[In vitro study of morphology of the bladder wall using MR tomography at 1.0 Tesla: correlation with histology]

Locational and Directional Dependencies of Smooth Muscle Properties in Pig Urinary Bladder

The urinary bladder is a distensible hollow muscular organ, which allows huge changes in size during absorption, storage and micturition. Pathological alterations of biomechanical properties can lead to bladder dysfunction and loss in quality of life. To understand and treat bladder diseases, the mechanisms of the healthy urinary bladder need to be determined. Thus, a series of studies focused on the detrusor muscle, a layer of urinary bladder made of smooth muscle fibers arranged in longitudinal and circumferential orientation. However, little is known about whether its active muscle properties differ depending on location and direction. This study aimed to investigate the porcine bladder for heterogeneous (six different locations) and anisotropic (longitudinal vs. circumferential) contractile properties including the force-length-(FLR) and force-velocity-relationship (FVR). Therefore, smooth muscle tissue strips with longitudinal and circumferential direction have been prepared from different bladder locations (apex dorsal, apex ventral, body dorsal, body ventral, trigone dorsal, trigone ventral). FLR and FVR have been determined by a series of isometric and isotonic contractions. Additionally, histological analyses were conducted to determine smooth muscle content and fiber orientation. Mechanical and histological examinations were carried out on 94 and 36 samples, respectively. The results showed that maximum active stress (p_act ) of the bladder strips was higher in the longitudinal compared to the circumferential direction. This is in line with our histological investigation showing a higher smooth muscle content in the bladder strips in the longitudinal direction. However, normalization of maximum strip force by the cross-sectional area (CSA) of smooth muscle fibers yielded similar smooth muscle maximum stresses (165.4 ± 29.6 kPa), independent of strip direction. Active muscle properties (FLR, FVR) showed no locational differences. The trigone exhibited higher passive stress (p_pass ) than the body. Moreover, the bladder exhibited greater p_pass in the longitudinal than circumferential direction which might be attributed to its microstructure (more longitudinal arrangement of muscle fibers). This study provides a valuable dataset for the development of constitutive computational models of the healthy urinary bladder. These models are relevant from a medical standpoint, as they contribute to the basic understanding of the function of the bladder in health and disease.

Recent advances in imaging and understanding interstitial cystitis

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a debilitating condition associated with intense pelvic pain and bladder storage symptoms. Since diagnosis is difficult, prevalence estimates vary with the methodology used. There is also a lack of proven imaging tools and biomarkers to assist in differentiation of IC/BPS from other urinary disorders (overactive bladder, vulvodynia, endometriosis, and prostatitis). Current uncertainty regarding the etiology and pathology of IC/BPS ultimately impacts its timely and successful treatment, as well as hampers future drug development. This review will cover recent developments in imaging methods, such as magnetic resonance imaging, that advance the understanding of IC/BPS and guide drug development.

Neurochemical difference between somato- and viscero-projecting sensory neurons in the pig

The chemical coding of porcine somato (skin)- and viscero (urinary bladder)-projecting sensory neurons have been studied and compared using immunohistochemistry. Cell bodies of skin and bladder afferents were identified following Fast Blue injections into the skin of the hind leg as well as into wall of the urinary bladder, respectively. Immunohistochemistry revealed that small and medium-sized neurons projecting to both skin and bladder contained all of the studied substances i.e. substance P (SP), calcitonin gene-related pepide (CGRP), transient receptor potential vanilloid (TRPV1), lectin from Bandeiraea simplicifolia - Griffonia simplicifolia isolectin B4 (IB4) and galanin (GAL). Moreover, small-sized sensory neurons projecting to the bladder and skin of hind leg showed predominantly immunoreactivity to SP and TRPV1 and CGRP, as well as to CGRP and TRPV1 and IB4. It is worth stressing that the subset of sensory neurons innervating the skin exhibited these substances more often than bladder-projecting neurons. In addition, medium-sized skin-projecting neurons contained SP/GAL; SP/CGRP and CGRP/IB4 much more often than their bladder counterparts. On the other hand, small-sized perikarya that innervate the skin were less frequently expressed TRPV1, CGRP and GAL than the bladder-projecting neurons. In conclusion, the present report describes, for the first time, significant differences in the chemical coding between somato- and viscero-projecting sensory neurons in dorsal root ganglia. Moreover, these results provide morphological basis for further functional studies, which may explain the exact roles played by various subpopulations of somato- and viscero-projecting sensory neurons.

