Expression of alpha 2-adrenergic receptor genes in rat tissues.

Alpha-2 adrenergic receptor subtypes are coded for by three genes. Pharmacologically alpha 2 adrenergic receptors can be classified into four subtypes: alpha 2A, alpha 2B, alpha 2C, and alpha 2D. Although pharmacologically distinct, the amino acid sequences of the alpha 2A and alpha 2D subtypes are approx 90% identical and have not been detected in a single species. Thus, they should be considered species orthologs and may be referred to as alpha 2A/D. The tissue distribution of the mRNAs for the rat alpha 2A/D, alpha 2B, and alpha 2C was analyzed utilizing RNase protection assays with probes directed to the third cytoplasmic loops. Alpha-2 adrenergic receptor mRNA was found in all tissues tested. Kidney, brain, and spinal cord had transcripts for all three subtypes. Only one mRNA subtype was detected in several tissues. Aorta and spleen had only alpha 2A/D mRNA, whereas heart and liver had only alpha 2B mRNA. All other tissues had two alpha 2 adrenergic subtype transcripts present. In contrast to the rat CNS, which contains predominantly alpha 2A/D and alpha 2C mRNA with little alpha 2B mRNA, peripheral tissues contain predominantly alpha 2A/D and alpha 2B mRNA with little alpha 2C mRNA.