Laminin (LM) is a basement membrane glyco-protein which exhibits a number of biological activities, including the promotion of cell attachment and migration. In a static system, platelets attach to LM without spreading. In order to elucidate the mechanisms mediating platelet-LM interactions under flow conditions, we studied the effects of blocking subendothelial LM and its platelet receptor. We measured the extent of platelet adhesion to the endothelial cell extracellular matrix (ECM) using a parallel plate perfusion chamber. To do this, we performed the following experiments: i) blockade of subendothelial LM by incubation of ECM with an anti-LM antibody (Ab); ii) blockade of the platelet receptor for LM with: a) an anti-67 KDa receptor Ab; and b) three different LM-derived peptides (CFALRGDNP, IKVAV and CDPGYIGSR). In i) perfusates consisted of whole blood, whereas in ii) perfusates were prepared with washed platelets pre-incubated with Ab or peptides and reconstituted with plasma and washed red blood cells. Perfusions were carried out at 800 s-1 shear rate. Platelet deposition was morphometrically evaluated by a computerized system. Our results indicated that when ECM was pre-incubated with an anti-LM Ab (100 micrograms/ml, 30 min, 37 degrees C) a reduction of the surface coverage (SC) of 23.3 +/- 2.3% (p less than 0.01) was observed. When washed platelets were pre-incubated with an anti-67 KDa receptor Ab (40 micrograms/ml, 30 min, 37 degrees C) their interaction with ECM was decreased by 22.3 +/- 2.1% of SC (p less than 0.005). In other experiments platelets were pre-incubated with CFALRGDNP, IKVAV and CDPGYIGSR (200 micrograms/ml, 30 min, 37 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)