Hydrocortisone induces an increase of amylase content in individual zymogen granules from rat pancreas

Heterogeneous distribution of plasma membrane glycoconjugates in pancreatic acinar cells

Flow-cytometric studies of lectin binding to individual acinar cells have been carried out in order to analyse the distribution of membrane glycoconjugates in cells from different areas of the pancreas: duodenal lobule (head) and splenic lobule (body and tail). The following fluoresceinated lectins were used: wheat germ agglutinin (WGA), Tetragonolobus purpureus agglutinin (TP) and concanavalin A (Con A), which specifically bind to N-acetyl D-glucosamine and sialic acid, L-fucose and D-mannose, respectively. In both pancreatic areas, two cell populations (R1 and R2) were identified according to the forward scatter (size). On the basis of their glycoconjugate pattern, R1 cells displayed higher density of WGA and TP receptors than R2 cells throughout the pancreas. Although no difference in size was found between the cells from duodenal and splenic lobules, N-acetyl D-glucosamine and/or sialic acid and L-fucose residues were more abundant in plasma membrane cell glycoconjugates from the duodenal lobule. The results provide evidence for biochemical heterogeneity among individual pancreatic cells according to the distribution of plasma membrane glycoconjugates.

The recovery of acute pancreatitis depends on the enzyme amount stored in zymogen granules at early stages

Little is known about the changes in pancreatic enzyme storage in acute pancreatitis. We have performed flow cytometric studies of zymogen granules from rats with acute pancreatitis induced by hyperstimulation with caerulein. A comparison was made with rats treated with hydrocortisone (10 mg/kg/day) over 7 days before inducing pancreatitis in order to find out whether the amount of enzymes stored in the pancreas plays a key role in the development of pancreatitis. The potentially therapeutic effect of L-364,718 (0.1 mg/kg/day, for 7 days), a CCK receptor antagonist, was assayed in the rats with caerulein-induced pancreatitis which had previously received the hydrocortisone treatment. A significant increase in the intragranular enzyme content was observed 5 h after hyperstimulation with caerulein. The highest values were reached in the rats previously treated with hydrocortisone. The greatest pancreatic enzyme load was parallel to the highest values in plasma amylase, edema and haematocrit observed. Acute pancreatitis was reversed seven days later. At this stage smaller granules appeared in the pancreas whose enzyme content was similar to that of controls when no treatment was applied after pancreatitis. In contrast, L-364,718 administration prevented the favourable evolution of pancreatitis since the antagonism exerted on CCK receptors induced a blockade of secretion of the large amounts of enzymes stored in the pancreas. Moreover, the enzyme content in zymogen granules was below normal values since the stimulatory CCK action on enzyme synthesis can be inhibited by L-364,718. Our results suggest that the efficiency of CCK antagonists, as potential therapy, would also depend on the load of enzymes in the pancreas when acute pancreatitis is produced.

Zymogen granule alterations in caerulein-induced pancreatitis developed during continuous hydrocortisone administration

BACKGROUND

The amount of enzymes stored in individual zymogen granules and the glycosylation of their membrane have been analysed in rats with acute pancreatitis induced by caerulein after hydrocortisone treatment. The consequences of prolonging hydrocortisone administration after pancreatitis and the use of the cholecystokinin (CCK) receptor antagonist, L-364,718, have also been evaluated.

MATERIALS AND METHODS

Analysis was performed using flow cytometry.

RESULTS

Caerulein-induced pancreatitis in rats previously treated for 7 days with hydrocortisone (10 mg kg-1 per day) revealed alterations in enzyme storage in the pancreas. Significant increases in amylase and trypsinogen contents in zymogen granules were observed, an effect associated with a reduction in L-fucose glycoconjugates. Pancreatitis persists 7 days later if hydrocortisone treatment is prolonged. At this stage, a reduced granule fucosylation was still observed, and a significant decrease in the amount of trypsinogen stored in the granules was found. However, hydrocortisone administration led to an increase in intragranular amylase quantities up to normal values, even when L-364,718 was simultaneously administered, but it reverted to plasma as a consequence of pancreatitis. The amount of N-acetyl D-glucosamine in the zymogen granule membrane was not altered by caerulein acute pancreatitis induced under continuous hydrocortisone treatment, but it was decreased by the administration of L-364,718 over 7 days after pancreatitis induction.

