Estimation of plasma serotonin using isopycnic centrifugation.

The valid measurement of the concentration of serotonin (5-HT) in blood plasma is important when using the platelet as a model for the serotonergic neuron. The assay is hampered by the release of 5-HT by (residual) platelets during the preparation for assay. We developed an isopycnic method that separates cells gently and completely from plasma by centrifuging a diluted Percoll density-gradient to which whole blood was added. In this study this method was compared with the usual differential centrifugation method. The isopycnic method on average resulted in nine times lower levels of plasma 5-HT. This difference was linearly related to the number of residual platelets in plasma after differential centrifuging. The proportion of intra-individual variation decreased three-fold. Therefore, the use of a Percoll density-gradient may lead to a more precise and more accurate estimate of the level of plasma 5-HT. Copyright 2000 John Wiley & Sons, Ltd.