Different alpha1-adrenoceptor subtypes mediate contraction in rabbit aorta and urethra

Urodynamic and haemodynamic effects of a single oral administration of ephedrine or phenylpropanolamine in continent female dogs

This study investigated the effects of a single oral administration of ephedrine (2 mg/kg) or phenylpropanolamine (PPA) (1.5 mg/kg) on the vesico-urethral and cardiovascular functions in continent female dogs. Urethral pressure profilometry (UPP), arterial blood pressures and heart rate were measured in five control dogs and after single-dose treatment with ephedrine or PPA at T(0), T(2h), T(4h), T(6h), T(12h), T(18h) and T(24h). UPPs were performed under propofol anaesthesia and other measurements were performed on awake dogs. A telemetric urodynamic investigation was performed on three additional dogs for 24 h after the administration of each drug. Urethral pressures increased over 4-6 h and urethral functional lengths increased 2-6h after administration of both drugs. During micturition, a decrease in detrusor pressure coupled with an increase in bladder volume was observed after ephedrine administration and there was also an increase in bladder volume after PPA had been given. With both drugs increased arterial blood pressures at 4-6 h were compensated by a decreased heart rate over 12 h. Urethral function was improved after both ephedrine and PPA, and bladder function also improved during micturition following ephedrine.

Possible mechanisms of vasorelaxation for 5,7-dimethoxyflavone from Kaempferia parviflora in the rat aorta

The present study investigated the vascular effects of 5,7-dimethoxyflavone (DMF), isolated from the rhizomes of Kaempferia parviflora (KP), on rat isolated aortic rings and its possible mechanisms. DMF (1-100 μM) caused concentration-dependent relaxations in aortic rings precontracted with methoxamine. This effect was significantly reduced by removal of the endothelium, and after pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 300 μM), indomethacin (10 μM) and 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 μM), but not 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536, 100 μM). Relaxant responses to DMF were significantly inhibited by high KCl (60 mM) in both endothelium-intact and -denuded rings. In addition, the relaxations to DMF were significantly reduced by pretreatment with tetraethylammonium (TEA, 5 mM), glibenclamide (10 μM), 4-aminopyridine (1 mM) or barium chloride (10 μM). Preincubation with DMF (10 and 100 μM) for 30 min significantly inhibited the contractile responses to CaCl(2) in a Ca(2+)-free, high K(+) buffer. The present study demonstrated that DMF causes endothelium-dependent relaxation that is partly mediated by NO-cGMP and cyclooxygenase pathways. Interestingly, DMF-induced responses are mainly due to increasing K(+) efflux, and inhibition of Ca(2+) influx from the extracellular space. The vasodilator effects of DMF provide experimental support for the potential use of KP as a medical plant in the treatment of cardiovascular diseases.

Evaluation of the urodynamic and hemodynamic effects of orally administered phenylpropanolamine and ephedrine in female dogs

OBJECTIVE

To compare the urodynamic and hemodynamic effects of different dosages of phenylpropanolamine and ephedrine and determine effective dosages in increasing urethral resistance in female dogs.

ANIMALS

20 sexually intact female Beagles.

PROCEDURE

Dogs were allocated into 4 groups and received phenylpropanolamine once, twice, or 3 times daily, or ephedrine twice daily, for 14 days. On days 0, 7, and 14, urethral pressure profiles were performed while dogs were anesthetized with propofol. Variables recorded included maximum urethral pressure, maximum urethral closure pressure, integrated pressure, functional profile length, anatomic profile length, plateau distance, distance before maximum urethral pressure, and maximum meatus pressure. Arterial and central venous pressures were measured before anesthetic induction and 10 and 35 minutes after induction.