CONCLUSIONS

The administration of hydrocortisone after the development of pancreatitis prevented recurrence of the disease. L-364,718 proved to be detrimental, not only failing to reduce the symptoms of pancreatitis but also altering the glycoproteins of zymogen granule membrane.

Effect of cholecystokinin blockade on the recovery of alterations induced by acute pancreatitis in glycoconjugates of rat zymogen granules

Lectin-binding studies have been performed on rat zymogen granules to investigate alterations in the carbohydrate membrane composition that occur in acute pancreatitis induced by caerulein. The influence of treatment with hydrocortisone for seven days before inducing pancreatitis was also studied. Lectin labeling on zymogen granules was also analyzed seven days after inducing pancreatitis in rats that had previously received a hydrocortisone treatment. During this period L 364,718 (0.1 mg/kg)--specific cholecystokinin (CCK) receptor antagonist--was administered daily to some of the rats, and no treatment was applied to others. Using fluorescein-labelled T. purpureus (TP)lectin, a significant decrease in the amount of L-fucose in the granule membrane was observed in rats with caerulein-induced pancreatitis. This effect was directly caused by the pancreatitis and was not influenced by previous hydrocortisone treatment. Seven days later, the density of TP receptors in the granule membrane was similar to the controls both in L-364,718-treated and untreated rats. Therefore, we suggest that endogenous CCK is not an essential factor in the recovery of L-fucose containing glycoconjugates the granule membrane after pancreatitis. Acute pancreatitis did not alter the expression of wheat germ agglutinin (WGA) receptors in the zymogen granule membrane. WGA specifically binds N-acetyl glucosamine and sialic acids. L 364,718 administered for seven days after inducing pancreatitis significantly reduced WGA binding, untreated rats showed a normal zymogen granule membrane. Therefore, the blockade of CCK-induced alterations in membrane glycoconjugates enriched in N-acetyl glucosamine and sialic acid of newly formed granules after pancreatitis, a finding that could explain the delay in the regression of the disease.

Glucocorticoids regulate L-fucose glycoconjugates in rat pancreatic zymogen granules

Lectin-binding studies were performed on rat pancreatic zymogen granules to investigate the influence of glucocorticoid levels on saccharide membrane composition. The following animal groups were used: (1) control rats; (2) rats treated with hydrocortisone (1, 10 and 25 mg/kg/day) for 1, 3 and 8 days; (3) postadrenalectomized rats at days +1, +3 and +8; and (4) adrenalectomized rats receiving hydrocortisone therapy (10 mg/kg/day) for 8 days. By flow cytometry, fluoresceinated (FITC) lectins were used to measure the amount of Concanavalin A (Con A) (specific for D-mannose), wheat germ agglutinin (WGA) (specific for N-acetyl-D-glucosamine) and sialic acids and Tetragonolobus purpureus (TP) (specific for L-fucose) bound to individual zymogen granules from two subpopulations, Z1 and Z2, identified on the basis of their forward and side scatter properties. The molar ratio of the different FITC-lectins revealed significant differences in the glycoconjugate composition of Z1 and Z2 granules, the Z1 granules showing higher ratios of N-acetyl-D-glucosamine:L-fucose and N-acetyl-D-glucosamine:D-mannose, both in control, adrenalectomized and hydrocortisone-treated rats. It was also observed that N-acetyl-D-glucosamine and/or sialic acids were more abundant than L-fucose and D-mannose in the zymogen granule membrane. Z1 and Z2 granules had different glycosylation patterns. Neither adrenalectomy nor hydrocortisone treatments varied the Con A binding to zymogen granules. An increase in WGA binding was only induced by administration of very high doses of hydrocortisone (25 mg/kg/day) for 8 days, an effect not directly related to glucocorticoids. In contrast, a correlation between the FITC-TP labelling and glucocorticoid levels can be established, so that, in a time-dose dependent way, an increase was observed in zymogen granules of rats treated with hydrocortisone while a decreased TP binding was found in adrenalectomized rats-an effect which was reversed with hydrocortisone therapy. Therefore, glucocorticoids exert a direct influence on the saccharide composition of rat pancreatic zymogen granules, regulating the amount of L-fucose glycoconjugates, with Z2 granules more sensitive than Z1 ones.