Distribution and neurochemistry of porcine urinary bladder-projecting sensory neurons in subdomains of the dorsal root ganglia: A quantitative analysis

The aim of the present study has been to verify the inter- and intraganglionic distribution pattern of porcine urinary bladder-projecting (UBP) neurons localized in the sacral dorsal root ganglia (DRGs). The morphology and chemical phenotype of these cells have also been investigated. These neurons were visualized using the fluorescent tracer Fast Blue (FB) which was injected bilaterally into the urinary bladder wall of five juvenile female pigs. The intraganglionic distribution showed that small- and medium-sized FB+ perikarya were mainly located in the central (S₃-S₄) and periphero-central (S₂) region of the ganglia, while large cells were heterogeneously distributed. Immunohistochemistry revealed that the most frequently observed markers in small and medium-sized UBP perikarya were: neurofilament 200, lectin from Bandeiraea simplicifolia (Griffonia simplicifolia) isolectin B4, substance P, calcitonin gene-related peptide, pituitary adenylate cyclase-activating polypeptide and transient receptor potential vanilloid 1. Moreover, UBP neurons containing these substances were also mainly observed in the central and periphero-central region of the ganglion. Differences in the percentage of traced cells and their neuropeptide content were observed between the S₂, S₃ and S₄ DRGs. In conclusion, the present study, for the first time, describes the arrangement of UBP DRGs neurons within particular subdomains of sacral ganglia, taking into account their size and chemical phenotype.

The validation of a functional, isolated pig bladder model for physiological experimentation

Characterizing the integrative physiology of the bladder requires whole organ preparations. The purpose of this study was to validate an isolated large animal (pig) bladder preparation, through arterial and intravesical drug administration, intravesical pressure recording, and filming of surface micromotions. Female pig bladders were obtained from the local abattoir and arterially perfused in vitro. Arterial and intravesical pressures were recorded at varying volumes. Bladder viability was assessed histologically and by monitoring inflow and outflow pH. Arterial drug administration employed boluses introduced into the perfusate. Intravesical administration involved slow instillation and a prolonged dwell-time. Surface micromotions were recorded by filming the separation of surface markers concurrently with intravesical pressure measurement. Adequate perfusion to all bladder layers was achieved for up to 8 h; there was no structural deterioration nor alteration in inflow and effluent perfusate pH. Arterial drug administration (carbachol and potassium chloride) showed consistent dose-dependent responses. Localized movements (micromotions) occurred over the bladder surface, with variable correlation with fluctuations of intravesical pressure. The isolated pig bladder is a valid approach to study integrative bladder physiology. It remains viable when perfused in vitro, responds to different routes of drug administration and provides a model to correlate movements of the bladder wall directly to variation of intravesical pressure.

Comparison of healing after cystotomy and repair with fibrin glue and sutured closure in the porcine model

PURPOSE

We compared healing after laparoscopic cystotomy using fibrin glue, sutures, or a combination to determine whether fibrin glue can obviate the need for sutures and whether there is any detriment when glue is used in the presence of sutures.

MATERIALS AND METHODS

In 24 Yorkshire pigs, a 3.5 cm vertical cystotomy was created laparoscopically and repaired as follows: Group 1--no closure; group 2--fibrin glue closure; group 3--suture repair; group 4--combined fibrin glue and suture repair. All animals had a Foley catheter for 1 week. In each group, three animals were harvested at 1 week (acute) and three animals were harvested at 6 weeks (chronic).

RESULTS

Acute: Group 1--all pigs had an unhealed defect that leaked when evaluated by cystography. Groups 2, 3, 4--mean leak pressures were 80, 97, and 60 cm H(2)O (P = 0.36), respectively. Mean bladder capacity was not significantly different between groups. Chronic: No leakage seen on a cystogram at 1 week; at 6 weeks, bladders were filled at > or =95 to 100 cm H(2)O without leakage. Histologically, there was more inflammation in the acute group v chronic group pigs. In the acute group pigs repaired with glue or suture + glue, there was more inflammation and less epithelial continuity than in the suture alone group. At 6 weeks, there was no difference between groups.

