthday     

Amino acid transport in the rat exocrine pancreas

Summary The two calcium antagonistic agents lanthanum and tetracaine cause severe disturbances in the secretory process of the exocrine pancreas, including inhibition of the rate of protein synthesis and exocytosis. The former effect resulted mainly from the inhibition of amino acid transport. Lanthanum in a concentration up to 1 mM inhibited transport of different species of amino acids in an unspecific way whereas tetracaine interfered specifically with the Na⁺-dependent transport system for neutral amino acids (¹⁴C--amino-isobutyric acid). Na⁺-independent transport of neutral amino acids (³H-leucine) was not affected. Transport inhibition was correlated to the activity of the Na⁺, K⁺-ATPase system which was measured in isolated plasma membrane fractions. At higher concentrations (5–10 mM) some uptake of lanthanum into the cells by limited endocytosis was observed. At lower concentrations lanthanum seemed to bind exclusively to certain components of the plasma membrane, mainly at the lateral and basal cell surface. Even at a concentration of 5–10 mM, no binding to the apical surface occurred. Similarly, no binding of lanthanum was observed to the limiting membrane of isolated zymogen granules, while mitochondria, contained in the same fraction, showed considerable binding affinity. The action of lanthanum and tetracaine on membrane carrier systems did not affect the interior organization of the plasma membrane. Particle density and distribution in freeze-fracture replicas as well as the submembrane microfilamentous-microtubular system and the junctional elements remained unaffected.Supported by a grant from the Deutsche Forschungsgemeinschaft (Ke 113/10). The expert technical assistance of Miss Helga Hollerbach and Miss Hiltraud Hosser and the editorial help of Mrs. Gisela Lesch is gratefully acknowledged     

Effect of jejunoileal bypass in the rat on the enteroinsular axis

The effect of jejunoileal bypass (JIB) on the enteroinsular axis was studied in vivo and in vitro in the rat. Glucose, insulin and GIP responses to oral glucose were compared in JIB and control rats. The effect of glucose and GIP on insulin release from the isolated perfused pancreas of the same animals was investigated to determine if JIB altered the sensitivity of the beta cell. Immunocytochemical studies of gut and pancreas were also carried out. Glucose, insulin and GIP responses to a glucose load were blunted after JIB, although basal GIP levels were elevated in these animals. The insulin response of the perfused JIB pancreas to GIP was 70% reduced from controls although the insulin response to glucose appeared normal. The size and area of JIB islets were unchanged from controls as was the distribution of insulin, glucagon, somatostatin and pancreatic polypeptide. GIP immunoreactive cells were present in all regions of the intestine including the JIB blind loop. This study confirms the findings of others that a relationship exists between reduced GIP and insulin response to oral glucose after JIB, and indicates that a decrease in sensitivity of the beta cell to GIP occurs following JIB that is not rapidly reversible. GIP secreted from blind loop mucosa may contribute to the high basal GIP found in JIB rats and may be causally connected to the fall in beta cell sensitivity.     

Studies on secretory glycoproteins in the rat exocrine pancreas

Summary Using a double-label technique on isolated rat pancreatic lobules, the rate of synthesis and discharge of regular and fucosylated secretory proteins was studied under control conditions and after in vivo prestimulation with caerulein. Both labeled leucine and fucose were incorporated into pancreatic proteins at a linear rate, which was potentiated by in vivo stimulation. In pulse-chase experiments both regular and fucosylated secretory proteins were discharged into the medium in parallel. The in vivo pretreatment with caerulein caused an earlier discharge and increased the total amount released. Kinetic analysis of unstimulated (baseline) discharge of both classes of secretory proteins indicated a striking in vitro sensitivity by the previous in vivo treatment with caerulein.The biochemical data were compared to the fine structure of the Golgi complex under both control and prestimulated conditions. The Golgi stacks were composed of four to six individual cisternae which in some cases were connected by intercisternal pores. Transporting vesicles were observed fusing along the total length of the outermost cisterna on both the cis- and transside and with the lateral ends of the intermediate cisternae. Under control conditions only the last trans-cisterna contained some electron opaque material; in vivo prestimulation led to distension and filling of all cisternae in an individual Golgi-unit. Numerous stages of transformation of the last transcisterna into condensing vacuoles were observed, lending support to the hypothesis that during packaging of secretory products the membranes of the Golgi complex undergo a continuous turnover.Supported by a grant from the Deutsche Forschungsgemeinschaft, Bonn-Bad-Godesberg (Ke 113/10). The competent technical assistance of Miss Hiltraud Hosser and Miss Helga Hollerbach and the editorial help of Miss Annemarie Erben is gratefully acknowledged     

Studies on secretory glycoproteins in the rat exocrine pancreas

Summary A fetuin, fucosyl transferase has been identified in the smooth microsomal fraction from the rat exocrine pancreas. This enzyme is involved in the glycosylation of secretory proteins and is bound to membranes, predominantly of the Golgi complex. Optimal in vitro conditions for the assay of the enzyme activity were established: a pH of 5.5–6.0, a temperature of 21° C and concentrations of Mg^{+ +} at 5.0 mM and ATP at 2.0 mM.Supported by a grant from the Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg (Ke 113/10). Dedicated to Professor Helmut Ferner, Vienna, on the occasion of his 65^th birthday.     

