Effect of 16, 16 dimethyl prostaglandin E2 on aspirin-induced permeability changes in the pancreatic duct

Prostanoid imbalance in experimental acute necrotizing pancreatitis in rats

In an investigation of the pathogenesis of acute necrotizing pancreatitis (ANP) the plasma levels of TXB2, 6-keto-PGF1 alpha, and PGE2 were measured in rats. After induction of ANP by injection of 5% sodium taurocholate into the pancreatic duct, a marked increase in TXB2 levels and a slight increase in 6-keto-PGF 1 alpha levels were found. PGE2 levels decreased. Mortality was 100% within 30 h. Pretreatment with chloroquine, a phospholipase A2 inhibitor, led to a inhibition of TXB2 production, whereas 6-keto-PGF1 alpha and PGE2 levels showed a surprising slight elevation in the first 6 h. Pretreatment with chloroquine decreased mortality by 30%. Pretreatment with FPL 55712, a leukotriene synthesis blocker, caused an increase in TXB2 and PGE2 levels, whereas the formation of 6-keto-PGF1 alpha remained unaltered. Two out of nine animals survived after pretreatment with FPL 55712. The results of the present study indicate that arachidonate end products are involved in ANP. The significance of the high TXB2 levels, decreased PGE2 levels, and only slightly elevated 6-keto-PGF1 alpha levels during ANP requires further investigation. The thromboxane A2 to prostacyclin ratio may be important.

Effect of 15(R),15-methyl prostaglandin E2 and indomethacin on pancreatic secretion in man

In addition to gastric mucosal cytoprotective and antisecretory effects, prostaglandin E2 has a beneficial effect on experimental pancreatitis in some animal models, while prostaglandin synthesis inhibitors such as indomethacin and salicylates may induce pancreatitis at maximal doses. However, their effect on human pancreas is unclear. For this reason we considered it necessary to delineate their actions on human pancreatic secretion. Six healthy volunteers were studied on six separate days. On day 1, against a background of 1 pmol/kg/hr secretin, increasing doses of CCK were infused intravenously. On day 2, increasing doses of an amino acid mixture were infused intraduodenally and both studies were repeated on two occasions, following 100 micrograms 15(R), 15-methyl prostaglandin E2 per os on one and following indomethacin 50 mg orally 12 and 1 hr prior to the study on the other. Both indomethacin and PGE2 had no significant effect on pancreatic secretion in response to graded doses of CCK. 15(R),15-Methyl prostaglandin E2 and indomethacin caused a reduction of amylase output in response to the higher doses of intraduodenal amino acids. The prostaglandin E2 derivative also elicited a significant increase in basal bicarbonate output.

IN CONCLUSION

the acute effects of 15(R),15-methyl prostaglandin E2 and indomethacin on human pancreatic secretion do not seem to offer an explanation for the mechanisms of protection against experimental acute pancreatitis or an association with pancreatitis, respectively.

A model of hemorrhagic pancreatitis in cats--role of 16,16-dimethyl prostaglandin E2

Acute edematous pancreatitis was induced in cats by perfusing activated pancreatic enzymes through their pancreatic ducts. The ducts had been made permeable to large molecules by one of two techniques. The cats either received ethanol (2 ml/kg every 8 h) and aspirin (25 mg/kg every 8 h) orally for 48 h or had their pancreatic ducts perfused for 1 h with 7.5 mM glycodeoxycholate. When the same procedure was followed, but using 16,16-dimethyl prostaglandin E2 (dmPGE2) (2 micrograms/kg X h infused intravenously for 1 h before and during ductal perfusion with activated enzymes), hemorrhagic pancreatitis developed instead. To investigate whether an increase in pancreatic blood flow or microvascular permeability (both caused by dmPGE2) was important in this phenomenon, we tested the effects of isoproterenol (which increased blood flow) and histamine (which increased microvascular permeability) in the model. Thus in similar experiments, either isoproterenol (0.3 micrograms/kg . min) or histamine phosphate (2 micrograms/kg . min) was infused instead of dmPGE2. The animals that received histamine also developed hemorrhagic pancreatitis. Those that received isoproterenol did not. These observations suggested that an increase in microvascular permeability in the pancreas converted edematous pancreatitis to hemorrhagic pancreatitis. These findings suggest also that clinical studies using prostaglandins to treat patients with pancreatitis should be approached with caution.

Intestinal absorption in the mechanically obstructed rat intestine: protection by prostaglandins

Intestinal obstruction inhibits amino acid absorption. The inhibition, being dependent on the pathological changes of the absorptive epithelium, was considered as an index of injury and measured after varying periods of obstruction and after pretreatment with clindamycin, indomethacin, 16,16-dimethyl-PGE2 or arachidonic acid. A reduction in amino acid uptake was apparent after 2h of obstruction and was increasingly evident after 4, 6 and 18 h. During the late phase (after 6 h), inhibition was partly prevented by pretreatment with clindamycin, but the antibiotic was ineffective during the early phase (within the first 2 h). Bacterial colony counts of luminal contents of rats obstructed for 2 h, were not different from counts obtained in controls, but significantly lower than counts in rats that have been obstructed for 6 h. Pretreatment of rats with 16,16-dimethyl-PGE2 or with arachidonic acid prevented the early inhibitory effects of the obstruction. The findings suggest that the early inhibition in amino acid uptake may be related to metabolic changes that are correctable by the administration of 16,16-dimethyl-PGE2 or of arachidonic acid. The inhibition, during the late phase, is mainly related to an overgrowth of the enteric bacteria.

Effects of bile, infection and pressure on pancreatic duct integrity

Ionic flux, potential difference and mucosal ultrastructure have been studied in the rat bile-pancreatic duct and the effects of pressure, bile and infection on the duct evaluated. The duct remained stable after perfusion with control solution under low pressure and high pressure produced widening of intercellular spaces only. Perfusion with a bacterial solution of Escherichia coli did not effect significant changes. Sterile human bile disturbed the integrity of the duct by increasing ionic flux, altering potential difference and producing reversible ultrastructural changes of cell oedema. High pressure increased these changes. Infected human bile under high or low pressure was by far the most toxic substance tested. Perfusion with infected bile led to irreversible duct damage and complete loss of duct integrity. Pressure and infected bile may have a role in damaging duct integrity and could thus play an integral part in the genesis of acute gallstone pancreatitis.

Factors that modify the effects of prostaglandin on diet-induced acute pancreatitis in mice

Considerable disagreement exists as to whether prostaglandins improve survival in animals with experimental pancreatitis. In prior studies we have demonstrated a beneficial effect of prostaglandin in the choline deficient, ethionine supplemented diet model of acute hemorrhagic pancreatitis. In the present study we have examined the effects of 1) delaying treatment with 16,-16-dimethyl prostaglandin E2 (PGE2) till 24 h after introduction of the diet and 2) exposing animals to the test diet for 3 days instead of 2. Following delayed treatment mortality in the saline control group (57%) was significantly higher on the fourth day compared to the PGE2 treatment group (3%). However, the overall mortality on day 7 was not significantly different from that seen in the control group (43% versus 60%). In the second series of experiments, PGE2 no longer had a beneficial effect if animals were fed the CDE diet for 3 days. We would conclude from this study and others that the ability to demonstrate a protective effect of PGE2 on the pancreas is dependent upon the experimental protocol employed. Thus, the ability to demonstrate this effect is dependent upon the dose and type of prostaglandins employed, the length of exposure to the test diet, and the time at which treatment is started relative to the induction of the pancreatitis.