CONCLUSION

Fibrin glue provoked an intense inflammatory response that might have delayed healing acutely, resulting in a lower burst pressure in both scenarios in which it was used (i.e., alone or in combination with sutures). However, by 6 weeks, there did not seem to be any difference between groups either clinically or histopathologically.

The extracorporeal perfusion of the female pig detrusor as an experimental model for the study of bladder contractility

AIMS

The objective of the study was to establish an experimental model for the extracorporeal perfusion of the pig detrusor. In order to validate this model we examined some biochemical parameters and determined the effect of carbachol on the contractility of perfused female pig bladders.

METHODS

Twenty-six pig bladders were perfused with Krebs-Ringer bicarbonate-glucose buffer for a period up to 5 hr with the aim to preserve a viable organ, which would be responsive to contraction-inducing agents. The intravesical pressure of the bladder as well as the intraarterial pressure of the vesical arteries were recorded before and after administration of carbachol.

RESULTS

The perfusate pH, lactate, partial carbon dioxide tension, and the ATP content in the perfused tissue, all indicators of tissue ischemia or cell necrosis, showed a good preservation of the organ for up to 5 hr. Carbachol was able to induce contractions of the prefilled bladder with a complete draining of the bladder throughout the whole perfusion period.

CONCLUSIONS

We could demonstrate that this perfusion system was able to preserve the pig bladder in a functional condition, appropriate for the study of physiological questions.

Contractile properties of the proximal urethra and bladder in female pig: morphology and function

AIMS

To compare the contractile properties of proximal urethral and bladder muscle of the female pig.

MATERIALS AND METHODS

In two proximal segments (I and II) of the urethra, small muscle bundles were excised to measure the force-length (maximum force) and the force-velocity (unloaded shortening velocity) relation using the stop-test. The rate of force development was calculated using phase plots. Contractile properties of urethral and bladder segments were statistically compared using the Mann-Whitney U-test. Immunohistochemical staining of whole circumference urethral cross sections was used to identify the location of smooth and striated muscle fibres.

RESULTS

On isometric force development, the urethral muscle bundles revealed a fast ( approximately 0.5 sec) and a slow ( approximately 2.1 sec) time constant, whereas in bladder only a slow ( approximately 2.3 sec) component was measured. On average, isometric force was highest in bladder. The length range over which force was produced was smallest in urethral segment II, followed by urethral segment I and finally bladder. The unloaded shortening velocity was 0.15, 0.25 and 0.35 1/sec, respectively. Histological preparations showed that smooth as well as striated muscle was present in proximal urethra. In urethral muscle bundles, spontaneous contractions were measured with a frequency of 0.4 Hz.

CONCLUSIONS

Differences in contractility found between urethra and bladder may be ascribed to the presence of striated muscle in the proximal urethra. The regulation of tone and spontaneous contractions may be part of the continence mechanism in the female pig urinary tract.

Contractile properties of inner and outer smooth muscle bundles from pig urinary detrusor

Like in the human detrusor, the pig urinary detrusor muscle consists of two layers: compactly arranged smooth muscle bundles on the mucosal side (inner layer) and loosely arranged smooth muscle bundles on the serosal side (outer layer). The contractile properties of muscle bundles of both layers were measured using the stop test followed by an isometric contraction. Total and passive forces were measured in ten muscle bundles from the inner and outer muscle layers. Active force was defined as the difference between total and passive force. The curvature and the unloaded shortening velocity of the force-velocity relation were calculated from the shortening forces measured during the stop test. The rate of force development was calculated from the isometric contraction. Differences in contractile properties between both layers were pairwise tested using the Wilcoxon Signed Ranks test. Percentage wise, the outer layer muscle bundles produced the highest active isometric force. The shortening forces were also higher in the outer layer bundles. As a result, both the curvature and the unloaded shortening velocity, derived from the average force-velocity relations fitted to the data sets, were higher in the muscle bundles from this layer. Finally, the outer layer muscle bundles contracted significantly faster than those of the inner layer. Muscle bundles from the outer layer of pig detrusor were found to be faster and stronger (more phasic) than the weaker and slower (more tonic) bundles from the inner layer, suggesting that during bladder contraction the outer layer of the detrusor does more work than the inner layer.