Studies on prostaglandin synthetic activities in mouse salivary glands.

Prostaglandin (PG) synthetic activities in mouse salivary glands were studied. When mouse submandibular gland homogenate was incubated with radioactive arachidonic acid, three radioactive metabolites were detected which were identified with PGE2, PGF2α, and PGI2. Thromboxane A2 (TXA2) and PGD2 were not detected. Optimal biosynthesis was obtained in an 0.05M sodium phosphate buffer at pH7.4. Under this condition PG formation was linear up to the arachidonic acid concentration of 40μM. Reduced glutathion did not affect the biosynthesis, but catecholamines i.e. L-adrenaline, L-noradrenaline and L-isoproterenol produced only a small stimulation of all three PG synthesis in the submandibular gland homogenate. Major cyclooxygenase products of the parotid gland and the sublingual gland were also PGE2, PGF2α, and PGI2. Total PG synthetic activities of three PGs in both the submandibular gland and the parotid gland were higher than those in the pancreas, liver and brain, and that of the submandibular gland was the highest of the examined tissues. Both PGE2 and PGI2 synthetic activities were higher in the order of submandibular gland>parotid gland>sublingual gland. PGF2α synthetic activity was higher in the order of parotid gland>submandibular gland>sublingual gland PGI2 synthetic activity in the submandibular gland of male mouse was about 1.5 times higher than that of female one.Next, the relationship between PG metabolism and DNA synthesis in isoproterenol (IPR)-stimulated salivary glands was investigated. Administration of indomethacin, a PG synthesis inhibitor, suppressed the effect of IPR on the DNA synthesis in the submandibular gland and the parotid gland. Cyclooxygenase activity did not change in IPR-stimulated salivary glands. From these results, it is suggested that PGs are involved in the stimulation of the DNA synthesis by IPR in the salivary glands. It is also possible that IPR activates not a cyclooxygenase, but a phospholipase, in the salivary glands.