α2-Adrenergic receptors appear in rat salivary glands after reserpine treatment

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Abstract
The regulation of central and peripheral adrenergic receptors by various chemical, physiological, pharmacological and pathological stimuli has been the subject of intense study. For example, drug treatments can produce relatively small changes in the density of existing receptor binding sites in a variety of tissues. The alpha-adrenergic receptors in rat salivary gland tissue have been studied using radioligand receptor binding techniques. We have recently identified and characterised alpha 1-adrenergic receptors in the rat submandibular gland, but surprisingly, alpha 2-adrenergic receptor binding was not detectable. We now report that a single treatment of reserpine results in the appearance of alpha 2-adrenergic binding sites within 12 h. Continued treatment with the drug produces further increases in the number of alpha 2-adrenergic receptors, such that after 7 days the levels of alpha 1- and alpha 2-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.