Renal aging change of alpha 1-adrenoceptor in Wistar rats

1. The aging changes of density of the alpha 1-adrenoceptors in the kidney were evaluated with Wistar rats of several ages (8, 52 and 104 weeks old). 2. [3H]prazosin and [3H]YM617 (newly synthesized alpha 1-blocker) were used for the ligand. The Bmax of [3H]prazosin was 74.0 +/- 9.5 fmol/mg/protein in 8 week, 52.1 +/- 7.3 fmol/mg protein in 52 week, and 31.3 +/- 4.2 fmol/mg protein in 104 week rats, and that of [3H]YM617 was 45.0 +/- 6.6 fmol/mg/protein in 8 week, 32.4 +/- 5.7 fmol/mg/protein in 52 week, and 19.3 +/- 5.5 fmol/mg/protein in 104 week rats. 3. The Bmax of both ligands for 104 week rats was significantly decreased compared to 8 week rats, however, 52 week rats showed no decrease of Bmax for both ligands. 4. The Kd values showed no difference in these three age groups for both ligands. 5. Autoradiographic study supported the result above mentioned. Furthermore, the binding sites of alpha 1-adrenoceptors were mainly in the cortex (vascular wall and peritubular area) and that alpha 1-adrenoceptors were chiefly chlorethylclonidine dihydrochloride (CEC) insensitive.