Effect of Mucosal Removal on the Response of the Feline Bladder to Pharmacological Stimulation

The urothelium plays an important role in the maintenance of normal bladder function. It provides a nonpermeable barrier to the contents of urine. The urothelium is directly involved in the transduction of both intravesical pressure and intravesical volume information to the afferent nerve fibers located within the lamina propria area. A third function may be to modulate bladder contractile function through local secretion of bioactive substances into the muscularis layers adjacent to the urothelium. To test this last hypothesis, the following experiments were performed: Strips of female cat bladders were isolated from the bladder body, base and urethra. The mucosa of alternate adjacent strips was removed, and the contractile response to field stimulation (FS), bethanechol (body), phenylephrine (base, urethra) and KCl was determined.For the bladder body, the strips without mucosa responded to FS, bethanechol, adenosine triphosphate (ATP) and KCl significantly greater than the strips with mucosa intact. For the bladder base and urethra, the contractile responses to FS, KCl and phenylephrine were significantly greater for the strips with mucosa removed as compared with the strips with mucosa intact. For the urethra and bladder base, FS in the presence of phenylephrine produced a relaxation. For the bladder base, the degree of FS relaxation of the isolated strips with mucosa removed was significantly greater than the strips with mucosa intact. For the urethra, FS relaxation was similar for the two groups. In conclusion, removal of the urethelium significantly and substantially increased the contractile response to FS, KCl, bethanechol and phenylephrine. Field stimulation relaxation in the bladder base was also enhanced. Thus in the cat, the mucosa has a significant inhibitory effect on the contractile response of the bladder to stimulation. The mechanism of this activity is not clear at the present time but will be the subject of further study.     

In-vitro contractile response of the rabbit corpus cavernosa to field stimulation and autonomic agonists and antagonists: A qualitative study

Field stimulation of rabbit corporus cavernosum tissue strips can result in relaxation, contraction, or a biphasic response depending on the frequency and the power utilized. In this study we characterized the autonomic components of this response by exposing corporal tissue strips to a variety of autonomic agonists and antagonists including phentolamine, isoproterenol, methoxamine, propranolol, bethanechol, atropine, and ATP. Low frequency electrical field stimulation produced a bi-phasic response characterized by an initial relaxation followed by a contraction. High frequencies (≥ 32 Hz) produced contraction only. All responses were abolished by tetrodotoxin, indicating that both the contractile and relaxant responses to field stimulation are mediated by complex neural mechanisms. The initial relaxation response involves a combination of mediators which include musca-rinic cholinergic stimulation, purinergic, beta-adrenergic, and non-adrenergic, non-cholinergic (NANC) stimulation. The non-cholinergic contribution to corporal smooth muscle relaxation appeared to be approximately equal in significance to the cholinergically mediated relaxation. Beta adrenergic stimulation mediated a direct relaxation of the corporal smooth muscle. The contractile portion of the bi-phasic response was mediated by alpha-adrenergic stimulation. Additionally we have noted a rebound contraction following termination of field stimulation at all frequencies that is not affected by adrenergic or cholinergic blockade and may reflect the field-stimulated release of an endogenous smooth muscle contractile factor.     

Effects of partial outlet obstruction on bladder-strip sensitivity to glucose deprivation: an in vitro study in the rat

Summary Partial outlet obstruction has been shown to result in contractile and metabolic dysfunctions. Specifically, there is a greater reduction in the response to field stimulation (FS) in comparison with the responses to bethanechol and KCl, a greater reduction in the tonic response to stimulation in comparison with the phasic response, and a reduction in oxidative metabolism of glucose accompanied by an increase in the glycolytic metabolism of glucose. The specific aim of the current study was to correlate the effects of partial outlet obstruction on the contractile responses of isolated strips of bladder smooth muscle to repetitive stimulation in the presence and absence of glucose. Adult male Sprague-Dawley rats were subjected to partial outlet obstruction by the surgical placement of silk ligatures around the urethra. After 2 weeks, each rate was anesthetized, the bladder was excised, and isolated strip studies were performed. These studies demonstrated that the maximal phasic response to FS was significantly decreased in the obstructed strips as compared with controls, with no difference being noted for responses to bethanechol or KCl; the tonic responses to all forms of stimulation were significantly decreased after obstruction, with the tonic response to FS being decreased to a greater degree than were the tonic responses to bethanechol and KCl; and in the absence of glucose, the tonic responses of control strips to all forms of stimulation were reduced to a greater degree than were the phasic responses. These studies demonstrate that the tonic response to FS is extremely sensitive to fatigue induced by repetitive stimulation.     

