QUANTITATION OF ALPHA-1 AND BETA ADRENERGIC RECEPTOR DENSITIES IN THE HUMAN NORMAL AND HYPERTROPHIED PROSTATE

Abstract

Using radioligand binding assays, both α₁ and β adrenergic receptors of the human normal and hypertrophied prostatic tissue were quantitated, for the first time. For α₁ adrenergic receptor assay, with ³H-prazosin as a ligand, the prostatic crude membrane fraction were incubated for 20min. at 30°C with or without 10μM phentolamine. The number of binding sites (NBS) and the dissociation constant (Kd) were calculated from the Scatchard analysis.
The number of binding sites of α₁ adrenergic receptors in the normal prostatic tissue was determined 35.7±12.7fmol/mg protein (mean±S. D.), on the other hand, the NBS of it in the hypertrophied prostatic tissue was 50.3±14.6fmol/mg protein. In the hypertrophied prostate it was noticed that there was a significantly greater density of α₁ adrenergic receptors than in normal prostate (p<0.05), although there was no difference in Kd between them.
It has recently been revealed that the human prostatic smooth muscle elicited supersensitive contractions to α₁ adrenergic stimulants in benign prostatic hypertrophy, in vivo and in vitro. This supersensitive reaction seems to be due to the increase of α₁ adrenergic receptors density in the hypertrophied prostatic tissue. Furthermore, it was speculated that the greater density of α₁ adrenergic receptors in the hypertrophied prostate was caused by the denervation effect in the tissue.
For β adrenergic receptor assay, ³H-DHA (dihydroalprenolol) was used as a ligand. Although the incubation was performed for 30min. at 25°C, the method of binding assay was similar to the α₁ adrenergic receptor assay. No difference in the NBS of β adrenergic receptors was revealed between normal and hypertrophied prostatic tissue. Lower affinity of β adrenergic receptors was obtained in the benign prostatic hypertrophy than normal prostate.