Platelet serotonin studies in hyperserotonemic relatives of children with autistic disorder.

Platelet serotonin (5-HT) studies were conducted with 12 hyperserotonemic and 12 normoserotonemic age-, sex-, and relationship-matched relatives of autistic probands. Each group consisted of 7 mothers, 4 fathers, and 1 sister of autistic children and adolescents. The density (Bmax) of platelet 5-HT2 receptor binding sites, labelled with [3H]-lysergic acid diethylamide (LSD), was significantly lower in 11 hyperserotonemic subjects compared to 12 normoserotonemic subjects (40.9 +/- 13.5 fmol/mg protein, 59.6 +/- 13.2; p < 0.004). The affinity (Kd) for [3H]-LSD binding did not differ. Although the density (Bmax) of [3H]-paroxetine binding did not differ between groups, there was a small difference in the affinity (Kd) for [3H]-paroxetine binding (hyperserotonemic 47.6 +/- 9.0 pM, normoserotonemic 54.8 +/- 12.1; p < 0.05). There were no significant differences in platelet 5-HT uptake, or in thrombin-stimulated 5-HT release. Basal, 5-HT-stimulated, and arginine-vasopressin (AVP)-stimulated inositol phosphate production, as well as basal, prostaglandin E1 (PGE1)-, and forskolin-stimulated cAMP production did not differ. There were significant correlations between whole blood 5-HT levels and LSD Bmax (rs = -0.63, N = 23, p < 0.002) and whole blood 5-HT levels and 5-HT uptake Vmax (rs = 0.56, N = 18, p < 0.02). However, [3H]-LSD labelled 5-HT2 binding and 5-HT uptake were not correlated with each other. Hyperserotonemia of autism may be heterogeneous with one subgroup of subjects with increased 5-HT uptake and another subgroup with decreased 5-HT2 binding.