Phasic non-micturition contractions in the bladder of the anaesthetized and awake rat.

OBJECTIVE: To characterize the contractile activity that occurs in the bladder during the filling phase of the micturition cycle (non-micturition contractions, NMCs), which generate transient rises in intravesical pressure not associated with urine flow. MATERIALS AND METHODS: The experiments were conducted using anaesthetized (chloral hydrate) and un-anaesthetized rats. In un-anaesthetized rats bladder contractile activity was measured using an intravesical cannula implanted under full surgical anaesthesia 3 days previously. In the anaesthetized rats the bladder was exteriorized and a cannula inserted through the dome. In these experiments electrical activity within the detrusor was also measured with a suction electrode on the bladder surface. For each rat, the experimental protocol involved filling the bladder at a constant rate (10 mL/h) to evoke micturition cycles, or infusion of a fixed volume and recording made under effective isovolumetric conditions. RESULTS: In both anaesthetized and un-anaesthetized rats there were transient rises in bladder pressure (0.5-3 cmH2O). In the anaesthetized rats the amplitude of the transients increased throughout the filling phase, with little change in frequency. The phasic NMCs generating these pressure transients were accompanied by electrical changes in the detrusor. In the middle phase of bladder filling the slow pressure changes were accompanied by slow waves of electrical activity which changed in the pressure cycles immediately before micturition to high-frequency low-amplitude signals. In the un-anaesthetized rats there was a period immediately after voiding where there was no activity. As filling proceeded, low-amplitude low-frequency NMCs appeared that gradually increased in frequency and amplitude during the filling phase. However, the frequency of the transients decreased immediately before micturition despite an increase in amplitude. Similar responses were seen during isovolumetric recording. CONCLUSION: The present results show the presence of NMCs in the rat bladder, identify volume-dependent changes in the pattern of this activity during the micturition cycle, and show that NMCs are accompanied by electrical changes in the detrusor. The physiological significance of NMCs is not known but it might be linked to the generation of afferent discharge from mechanoreceptors in the wall, so contributing to sensations related to bladder volume.

Division of the male rat rhabdosphincter into structurally and functionally differentiated parts.

In order to understand the structure-function relationship in the male rat rhabdosphincter, the 3D structure of the striated muscle and associated dense connective tissue was reconstructed from representative serial sections cut from the proximal urethra harboring the muscle. The 3D structure was correlated with electromyography (EMG) of the rhabdosphincter, urodynamic parameters (bladder pressure and flow rate), and longitudinal contraction force of the proximal urethra. The muscular component of the rhabdosphincter consisted of a homogeneous population of the fast-twitch-type fibers. In the cranial part, striated muscle formed a complete ring encircling the urethra, deferent ducts, and ducts from seminal vesicles and prostatic lobes. Toward the middle part, the amount of densely packed connective tissue lacking type III collagen increased anteriorly and posteriorly and penetrated the muscular ring that became divided first posteriorly and then anteriorly into two symmetrical halves. In the caudal part, a thin midsagittal dense connective tissue septum remained posteriorly. EMG recordings suggested that the rhabdosphincter muscle was functionally divided into two parts. Unlike the cranial and middle parts, the caudal part did not show the first depolarization peak. It appears that rapid oscillatory oblique-to-circular muscular contractions proceeding in craniocaudal direction in the cranial and middle part draw the anterior wall supported by arch-like dense connective tissue closer to the posterior wall supported by a more rigid rhomboidal raphe. Longitudinal contractions of the urethra are possibly evoked from the proximal and caudal parts of rhabdosphincter. These could lead to simultaneous increase in urethral pressure ensuring rapid urine flow rate. The caudal part could augment the opening of urethral lumen during oscillatory voiding.

A dose-dependent dual effect of oestrogen on voiding in the male mouse?