RESULTS

Administration of phenylpropanolamine once daily or ephedrine twice daily significantly increased maximum urethral pressure and maximum urethral closure pressure. Values for integrated pressure were significantly increased after 14 days of once-daily administration of phenylpropanolamine. Variables did not change significantly from day 7 to day 14. Diastolic and mean arterial blood pressures increased significantly during the treatment periods, and arterial pressure decreased during propofol infusion.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of phenylpropanolamine once daily or ephedrine twice daily increased urethral resistance in clinically normal dogs and may be recommended for management of urethral sphincter mechanism incompetence. Treatment efficacy may be assessed after 1 week. Dogs with concurrent cardiovascular disease should be monitored for blood pressure while receiving alpha-adrenergic agents because of the effects on diastolic and mean arterial pressure.

The effects of alpha1A-adrenoceptor antagonists on the urethral perfusion pressure of the female rat

OBJECTIVE

To assess the effects of alpha(1A)-adrenoceptor antagonists on urethral perfusion pressure (UPP) in the female rate and their therapeutic potential for treating female bladder outlet obstruction (BOO).

MATERIALS AND METHODS

A cannula was inserted into the femoral arteries of female rats to administer tamsulosin (group I), doxazosin (group II) or phentolamine (group III) and to monitor systemic blood pressure. Tamsulosin was also administered to male rats (group IV). UPP and vesical pressures (Pves) were monitored using a triple-lumen catheter.

RESULTS

After administration of tamsulosin to group I the frequency of bladder contractions decreased significantly and the duration of minimal urethral relaxation with high-frequency oscillations (HFOs) was significantly prolonged. Except for mean arterial blood pressure (MAP), none of the variables in group I differed significantly from those in group II and group III. The change in MAP after tamsulosin treatment was significantly lower than after doxazosin or phentolamine. Except for the maximum Pves, which was significantly higher in males (group IV) than in females of group I, the UPP and Pves curves of male rats were similar to those of females before giving tamsulosin. The prolonged frequency and duration of HFO in group IV (with tamsulosin) were significantly different from those of females.

CONCLUSIONS

The alpha(1A)-adrenergic receptor may be a functional subtype in the female rat urethra. alpha(1A)-adrenoceptor antagonists prolonged the duration of HFOs and decreased the frequency of involuntary bladder contraction. It is possible that treatment with alpha(1A)-adrenoceptor antagonists would not only improve obstructive symptoms, but also ameliorate irritative symptoms by prolonging HFOs and the frequency of involuntary bladder contractions.

Recent advances in the identification of a 1- and a 2-adrenoceptor subtypes: therapeutic implications

The cloning of multiple subtypes of both alpha1- and alpha2-adrenoceptors has renewed interest in the therapeutic application of agents interacting with these receptors. Effort has primarily been directed towards the design of uroselective alpha1-adrenoceptor antagonists for the treatment of benign prostatic hyperplasia (BPH). Evidence is accumulating for the involvement of a novel alpha1-adrenoceptor, designated as alpha1L-adrenoceptor, in alpha1-adrenoceptor-mediated smooth muscle contraction in prostatic and other urogenital tissues. While several antagonists showing a high degree of uroselectivity in animal models have been identified, their clinical superiority over the currently available alpha1-adrenoceptor antagonists has not yet been demonstrated. It is possible that the interaction with alpha1-adrenoceptors, as yet uncharacterised subtypes, at non-prostatic sites contributes to the therapeutic activity of this drug class in BPH. The alpha1-adrenoceptor subtypes involved in the control of vascular tone are currently being evaluated, and the profile of interaction with the various alpha1-adrenoceptor subtypes may play a key role in the efficacy of cardiovascular drugs such as carvedilol. Alpha2-adrenoceptor agonists are now being employed for a variety of therapeutic applications, most involving actions on receptors within the central nervous system (CNS). These agents are useful in the treatment of hypertension, glaucoma, opiate withdrawal and attention deficit hyperactivity disorder (ADHD), and as analgesics and adjuncts to general anaesthesia. While subtype selectivity has not yet been applied to the design of new alpha2-adrenoceptor agonists for these applications, recent gene mutation/knock-out experiments have identified the alpha2-subtypes involved in some of these actions, and optimisation of a therapeutic profile may be possible. Furthermore, the design of agents combining affinities for multiple adrenoceptor subtypes, or the combination of a specific adrenoceptor affinity profile with another pharmacological action, may offer advantages over molecules selective for an individual adrenoceptor subtype.

