Age-related changes in alpha1-adrenoceptors in rat prostate

The age-related changes in the density of alpha₁-adrenoceptors in the dorsolateral lobe of the rat prostate were evaluated in Wistar rats at 8, 52, and 104 weeks of age. [³H]YM617, a newly senthesized alpha₁-adrenergic blocker, was used as the ligand. The mean maximum number of binding sites, or alpha₁-adrenoceptor density (B_max)±SE of 104-week-old rats (11.0±1.2 fmol/mg protein) was significantly lower than that in the 8-week-old rats (37.0±4.3 fmol/mg protein) and 52-week-old rats (37.2±3.4 fmol/mg protein) respectively, P<0.01. In contrast, mean affinity (K_d) values±SE of these groups showed no significant differences (8-week-old rats, 115.8±9.1; 52-week-old rats, 100.5±5.8; and 104-week-old rats, 116.4±9.8 pM). Mean volumes±SE of muscle cells of the prostate were 3.7±1.1x10³ m³ at 8 weeks, 30.0±6.2x10³ m³ at 52 weeks, and 18.6±8.2x10³ m³ at 104 weeks. Volumes for 8-week-old rats were significantly smaller than those for 52-week-old (P<0.01) and 104-week-old rats (P<0.05). However, the mean area density of the muscle cells showed no difference among the three groups: 20.1±2.2% at 8 weeks, 27.3±2.9% at 52 weeks and 20.3±3.4% at 104 weeks. In conclusion, the density of YM617-binding sites (alpha₁-adrenoceptors) in 104-week-old rats was lower than in 8- and 52-week-old rats. Muscle volume in the rat prostate was larger in rats aged 52 and 104 weeks than in 8-week-old rats, but no correlation was found between alpha₁-adrenoceptor density and the muscle volume or muscle density in aging.