The effect of labor and/or ovariectomy on rodent continence mechanism--the neuronal changes

The Anatomical Pathogenesis of Stress Urinary Incontinence in Women

Stress urinary incontinence is a common disease in middle-aged and elderly women, which seriously affects the physical and mental health of the patients. For this reason, researchers have carried out a large number of studies on stress urinary incontinence. At present, it is believed that the pathogenesis of the disease is mainly due to changes related to age, childbirth, obesity, constipation and other risk factors that induce changes in the urinary control anatomy, including the anatomical factors of the urethra itself, the anatomical factors around the urethra and the anatomical factors of the pelvic nerve. The combined actions of a variety of factors lead to the occurrence of stress urinary incontinence. This review aims to summarize the anatomical pathogenesis of stress urinary incontinence from the above three perspectives.

Large Animal Models for Investigating Cell Therapies of Stress Urinary Incontinence

Stress urinary incontinence (SUI) is a significant health concern for patients affected, impacting their quality of life severely. To investigate mechanisms contributing to SUI different animal models were developed. Incontinence was induced under defined conditions to explore the pathomechanisms involved, spontaneous recovery, or efficacy of therapies over time. The animal models were coined to mimic known SUI risk factors such as childbirth or surgical injury. However, animal models neither reflect the human situation completely nor the multiple mechanisms that ultimately contribute to the pathogenesis of SUI. In the past, most SUI animal studies took advantage of rodents or rabbits. Recent models present for instance transgenic rats developing severe obesity, to investigate metabolic interrelations between the disorder and incontinence. Using recombinant gene technologies, such as transgenic, gene knock-out or CRISPR-Cas animals may narrow the gap between the model and the clinical situation of patients. However, to investigate surgical regimens or cell therapies to improve or even cure SUI, large animal models such as pig, goat, dog and others provide several advantages. Among them, standard surgical instruments can be employed for minimally invasive transurethral diagnoses and therapies. We, therefore, focus in this review on large animal models of SUI.

ANO1 in urethral SMCs contributes to sex differences in urethral spontaneous tone

Stress urinary incontinence (SUI) is more common in women than in men, and sex differences in anatomic structure and physiology have been suggested as causes; however, the underlying cellular and molecular mechanisms remain unclear. The spontaneous tone (STT) of the urethra has been shown to have a fundamental effect on preventing the occurrence of SUI. Here, we investigated whether the urethral STT exhibited sex differences. First, we isolated urethral smooth muscle (USM) and detected STT in female mice and women. No STT was found in male mice or men. Furthermore, caffeine induced increased contractility and intracellular Ca²⁺ concentration in urethrae from female mice compared with male mice. EACT [an N-aroylaminothiazole, anoctamin-1 (ANO1) activator] elicited increased intracellular Ca²⁺ concentration and stronger currents in female mice than in male mice. Moreover, ANO1 expression in single USM cells from women and female mice was almost twofold higher than that found in cells from men and male mice. In summary, ANO1 in USM contributes to sex differences in urethral spontaneous tone. This finding may provide new guidance for the treatment of SUI in women and men.

Stem cell therapy for faecal incontinence: Current state and future perspectives

Faecal continence is a complex function involving different organs and systems. Faecal incontinence is a common disorder with different pathogeneses, disabling consequences and high repercussions for quality of life. Current management modalities are not ideal, and the development of new treatments is needed. Since 2008, stem cell therapies have been validated, 36 publications have appeared (29 in preclinical models and seven in clinical settings), and six registered clinical trials are currently ongoing. Some publications have combined stem cells with bioengineering technologies. The aim of this review is to identify and summarise the existing published knowledge of stem cell utilization as a treatment for faecal incontinence. A narrative or descriptive review is presented. Preclinical studies have demonstrated that cellular therapy, mainly in the form of local injections of muscle-derived (muscle derived stem cells or myoblasts derived from them) or mesenchymal (bone-marrow- or adipose-derived) stem cells, is safe. Cellular therapy has also been shown to stimulate the repair of both acute and subacute anal sphincter injuries, and some encouraging functional results have been obtained. Stem cells combined with normal cells on bioengineered scaffolds have achieved the successful creation and implantation of intrinsically-innervated anal sphincter constructs. The clinical evidence, based on adipose-derived stem cells and myoblasts, is extremely limited yet has yielded some promising results, and appears to be safe. Further investigation in both animal models and clinical settings is necessary to drawing conclusions. Nevertheless, if the preliminary results are confirmed, stem cell therapy for faecal incontinence may well become a clinical reality in the near future.