Pharmacological characteristics of Ro 115-1240, a selective alpha1A/1L-adrenoceptor partial agonist: a potential therapy for stress urinary incontinence

OBJECTIVE

To describe the preclinical pharmacology of Ro 115-1240, a peripherally acting selective alpha1A/1L-adrenoceptor (AR) partial agonist, compared with the alpha1A/1L-AR full agonist amidephrine, as AR agonists have some utility in the treatment of stress urinary incontinence (SUI) but are limited by undesirable cardiovascular and central nervous system side-effects.

RESULTS

In radioligand-binding studies Ro 115-1240 had greater affinity for alpha1A than for alpha1B and alpha1D subtypes. The potency and intrinsic activity of amidephrine and Ro 115-1240 relative to noradrenaline were determined in native and cell-based assays using human recombinant alpha1-ARs; they acted as selective alpha1A/1L-AR full and partial agonists, respectively. In anaesthetized micropigs and rabbits, amidephrine and Ro 115-1240 produced non-selective, dose-dependent increases in intraurethral and arterial blood pressures but the magnitude of the pressure increases evoked by Ro 115-1240 were about a third of those with amidephrine. In conscious micropigs both agents produced dose-dependent increases in urethral tension. Again, the magnitude of the urethral response to Ro 115-1240 was about a third of that with amidephrine. More importantly, only amidephrine produced dose-dependent increases in blood pressure and decreases in heart rate. Ro 115-1240 produced a maximum increase in urethral tension with no effect on blood pressure or heart rate.

CONCLUSION

These results show that by combining selectivity for the alpha1A/1L-AR subtype with a reduction in intrinsic agonist efficacy, Ro 115-1240 has reduced haemodynamic effects while retaining to some degree the contractile effects on urethral smooth muscle. These studies indicate that Ro 115-1240 may be useful as a novel treatment for SUI.

Method for simultaneous recording of the prostatic contractile and urethral pressure responses in anesthetized rats and the effects of tamsulosin

We simultaneously recorded the prostatic contractile and urethral pressure responses to electrical stimulation (ES) of the hypogastric nerves (HGNs) or phenylephrine in anesthetized rats and studied the effects of tamsulosin on these responses. At 0.01 and 0.1 mg/kg, i.v., tamsulosin inhibited the prostatic responses to ES of the HGNs in a dose-dependent manner, while at 1 microg/kg, i.v., it reduced the response to phenylephrine (0.01 mg/kg, i.v.) to about 26% of the nonantagonized level. These inhibitory effects on prostatic responses were maintained for 60 min. Tamsulosin exerted an inhibitory effect on the urethral response to ES of the HGNs at 0.01 mg/kg, i.v. but not at 0.1 mg/kg, i.v. At 1 microg/kg, i.v., tamsulosin also reduced the urethral response to phenylephrine to about 46% of the nonantagonized level; this effect was maintained for 60 min. Furthermore, tamsulosin was found to exert a stronger inhibitory effect on the prostatic response than on the urethral response induced by sympathetic nerve activation. Our findings suggest that rat urethral sympathetic nerve terminals may contain prejunctional alpha1 adrenoceptors that modulate the release of norepinephrine.

N-[3-(1H-imidazol-4-ylmethyl)phenyl]ethanesulfonamide (ABT-866, 1),(1) a novel alpha(1)-adrenoceptor ligand with an enhanced in vitro and in vivo profile relative to phenylpropanolamine and midodrine

N-[3-(1H-Imidazol-4-ylmethyl)phenyl]ethanesulfonamide (ABT-866, 1) is a novel alpha(1) agent having the unique profile of alpha(1A) (rabbit urethra, EC(50) = 0.60 microM) agonism with alpha(1B) (rat spleen, pA(2) = 5.4) and alpha(1D) (rat aorta, pA(2) = 6.2) antagonism. An in vivo dog model showed 1 to be more selective for the urethra over the vasculature than A-61603 (2), ST-1059 (3, the active metabolite of midodrine), and phenylpropanolamine (4).

