RESUMEN
Previous reports have alluded to variability in the aggregation response of normal human platelets to the neuropeptide arginine vasopressin (AVP). Since it has not been well documented, the current studies were undertaken to characterize this response. AVP (1-100 nM) produced a concentration-dependent aggregation response. Although the aggregation response to 100 nM AVP did not correlate with age or sex, there was a bimodal response distribution based on the presence or absence of a second wave of aggregation. In kinetic studies, the apparent km of AVP was 18.3 +/- 5.4 nM. There was a significant inverse relationship between the maximal aggregation response to 100 nM AVP and the km (r = -0.82). One hundred nanomolar AVP increased the intracellular calcium concentration of platelets by 406 +/- 120 nM in calcium free buffer and by 658 +/- 233 nM in the presence of 1.0 mM CaCl2. The aggregation response to 100 nM AVP correlated most strongly with the transmembrane influx of calcium (r = 0.84). In individuals whom 100 nM AVP was able to generate a second wave of aggregation, the selective protein kinase C inhibitor bis-indolylmaleimide significantly decreased the platelet aggregation response. Thus, there is significant heterogeneity in the aggregation response of normal human platelets to AVP. Based on our kinetic studies and the effects of PKC inhibition on the aggregation response to AVP, we would hypothesize that the variability of the aggregation response of normal human platelets to AVP is related to a polymorphism of the platelet AVP V1 receptor.