Respiratory tract eicosanoid measurement using microdialysis sampling and GC/MS detection.

Abstract

Eicosanoids are important mediators in many physiological and pathophysiological conditions. Sampling the eicosanoids remains a challenge, particularly in the respiratory tract. We examined the possibility that microdialysis might offer a means for sampling the large airways which would provide profiles of local eicosanoid levels before and after challenge. Guinea-pigs were anesthetized by ip injection of urethane and a tracheotomy performed. Microdialysis probes were inserted 2 cm into the tracheal opening, and samples were collected for 1 h intervals over 5 h. Injections of arachidonic acid, leukotriene (LT) D4, or saline vehicle were made iv at the beginning of the third hour. Prostaglandins (PG) E2, D2, F2 alpha and 6-keto-F1 alpha and thromboxane (TX) B2 were determined by GC/MS. Significant post-treatment increases in levels were observed following the injection of arachidonic acid for all eicosanoids except 6-keto-PGF1 alpha. The greatest change was an 8.1-fold increase for PGD2 (P < 0.025) while the smallest change was a 3.5-fold increase for TXB2 (P < 0.025). Intravenous administration of LTD4 caused significant increases in levels of PGE2 (P < 0.025), PGF2 alpha (P < 0.05) and 6-keto-PGF1 alpha (P < 0.025) in the first hour after challenge. No increase was observed in control experiments following saline injection. These results indicate that microdialysis provides a useful methodology for sampling local eicosanoid production.