Comparison of [3H]clonidine and [3H]guanfacine binding to alpha 2 adrenoceptors in membranes from rat cerebral cortex.

[3H]Clonidine and a new phenylacylguanidine antihypertensive drug, [3H]guanfacine, bind with a high affinity to alpha 2 adrenoceptors in membranes from rat cerebral cortex. Dissociation curves for [3H]clonidine binding indicated the presence of high and low affinity binding sites, whereas with [3H]guanfacine, two components could be distinguished only with difficulty; the major part of the binding being to a high affinity component. Saturation experiments revealed that both ligands bind with similar high affinity but that [3H]guanfacine labels twice the number of sites labeled by [3H]clonidine.