Behavioral outcomes of a novel, pelvic nerve damage rat model of fecal incontinence

BACKGROUND

Fecal incontinence (FI) has a multifactorial pathophysiology with a severe social impact. The most common cause for FI is pudendal nerve damage, which mostly occurs in women during or after labor. A better understanding of the pathophysiology is required to optimize treatment of FI. In this study, we evaluate the use of a novel pelvic nerve damage rat model of FI.

METHODS

This new model simulates the forces on the pelvic floor during labor by prolonged transvaginal, retro-uterine intrapelvic balloon distention in female rats. Number of fecal pellets produced per day and defecation pattern was compared between the experimental and control group for 2 weeks. The cages of the rats were divided in food, nesting and latrine areas to evaluate changes in defecation pattern. The FI Index (FII) was calculated to assess the ratio of fecal pellets between the non-latrine areas and the total number of pellets. A higher score represents more random distribution of feces outside the latrine area.

RESULTS

Total number of fecal pellets was higher in the experimental group as compared with the controls. In both groups most fecal pellets were deposited in the nesting area, which is closest to the food area. The experimental group deposited more fecal pellets in the latrine area and had a lower FII indicating less random distribution of feces outside the latrine area.

CONCLUSION

Transvaginal, retro-uterine intrapelvic balloon distention is a safe and feasible animal model simulating the human physiologic impact of labor by downwards pressure on the pelvic floor.

Stress urinary incontinence animal models as a tool to study cell-based regenerative therapies targeting the urethral sphincter

Urinary incontinence (UI) is a major health problem causing a significant social and economic impact affecting more than 200million people (women and men) worldwide. Over the past few years researchers have been investigating cell therapy as a promising approach for the treatment of stress urinary incontinence (SUI) since such an approach may improve the function of a weakened sphincter. Currently, a diverse collection of SUI animal models is available. We describe the features of the different models of SUI/urethral dysfunction and the pros and cons of these animal models in regard to cell therapy applications. We also discuss different cell therapy approaches and cell types tested in preclinical animal models. Finally, we propose new research approaches and perspectives to ensure the use of cellular therapy becomes a real treatment option for SUI.

Synergistic effect of vaginal trauma and ovariectomy in a murine model of stress urinary incontinence: upregulation of urethral nitric oxide synthases and estrogen receptors

The molecular mechanisms underlying stress urinary incontinence (SUI) are unclear. We aimed to evaluate the molecular alterations in mice urethras following vaginal trauma and ovariectomy (OVX). Twenty-four virgin female mice were equally distributed into four groups: noninstrumented control; vaginal distension (VD) group; OVX group; and VD + OVX group. Changes in leak point pressures (LPPs), genital tract morphology, body weight gain, plasma 17β-estradiol level and expressions of neuronal nitric oxide synthase (nNOS), induced nitric oxide synthase (iNOS), and estrogen receptors (ERs—ERα and ERβ) were analyzed. Three weeks after VD, the four groups differed significantly in genital size and body weight gain. Compared with the control group, the plasma estradiol levels were significantly decreased in the OVX and VD + OVX groups, and LPPs were significantly decreased in all three groups. nNOS, iNOS, and ERα expressions in the urethra were significantly increased in the VD and VD + OVX groups, whereas ERβ expression was significantly increased only in the VD + OVX group. These results show that SUI following vaginal trauma and OVX involves urethral upregulations of nNOS, iNOS, and ERs, suggesting that NO- and ER-mediated signaling might play a role in the synergistic effect of birth trauma and OVX-related SUI pathogenesis.

Nitrergic relaxations and phenylephrine contractions are not compromised in isolated urethra in a rat model of diabetes

