Autoradiographic Localization and Computerized Quantification of α₁- and α₂-Adrenoceptors in Spontaneously Hypertensive Rat Kidney: [³H]Bunazosin and [³H]Yohimbine Binding Studies

The autoradiographic localization of α₁- and α₂-adrenoceptors was identified in 22-week-old Wistar – Kyoto rat kidney, using α₁-selective ([³H]bunazosin) and α₂-selective ([³H]yohimbine) antagonists. [³H]Bunazosin binding was distributed predominantly over the cortex, less over the outer medulla and was absent from the inner medulla. [³H]Yohimbine binding was distributed predominantly over the medulla, less over the renal cortex and was absent from the inner medulla. In addition, the distribution of renal α-adrenoceptors was investigated in 3-, 7- and 22-week-old spontaneously hypertensive rats (SHRs) using a computerized image analysis system. Renal α-adrenoceptors were both found to be increased in SHRs at all ages tested compared with their respective controls and were increased in both the cortex and the outer medulla. The increase in renal α-adrenoceptors was already present in 3-week-old SHRs whose systolic blood pressures did not differ significantly from those of the controls. The results strongly suggest that these abnormalities of renal α-adrenoceptors may play a critical role in the development of hypertension in SHRs.