Beta-adrenergic activity in human proximal urethra: a study with terbutaline

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Identification of beta-adrenoceptor subtypes in lower urinary tract of the female pig

PURPOSE

We investigated the presence and functional role of beta-adrenoceptor subtypes in the bladder base and proximal urethra of the female pig.

MATERIALS AND METHODS

Saturation experiments were done with 7 concentrations (0.25 to 16 nM.) of [(3)H]-dihydroalprenolol (NEN Life Science Products, Boston, Massachusetts). Competition experiments with [(3)H]-dihydroalprenolol were performed with unlabeled antagonists (beta1 selective CGP20712A, beta2 selective ICI118551 and beta3 selective SR59230A). In functional studies concentration-relaxation curves to the beta3-agonist BRL37344 were obtained and antagonist affinities for SR59230A were determined.

RESULTS

CGP20712A displaced [(3)H]-dihydroalprenolol with low affinity, suggesting that beta1-adrenoceptors were not present. Displacement with ICI118551 in the bladder base and urethra best fitted a 2-site model with 20% and 28% high affinity sites (beta2), respectively. Displacement experiments with SR59230A in the bladder base demonstrated that 59% of binding sites had high affinity (beta3). In the urethra displacement with SR59230A best fitted a 1-site model but with a pK(i) of 7.2 that was intermediate between that expected for beta2 and beta3-adrenoceptors. In functional studies BRL37344 induced relaxation with pEC50 values of 5.5 and 8, and a maximum relaxation response relative to 30 microM. isoprenaline of 79% and 90% in the bladder base and urethra, respectively. The affinity value of SR59230A for the response to BRL37344 was 7.87 and 7.71 in the bladder base and urethra, respectively, which were intermediate between those of beta2 and beta3-adrenoceptors.

CONCLUSIONS

Apparently beta3-adrenoceptors are the predominant beta-adrenoceptor subtype present in the lower urinary tract of the pig.

The urethral resistance to rapid dilation: an analysis of the effect of autonomic receptor stimulation and blockade and of pudendal nerve blockade in healthy females

The urethral closure function is based upon permanently as well as adjunctively acting closure forces during rest and stress episodes, respectively. During urine ingression intra- and peri-urethral structures are suddenly stretched resulting in a pressure response which strengthens the closure function by sustaining the resistance to dilatation of the urethra. A method for measurement of the resistance to rapid urethral dilatation was used to evaluate the influence of noradrenaline, prazosin, terbutaline, propranolol, carbachol, and atropine, as well as bilateral pudendal nerve blockades in 40 healthy women. The drugs caused no significant change in the urethral resistance to dilatation, whereas the pudendal blockade produced a significant (p < 0.05) reduction at the bladder neck and in the high pressure zone. Although a quantitative assessment of their contribution cannot be obtained from this study, it may be concluded that the striated muscles innervated by the pudendal nerve are of major importance for the urethral resistance to dilatation.

Facilitatory and inhibitory effects of selective norepinephrine reuptake inhibitors on hypogastric nerve-evoked urethral contractions in the cat: a prominent role of urethral beta-adrenergic receptors

Tricyclic antidepressants (TCA), such as imipramine, are well-accepted for the treatment of urinary incontinence and enuresis, but their mechanism of action remains undefined due to their multiple pharmacological actions. To explore only the contribution imparted by sympathomimetic effects on the urethra by norepinephrine (NE) reuptake inhibition, two selective NE reuptake inhibitors (nisoxetine and tomoxetine) that possess no antimuscarinic or serotonergic properties were examined for their effects on sympathetic hypogastric nerve (HgN) evoked urethral contractions in chloralose anesthetized cats. Under control conditions, HgN stimulation produced a biphasic response composed of a consistent initial contraction that was prazosin- (alpha adrenergic antagonist) sensitive, followed by a more variable relaxation that was propranolol- (beta adrenergic antagonist) sensitive. Unexpectedly, nisoxetine (0.03 to 1.0 mg./kg. intravenously, n = 6) and tomoxetine (0.3 to 3 mg./kg. intravenously, n = 3) produced decreases (about 50% to 60% of control) in HgN-evoked contractions. These inhibitory effects of the reuptake inhibitors were reversed by propranolol. In cats that were pretreated with propranolol, nisoxetine produced a significant increase in HgN-evoked contractions. In conclusion, these results indicate that inhibition of NE reuptake into the sympathetic nerve terminal produces a relative increase in the activation of beta adrenergic receptors compared with alpha adrenergic receptors in the urethra. This increased beta receptor stimulation might be due to a greater diffusion of NE away from the neuro-effector junction to extrajunctional sites following blockade of junctional reuptake. These findings should highlight the importance of urethral beta adrenergic receptors, which is not well-recognized in the literature.

Effects of beta 2-stimulants on contractility and fatigue of canine urethral sphincter

The effects of beta 2-stimulants [clenbuterol (CB) and terbutaline (TB)] on the contractility of the urethral sphincter of female dogs were studied by measuring intraurethral pressure (IUP) during stimulation of bilateral pudendal nerves. In nine dogs 1, 10 and 100 micrograms/kg. of CB were administered, but no changes in IUP were observed. In the other 33 dogs, sphincteric fatigue was experimentally prepared by electrically stimulating the pudendal nerves at 15 V, 20 Hz for 30 to 40 minutes. In fatigued sphincters, CB (n = 17) and TB (n = 7) increased the contracting pressure (pressure difference between stimulation-generated peak level and baseline level of IUP). The inotropic effect of beta 2-stimulant (TB) on the fatigued urethral sphincter was abolished by a beta-blocker, propranolol. From the present study it was concluded that beta 2-stimulants have little effect on the total contractility of the nonfatigued urethral sphincter because it is composed of smooth and striated muscles (fast- and slow-contracting muscles). However, beta 2-stimulants enhanced the contractility of fatigued urethral sphincter. These results suggest that beta 2-stimulants act on fast-contracting fibers in the urethral sphincter because the inotropic effect of sympathomimetic amine is much greater on fatigued, fast-contracting fibers than on nonfatigued ones and its depressive effect on slow-contracting fibers is not potentiated after fatigue.

The influence of beta-adrenoceptor and muscarinic receptor agonists and antagonists on the static urethral closure function in healthy females

The effects of terbutaline, propranolol, carbachol, and atropine on the static urethral closure function were investigated in 20 healthy women. Terbutaline caused a statistically reduction of the urethral pressure in the high pressure zone, but not at the bladder neck or in the distal urethra. The other drugs caused no significant pressure changes. None of the drugs used produced significant changes in the static viscoelastic properties, elastance, and hysteresis of the resting urethra. It is suggested that terbutaline partly reduces intraurethral pressure by reducing muscular tone in the rhabdosphincter and pelvic floor.

Antibiotic prophylaxis after instrumentation for urodynamic testing

This study of 96 women shows that there is doubtful value in routine antibiotic prophylaxis after urodynamic investigation. An unexpectedly high number of women harboured unsuspected infections at the time of evaluation despite prior screening, which suggests prophylaxis would be more useful if given before the tests.