In vivo experiments in a diabetic rat model revealed compromised nitrergic urethral relaxations and increased sensitivity to adrenergic agonists. This study evaluated contractile and relaxation properties of urethral smooth muscle after streptozotocin (STZ)-induced diabetes, in vitro, with the aim of determining whether in vivo deficiencies are related to smooth muscle dysfunction. Urethral tissue was collected from adult female Sprague-Dawley rats naive, STZ-treated, vehicle-treated and sucrose-fed at 9-12 week post treatment. Strips from proximal, mid, and distal urethra were placed in tissue baths and stimulated using electric field stimulation (EFS) and pharmacological agents. nNOS staining was evaluated using immunohistochemistry. Phenylephrine (PE, 10μM) contracted all urethral strips with the highest amplitude in mid urethra, in all treatment groups. Likewise, EFS-induced relaxation amplitudes were larger and were observed more frequently in mid urethra. Relaxations were inhibited by the NOS inhibitor, L-NAME (1-100μM). Sodium nitroprusside (0.01-1μM), an NO donor, reversed PE-induced contractions. No statistical differences were observed between treatment groups with respect to any parameters. Qualitative immunohistochemistry showed no differences in the urethral nNOS innervation patterns across the treatment groups. In summary, nitrergic relaxations and adrenergic-induced contractions in the isolated diabetic rat urethra display similar properties to controls, suggesting no dysfunction on the nitrergic or alpha1 adrenergic receptor function in the smooth muscle. This further implies that compromised urethral relaxation and increased adrenergic agonist sensitivity observed in vivo in this model may be due to the disruption of neural signaling between the urethra and the spinal cord, or within the CNS.

Development of a rabbit's urethral sphincter deficiency animal model for anatomical-functional evaluation

OBJECTIVE

The aim of the study was to develop a new durable animal model (using rabbits) for anatomical-functional evaluation of urethral sphincter deficiency.

MATERIALS AND METHODS

A total of 40 New Zealand male rabbits, weighting 2.500 kg to 3.100 kg, were evaluated to develop an incontinent animal model. Thirty-two animals underwent urethrolysis and 8 animals received sham operation. Before and at 2, 4, 8 and 12 weeks after urethrolysis or sham operation, it was performed cystometry and leak point pressure (LPP) evaluation with different bladder distension volumes (10, 20, 30 mL). In each time point, 10 animals (8 from the study group and 2 from the sham group) were sacrificed to harvest the bladder and urethra. The samples were evaluated by H&E and Masson 's Trichrome to determine urethral morphology and collagen/smooth muscle density.

RESULTS

Twelve weeks after urethrolysis, it was observed a significant decrease in LPP regardless the bladder volume (from 33.7 ± 6.6 to 12.8 ± 2.2 cmH₂O). The histological analysis evidenced a decrease of 22% in smooth muscle density with a proportional increase in the collagen, vessels and elastin density (p < 0.01).

CONCLUSIONS

Transabdominal urethrolysis develops urethral sphincter insufficiency in rabbits, with significant decrease in LPP associated with decrease of smooth muscle fibers and increase of collagen density. This animal model can be used to test autologous cell therapy for stress urinary incontinence treatment.

Effect of extended-term estrogen on voiding in a postpartum ovariectomized rat model

INTRODUCTION

We tested the hypothesis that extended-term (5-week) estrogen therapy would negatively impact voiding function in a postpartum, ovariectomized rat model.

METHODS

Immediately after delivery, 30 primiparous Sprague-Dawley rats underwent intravaginal balloon dilation, followed by ovariectomy 1 week later. Cystometry at postpartum week 2 determined normal or abnormal voiding patterns. After randomization, one-half the normal and abnormal voiding rats received 5 weeks of estrogen therapy, while the remainder received placebo. Estrogen effect was determined by repeat cystometry and immunohistochemical analysis of the urethra and vagina.

RESULTS

Abnormal voiding increased from 60.0% to 73.3% in the estrogen- treated group and declined from 60% to 33% for the placebo group. Rats were then divided into 4 groups for comparison: normal voiding versus placebo (group 1), abnormal voiding versus placebo (group 2), normal voiding versus estrogen (group 3) and abnormal voiding versus estrogen (group 4). Bladder capacity, leak point pressure and maximum voiding pressure were most depressed in group 4. Estrogen treatment was associated with a significant downregulation of alpha(1A) and alpha(1D)-adrenoceptors in the urethral submucosa but an upregulation of nNOS in the urethral smooth muscle.

CONCLUSION

Extended-term estrogen therapy in a rat model of simulated birth trauma and ovariectomy resulted in a higher rate of incontinence. Immunohistochemical examination demonstrated significant downregulation of urethral alpha(1A)- and alpha(1D)-adrenoceptors and upregulation of neuronal nitric oxide synthase (nNOS) in the urethra of estrogen-treated groups. These studies question the use of hormone replacement therapy in the treatment of postmenopausal incontinence.

