Influence of age, sex and diurnal variability on imipramine receptor binding and serotonin uptake in platelets of normal subjects.

Imipramine (IMI) binding and serotonin (5-HT) uptake were determined in platelets of 98 healthy volunteers; and their association with age, sex and circadian rhythm were evaluated. A large interindividual variability was found for both IMI and 5-HT parameters. There was a negative correlation of IMI affinity constant (Kd) and binding (Bmax) with age, but no such correlation of 5-HT affinity constant (Km) or uptake (Vmax). Significant age-related diurnal variability was found for 5-HT Km in the whole group as well as for IMI Kd in males, but not in females. There was no significant correlation between 5-HT Vmax and IMI Bmax. Our results underscore a cautious approach to the interpretation of platelet serotonergic studies. In light of the multiple variables influencing the results, the usefulness of IMI or 5-HT as clinical markers should be re-evaluated.