3H-imipramine binding in the blood platelets of normal twins

3H-Imipramine binding (IB) was studied in the blood platelets of 13 pairs of monozygotic (MZ) and dizygotic (DZ) twins, and 15 pairs of unrelated normal volunteers, to determine if IB is under genetic control. The intrapair variance of Bmax (the maximum number of 3H-IB sites) was significantly smaller in MZ twins and unrelated control pairs than in DZ twins. The intraclass correlations (ICC) of Bmax were significant for all the pairs with no difference between these correlations. The ICC of the Kd (inversely related to the affinity for 3H-imipramine) of IB was significant only for the normal control pairs and the DZ twins. These results suggest that the kinetic constants of IB in blood platelets are not under genetic control and that interassay variance significantly affects the absolute values for Kd and Bmax of 3H-IB. The environmental and assay factors that influence 3H-IB may account for the numerous discrepancies in platelet 3H-IB between various research reports.