Effect of hypertension on hearing function, LDH and ChE of the cochlea in older rats

The relationship between the hypertension and the aging process of hearing organ was investigated. Twenty Wistar 3-month old rats and 20 Wistar 12-month old rats, 20 spontaneously hypertensive rat stroke-prone (SHRSP) 3-month old rats and 20 SHRSP 12-month old rats free of middle ear infections as observed under otomicroscopy, with normal tympanic membrane and auricle reflex, were selected to be divided into two experimental groups and two control groups respectively. The tail artery blood pressure was measured non-invasively. The threshold of auditory brain-stem response (ABR) was measured by Spirit™ evoked potential meter. The LDH and ChE staining in the inner ear was performed and the optical density was analyzed by the HPIAS analysis system. The results showed that there was no difference in the ABR thresholds, the activities of LDH and ChE between Wistar 3-month old group and SHRSP 3-month old group (P>0.05). The mean value of ABR threshold and the activities of LDH and ChE in the Wistar 12-month old group at relevant sections were significantly greater than those in the two 3-month old groups (P<0.05), whereas the mean value of ABR threshold and the activities of LDH and ChE in the SHRSP 12-month old group at relevant sections were significantly higher than those in the 3-month old control group (P<0.01). It was concluded that presbycusis existed in the Wistar 12-month old group rats. The glycogenosis and the abnormal secretion of neural transmitter were discerned after hypertension. All the above factors may worsen the aging of the hearing system.