16-16-dimethylprostaglandin-e and Hemorrhage

Histamine dihydrochloride (40 or 80 mg/kg, dissolved in 10% gelatin) subcutaneously administered to fasted rats induced few lesions in the gastric mucosa within 4 h. Pretreatment with subcutaneously administered 16,16-dimethyl prostaglandin E2 (dmPGE2; greater than or equal to 10 micrograms/kg) dose-dependently worsened mucosal injury induced by histamine, mostly with severe hemorrhage in the corpus mucosa along the greater curvature, although dmPGE2 alone did not induce any macroscopic damage. The mucosal vascular permeability as measured using Evans blue was slightly but significantly augmented by either dmPGE2 (30 micrograms/kg) or histamine (80 mg/kg) alone, but was markedly increased by histamine in the presence of dmPGE2. The increased vascular permeability occurred within 2 h, and preceded the appearance of hemorrhagic mucosal injury. Both the mucosal injury and the increased vascular permeability caused by histamine (80 mg/kg) in the presence of dmPGE2 (30 micrograms/kg) were significantly reduced by pretreatment with tripelennamine (30 mg/kg) and prednisolone (3 mg/kg), but not affected by atropine sulfate, cimetidine, methysergide, or indomethacin. The stimulation of acid secretion caused by histamine was significantly inhibited by dmPGE2 (30 micrograms/kg). Repeated administration of histamine (40 or 80 mg/kg) in the same area of the stomach in the presence of dmPGE2 (30 micrograms/kg), once or twice daily for 4 days to fed rats, induced more pronounced damage than single-dose treatment. These results suggest that dmPGE2 may aggravate gastric mucosal injury induced by histamine in rats probably due to potentiation of the increased vascular permeability caused by histamine through stimulation of H1-receptors.

Topics: Animals; Capillary Permeability; Drug Synergism; Gastric Mucosa; Gastritis; Hemorrhage; Histamine; Male; Prednisolone; Prostaglandins E, Synthetic; Rats; Stimulation, Chemical; Tripelennamine

We investigated the mechanisms by which 16,16-dimethyl prostaglandin E2 and histamine induced pancreatic hemorrhage in an experimental model of acute pancreatitis in cats. In normal animals, when large molecular weight dextran molecules were infused into the systematic circulation, they were recovered in secretin-stimulated pancreatic juice in low concentrations. Both 16,16-dimethyl prostaglandin E2 (in a dose that increased splenic artery blood flow and microvascular permeability) and histamine (in a dose that increased permeability only) increased the amount of dextran recovered in pancreatic juice. Isoproterenol, in a dose that produced the same increase in blood flow as 16,16-dimethyl prostaglandin E2 but which did not increase microvascular permeability, did not alter the amount of dextran recovered. This suggested that the increase in dextran output after 16,16-dimethyl prostaglandin E2 was primarily due to the increase in microvascular permeability caused by the drug. In other experiments, a combination of H1- and H2-receptor antagonists (mepyramine and cimetidine) protected against the development of pancreatic hemorrhage in both the prostaglandin- and histamine-treated animals. Indomethacin (a cyclooxygenase inhibitor) protected against the development of hemorrhage in the histamine-treated animals. Our results support the hypothesis that changes in microvascular permeability may be important in the pathogenesis of parenchymal hemorrhage in this model.

Topics: Animals; Capillary Permeability; Cats; Cimetidine; Drug Synergism; Female; Hemorrhage; Histamine; Indomethacin; Male; Pancreatitis; Prostaglandins E, Synthetic; Pyrilamine