OBJECTIVETo investigate the effects of atrial natriuretic peptide (ANP) on ischemia and reperfusion cochlea in guinea pigs.

METHODSThe guinea pigs were randomly allocated into four groups: experiment groups (A1 and B1) and control groups (A2 and B2). Cochlear ischemia and reperfusion was induced by thrombus and thrombolysis method. In experiment group A1, ANP was administered 10 min before the ischemic insult. In experiment group B1, ANP was administered at the beginning of reperfusion. In control groups, instead of ANP, normal sodium was injected. The blood flow of cochlea (CoBF) was monitored continuously with laser Doppler flow meter and the threshold of auditory brainstem response (ABR) was measured.

RESULTSBefore the induction of ischemia, the CoBF of experiment group A1 was higher than that of the control group A2. From the reperfusion moment to the end of the experiment, there was no difference between the CoBF of the two groups. In B1 and B2 groups, no difference could be seen between the two groups before the induction of ischemia. After reperfusion, the blood flow of control group B2 recovered to 70% of the base level, while the CoBF of experiment group B1 restored to almost the same level of the beginning. Before ischemia, the ABR threshold of the four groups had no difference. At 30 min of ischemia, the threshold of experiment group Al was lower than that of control group A2. And there was no difference in experiment group B1 and control group B2. At 30 min and 60 min of reperfusion, the threshold of experiment group B1 was significantly lower than that of control group B2. No difference could be seen between experiment group A1 and control group A2.

CONCLUSIONSAdministration of ANP at the beginning of reperfusion protects the cochlea from ischemia and reperfusion injury. The administration can not only increase the CoBF, but lower the ABR threshold.