Binding of [3H]clonidine to membranes from cow neurohypophysis and cerebral cortex of the rat.

The binding of [3H]clonidine to membranes prepared from rat cerebral cortex and cow neurohypophysis was compared. Both tissues showed a high affinity site and a low affinity site when examined using a variety of techniques. The binding data, together with displacement studies using a variety of alpha 2-adrenoceptor agonists and antagonists, indicated that the binding activity of clonidine in the two tissues was very similar, however when the putative sigma opiate compound SKF 10,047 was examined it was found to have only a weak activity in displacing clonidine on the cortical membranes but a much stronger activity on the neurohypophysial membranes, other opiates showed little activity on binding of clonidine in either tissue. It is proposed that the binding of clonidine to neurohypophysial membranes may explain in part the various reports of suppression by clonidine of release of hormones from the neurohypophysis and that the effects of SKF 10,047 may be similarly associated with the reports of diuresis induced by phencyclidine.