Based on the concept that ischemia is an important factor in the pathogenesis of acute pancreatitis, we developed a new model of complete ischemia/reperfusion of the pancreas in the rat. The aim of this study was to investigate the microcirculation of the pancreas after complete and reversible ischemia at different times after reperfusion by using intravital fluorescence microscopy. In addition, the effect of ischemia/reperfusion on the pancreas was assessed by means of light and electron microscopy and measurement of serum pancreas amylase concentration. In 35 adult Sprague-Dawley rats ischemia of the pancreas was induced by temporary occlusion of the four supplying arteries. Sham-operated animals served as controls (group A). After periods of 30 min (group B), 60 min (group C) or 120 min (group D) of ischemia the organ was reperfused. To exclude the influence of hypovolemia on microcirculation in group E (120 min ischemia) hydroxyethylstarch (HES) was given i.v. to maintain central venous pressure at baseline values. For intravital fluorescence microscopy the pancreas was exteriorized on a stage and quantitative analysis of microcirculation, including functional capillary density and leukocyte-endothelium interaction, was performed after 30 min, 1 h and 2 h of reperfusion. Serum pancreas-amylase was measured at control (prior ischemia) and at 2 h after reperfusion. Tissue samples for light and electron microscopy were taken 2 h after reperfusion. In sham-operated animals, functional capillary density (FCD) remained within baseline values (FCD 407.7 +/- 9 cm-1) during reperfusion. Dependent on the time of ischemia and time of reperfusion a gradual reduction in functional capillary density was observed; after 2 h of ischemia only 35% of capillaries were perfused (FCD 140.9 +/- 28.3 cm-1). Reduced functional capillary density was associated with an increase of perfusion heterogeneity to a maximum of 0.65 +/- 0.12, as against 0.13 +/- 0.02 in control animals. With a 2 h ischemia leukocyte-endothelium interaction was enhanced after 0.5 h of reperfusion (8-fold increase of adherent leukocytes in comparison to control) followed by a further significant increase until 2 h after the beginning of reperfusion. Amylase concentration after ischemia of 2 h (2967 +/- 289 U/l) was significantly higher as compared to controls (1857 +/- 99 U/l). Differences between group E and D were not observed. Pancreatic tissue injury was ascertained by histopathological studies. These results indicate that complete ischemia/reperfusion of the pancreas induces pancreatic microvascular failure. The severity of changes depends on duration of ischemia and duration of reperfusion. The morphological and biochemical changes suggest that ischemia/reperfusion causes an inflammatory reaction as observed in acute pancreatitis.
OPS imaging is a valid noninvasive method that analyzes the pancreatic microcirculation as accurately as the established intravital microscopy technique and therefore could be useful for clinical research and diagnosis during transplantation and operations.
To analyze the role of individual glycosylation pattern on PRL biopotency, monomeric prolactin (PRL), secreted by human prolactinoma cells in culture, was isolated by gel filtration and separated by affinity chromatography on Concanavalin A-Sepharose or Lentil-Agarose. These lectins allowed the isolation of PRL glycoforms containing either biantennary, mannose-rich or fucosylated complex carbohydrate structures, respectively. Endoglycosidase treatment and carbohydrate content of PRL was found to be consistent with N-linked oligosaccharides of mannose-rich structure and complex units terminated in sialic acid. Mannose-rich PRL and PRL with biantennary oligosaccharides promoted cell growth of rat lymphoma cells to a diminished extent compared to non-glycosylated PRL (NG-PRL), indicating that the two major types of carbohydrate structure are able to decrease the intrinsic bioactivity of PRL. Metabolic clearance of the various forms of PRL in rats was also found to be highly dependent upon hormone glycosylation. The various glycosylated forms (G-PRLs) proved to be totally eliminated from the circulation within 60 min, faster than NG-PRL 10% of which was still present at that time. Mannose-rich or biantennary G-PRLs were differently cleared in a biphasial fashion with a similar rapid phase of about 2 min followed by distinct slow phases of 12 and 27 min, respectively. The presence of fucose did not alter this distribution. In contrast, NG-PRL was eliminated with a half-time of approximately 5 min, followed by a very slow disappearance over several h. It thus appeared that glycosylation increased the metabolic clearance rate of PRL from 0.13 +/- 0.07 ml/min for NG-PRL to 0.47 +/- 0.12 ml/min for PRL with biantennary carbohydrate chains and 0.8 +/- 0.2 ml/min for the hormone with mannose-rich oligosaccharides. The distribution of PRL to target and elimination organs was also found to be different according to the carbohydrate structure present in the hormone. NG-PRL and mannose-rich G-PRL showed higher incorporation in liver than biantennary G-PRL which was preferentially eliminated by the kidney. Altogether, the current data show that addition of oligosaccharides to PRL as well as carbohydrate structure contribute to modulate both the duration of the hormone in the blood and its distribution to different organs. It is proposed that glycosylation may selectively down-regulate PRL action at individual target tissues.
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