Brain-type prostaglandin D synthetase occurs in the rat cochlea

Prostaglandin D synthetase [(5Z, 13E)-(15S)-9 alpha, 11 alpha-epidioxy-15-hydroxyprosta-5,13-dienoate D-isomerase, EC 5.3.99.2] activity was found in the high-speed (100,000 x g, 1 hr) supernatant of the homogenate of the cochlea of adult rats. The specific activity (14.0 nmol/min per mg of protein) was 6- to 7-fold higher than that in the central nervous system. The enzyme showed full activity with 1 mM glutathione, 1 mM 2-mercaptoethanol, or 0.5 mM dithiothreitol and was almost completely inhibited by 1 mM 1-chloro-2,4-dinitrobenzene. The Km value for prostaglandin H2 was about 20 microM. These catalytic properties are the same as those of rat brain prostaglandin D synthetase but different from those of rat spleen prostaglandin D synthetase. The activity decreased to less than 20% of its initial level after incubation with excess amounts of a polyclonal or a monoclonal antibody against the brain enzyme, but the activity remained unchanged with a polyclonal antibody against the spleen enzyme, indicating that the brain-type enzyme synthesizes prostaglandin D2 in the cochlea. When cryosections of 5-week-old (adult) rat cochleas were stained by an immunoperoxidase method with antibodies against the brain enzyme, the immunoreactivity was found in inner and outer hair cells, Claudius' cells, Deiters' cells, marginal cells, basal cells, and cells of Reissner's membrane. In 8-day-old rats, the immunoreactivity was found in all of these cell types except hair cells. The immunoreactivity in hair cells was found in only one specimen from 9-day-old animals, and no immunoreactivity was found in spiral ganglion cells at any of the ages examined. These findings indicate that prostaglandin D2 is produced by the brain-type synthetase in the indicated types of cochlear cells.