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Based on radio-ligand binding assays, most of the aZB-adrenoceptors in rat kidney are found in the proximal tubules and are of the aZB-adrenoceptors subtype. To determine more accurately the distribution of the aZB-adrenoceptors in the rat kidney, we studied the expression of a2B-adrenoceptors mRNA in rat kidney slices and microdissected nephron fragments using reverse transcription-polymerase chain reaction (RT-PCR) technique. Sprague-Dawley rat kidney was dissected into cortex, outer medulla and inner medulla. Total RNA was prepared from the kidney slices. Microdissected single nephron segments about 1 mm in length were transferred to tubes containing lysis buffer. RT-PCR was performed using a GeneAmp RNA PCR kit from Perkin-Elmer Corporation. The PCR primers were designed based on the sequences of the third cytoplasmic loop of the rat aZB-gene. After the PCR, the products were analyzed by agarose gel electrophoresis.The specificity of PCR amplified products was examined by restriction endonuclease digestion and internal oligonucleotide hybridization.Our results indicate that aZB-adrenoceptors mRNA is expressed in rat kidney cortex, outer medulla and inner medulla. Microdissection and RT-PCR showed that aZB-adrenoceptor mRNA was expressed in the proximal straight tubules (S3), cortical and medullary thick ascending limbs of Henle (CTALH, MTALH) and cortical and outer medullary collecting tubules (CCT, OMCT). (Hypertens Res 1993; 16: 259-263)