Various cells release a stable small molecule that inhibits endothelium-dependent relaxation. Liu, James J., Bing Xie, Peter J. Thurlow, James S. Wiley, and Joan R. Chen. Vascular Biology Unit, University of Melbourne Austin Hospital, Departments of Cardiac Surgery, Hematology, and Medicine, Heidelberg, VIC 3084, Australia
APStracts 2:0173H, 1995.
Previous studies have shown that neutrophils release a stable factor that inhibits endothelium-dependent relaxation. In the present studies, the effects of supernatants derived from various cells on endothelium-dependent relaxation were studied. Cells were obtained from seven sources: human hematopoietic cells including mononuclear leukocytes (MONO), polymorphonuclear leukocytes (PMNs) and chronic lymphocytic leukemia (CLL) cells; cells of the cardiovascular system including human endothelial cell line ECV304, human smooth muscle cells and rat myocardial cells; and the tumor cell line HPB. These isolated or cultured cells were incubated for 1 hour in Krebs' solution to release the factor. The results showed that the supernatants from 105cells/ml of all cells except the tumor cell line HPB produced a potent inhibitory effect on endothelium-dependent relaxation of rat aortic rings in response to acetylcholine and Ca2+ ionophores A23187 and ionomycin; but not on endothelium-independent relaxation to nitroprusside and glyceryl trinitrate. When the concentration increased to 106cell/ml, the supernatants from the tumor cell line HPB also slightly but significantly inhibited endothelium-dependent relaxation. The potency order was PMNs = MONO = CLL cells > cardiac cells > smooth muscle cells > the endothelial cell line ECV304 > the tumor cell line HPB. It seems that the hematopoietic cells and the cardiac cells are more active in release of the factor. The effect of this factor was rapid in onset and hard to wash out. A cyclooxygenase inhibitor or a thromboxane A2/prostaglandin H2 receptor antagonist partially but significantly reduced the effect of the factor. In contrast, 5-lipoxygenase inhibitors potentiated its effect. However, these agents did not inhibit the release of the factor from the cells. Chemical characterization showed that the factor was stable to heat, extreme pH and protease, with a Mr under 500 Dalton. In conclusion, a naturally occurring, stable, non-protein, small, novel molecule produces a potent, rapid, long-lasting, inhibitory effect on endothelium-dependent relaxation. Since it can be released from various cells, it may have functions beyond the inhibition of the vascular relaxation. 

Received 6 July 1994; accepted in final form 20 April 195.
APS Manuscript Number H585-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  2 May 1995.