The Thromboxane/Prostacyclin Balance in Guinea Pig Cochlea

Abstract

Thromboxane and prostacyclin as metabolites of arachidonic acid are substances with opposite effects. While the first acts vasoconstrictively and is accumulated in impaired tissue, the latter is attributed as cytoprotective, vasodilative substance. They represent the opposite pole of the same homeostatic mechanism and their ratio reflects the viability and responsiveness of the corresponding tissue to stimuli, such as hypoxia, vascular impairment or metabolic changes (Oates and Fitz- Gerals, 1985). The balance between thromboxane and prostacyclin can be selectively influenced by drugs favouring the last (Deckmyn et al., 1983). This is also possible in the vital cochlea where these substances can cross the blood-labyrinth barrier (Ernst et al., 1987). Although the involvement of prostanoids in drug ototoxicity affecting the hair cells is hardly credible (Schacht, 1986), it remains tempting to speculate on changes of eicosanoids linked to alterations of the non-sensory tissue caused by either noise or e.g. loop diuretics (McFadden, 1986; Rybak et al., 1986). It was demonstrated by Tachibana and Nishimura (1986) that precursors of arachidonic acid are preferably incorporated in non-sensory cochlear structures, i.e. stria vascularis and spiral ligament. These findings correspond to what was found in the CNS (Keller et al., 1985).