OBJECTIVES: To explore the effect of different degrees of oestrogenization on male voiding, by treating adult castrated and 5alpha-dihydrotestosterone (DHT)-maintained male mice with different doses of oestrogens, as exposure of male mice to excessive amounts of oestrogens can cause bladder outlet obstruction (BOO); in addition, male mice lacking oestrogen receptor (ER)alpha (ERKO) or ERbeta (BERKO) were studied to assess the importance of ER subtypes. MATERIALS AND METHODS: Castrated, DHT-maintained adult mice were treated with 17beta-oestradiol (E(2); 50 and 250 microg/kg) or oestrone (E(1); 5, 50 and 500 microg/kg) daily for 10 days. Control mice were treated only with the vehicle. BERKO and ERKO mice, and their wild-type littermates used as their controls, remained untreated. Under anaesthesia, the bladder and distal urethra were exposed to record simultaneously the bladder pressure and urinary flow rate from the distal urethra. RESULTS: E(2)-treated mice showed obstructive voiding, seen as increased bladder pressure, decreased average flow rate and prolonged micturition time. This was also evident when a high dose (500 microg/kg) of E(1) was used. After treatment with a dose of 50 microg/kg, the urodynamic variables were similar to those in the control mice. Surprisingly, after treatment with a low dose (5 microg/kg) all urodynamic variables improved. There was a minor increase in the bladder pressure in BERKO mice; ERKO mice had a significantly lower urinary flow rate. CONCLUSIONS: High doses of oestrogens caused BOO in castrated, DHT-maintained male mice. A small dose of E(1) had a positive effect on voiding, suggesting that oestrogens are needed for normal male voiding. Reduced urinary flow rates in ERKO mice suggest that oestrogen effects on voiding are mediated at least partly via ERalpha.

Transmitters contributing to the voiding contraction in female rats.

OBJECTIVES: To assess in detail the contribution of acetylcholine and ATP to the different phases of the voiding contraction, urine flow and rhabdosphincter electromyographic (RB-EMG) activity in rats, using alpha,beta-methylene-ATP (desensitizing purinoceptors) and atropine (blocking muscarinic receptors). These agents and possibly other transmitters contribute to bladder emptying in rats, but how they contribute to the different phases of the micturition cycle, including the intraluminal pressure high-frequency oscillations (IPHFOs) is unclear. MATERIALS AND METHODS: Adult anaesthetized female Sprague-Dawley rats were used; intravesical pressure, RB-EMG and urine flow from the distal urethra were recorded. After baseline recordings, alpha,beta-methylene-ATP (0.5 mg/kg), atropine (1 mg/kg), or both, were injected intravenously. RESULTS: Alpha,beta-Methylene-ATP significantly decreased the maximum bladder pressure during the first micturition phase, whereas atropine had little effect; the maximum bladder pressure during the second phase was also reduced. IPHFOs were apparent after both treatments. Atropine significantly reduced the maximum bladder pressure during the third phase. The maximum urinary flow rate was reduced by both alpha,beta-methylene-ATP and atropine; after exposure to both agents together, urinary flow was markedly reduced or stopped, and overflow incontinence developed. CONCLUSIONS: ATP contributes mainly to the initial and acetylcholine to the later phases of the voiding cycle in the rat. Neither agent abolished the IPHFOs; even after blocking the receptors for one transmitter and in the presence of IPHFOs, the bladder can still empty. However, if both receptors are blocked, overflow incontinence develops, suggesting that even if further transmitters are taking part in the voiding contraction, their physiological significance is questionable.

The role of the rhabdosphincter in female rat voiding.

OBJECTIVES: To obtain information on the mechanisms of female rat micturition using a model in which pressure was measured in the bladder and distal part of the urethra corresponding to the location of the rhabdosphincter, providing information on the role of the sphincter in opening and closing the urethral lumen. MATERIALS AND METHODS: A micturition reflex was induced in adult anaesthetized (chloral hydrate and urethane) female rats by filling the bladder with saline. Bladder pressure (BP), urethral pressure (UP), electromyography (EMG) of the middle part of the rhabdosphincter, and urinary flow rate in the distal urethra were simultaneously recorded. RESULTS: There were four phases of the micturition contraction, the second characterized by intraluminal pressure high-frequency oscillations (IPHFOs) of BP. When a non-oscillatory micturition contraction started, the BP increased and exceeded UP for the rest of the micturition contraction. Even though the BP increased during this first phase, the urethral lumen stayed closed. Its opening was indicated by a simultaneous decrease in BP and increase of UP as the fluid flowed from the bladder to the urethra. When the rhabdosphincter closed, as indicated by an EMG-burst of the muscle, the UP declined, bladder pressure increased and the flow ceased. Because of momentary contractions of the rhabdosphincter, the UP and urine flow rate had the same periodicity as the IPHFOs of BP. CONCLUSIONS: The simultaneous recording of the BP, UP, EMG of the rhabdosphincter and urinary flow rate showed the sequence of events during micturition. The rhabdosphincter acts as an 'on-off' switch, causing interruptions in the urinary flow rate.

Developmental, estrogen induced infravesical obstruction is reversible in adult male rodents.

