IGF-1 potentiates PAR-1–mediated platelet aggregation in a secretion-independent manner. Washed platelets were incubated with 100 nM IGF-1 for 5 minutes before stimulation with the PAR-1 agonist SFLLRN (0.5 μM or 2 μM where indicated). ATP secretion and aggregation was subsequently recorded in a PICA (A) and Chrono-log 490–4D aggregometer (B), respectively. Secretion and aggregation and were recorded for a total of 5 minutes. One tick mark on the y-axis represents 20% increase in light transmission. The error bars on the graph (A) are expressed as SEM for n = 3. Results (B) are representative of 3 experiments.