Eicosanoid Synthesis and Inactivation in Healthy and Infected Chinchilla Middle Ears

Abstract

Otitis media (OM) is an inflammatory reaction of the middle ear (ME) elicited by a variety of stimuli including tubal obstruction, allergy and bacterial infection. The leukotrienes and prostaglandins are among the earliest mediators produced in response to these insults. Their measured levels in human and animal models span a broad range of concentrations. However, their baseline levels and metabolic fates are unknown for the ME. Their dynamics in the ME were examined using the chinchilla animal model, tritiated eicosanoids and a lavage procedure. Prostaglandin levels in the normal ME were 10 times higher than the 34 pg/ear observed for the leukotrienes and thromboxane B₂. These levels were significantly increased by the calcium ionophore A23187 and bacterial infection. Leukotrience C₄ was the most and prostaglandin E, the least persistent eicosanoid in the ME. Their residence time in the ME was increased by infection. The rank order of eicosanoid concentrations among comparable studies was surprisingly constant, with prostaglandin E, the most abundant and the leukotrienes the least. Comparisons of eicosanoid levels from A23187 stimulation and the infectious models sampled at 3 days suggest that the higher levels observed in the infectious models may represent basal eicosanoid production for hyperplastic ME mucosa.

Key Words:

• chinchilla
• acute otitis media
• eicosanoids
• metabolism
• A23187
• middle ear lavage