Synthesis of prostaglandins I2 and E2 by the canine gallbladder in vitro: studies using a new incubation chamber

Using a specially designed incubation chamber, differential synthesis and the response to added arachidonic acid (25 mM) and L-alpha-phosphatidylcholine (LAP; 2 mM) was quantified in gallbladders from male and female dogs. Prostaglandin I2 (PGI2) was the predominant prostanoid synthesized, and tissues from females produced much more PGI2 under basal conditions than did gallbladders harvested from male dogs. Addition of arachidonic acid stimulated PGI2 synthesis by almost 100 per cent. Arachidonate-stimulated mucosal and serosal production of PGI2 were (mean(s.e.m.] comparable, 343(178) and 375(89) pg/cm2/min, respectively. Gallbladders from female animals synthesized significantly more PGI2 than did tissue from males. Indomethacin inhibited PGI2 synthesis in a dose-response manner; at 7 x 10(-5) M, prostanoid synthesis was inhibited by greater than 80 per cent. Arachidonic acid did not stimulate prostaglandin E2 (PGE2) production by gallbladder tissue. LAP similarly stimulated PGI2 biosynthesis, but in contrast to the effect of arachidonic acid, the effect was significantly greater in the serosa than the mucosa, 355(107) and 213(59) pg/cm2/min, respectively. LAP also stimulated PGE2 biosynthesis by the canine gallbladder in a pattern very similar to that of PGI2. Based on the differences in response to the two agents added, we conclude that arachidonic acid and L-alpha-phosphatidylcholine stimulate prostaglandin biosynthesis via independent pathways. We advocate the use of the incubation chamber for the assessment of prostanoid biosynthesis by the gallbladder in vitro.