Proximal tubular alpha 2-adrenoceptor density in the spontaneously hypertensive rat. In the kidney of the spontaneously hypertensive rat (SHR), alpha 2-adrenoceptors are increased and may be related to hypertension. We measured alpha 2-adrenoceptor density and characteristics in a proximal tubule suspension with the alpha 2-adrenoceptor antagonist, 3H-rauwolscine. SHR had a significantly greater density of alpha 2-adrenoceptors when compared to their normotensive controls, the Wistar-Kyoto (WKY) rats (146 +/- 13 v 58 +/- 7 fmol/mg protein; P less than .001). Competition experiments determined the alpha 2-adrenoceptor to be an alpha 2B-subtype. Agonist competition curves were shallow and exhibited pseudo-Hill slopes of less than 1, indicating that they bind to both high and low affinity receptor sites. In summary, alpha 2-adrenoceptors are increased in the proximal tubule of SHR and appear to be of the alpha 2B-subtype. An increase in alpha 2-adrenoceptors may be related to abnormalities in hypertension. 