PURPOSE: We treat neonatally estrogenized rats and aromatase over expressing AROM+ male mice with infravesical obstruction using the specific aromatase inhibitors finrozole and letrozole, and analyzed whether developmentally induced alterations in urodynamics and rhabdosphincter are reversible in adulthood. MATERIALS AND METHODS: Adult estrogenized rats and AROM+ mice were treated with aromatase inhibitors for 6 weeks. Maximal and mean bladder pressure, the urinary flow rates and electromyography activity were recorded from the proximal rhabdosphincter. In addition, proximal rhabdosphincter thickness in the AROM+ mouse was measured and correlated with seminal vesicle size and serum testosterone concentrations. RESULTS: Finrozole and/or letrozole treatment significantly increased the mean maximal flow rate plus or minus SD in AROM+ mice (4.7 +/- 2.0 versus 13.3 +/- 4.4 ml. per minute, p = 0.0004) and in estrogenized rats (18.4 +/- 6.18 versus 31.1 +/- 10.85 ml. per minute for finrozole p = 0.005) and 32.4 +/- 14.3 for letrozole, p = 0.005), while bladder pressure slightly decreased. The reappearance of transient repolarization, indicating urethral lumen opening, coincided with an increased flow rate on electromyography in the proximal rhabdosphincter in rats. Relative thickness of the proximal rhabdosphincter (p = 0.007), seminal vesicle size (p = 0.0002) and mean serum testosterone concentration (472.5 +/- 230.35 versus 3,065.6 +/- 1,994.67 pg./ml., p = 0.0002) were restored after finrozole treatment in AROM+ mice. CONCLUSIONS: Current findings indicate that alterations in urodynamics, seminal vesicle size, and rhabdosphincter size and function in developmentally estrogenized male rodents are reversible when treated with aromatase inhibitor.

Infravesical obstruction in aromatase over expressing transgenic male mice with increased ratio of serum estrogen-to-androgen concentration.

PURPOSE: The potential role of estrogen in the development of infravesical obstruction is still unresolved. Aromatase over expressing transgenic mice provide a novel instrument for investigating the consequences of prolonged systemic or local increases in endogenous estrogen concentrations. Two aromatase over expressing transgenic mouse strains with different prostatic phenotypes (reduced and normal size, respectively) were compared in urodynamic studies with each other and with the wild-type strain. MATERIALS AND METHODS: The bladder and urethra were exposed in adult male wild-type or transgenic mice. High frequency oscillations of intraluminal bladder pressure and flow rate from the distal urethra were simultaneously recorded with the mice under anesthesia. RESULTS: No changes were observed in voiding in MMTV-arom+ mice. These mice are known to have only slightly elevated estradiol concentrations in serum, suggesting a localized increase in estrogen production. In AROM+ mice the aromatase gene was detected in several organs, including the testis and bladder. These mice are known to have markedly increased estrogen and decreased serum androgen concentrations, and reduced prostate size. Compared with wild-type mice AROM+ mice showed higher mean maximal bladder pressure plus or minus standard deviation (33.1 +/- 6.4 versus 25.6 +/- 4.8 mm. Hg, p = 0.046) and decreased mean maximal flow rate (3.1 +/- 1.6 versus 17.7 +/- 5.4 ml. per minute, p <0.0001), consistent with the presence of the infravesical obstruction. Morphologically the proximal rhabdosphincter in AROM+ mice showed atrophy (relative mean thickness 0.005 +/- 0.015 versus 0.013 +/- 0.002 mm., p <0.0001). CONCLUSIONS: Activation of the aromatase gene during an earlier developmental stage under the ubiquitin C promoter and highly elevated serum estrogen concentrations may explain the differences in voiding and prostate size in the AROM+ mouse strain.

Similarities and differences in female and male rat voiding.

We measured in adult rats, under anaesthesia, bladder pressure by transvesical cystometry and flow rate by an ultrasound transducer in the distal urethra. The urinary flow was discontinuous in both sexes. No difference between the sexes in bladder pressure oscillations or in non-oscillatory voiding was found but during the oscillatory activity there was a difference in the relationship between bladder pressure and urinary flow. In the female, the bladder pressure decreased when the flow started and increased when the flow decreased resembling species whose urinary flow is continuous. Basically the flow was stable but it was divided into periods of variable duration by full or partial closure of urethral sphincter. In the male rat, the oscillatory flow consisted of short, fast spikes occurring just before the bladder pressure reached the maximum, after which the flow spike decreased slowly. Overall, no differences were seen in bladder pressure data between the genders. However, the maximal flow rate was lower and micturition time was shorter in female rats. When we recorded occasionally occurring micturitions without high-frequency oscillations of intraluminal pressure (IPHFOs) (non-oscillatory voiding), no differences between the genders were seen. The difference during oscillatory voiding between male and female rat can be understood against anatomical and hormonal backgrounds, and by the relative role of rhabdosphincter, which did not activate during non-oscillatory voidings when no differences were detected.