Distortion product otoacoustic emissions in normal and impaired adult ears.

Distortion product otoacoustic emissions (DPOEs) were recorded in a group of normally hearing subjects (29 ears) and a group of subjects whose conditions were diagnosed as sensorineural hearing loss (23 ears) to study any correlation that might exist between DPOE characteristics and hearing impairment of different configurations. Three different DPOE paradigms have been used to investigate the influence of different test parameters on the DPOE data for normal and hearing-impaired ears. All normally hearing ears demonstrated detectable DPOEs, provided that the primary tone level was above a certain value. Hearing-impaired ears produced substantially reduced DPOEs compared with normally hearing subjects when the primary frequencies f1 and f2 corresponded to the region of hearing loss. Our data also suggested that, in general, more than one f2/f1 ratio is needed to examine any particular frequency region. The DPOEs provide frequency-specific information about cochlear function, which after further development, may form a basis for a noninvasive, objective method of evaluating cochlear function.

The role of fatty acids in the regulation of brush-border Ca2+ transport.

The role of the fatty-acid composition of the intestinal brush-border membrane in the control of transmembrane Ca2+ transport was examined by in vitro acylation of endogenous phospholipids. The initial rate of Ca2+ uptake into brush-border membrane vesicles was stimulated 1.6-fold by incubation with 50 microM linoleoyl CoA, which was the most effective CoA ester examined. Oleoyl CoA was also active, but stearoyl CoA, palmitoyl CoA and arachidonyl CoA displayed no activity. The effect of linoleoyl CoA was specific for Ca2+ transport; sodium-dependent phosphate uptake was slightly inhibited and the activity of alkaline phosphatase, a brush-border enzyme, was unaffected. Incubation of brush-border vesicles with either stimulatory (oleate) or nonstimulatory (stearate) CoA esters resulted in the incorporation of fatty acid into the four major phospholipid classes, suggesting a fatty-acid specificity of the Ca2+ transport phenomenon. These results are consistent with the hypothesis that fatty acids are important elements in the control of brush-border Ca2+ transport.