Characterisation of the functional alpha-adrenoceptor subtype in the isolated female pig urethra

The aim of the present study is to characterise the contraction-mediating functional alpha-adrenoceptor of the female pig urethra. Alpha-adrenoceptor reference agonists were used to contract the isolated female pig urethra. The relative intrinsic activity was noradrenaline (1.0), phenylephrine (0.91), methoxamine (0.74), (+/-)-3'-(2-amino-1-hydroxyethyl)-4'-fluoromethane-sulfonanilid e hydrochloride (NS-49) (0.68), oxymetazoline (0.60), dopamine (0.50), clonidine (0.43), midodrine (0.32), ephedrine (0.30), 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK 14,304) (0.11), and phenylpropanolamine (0.11). The 21 competitive antagonists used caused parallel rightward shifts in the alpha-adrenoceptor agonist concentration-response curves, giving linear Schild-plots with slopes not significantly different from unity, suggesting that contraction was mediated by a single receptor. The antagonist pK(B) values calculated were R(-)-tamsulosin (9.68), risperidone (9.19), 2-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-4,4-dimethyl-1,3(2H,4H)-+ ++isoquinolinedione (AR-C 239) (9.09), 2-([2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB-4101) (8.87), N-[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]-3-methyl-4-oxo-2-phenyl- 4H-1-benzopyran-8-carboxamide monomethanesulfonate (Rec 15/2739/3) (8.81), 5-methylurapidil (8.59), prazosin (8.57), benoxathian (8.56), S(+)-tamsulosin (8.27), indoramin (8.11), doxazosin (7.96), alfuzosine (7.82), phentolamine (7.70), terazosin (7.52), spiperone (7.48), oxymetazoline (7.40), 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]deca ne-7,9-dione dihydrochloride (BMY 7378) (7.05), corynanthine (6.98), rauwolscine (6.40), yohimbine (6.22), and N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alpha-dime thyl-1H-indole-3-ethanamine hydrochloride (RS 17053) (6.07). Correlation of subtype-selective antagonist pK(B) values was best with published values for the alpha1a/1A-adrenoceptor subtype. Therefore, the present results suggest that contraction of the female pig urethra is caused by activation of the alpha1A-adrenoceptor.

Antagonism to noradrenaline-induced lethality in rats is related to affinity for the alpha1A-adrenoceptor subtype

The potency of several alpha1-adrenoceptor antagonists in preventing the noradrenaline-induced lethality in conscious rats, their binding affinity for the native alpha1A- and alpha1B-adrenoceptors, the recombinant animal alpha1a-, alpha1b- and alpha1d-adrenoceptor subtypes, as well as their functional affinity for the alpha1L-adrenoceptor subtype were evaluated. The potency of the tested compounds as antagonists of noradrenaline-induced lethality was correlated with the affinity for the alpha1A- (and alpha1a-) adrenoceptor subtype, but not with the affinity for the other subtypes. On the contrary, the hypotensive effects of the compounds, assessed in anesthetized rats, were not clearly related with the affinity for any of the alpha1-subtypes. These results suggest that the alpha1A-subtype plays a determining role in preventing lethality induced by noradrenaline in the rats, and that this activity is unrelated to the hypotensive effect of the compounds, which cannot be clearly correlated with affinity for a particular alpha1-adrenoceptor subtype.

Subtype-specific differences in subcellular localization of alpha1-adrenoceptors: chlorethylclonidine preferentially alkylates the accessible cell surface alpha1-adrenoceptors irrespective of the subtype

