Effect of clonidine on platelet alpha 2-adrenoreceptors and plasma norepinephrine of children with Tourette syndrome.

Clonidine, an alpha 2-adrenoreceptor agonist, is useful for treating some patients with Tourette syndrome, and it has been suggested that their noradrenergic receptors are 'subsensitive'. The authors measured plasma norepinephrine and specific binding of 3H-clonidine and 3H-yohimbine, an alpha 2-adrenoreceptor antagonist, to receptors on platelet membranes from children with Tourette syndrome. Before clonidine treatment, plasma norepinephrine, the maximum number of binding sites and the dissociation constants for both ligands were the same as for the controls. After two weeks of treatment there was little clinical improvement, but the number of binding sites for 3H-yohimbine decreased and plasma norepinephrine also decreased in four of the five patients. Over the next six months all five patients continued to improve clinically, but both indices of noradrenergic activity returned towards baseline values. The data suggest that clonidine's action may be independent of its prominent effects on alpha 2-adrenergic receptors and norepinephrine release.