Rabbit mononuclear leukocytes cause contraction of isolated aorta by the release of serotonin

Objective: The aim of this study was to examine the vasoactive effects of rabbit isolated mononuclear leukocytes, and to identify the mediators responsible for those vasoactive effects. Methods: Mononuclear leukocytes (MNLs) were isolated from New Zealand White rabbit whole blood, suspended at 5x10(7) cells/ml and incubated for 30 min at 37 degrees C. This cell suspension, or the cell-free supernatant from this suspension, were then examined for vasoactive effects in rabbit isolated thoracic aorta. Results: Both the MNL suspension and the cell-free supernatant from this suspension caused endothelium-independent contraction of aortic ring, both from resting tension and when pre-contracted. The MNL suspension caused a significantly greater contraction than the MNL supernatant under all conditions. The contractions to the MNL product were significantly inhibited by the 5-HT2, receptor antagonist ketanserin (0.1 mu M), but not by the alpha(1)-adrenoceptor antagonist prazosin (10 mu M). High-performance liquid chromatography (HPLC) analysis showed that the MNL supernatant contained serotonin (5-hydroxytryptamine, 5-HT) at an average concentration of 5 mu M. Conclusions: We conclude that MNLs cause contraction of rabbit isolated aortic rings by the release of 5-HT. (C) 1999 Elsevier:Science B.V. All rights reserved.