Effects of ethanol and prostaglandin on rat gastric mucosal tight junctions

The effect of 16,16 dimethyl prostaglandin E2 (PG) upon tight junctions (TJs) of adjacent surface mucous cells (SMCs) as a possible mechanism by which PGs mediate their protective effects was studied using transmission electron microscopy (TEM) and freeze fracture (FF) techniques. Fasted rats were subcutaneously injected with 10 micrograms/kg of PG or an equal volume of saline, followed 30 min later by 1 ml of oral 100% ethanol or saline. Ten or sixty minutes later, animals were sacrificed and stomach blocks were prepared for TEM or FF using standard techniques. Electron micrographs (X60,000) were obtained and the distance between SMC inner membrane leaflets was measured with a micrometer and expressed as TJ width. Stomach blocks for FF were stored at 4 degrees C, cryoprotected, freeze fractured, and photographed by TEM (X30,000). At 0.5-micron intervals, measurements of TJ strand number and depth were made. No statistical differences were found in TJ width or strand number of SMCs among the various experimental groups when compared with controls at each sacrifice time. At the 60 but not 10 min sacrifice time, TJ depth was greatly increased in cells treated with 10 micrograms/kg PG prior to ethanol exposure (P less than 0.025) in contrast to control mucosae. We conclude that 16,16-dimethyl PGE2 induces no changes in the structural composition of TJs as a possible explanation for its protective properties. The increase in TJ depth observed in ethanol exposed mucosa following PG pretreatment at the 60 min sacrifice time is most likely related to the architectural restructuring that occurs during reconstitution of damaged surface epithelium.