Classification of the α1-adrenoceptors on the porcine superior vesical artery.

Nilsson D1, Chess-Williams R1, Sellers D1

Research Type

Pure and Applied Science / Translational

Abstract Category

Pharmacology

Abstract 528
Open Discussion ePosters
Scientific Open Discussion Session 28
Friday 31st August 2018
12:55 - 13:00 (ePoster Station 4)
Exhibition Hall
Pharmacology Overactive Bladder Detrusor Overactivity
1. Bond University
Presenter
D

Damian Nilsson

Links

Poster

Abstract

Hypothesis / aims of study
Lower urinary tract symptoms (LUTS) are common among the global population, where the prevalence of LUTS increases with age. Until recently, studies focusing on bladder dysfunction have primarily investigated the role of the detrusor smooth muscle or urothelium. However, the bladder’s vasculature has been an emerging suspect as a cause for dysfunction. It has been shown that hypoperfusion-induced hypoxia causes bladder dysfunction and that an increase in perfusion can improve symptoms (1). The main regulator of vascular smooth muscle contraction is noradrenaline acting via α1-adrenoceptors to cause vasoconstriction. There are 3 cloned subtypes of α1-adrenoceptor (α1A-, α1B- and α1D-) with another subtype identified in functional studies that is a version of the α1A-adrenoceptor but with a low affinity (pKD<9.0) for prazosin, and this has been termed the α1A/L-adrenoceptor. The superior vesical artery, which branches from the internal iliac artery, supplies the bladder with blood and is a resistance artery and was chosen due to it proximity to the bladder. Which functional subtype causes constriction of the superior vesical artery supplying the bladder is unknown. The aim of this study was to investigate the α1-adrenoceptors on the porcine superior vesical artery
Study design, materials and methods
Sections (~4mm) of the porcine superior vesical artery (internal diameter ~1mm) from 6-month old pigs were isolated and mounted between two horizontal stirrups in baths containing gassed Krebs-bicarbonate solution. Tension developed by the circular smooth muscle was recorded to a Powerlab. The potencies of phenylephrine and the α1A-adrenoceptor selective agonist A-61603 was investigated. Cumulative concentration-response curves to phenylephrine were then obtained in the absence and presence of the α1-adrenoceptor antagonists RS-100329 (α1A-selective), BMY-7387(α1D-selective) and prazosin (α1A- > α1L- selective). Control experiments without the addition of antagonists were also performed and used to correct for any time dependent changes in tissues sensitivity.
Results
Both phenylephrine and A-61603 caused concentration related increases in contraction (Figure 1A) but A-61603 was 100-fold more potent than phenylephrine with pEC50 values of 7.5 and 5.99 respectively (P<0.05, n=4 and n=6). Maximum contractions to A-61603 (1.49±0.105g/mg) were also significantly greater (P<0.05) than those to phenylephrine (1.02±0.027g/mg). Relatively high concentrations of the α1D-specific antagonist BMY-7387 (up to a concentration of 30μM) did not antagonise responses to phenylephrine (Figure 1B). However the α1A-selective antagonist RS-100329 produced concentration-dependent rightward shifts of phenylephrine curves (Figure 1C), the antagonist increasing pEC50 values from 5.86±0.089 to 5.56±0.144 (P<0.05) at a concentration of 10nM, with a further shift at 30nM (pEC50 of 5.36±0.116, P<0.05). However the maximal responses to phenylephrine was significantly depressed in the presence of 30nM from 0.99±0.03g/mg to 0.71±0.031g/mg, but was not significantly reduced in the presence of either 10nM or 100nM (0.84±0.042g/mg and 0.99±0.066g/mg respectively). Prazosin (30-300nM) also shifted concentration-response curves to phenylephrine but with a relatively low affinity (pKD estimate of 8.53). Maximum responses were unchanged in the presence of 100 and 300nM (1.01±0.035g/mg and 1.05±0.064g/mg, respectively) but reduced by 30nM prazosin (Figure 1D) from 0.99±0.03g/mg to 0.65±0.037 (P<0.05).
Interpretation of results
The results indicate that the superior vesical artery possesses functional α1-adrenoceptors. The high potency of A-61603 suggests the presence of functional α1A-adrenoceptors, which was supported by the antagonist data where RS-100329 (α1A-subtype selective versus α1B-subtype selective), but not BMY-7378 (α1D-selective) antagonised responses. The low affinity estimate for prazosin suggests the presence of the low affinity form of the α1A-adrenoceptor on the superior vesical artery.
Concluding message
In conclusion, contraction of the superior vesical artery is mediated via the low affinity form of the α1A-adrenoceptor (i.e. α1A/L-adrenoceptor), the same α1A-adrenoceptor subtype known to mediate contraction of the prostate.
Figure 1
References
  1. Okutsu H, Mastumoto S, Ohtake A, Suzuki M, Sato S. Effects of tamsulosin on bladder blood flow and bladder function in a rat model of bladder over-distension/emptying induced bladder overactivity. Journal of Urology. 2011; 186(6): 2470-2477.
Disclosures
Funding Funding was supplied through Bond University Healtch Science and Medicine Faculty Clinical Trial No Subjects Animal Species Pig (Porcine) Ethics not Req'd The tissues were sourced from a local abattoir, with the animals already being killed for slaughter, ethics was not needed to use the already available tissues.
27/03/2024 23:28:48