| As development of our society and progress of martial high-tech, noise pollution becomes more severe, and battle environment turns more compilicated, especially in intricated high altitude conditions such as altiplano and upper air combined by noise. This multiple environment can aggravate noise trauma to body, particularly to hearing system.The purpose of this study is to investigate the effects of Puerarin on noise induced hearing loss in acute hypobaric and hopoxic environment, and to discuss the associated mechanisms.Methods Normal guinea pigs were randomly distributed into 5 groups (normal group, control group, hypobaric group, Pue-prophylactico-therapeutic group, and Pue-treated group). The last three groups were exposed to 130dB white noise in low pressure chamber, modeling low pressure environment of 5500m, which successively lasting for 8 hours. The last two groups were treated by intraperitoneal injection with Puerarin at the dosage of 150mg kg-1 per day. The animals' behavior and performance in the acute hypobaric and noising environment were observed. Acoustic brainstem response (ABR), the surface preparation and transmission electron were utilized to evaluate the hearing thresholds and cochlear morphology. To explore the, mechanism associated with Puerarin protection, hemorheology index together with serum levels of MDA and SOD were measured. Immunohistochemical stainingtechniques were used (SABC method), and immunostained sections (10 m) of both sides of cochlear basilar membrane from the first three groups were observed under a light microscopy, moreover, examined and analysed by computer image. Results1. All animals with hypobaric environment exposure had anoxic signs and symptoms to various extents, such as uneasy behavior and rapid respiration at the beginning of exposure, then turned to be decreasing activity and breath slowed down. Control group which had noise stimulation synchronously had more obvious responses compared with Pue-intervening group.2. The ABR thresholds of normal group had no changes at experimental time points(P>0.05). However, the rest four groups had obvious threshold shifts. Elevation of the ABR threshold (click) was greatest in hypobaric group just after exposure which developed up to 10.71 4.83dB SPL(P<0.01), whereas the threshold shifts come back to normal on the 8th hour after exposure. Mean threshold shifts at 1kHz & 8KHz (tone burst) of control group (ie. group with hypobaric and noising environment exposure and physiological saline injection) on the 8th hour after exposure developed up to 33.67 5.40 and 59.33 5.20dB SPL, while the mean threshold shifts of Pue-intervening group developed only 26.50 4.76 and 48.67 4.70dB SPL(P<0.01). The threshold shifts at high frequencies were significantly larger than that at low(P<0.01). Then the hearing of all groups recovered gradually, and the two Pue-utilized groups recovered more rapidly than control group(P<0.01). On the 3rd day after exposure, the ABR threshold shifts at 4kHz & 8KHz have no difference between the two Pue-utilized groups(P>0.05); while on the 7th day, the threshold shifts of Pue-prophylactico-therapeutic group at high frequencies (15.33 3.92 and 24.50 4.22dB SPL) were significantly smaller than that of Pue-treated group(19.5016.34 and 28.87 4.54dB SPL) (P<0.01).3. Morphological results were consistent with functional changes. The worst serious damages of cochlear hair cells occurred in control group and were showed in the basal turn of basilar membrane, and damages in the upper turns were lighter. And damages of outer hair cells are getting heavier from 1st row to 3rd row. Transmission electron microscope showed that edema of neuronal and hair cells, swelling of mitochondria, and injury of nerve fibers. Such morphological changes could also be observed in the two Pue-utilized groups, but they were lighter than those of control group, especially in the 2nd and 3rd turns, and the neurites.4. The hemorheological index of whole blood viscosity of...
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