Animal models of stress urinary incontinence

Stress urinary incontinence (SUI) is a common health problem significantly affecting the quality of life of women worldwide. Animal models that simulate SUI enable the assessment of the mechanism of risk factors for SUI in a controlled fashion, including childbirth injuries, and enable preclinical testing of new treatments and therapies for SUI. Animal models that simulate childbirth are presently being utilized to determine the mechanisms of the maternal injuries of childbirth that lead to SUI with the goal of developing prophylactic treatments. Methods of assessing SUI in animals that mimic diagnostic methods used clinically have been developed to evaluate the animal models. Use of these animal models to test innovative treatment strategies has the potential to improve clinical management of SUI. This chapter provides a review of the available animal models of SUI, as well as a review of the methods of assessing SUI in animal models, and potential treatments that have been tested on these models.

Ex vivo biomechanical, functional, and immunohistochemical alterations of adrenergic responses in the female urethra in a rat model of birth trauma

Birth trauma and pelvic injury have been implicated in the etiology of stress urinary incontinence (SUI). This study aimed to assess changes in the biomechanical properties and adrenergic-evoked contractile responses of the rat urethra after simulated birth trauma induced by vaginal distension (VD). Urethras were isolated 4 days after VD and evaluated in our established ex vivo urethral testing system that utilized a laser micrometer to measure the urethral outer diameter at proximal, middle, and distal positions. Segments were precontracted with phenylephrine (PE) and then exposed to intralumenal static pressures ranging from 0 to 20 mmHg to measure urethral compliance. After active assessment, the urethra was rendered passive with EDTA and assessed. Pressure and diameter measurements were recorded via computer. Urethral thickness was measured histologically to calculate circumferential stress-strain response and functional contraction ratio (FCR), a measure of smooth muscle activity. VD proximal urethras exhibited a significantly increased response to PE compared with that in controls. Conversely, proximal VD urethras had significantly decreased circumferential stress and FCR values in the presence of PE, suggesting that VD reduced the ability of the proximal segment to maintain smooth muscle tone at higher pressures and strains. Circumferential stress values for VD middle urethral segments were significantly higher than control values. Histological analyses using antibodies against general (protein gene product 9.5) and sympathetic (tyrosine hydroxylase) nerve markers showed a significant reduction in nerve density in VD proximal and middle urethral segments. These results strongly suggest that VD damages adrenergic nerves and alters adrenergic responses of proximal and middle urethral smooth muscle. Defects in urethral storage mechanisms, involving changes in adrenergic regulation, may contribute to stress urinary incontinence induced by simulated birth trauma.

Evaluation of different techniques to create chronic urinary incontinence in the rat

OBJECTIVE

To evaluate models for chronic urinary incontinence (UI) in the rat.

MATERIALS AND METHODS

Two models were fully evaluated: one of repeated dilatation of the vagina, simulating birth trauma, the vaginal dilatation (VD) group; the other, with surgical transposition of the urethra to a vertical position, the urethral transposition (UT) group. The VD rats were evaluated by the sneeze test. When negative, vaginal dilatation was repeated in a similar way. The UT group was evaluated by observation of continuous urine leakage. The leak-point pressure (LPP) was measured at study end in all the rats.

RESULTS

All the VD rats had occasional negative sneeze tests and all had to be dilated again. This resulted in persistent UI on sneeze testing for the entire period. In the UT group, 12 rats leaked continuously during the whole study period; in the other four UI became less at 4, 5, 6, and 7 weeks, respectively. The LPP in the rats with UI was significantly lower than in the respective control groups.

CONCLUSIONS

These models permit study of chronic stress UI and continuous UI in the rat. Spontaneous recovery of continence was seen mostly in the VD group.

Animal models of female stress urinary incontinence

PURPOSE

Urinary incontinence affects 40% of women in the United States and stress urinary incontinence accounts for a large portion of affected patients. As defined by the International Continence Society, stress urinary incontinence is the involuntary leakage of urine upon effort, exertion, sneezing or coughing. Since the ultimate success of long-term management for any condition is based on an understanding of its pathophysiology, and because the pathophysiology of stress urinary incontinence is incompletely defined, animal models have recently been developed to better understand stress urinary incontinence and develop novel treatment alternatives.

MATERIALS AND METHODS

Several animal models for urethral dysfunction have emerged in the last few years, including those based on pathophysiological theories of urethral sphincter dysfunction that were designed to simulate maternal birth trauma. Other models have focused on the creation of a durable model of dysfunction for investigating novel treatments.

