Evidence for the Presence of α 1 Adrenoceptor Subtypes in the Human Ureter

Abstract

Several studies proposed a role for α₁ adrenoceptors (α₁ ARs) in the ureteral physiology, indicating that they are present in the ureter; however, few studies have been made to identify α₁ AR subtypes present in this area. Thus, this study was carried out to characterize the α₁ AR subtype gene and protein expression in proximal, medial and distal region of the human ureter.

Methods

Molecular characterization of α₁ AR subtypes was done by semi-quantitative RT-PCR. The α₁ AR protein expression was studied by saturation binding curves using the α₁ AR antagonist ¹²⁵I-HEAT. Analysis of data was performed using the GraphPad PRISM 4 software.

Results

Analysis of saturation binding curves revealed an heterogeneous distribution of α₁ AR binding sites; the Bmax for the distal ureter was indeed 52.5 ±5.4 fmol/mg prot, while a lower similar density of α₁ ARs was demonstrated in the medial (25.2 ±1.7 fmol/mg prot) and proximal (23.4 ±0.4 fmol/mg prot) ureters. Molecular characterization of α₁ AR subtypes indicated that each receptor was present, although with differences in term of the amount expressed.

Conclusions

Human ureter was endowed with each α₁ AR subtype, although α_1D and α_1A ARs were prevalent over α_1B ARs. Radioligand binding results revealed that there were no significant differences in the Kd between ureteral regions, while an heterogeneous distribution of α₁ AR binding sites was detected, with the highest density of α₁ ARs in the distal ureter and a lower similar density in the medial and proximal ureter.