Ultrastructural analysis of the effect of vagotomy on the state of the exocrine portion of the rat pancreas

Dynamics of reactions in the main components of the exocrine part of the rat pancreas (capillary, nerve, pancreocyte) was subjected to ultrastructural analysis at bilateral subdiaphragmatic vagotomy within 24 hours--30 days. It was stated that certain ultrastructural shifts developed in all the components mentioned above; at first they are within the limits of physiological parameters (the first three days), and then destructive processes occur (up to destruction of a part of cells) reaching their maximum by the end of the first--beginning of the second week and having a focal character. Then compensatory-recovery rearrangements begin to predominate, and by the 30th day they result in a considerable but not yet complete normalization of the ultrastructural organization of the gland. Three stages (phases) can be mentioned in the development of the neurodistrophic process: the first--stress reaction of the organ and the whole organism to the operation; the second--predominance of destructive changes; the third--development of compensatory-adaptive processes. Possible mechanisms of the rearrangements occurring are discussed.     

Biochemical changes in the exocrine pancreas of rats fed caffeine

Coffee consumption has been associated with pancreatic disorders, but the mechanisms involved remain to be elucidated. This investigation examines the effects of caffeine consumption on the structure and function of the exocrine pancreas. Groups of rats, fed ad libitum commercial laboratory diet, were given drinking water which contained either caffeine (0.09 mg/ml) or nothing at all. The rats were allowed drink ad libitum and were killed 6 weeks later. Final body and pancreatic weights were not significantly different between the groups at the end of the experimental period. Although no ultrastructural effects of caffeine on the pancreas were observed, amylase and trypsinogen activity was 35% higher in pancreatic homogenates from caffeine-fed rats compared with controls. In addition, levels of immunoreactive cationic trypsin(ogen) were 41% higher than control levels in pancreases from the caffeine-fed rats. Also, the circulating levels of amylase and immunoreactive cationic trypsin(ogen) in serum were lower in the caffeine group compared with controls. When dispersed pancreatic acini isolated from the caffeine-fed rats were incubated in vitro with increasing concentrations of CCK-8 or nicotine, the rate of release of amylase, trypsinogen, and chymotrypsinogen was lower than in the control rats. This effect did not appear to be due to inhibition of protein synthesis, as determined by [3H]leucine incorporation into acinar protein. These data suggest that prolonged intake of caffeine at common dietary levels inhibits pancreatic enzyme secretion.     

The morphological changes of exocrine pancreas in chronic pancreatitis

The following changes were found by either light or electron microscopic observation of the pancreas in spontaneously developed chronic pancreatitis models (WBN/Kob rats, spontaneously hypertensive rats, and rats with common bile-pancreatic duct stones) and in experimental models of chronic pancreatitis (alcoholic pancreatitis, ischemic pancreatitis, and obstructive pancreatitis): 1) the units of lobules, which were constituted by acinar cell deletion, ductular proliferation, and fibrosis; and 2) tortuous or helical ductal channels of pancreatic ducts with periductal fibrosis, which had many crater-like depressions and very long cilia in their inner surface. These are considered to be the results of obstructive pancreatitis, which are caused by the reactions of defensive factors against the increase of pancreatic duct pressure, including the apoptosis of acinar cells, the hyperplasia and hypertrophy of duct cells, a tighter junctional complex of duct cells, and periductal fibrosis.     

Ultrastructural changes in rat palatal epithelium after beta-aminopropionitrile.

Beta-Aminopropionitrile (BAPN) retarded or suppressed epithelial changes in the medial edge of the palatal process in later stages of gestation in rats. Programmed cell death did not follow the usual pattern, and only a few lysosomes were observed on day 18 of gestation. The sensitivity of the medial epithelium to BAPN appeared to be different in various areas of the palatal epithelium; the epithelium on the anterior region of the palatal process was hypertrophied and keratinized, while posteriorly the medial or neighboring epithelium was very thin and, in neonatal rats, the covering was absent. A basal lamina was distinct in the anterior region and indistinct or fragmented posteriorly. Collagen fibers did not develop adjacent to the basal lamina, and an amorphous material was scattered throughout the mesenchymal tissue. These findings suggest that BAPN decreases the "connecting capacity" between mesenchyme and epithelium, and results in a modification of epithelial changes.     

Circadian rhythmicity in the rat exocrine pancreas: chronomorphological patterns

Circadian rhythmicity of the structural morphometric model of rat endocrine pancreas has been studied in 24 Wistar female rats, four months old, kept in LD 12:12. The following parameters were evaluated: the volume fractions of nucleus and cytoplasm of exocrine cells, the size distribution and number in unit tissue volume of acinar cell nuclei, the mean nuclear diameter, the shape coefficient of glandular acini (that is the ratio acinar area/perimeter2 which indicates the shifting of structures from circularity). A statistically significant circadian rhythm was demonstrated for the shape coefficient of glandular acini. Results obtained in the present experiment are compared with data recorded in a previous study.