RESULTS

Since animals cannot express intent, these animal models have focused on measuring decreased urethral resistance. The most widely used methods are the sneeze test, the tilt table technique and the leak point pressure test. Newer techniques include abdominal leak point pressure, urethral pressure measurement and retrograde urethral perfusion pressure. In addition to the advantages and disadvantages of each technique, all methods measure the composite contribution to urethral resistance from smooth and striated muscle, urethral closure and connective tissue, although none measures intent.

CONCLUSIONS

We critically reviewed the different models of stress urinary incontinence and urethral dysfunction as well as the different methods of measuring urethral resistance.

Role of vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide in the vaginal wall of women with stress urinary incontinence and pelvic organ prolapse

Pelvic floor connective tissue degeneration is closely associated with retrogradation of its dominating nerve fibers. We hypothesized that some neuropeptides from pelvic floor tissue might be involved in the pathological progress of stress urinary incontinence (SUI) and pelvic organ prolapse (POP) in women. Thirty premenopausal and 31 postmenopausal patients participated in the study. The morphological appearance in the vaginal tissue was examined. The vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide-38 (PACAP) immunoreactivities (ir-VIP, ir-PACAP) were tested by immunohistochemistry and radioimmunoassay. We found that the VIP and PACAP immunostainings were weaker and sparser, and ir-VIP and ir-PACAP levels were significantly decreased in the anterior vaginal wall in the premenopausal and postmenopausal SUI or POP patients. Ir-VIP and ir-PACAP levels were reversely correlated with the age and menopausal status in the SUI or POP patients. Our data suggest that VIP and PACAP may participate in the pathophysiological process of SUI and POP.

A mouse model of simulated birth trauma induced stress urinary incontinence

AIMS

To facilitate future applications of transgenic or knockout technologies in studies of simulated birth trauma induced stress urinary incontinence (SUI), we aimed to create a mouse model of SUI and explore the possible pathogenesis of this condition.

METHODS

Thirty female C57BL/6 mice were randomly distributed into five groups. Four groups underwent vaginal distention (VD) for 1 hr, using a modified 6-Fr. Foley catheter with a balloon dilated to 0.3, 0.2, or 0.1 ml or sham distention. Four days after VD, all mice underwent leak-point pressure (LPP) measurement via an implanted suprapubic tube (SPT). The normal control group only had SPT placement and LPP measurement. After sacrifice, the urethras of the mice were harvested for routine histological examination and nerve staining.

RESULTS

LPPs were significantly lower in groups after VD with 0.3- or 0.2-ml balloon than in control and sham distention groups (10.29 +/- 6.70, 14.65 +/- 6.51, 37.78 +/- 5.10, and 30.30 +/- 5.30 cm H(2)O, respectively). There were no significant differences in LPP between control and sham groups. Histology showed no significant differences in urethral striated muscle among the five groups. The density of immunoreactive neurofilaments in the urethra decreased after VD with 0.3- or 0.2-ml balloon.

CONCLUSION

As a model of birth trauma, VD can induce SUI in female mice, the severity of which is related to intravaginal balloon size. Partial urethral denervation plays a plausible role in the pathogenesis of SUI. This novel mouse model could be used for further mechanistic studies of female SUI.

Striated muscle and nerve fascicle distribution in the female rat urethral sphincter

The anatomical basis for urinary continence depends on a thorough understanding of the tissues in the urethra. The objective of this study was to evaluate the morphology and neuroanatomy of urethral striated muscle, called the rhabdosphincter or external urethral sphincter, in normal female rats. Urethras from 12 female rats were dissected from the bladder, fixed, embedded in paraffin or epon, and sectioned every 1 mm. Striated muscle content was taken as the ratio of the striated muscle area to net urethral area. Nerve fascicles containing myelinated axons near the rhabdosphincter were counted and mapped. Both striated muscle content and number of nerve fascicles peak in the proximal third of the urethra, with a secondary peak at the distal end of the urethra. This secondary peak may correspond to an analog of the combined compressor urethrae/urethrovaginal sphincter located in the distal urethra in human. The rhabdosphincter has a variable distribution along the length of the urethra. In the middle and distal thirds of the urethra, the dorsal striated muscle fibers between the urethra and vagina become more sparse. The majority of nerve fascicles are contained in the lateral quadrants of the urethra, similar to the lateral distribution of somatic nerves in humans. In conclusion, this study demonstrates the normal distribution of the striated musculature and neuroanatomy in the urethra, with similarities to the human. It thus supports and extends the usefulness of the rat as an experimental model for studying urinary incontinence.

