Density and Localization of Alpha1-Adrenoceptors in Hypertrophied Prostate

Alpha-adrenoceptors have been considered to play an important role in the regulation of the voiding force. In order to determine the density and localization of the alpha-adrenoceptors in the prostate, binding assays for alpha-adrenoceptors were performed with [3H]prazosin and [3H] yohimbine in membrane preparations from enucleated hyperplastic prostate tissues. Furthermore, autoradiographic analysis of alpha-adrenoceptors in the sliced tissue specimens from benign prostatic hypertrophy was performed. Specific bindings of both ligands were saturable and of high affinity in membrane preparations, and Scatchard analyses indicated Bmax = 104fmole/mg. protein, Kd = 0.488nM for [3H]prazosin, and Bmax = 41fmole/mg. protein, Kd = 1.83nM for [3H] yohimbine. Bmax and Kd for [3H]prazosin were greater in the adenoma than in the submucosal tissue of the prostatiac urethra. No relationship was noted between the size of enucleated prostate and the density of alpha-adrenoceptors. Image analysis of autoradiograms using [3H]prazosin showed specific binding sites could not be clearly demonstrated, but only [125I]HEAT slightly exposed specific binding sites in the prostate.