Age depresses α1-adrenoceptor mediated vasoconstriction of the porcine superior vesical artery.

Nilsson D1, Chess-Williams R1, Sellers D1

Research Type

Pure and Applied Science / Translational

Abstract Category

Pharmacology

Abstract 649
E-Poster 3
Scientific Open Discussion Session 31
Friday 6th September 2019
13:15 - 13:20 (ePoster Station 10)
Exhibition Hall
Basic Science Pharmacology Pre-Clinical testing
1.Bond University
Presenter
D

Damian Nilsson

Links

Poster

Abstract

Hypothesis / aims of study
With the growing worldwide elderly population the incidence of bladder dysfunction and incontinence is increasing (1). Age is not only a common risk factor for the development of lower urinary tract symptoms but is also an independent risk factor for cardiovascular diseases such as atherosclerosis.  Impaired blood flow, or ischemia, of the bladder may play a role in the etiology of bladder dysfunction, although the underlying mechanisms are not yet clear (2).  We have shown that vasoconstriction of the superior vesical artery is mediated via the low affinity form of the α1A-adrenoceptor (i.e. the α1A/L-adrenoceptor), the same subtype known to mediate contraction of the prostate and erectile tissue.  The aim of this study was to determine the effect of ageing on functional α1-adrenoceptor subtypes of the porcine superior vesical artery.
Study design, materials and methods
Superior vesical artery from two age groups of pigs were used (young 6-month and older 3-year old pigs). Sections (~4mm length, ~1mm internal diameter) were isolated and mounted between two horizontal stirrups in 10mL organ baths (GlobalTowns, CA) containing carbogen (5% CO2) gassed Krebs-bicarbonate solution at 37˚C.  Tension developed by the circular smooth muscle was recorded to a PowerLab using LabChart software. Cumulative concentration-response curves to phenylephrine, noradrenaline and methoxamine were obtained in the presence of corticosterone (1µM), desipramine (1µM) and propranolol (1µM) to block neuronal & extra-neuronal uptake and β & α2 receptors. In addition, responses to phenylephrine were obtained in the absence and presence of α1-adrenoceptor antagonists prazosin (α1- > α1L-selective), BMY-7378 (α1D-selective), tamsulosin (α1A/D-selective) and RS-100329 (α1A-selective) in arteries from both age groups. Responses to KCl 60mM were also recorded. Control experiments without the addition of antagonists were also performed to correct for any time dependent changes in tissues sensitivity. Statistical significance of differences in responses between age groups were determined using two-tailed unpaired t-tests, with P<0.05 considered significant.
Results
Phenylephrine caused concentration dependent increases in contraction (Figure 1). Maximal contractile responses were significantly depressed, by approximately 88%, in the superior vesical artery from older animals. The potency of phenylephrine was similar in arteries from both young and older animals (Figure 1, Table 1). Responses to the endogenous agonist noradrenaline were also significantly depressed, and potency and maximal contractions were decreased in arteries from older animals (Figure 1, Table 1). Vesical arteries from young animals did not respond to methoxamine, however methoxamine did produce a response in arteries from older animals, although this agonist was significantly less potent than both phenylephrine and noradrenaline (Figure 1, Table 1). In contrast, contractile responses to KCl were not affected by age, with similar contractions in arteries from young and older animals (0.68±0.13 and 0.76±0.13, respectively, ns).
The α1D-selective antagonist BMY-7378, at relatively high concentrations, did not significantly shift responses to phenylephrine in arteries from either young or older animals. The clinically used antagonist tamsulosin significantly shifted phenylephrine responses in both age groups. Tamsulosin, at 3nM, shifted phenylephrine responses, yielding an affinity estimate (pKD) of 9.99±0.27 in arteries from young animals and a pKD 9.85±0.39 in arteries from older animals.  Prazosin (α1->α1L-selective) (10-30nM) significantly shifted the phenylephrine curves in arteries from both age groups. Whilst prazosin shifted responses in young arteries with a relatively low affinity (pKD and pA2 of 8.09±0.09 and 8.43 respectively), in arteries from older animals a relatively higher affinity estimate was obtained for prazosin (pKD of 9.41±0.21 and pA2 9.13). The α1A-selective antagonist RS-100329 antagonised phenylephrine responses with a pKD of 8.53±0.16 in arteries from young animals and 9.2±0.09 in older animals. None of the antagonists significantly affected maximal responses to phenylephrine.
Interpretation of results
Age depresses α1-adrenoceptor-mediated contractile responses of the porcine superior vesical artery. Vasoconstriction responses to KCl were not depressed with age. This suggests that depressed agonist-induced responses are not due to a general decrease in contractility of the arteries with age, but more likely an alteration in the intracellular signalling pathway downstream from the α1-adrenoceptors.
The apparent low affinity of α1D-selective antagonist BMY-7378 in arteries from the young animals, and the lack of shift in the older animals, suggests little role for the α1D-adrenoceptor in mediating vasoconstriction in arteries from either age group. Tamsulosin yielded high affinity estimates in both young and old age groups, indicating a role for the α1A/L-subtype. RS-100329 also yielded high affinity values, supporting a role for the α1A/L-subtype. Affinity estimates for prazosin however were different in young and older animals. Typically, prazosin has a high affinity for α1-adrenoceptors, and this was observed arteries from older animals. However, at the functional phenotype of the α1A-adrenoceptor subtype (α1L-) prazosin has a low affinity. This was observed in the young animals and is the same in the human vas deferens (3) (8.6) and erectile tissue (8.4) Based on prazosin’s relatively high affinity in arteries from older animals, the α1- subtype mediating vasoconstriction appears to change with age, with the α1A-subtype mediating vasoconstriction in the older arteries.
Concluding message
Age depresses α1-adrenoceptor-mediated contractile responses of the porcine superior vesical artery. Preliminary antagonist affinity data suggest that in older animals vasoconstriction of the porcine superior vesical artery may be mediated by the α1A-adrenoceptor.
Figure 1 Cumulative-concentration vasoconstriction responses to α1-adrenoceptor agonists in porcine superior vesical artery from young (A) and older (B) animals.
Figure 2 pEC50 and maximal contractile responses to agonists in superior vesical artery from young and older animals. *P <0.005 vs Young (phenylephrine), **P <0.005 vs Young (Noradrenaline)
References
  1. R, Dmochowski, Ther Adv Urol, 2009, 1(4), 209-221.
  2. M, Michel; R, Chess-Williams, S, Hegde, Naunyn-Schmiedeberg’s Arch Pharmacol, 2015, 388, 687-694.
  3. B, Davis; M, Weiner; C, Chapple; R, Chess-Williams, Auton Autacoid Pharmacol, 2015, 34(3-4), 41-49.
Disclosures
Funding This research is supported by an Australian Government Research Training Program Scholarship and Bond University. Clinical Trial No Subjects Animal Species Pig Ethics not Req'd The pig samples were sourced from a local abattoir from animals originally killed for food, thus ethical approval was not needed.
28/03/2024 09:59:47