The Role of M2 Muscarinic Receptor Subtypes Mediating Contraction of the Circular and Longitudinal Smooth Muscle of the Pig Proximal Urethra:

Alpha1A/L-adrenoceptors mediate contraction of the circular smooth muscle of the pig urethra

Sympathetically mediated urethral tone is essential for the maintenance of continence and involves the activation of postjunctional alpha(1)-adrenoceptors. This study characterizes the alpha(1)-adrenoceptor subtypes responsible for mediating contraction of the urethral circular smooth muscle of the pig. The potency order of a number of agonists and the affinities of several receptor selective antagonists were determined on pig-isolated circular smooth muscle strips in the presence of cocaine (1 microm) and corticosterone (10 microm) to inhibit amine uptake and propranolol (1 microm) to antagonize beta-adrenoceptors. The potency order for agonists was N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulphonamide (A61603) > noradrenaline = phenylephrine = M6434 > methoxamine with pEC(50) values of 7.3, 5.8, 5.7, 5.6 and 5.0 respectively. 4 The alpha(1D)-adrenoceptor-selective antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]decane-7,9-dione (BMY7378) caused rightward shifts of the concentration-response curves to noradrenaline, yielding a low affinity estimate (6.6) for the urethral receptor. The alpha(1A)-adrenoceptor-selective antagonists, RS100329 and 5-methylurapidil, gave relatively high affinity estimates (9.6 and 8.8 respectively) for this receptor. All three antagonists produced Schild plots with slopes close to unity but did reduce maximum responses at higher concentrations. Prazosin antagonized responses of the urethra to noradrenaline, yielding a mean affinity estimate of 9.0. Although the Schild plot for prazosin again had a slope of unity, this drug also reduced maximum responses to noradrenaline at all concentrations examined (10-100 nm). N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alpha-dimethyl-1H-indole-3-ethanamide (RS17053), which discriminates between responses mediated via alpha(1A) (high affinity) and alpha(1L)-adrenoceptors (low affinity) at concentrations up to 3 microm, failed to antagonize responses of the urethra. 5 These results suggest that contraction of urethral circular smooth muscle in the pig is mediated via a single population of adrenoceptors with the pharmacological characteristics of the alpha(1A/L)-adrenoceptor, most probably the alpha(1L)-adrenoceptor.

Combination of a cholinergic drug and an alpha-blocker is more effective than monotherapy for the treatment of voiding difficulty in patients with underactive detrusor

AIM

The aim of the present study was to compare the effectiveness of a cholinergic drug, an alpha-blocker and combinations of the two for the treatment of underactive detrusor.

METHODS

One hundred and nineteen patients with underactive bladder were assigned to three groups: the cholinergic group, consisting of 40 patients taking bethanechol chloride (60 mg/day) or distigmine bromide (15 mg/day); the alpha-blocker group, consisting of 38 patients taking urapidil (60 mg/day); and the combination group, consisting of 41 patients taking both a cholinergic drug and an alpha-blocker. The effectiveness of each therapy was assessed 4 weeks after initialization of the therapy.

RESULTS

Total urinary symptom scores (International Prostate Symptom Score, IPSS) remained unchanged after the cholinergic therapy, but were significantly lower after the alpha-blocker treatment (P = 0.0001) and the combination therapy (P = 0.0001). With regard to the total IPSS, there were significant differences between the cholinergic and the alpha-blocker groups (P = 0.0008), and also between the cholinergic and combination groups (P = 0.0033), in favor of the latter. The average and maximum flow rates did not increase significantly after monotherapy with either the cholinergic drug or the alpha-blocker, but they significantly increased after combination therapy compared to baseline values (P = 0.0033 and P= 0.0004, respectively). Postvoid residual volume did not decrease significantly after the cholinergic drug therapy, but decreased significantly after the alpha-blocker (P = 0.0043) and the combination therapies (P = 0.0008). The percentage of residual urine decreased significantly after therapy in all groups (P = 0.0005, P= 0.0176 and P= 0.0001, respectively).

CONCLUSION

Combination therapy with a cholinergic drug and an alpha-blocker appears to be more useful than monotherapy for the treatment of underactive detrusor.