The regulation of central and peripheral adrenergic receptors by various chemical, physiological, pharmacological and pathological stimuli has been the subject of intense study1,2. For example, drug treatments can produce relatively small changes in the density of existing receptor binding sites in a variety of tissues. The α-adrenergic receptors in rat salivary gland tissue have been studied using radioligand receptor binding techniques3. We have recently identified and characterised α1-adrenergic receptors in the rat submandibular gland4, but surprisingly, α2-adrenergic receptor binding was not detectable. We now report that a single treatment of reserpine results in the appearance of α2-adrenergic binding sites within 12 h. Continued treatment with the drug produces further increases in the number of α2-adrenergic receptors, such that after 7 days the levels of α1- and α2-adrenergic receptors are similar. This is the first example of a drug treatment resulting in the appearance of a receptor type which was not previously detectable.
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