Thrombin cleaves its receptor at arginine-41, resulting in the generation of a new receptor NH2-terminus with the sequence SFLLRNPNDKYEPF. This peptide (TRP-14) may signal a variety of thrombin's responses. We examined the effects of TRP-14 in inducing endothelial cell hyperadhesivity and neutrophil (PMN) adhesion to endothelial cell monolayers. Human umbilical vein endothelial cells (HUVECs) challenged with TRP-14 (10−4to 10−5M) produced concentration-dependent increases in endothelial adhesivity to PMN. In contrast, position 1 to 2 inverted peptide (FSLLRNPNDKYEPF) did not induce the response. The adhesion response was transient; that is, PMN adhesion increased within 15 minutes and decreased by 75 minutes after TRP-14 challenge of HUVECs. The transient endothelial adhesiveness paralleled the time course of P-selectin expression. TRP-14-induced release of P-selectin from intracel-lular stores may be a critical determinant of the response since treatment of endothelial cells with anti-P-selectin monoclonal antibody (mAb) G1 prevented the increase in PMN adhesion. Control nonneutralizing anti-P-selectin mAb S12 and mAb RR1/1 directed against intercellular adhesion molecule-1 (ICAM-1) on HUVECs were ineffective. The results indicate that the “tethered ligand” of the thrombin receptor created by the proteolytic action of thrombin on its receptor (i.e., TRP-14) signals increased endothelial adhesiveness by a P-selectin-dependent mechanism. Thrombin-induced PMN adhesion may involve formation of a new NH2-terminus of the endothelial thrombin receptor with the sequence SFLLRNPNDKYEPF followed by activation of endothelial second messenger pathways and the transient expression of P-selectin.