Release of prostacyclin (PGI2) by the layers of corpus of rat stomach

Stimulation of prostaglandin production by (2E,6Z,10E)-7-hydroxymethyl-3,11,15-trimethyl-2,6,10,14-++ +hexadecatetrae n-1-ol (plaunotol), a new anti-ulcer drug, in vitro and in vivo

Plaunotol [(2E,6Z,10E)-7-hydroxymethyl-3,11,15-trimethyl-2,6,10,14- hexadecatetraen-1-ol], a new anti-ulcer drug, was investigated for its effect on prostaglandin (PG) production. In cultured cells of 3T6 fibroblasts, plaunotol and its main metabolite (1-carboxylic plaunotol) at concentrations of 10-100 microM increased PGE2 and PGI2 production 2- to 4-fold. These compounds increased the release of radioactive arachidonic acid from [14C]arachidonic acid prelabeled 3T6 fibroblast cells 2-fold at 30 microM, and this increase was inhibited by addition of mepacrine, a phospholipase inhibitor. Plaunotol and its main metabolite had no effect on PG cyclooxygenase activity. These results indicate that plaunotol and its main metabolite stimulate PG production by activating cellular phospholipase. In gastric-mucosa slices, PGE2 and PGI2 production was increased significantly either by oral administration of plaunotol to rats at a dose of 300 mg/kg or by addition of the main metabolite to the incubation medium. All these results suggest that plaunotol increases the PG levels in gastric mucosa by stimulating the PG biosynthesis, particularly the cellular phospholipase activity. The increased levels of PG may participate in the anti-ulcer activity of plaunotol.

Phospholipase inhibition and prostacyclin generation by gastric muscularis and mucosa layers

The effects of drugs which interfere with arachidonate metabolism as well as glucocorticoid-induced anti-phospholipase proteins (APP) have been studied on PGI2 generation by rat stomach tissue. Indomethacin inhibited PGI2 generation both in vitro and ex vivo while dexamethasone was ineffective in both instances. APP inhibited PGI2 generation in vitro. The results are discussed in the light of the possible mode of action of glucocorticoids. Prostacyclin (PGI2) is the major cyclo oxygenase metabolite in the rat gastric mucosa and exerts gastroprotective actions. Therefore a correlation between the inhibition of PGI2 synthesis and the induction of gastric damage has been suggested for the non-steroidal anti-inflammatory drugs. Glucocorticoids inhibit phospholipase A2 (PLA2) by inducing in the target cells the synthesis of inhibitory proteins, the lipocortins, and consequently reduce the release of eicosanoids in a number of cells and tissues. However, there is a surprising paucity of information on the effect of glucocorticoids on arachidonic acid (AA) metabolism in the gastro-intestinal tract. Moreover, the relationship between steroid administration and gastric damage is still controversial. The present work was undertaken to investigate the effect of drugs which interfere with AA metabolism on the synthesis of PGI2 by rat stomach mucosa and by the underlying muscularis layer both in vitro and ex vivo.

A rat gastric mucosal preparation for studying agents which affect the in vitro production of prostanoids

A convenient and reproducible method for measuring the production of prostanoids from either the rat gastric mucosa or whole corpus tissue is described. Use of selective radio-immunoassay was employed to measure production of 6-keto- PGF1 alpha, the stable hydrolysis product of PGI2, and PGE2. The mucosal tissue generated approximately 10 times more 6-keto-PGF1 alpha than PGE2. Gastric muscle tissue, however, produced 2-3 times more 6-keto-PGF1 alpha than the mucosa. Exogenous arachidonic acid was found to elevate the amount of both prostanoids although the rate of formation of 6-keto-PGF1 alpha appeared to be less than that of PGE2. A possible explanation for this was that PGE2 production, in part, was non-enzymic. Mepacrine, a phospholipase inhibitor, was found to inhibit both the control amounts of 6-keto-PGF1 alpha and the increased production of this prostanoid due to exogenous phospholipase activity. The generation of prostanoids was also inhibited by indomethacin in a concentration-related manner which suggested that the method is suitable for screening non-steroidal anti-inflammatory agents in vitro or ex vivo. Preliminary results with the above method have been reported elsewhere.