ROLE OF THE 5-HT RECEPTOR IN NEUROGENIC INFLAMMATION IN FISHER-344 RAT AIRWAYS

The increased plasma protein extravasation in the airways of Fisher 34 4 rats upon stimulation of sensory nerves is in part due to the degran ulation of mast cells. In this study, we examined the role of 5-HT and histamine receptors in the capsaicin-induced increase in plasma prote in extravasation in Fisher 344 rat airways, using Evans blue as an int ravascular marker. We found that only 5-HT2 receptor agonists increase d baseline plasma protein extravasation. Furthermore, the 5-HT2 recept or antagonist ketanserin reduced the capsaicin-induced increase in pla sma protein extravasation. Combining ketanserin with the tachykinin NK 1 receptor antagonist (+/-)-RP 67,580 2-methoxyphenylethyl)-perhydrais oinositol-4-one))) abolished the neurogenic increase in plasma protein extravasation. Finally, using selective receptor agonists and antagon ists, we demonstrated that there was no modulation of the capsaicin-in duced rise in plasma protein extravasation by stimulation of either hi stamine receptors or 5-HT1, 5-HT3 and 5-HT4 receptors. We conclude tha t. in the airways of Fisher 344 rats, the neurogenic increase in plasm a protein extravasation is caused by activation of both tachykinin NK1 receptors and 5-HT2 receptors. (C) 1997 Elsevier Science B.V.