Vervet monkey (Cercopithecus aethiops sabaeus) whole blood serotonin level is determined by platelet uptake sites

Whole blood serotonin levels in adult male vervet monkeys living in social groups are sensitive to the animals' social environment. The mechanisms that translate different behavioral and environmental cues into altered whole blood serotonin levels are unknown. In this study, we have measured platelet number, size, serotonin content, and serotonin uptake, as well as the serum concentrations of tryptophan, Mg+2 and Ca+2. Results showed that whole blood serotonin levels, platelet serotonin content, and the serotonin uptake parameter Vmax were stable within animals on repeated sampling. The whole blood serotonin level was highly positively associated with platelet serotonin content, and the platelet serotonin content was highly positively associated with Vmax. These findings suggested that whole blood serotonin levels were a function of the number of platelet uptake sites.