Ex vivo biomechanical properties of the female urethra in a rat model of birth trauma

Stress urinary incontinence (SUI) is the involuntary release of urine during sudden increases in abdominal pressures. SUI is common in women after vaginal delivery or pelvic trauma and may alter the biomechanical properties of the urethra. Thus we hypothesize that injury due to vaginal distension (VD) decreases urethral basal tone and passive stiffness. This study aimed to assess the biomechanical properties of the urethra after VD in the baseline state, where basal muscle tone and extracellular matrix (ECM) are present, and in the passive state, where inactive muscle and ECM are present. Female rat urethras were isolated in a rat model of acute SUI induced by simulated birth trauma. Our established ex vivo system was utilized, wherein we applied intraluminal static pressures ranging from 0 to 20 mmHg. Outer diameter was measured via a laser micrometer. Measurements were recorded via computer. Urethral thickness was assessed histologically. Stress-strain responses of the urethra were altered by VD. Quantification of biomechanical parameters indicated that VD decreased baseline stiffness. The passive peak incremental elastic modulus of the distal segment in VD urethras was less than for controls (1.84 ± 0.67 vs. 1.19 ± 0.70 × 106 dyne/cm2, respectively; P = 0.016). An increase was noted in passive low-pressure compliance values in proximal VD urethras compared with controls (9.44 ± 2.43 vs. 4.62 ± 0.60 mmHg−1, respectively; P = 0.04). Biomechanical analyses suggest that VD alters urethral basal tone, proximal urethral compliance, and distal stiffness. Lack of basal smooth muscle tone, in combination with these changes in the proximal and distal urethra, may contribute to SUI induced by VD.

Increased duration of simulated childbirth injuries results in increased time to recovery

Stress urinary incontinence (SUI) development is strongly correlated with vaginal childbirth, particularly increased duration of the second stage of labor. However, the mechanisms of pelvic floor injury leading to SUI are largely unknown. The aim of this study was to determine the effects of increased duration of vaginal distension (VD) on voiding cystometry, leak point pressure testing, and histology. Sixty-nine virgin female rats underwent VD with an inflated balloon for either 1 or 4 h, while 33 age-matched rats were sham-VD controls. Conscious cystometry, leak point pressure testing, and histopathology were determined 4 days, 10 days, and 6 wk after VD. The increase in abdominal pressure to leakage (LPP) during leak point pressure testing was significantly decreased in both distension groups 4 days after distension, indicative of short-term decreased urethral resistance. Ten days after VD, LPP was significantly decreased in the 4-h but not the 1-h distension group, indicating that a longer recovery time is needed after longer distension duration. Six weeks after VD, LPP was not significantly different from sham-VD values, indicating a return toward normal urethral resistance. In contrast, 6 wk after VD of either duration, the distended rats had not undergone the same increase in voided volume as the sham-VD group, suggesting that some effects of VD do not resolve within 6 wk. Both VD groups demonstrated histopathological evidence of acute injuries and tissue remodeling. In conclusion, this experiment suggests pressure-induced hypoxia as a possible mechanism of injury in vaginal delivery.

Collagen I:III ratio in canine heterologous bladder acellular matrix grafts

The objective of this study was to investigate the limitations of a heterologous bladder acellular matrix graft (BAMG) and the influence of the collagen ratio on functional regeneration in a large animal model. Ten female dogs underwent partial cystectomy; eight received BAMG (two homologous; six heterologous) and two partial cystectomy only. A cystometry was performed prior to surgery and 7 months postoperatively when all animals underwent sacral root stimulation. Tissue specimens were studied by histologic and immunohistochemical techniques and for collagen types. At month 7, all animals survived and bladder capacity in the grafted animals was increased. All grafts demonstrated all components of a normal bladder wall. Nerves were seen with the density decreasing with distance from the anastomosis. The BAMG processing and follow-up demonstrated no changes in the homologous tissue, whereas in the heterologous tissue, the amount of collagen changed with the processing during implantation. None of these heterologous specimens demonstrated a similar collagen ratio to the hosts'. The homologous BAMG undergoes more complete regeneration. In the heterologous BAMG, collagen seems not to be replaced. The amounts and ratio of collagen types I and III seem to influence smooth muscle regeneration.