Prostaglandin synthesis by the cochlea

Abstract

The exogenous and endogenous syntheses of prostaglandins (PG's) by the cochlea of adult mongolian gerbils were studied in vitro . After incubation of the whole membraneous cochlea with [ 3H]-arachidonic acid (AA), syntheses of PGF 2α, 6-keto PGF 1α, PGE 2, thromboxane (TX) B 2 and PGD 2 were evidenced in this order. The synthesis of radioactive PG's was almost completely inhibited by incubation with 10 −5 M indomethacin. No significant amounts of those PG's were detected by radioimmunoassay (RIA) in the cochlea obtained from animals killed by microwave irradiation at 5.0 kw for 0.8 sec. However, when the homogenate of the whole membraneous cochlea obtained from animals without microwave irradiation was incubated at 37°C for 0–15 min, PGD 2, PGE 2, PGF 2α and 6-keto PGF 1α were found to be formed from endogenous AA in the cochlea by RIA. PG's were formed already at 0 time to considerable level (PGD 2, PGF 2α and 6-keto PGF 1α, 90–120 pg/cochlea; PGE 2, 370 pg/cochlea), reached to the maximum level (PGD 2, PGF 2α and 6-keto PGF 1α, 170–200 pg/cochlea; PGE 2, 500 pg/cochlea) at a 5-min incubation, and then gradually decreased. On the other hand, the amount of TXB 2 was lower than the detection limit by RIA (<50 pg/cochlea) even after the incubation. The cochlea was dissected into three parts: organ of Corti + modiolus (OC + M), lateral wall (LW), and cochlear nerve (CN), and then PG's formed by these tissues were determined after a 5-min incubation of the homogenates. In the CN and OC + M, PGE 2 was the major PG (100 and 160 pg/tissue, respectively), and the amounts of PGD 2, PGF 2α and 6-keto PGF 1α were about 1 3 of those of PGE 2. In the LW, the amounts of PGD 2, PGE 2, PGF 2α and 6-keto PGF 1α were about the same level (70–100 pg/LW).