Effect of arachidonic acid on the inner ear blood flow measured with a laser Doppler flowmeter

The present study was undertaken to clarify the effect of arachidonic acid (AA) on the inner ear blood flow of rats as measured with a laser Doppler flowmeter. With the rats under anesthesia with sodium pentobarbital, the middle ear was approached ventrally and a laser Doppler probe was positioned over the lateral wall of the cochlea. Drugs were administered via the subclavicular artery. The dose range of each drug was determined so as not to affect the systemic blood pressure. The AA (20 to 70 micrograms) increased the inner ear blood flow dose-dependently; this effect was abolished by indomethacin (5 mg orally). Both prostaglandin E2 (PGE2; 1 to 50 ng) and CS-570, a PGI2 analogue (12.8 to 25.6 ng) caused a dose-dependent increase in the inner ear blood flow. The response of PGI2 was shorter than that of PGE2. On the other hand, a stable thromboxane A2 (STA2; 30 to 80 ng) decreased the inner ear blood flow dose-dependently. Administration of PGF2 alpha (0.2 to 3 micrograms) showed no effect on the inner ear blood flow. These results indicated that the effect of AA was mediated mainly via PGI2 and PGE2.