EXPRESSION OF ALPHA(2)-ADRENERGIC RECEPTOR GENES IN RAT-TISSUES

Alpha-2 adrenergic receptor subtypes are coded for by three genes. Pha rmacologically alpha(2) adrenergic receptors can be classified into fo ur 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 both been detected in a single species. Thus, they should be considered species orthologs and may be referred to as alpha(2A/D). The tissue distribut ion of the mRNAs for the rat alpha(2A/D), alpha(2B), and alpha(2C) was analyzed utilizing RNase protection assays with probes directed to th e 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) adr energic subtype transcripts present. In contrast to the rat CNS, which contains predominately alpha(2A/D) and alpha(2C) mRNA with little alp ha(2B) mRNA, peripheral tissues contain predominately alpha(2A/D) and alpha(2B) mRNA with little alpha(2C) mRNA.