OBJECTIVE The gastroprotective properties of prostaglandins in low concentrations are still unclear. In this study, we investigated the effects of prostaglandin E2 (PGE2), indomethacin, and intraluminally applied HCl or ethanol on intraglandular pressure, mucus thickness, acid secretion, and gastric mucosal blood flow. METHODS Glandular pressure and mucous gel thickness were measured with microelectrodes during intravital microscopy in thiobutabarbital sodium-anesthetized rats. Gastric blood flow was measured with laser Doppler flowmetry. RESULTS In pentagastrin-treated rats, glandular pressure increased significantly in response to topical (1 micrograms/mL) or intra-arterial (12 micrograms.kg-1.h-1) PGE2 from approximately 17 to 69 and 18 to 57 mm Hg, respectively, whereas blood flow, mucus thickness, and acid secretion were unaltered. Indomethacin (3 mg/kg intravenously) significantly decreased glandular pressure from approximately 20 to 11 mm Hg. Intraluminal application of 10 and 100 mmol/L HCl or 20% and 40% ethanol significantly increased glandular pressure but had no effect after indomethacin pretreatment. CONCLUSIONS Endogenous PGE2 is important for maintaining a high glandular pressure, and exogenous PGE2 potently increases glandular pressure at concentrations not altering blood flow, mucus thickness, or acid secretion. This suggests that high intraglandular pressures might be involved in gastroprotection.