Receptor interactions of imidazolines. V. clonidine differentiates postsynaptic alpha adrenergic receptor subtypes in tissues from the rat.

The alpha-adrenergic effects of clonidine were studied in five tissues of the rat. Postsynaptic alpha adrenergic receptors in these tissues may be divided into three distinct classes based on affinity of the receptors for clonidine. High affinity receptors are located in the aorta and low affinity receptors in the vas deferens. Receptors with intermediate affinity are found in the portal vein, spleen and bladder. The bladder may also contain, to a small extent, a population of receptors similar to those found in the vas deferens which may mediate a different response. Available data suggest that the alpha adrenergic receptor of the rat aorta with high affinity for clonidine may be of the alpha-2 type but located postsynaptically in this tissue.