Altered effect of arachidonic acid on inner ear blood flow in rats with streptozotocin-induced diabetes.

The present study was undertaken to clarify the altered effect of arachidonic acid on inner ear blood flow in rats with streptozotocin-induced diabetes by use of the laser-Doppler flowmeter. Drugs were administered intraarterially via the subclavian artery in a dose range that did not affect the systemic blood pressure. Both arachidonic acid and papaverine hydrochloride increased inner ear blood flow dose-dependently. Diabetic rats at 12 weeks, but not at 8 weeks, after the induction of diabetes showed a significant decrease in arachidonic acid response. However, there were no differences in papaverine response between diabetic and control rats. Pretreatment with ONO-3708, a selective thromboxane A2 antagonist, reversed the attenuated response to arachidonic acid found in diabetic rats. An increased response to thromboxane A2, which decreased inner ear blood flow, was also found in 12-week diabetic rats. In electrocochleograms, the latency in 12-week diabetic rats was significantly delayed compared with that in control rats, and this prolonged latency improved with insulin treatment. These results suggest that the responsiveness of inner ear blood flow to prostaglandins may be altered in individuals with diabetes mellitus.