Selective inactivation of alpha1B-adrenoceptor (AR) by the site-directed alkylating agent chlorethylclonidine (CEC) has been used as one of major pharmacological criteria to subclassify alpha1-AR; however, the mechanism for the differential CEC sensitivity of the two subtypes is uncertain, and the extent of CEC inactivation varies depending on the treatment employed. In this study, we examined the correlation between the subcellular localization of alpha1-AR subtypes (alpha1A and alpha1B) and CEC sensitivity. Constructing alpha1-AR tagged with the FLAG epitope at the amino terminus and/or green fluorescent protein (GFP) at the carboxyl terminus, we examined the subcellular distribution of alpha1-ARs expressed in COS-7 cells. Flow cytometry analysis showed that most populations of GFP-expressing alpha1B-AR cells, but very few GFP-expressing alpha1A-AR cells, were detected by the anti-amino terminus antibodies. The immunocytochemical and GFP-fluorescence confocal micrographs showed that alpha1A-ARs predominantly localize intracellularly, whereas alpha1B-ARs localize on the cell surface. Furthermore, CEC (10 microM) treatment of intact cells resulted in an inactivation of approximately 42% of alpha1A-ARs and 93% of alpha1B-ARs, whereas treatment of the membrane preparations resulted in an inactivation of approximately 83% of alpha1A-ARs and 88% of alpha1B-ARs, respectively. Together, the results showed that a hydrophilic alkylating agent CEC preferentially inactivates alpha1-AR on the cell surface irrespective of its subtype, and that the subtype-specific subcellular localization rather than the receptor structure is a major determinant for CEC inactivation of alpha1-AR. Subtype-specific subcellular localization suggests an additional class of functional properties that provide new insight into drug action.

Analysis of alpha1-adrenoceptors in rabbit lower urinary tract and mesenteric artery

In this study, we have investigated the effects of a series of alpha1-adrenoceptor antagonists on the phenylephrine-mediated contractions of rabbit isolated prostate, urethra, trigone and mesenteric artery. With the exception of RS-17053 (N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alpha-dim ethyl-1 H-indole-3-ethanamine hydrochloride), the antagonists displayed the lowest potency in the urethra. Catecholamine uptake1 and uptake2 appeared not to be the cause for the low pK(B)/pA2 values obtained in the urethra because cocaine and corticosterone had no effect on the potency of phenylephrine in this tissue. The low potencies displayed by prazosin. RS-17053 and HV723 (alpha-ethyl-3,4,5-trimethoxy-alpha-(3-((2-(2-methoxyphenoxy)ethyl)amino )propyl)benzene-acetonitrile fumarate) suggest that the functional receptors in all four tissues belong to the alpha(1L)-adrenoceptor class. Whether or not the significant between-tissue differences in antagonist potencies are due to heterogeneity of this receptor class remains to be elucidated.

Pharmacological characterization of alpha 1-adrenoceptor subtype mediating regulation of arterial pressure and urethral perfusion pressure in the anaesthetized rat

1. The alpha 1-adrenoceptor subtypes mediating the regulation of arterial pressure (AP) and urethral perfusion pressure (UP) in the anaesthetized rat were characterized by using selective alpha 1-adrenoceptor agonists and antagonists. 2. Intravenous administration of selective alpha 1-adrenoceptor agonists elicited a dose-dependent increase in AP and UP. The rank order of agonist potency: oxymetazoline (ED50, 6.2 and 8.2 nmol kg-1 > phenylephrine (ED50, 32 and 27 nmol kg-1 > methoxamine (ED50, 300 and 296 nmol kg-1 was the same for AP and UP, respectively. 3. The effects of phenylephrine on AP and UP were antagonized, in a dose related-manner, by pretreatment with alfuzosin, BMY 7378, 5-methyl-urapidil, phentolamine, prazosin, spiperone and WB 4101.5-methyl-urapidil was the only alpha 1-adrenoceptor antagonist more potent on UP than on AP. 4. The potency of the different alpha 1-adrenoceptor antagonists tested on AP and UP was significantly correlated with their binding affinity for the expressed recombinant alpha 1a-, but not alpha 1b- or alpha 1d-, adrenoceptor subtype. 5. The results suggest that in the anaesthetized rat (1) both AP and UP are regulated by the alpha 1A-adrenoceptor subtype; and (2) the urogenital selectivity of 5-methyl-urapidil may be due to the existence of multiple forms of the alpha 1A-adrenoceptor.