Angiotensin II and bradykinin regulate the expression of P-selectin on the surface of endothelial cells in culture.

Abstract

Cell-surface expression of endothelial P-selectin increases adhesion and migration of leukocytes and thus may participate in the pathogenesis of reperfusion injury and atherosclerosis. Angiotensin II (Ang II) is also thought to be involved in such disease states. Nitric oxide (NO) downregulates P-selectin expression, and bradykinin (BK) is known to stimulate NO release from endothelial cells. The objective of this study was to determine the effects of 10-min stimulation of cultured human umbilical endothelial cells (HUVECs) with Ang II, BK, or both on P-selectin expression. Ang II (10(-9)-10(-5) M) stimulated P-selectin expression in a concentration-dependent manner, exhibiting a significant effect at 10(-7) M and reaching a plateau at 5 x 10(-5) M. Pretreatment of HUVECs with the AT1 antagonist losartan and the AT1/AT2 antagonist saralasin but not the AT2 antagonist PD123319 (all at 10(-5) M) markedly attenuated the effect of 10(-7) M Ang II. The effects of Ang II on P-selectin expression were not affected by the presence of the NO synthase inhibitor nitro-L-arginine (L-NA, 5 x 10(-4) M) but were abolished by pretreatment with superoxide dismutase (SOD). BK (10(-6) M) abolished the effects of 10(-7) M Ang II on P-selectin expression but did not affect P-selectin expression induced by desmopressin (0.01-10 microM). L-NA obliterated the blunting effect of BK on the Ang II-induced P-selectin membrane expression. BK alone slightly stimulated P-selectin expression, but in the presence of L-NA, BK markedly enhanced P-selectin expression. The effects of BK in the presence of NA were not altered by SOD, indicating that at difference with Ang II, it acts by a mechanism other than superoxide generation. Thus, Ang II acting on AT1 receptors stimulates superoxide generation, which, in turn, induces expression of P-selectin on the endothelial cell surface. BK inhibits the effects of Ang II, likely acting via NO. We conclude that the balance between Ang II, BK, and NO can regulate P-selectin expression on the endothelial cell membrane, an important component of the cascade leading to leukocyte adhesion to the vascular endothelium.