Effect of chronic atropine administration on the rat urinary bladder

Micturition is accomplished via a coordinated contraction of the urinary bladder body mediated primarily by muscarinic receptor stimulation. Theoretically, bladder function may be modified by pharmacologically altering either the muscarinic receptor density and/or the magnitude of the response to receptor activation. In the central nervous system, autonomic receptor density can be modified by chronic administration of specific receptor agonists and antagonists. The chronic administration of receptor agonists induces a decrease in the specific receptor density whereas the chronic administration of antagonists induces an increase in the specific receptor density. Although these induced alterations in receptor density occur in the CNS, there have been few studies on peripheral tissue. For the current study, we have administered L-atropine chronically to rats (five mg./kg./day) using implanted osmotic pumps. Using direct radioligand binding techniques, the muscarinic receptor density of the rat brain (cortex) and urinary bladder were determined following six hours, 12 hours, one, two, four, seven, 11 and 14 days of atropine administration. In addition, we have also determined the effect of atropine administration on bladder weight and the response of isolated strips of the bladder to bethanechol, a specific muscarinic agonist. For both the brain and the bladder, the receptor density increased progressively and reached a maximum by seven days. At 14 days of atropine administration, the density of muscarinic receptors in rat brain increased significantly (p less than .05) from 2956 +/-74 fmoles/mg. protein to 3800 +/-170 fmoles/mg. protein. The muscarinic receptor density of the rat urinary bladder increased significantly from 115 +/-10 fmole/mg. protein to 165 +/-14 fmole/mg. protein. Although there was a 42% increase in bladder mass, the contractile response of isolated strips to bethanechol did not change significantly. This study demonstrates that the urinary bladder can respond to the chronic administration of atropine with a significant increase in the density of muscarinic receptors. The magnitude of the increase observed was slightly greater than the magnitude observed for muscarinic receptors isolated from the brain cortex.     

Autonomic innervation of rabbit urinary bladder following estrogen administration

The effects of estrogen administration on the autonomic innervation of the rabbit urinary bladder were studied. Immature female white rabbits were injected twice daily with estrogen (150 μg./Kg.) for four consecutive days. Control animals received injections of vehicle alone. The adrenergic innervation was identified using the glyoxalic acid method of catecholamine histofluorescence. The cholinergic innervation was visualized utilizing specific acetylcholinesterase staining. Additionally, the effect of estrogen administration on the response of smooth muscle strips of urinary bladder to specific autonomic agonists was determined. Estrogen administration induced a moderate increase in the adrenergic innervation of the rabbit bladder detrusor, whereas no change could be observed in the cholinergic innervation. It should be noted, however, that whereas the adrenergic innervation in the bladder of the control animal was sparse, the cholinergic innervation in the bladder body was quite dense. Estrogen induced a marked increase in the response to alpha -adrenergic (methoxamine) and muscarinic cholinergic (bethanechol) agonists. No alterations were noted in the response to beta-adrenergic agonists (isoproterenol). These findings indicate that the urinary bladder responds as a target organ of estrogen-induced alterations in autonomic innervation.     

The response of autonomic receptors to castration and testosterone in the urinary bladder of the rabbit

The effects of castration and testosterone on the autonomic receptor density and contractility in the urinary bladder smooth muscle of male rabbits were compared to untreated animals. Four groups of rabbits were studied over a similar time span with Group 1 animals serving as the untreated controls. Two groups (Groups 2 and 3) were castrated 28 days prior to sacrifice, Group 2 animals received corn oil for 14 days, and Group 3 animals received testosterone, 10 mg./day, for 14 days. The Group 4 animals were non-operated and received testosterone 10 mg./day for 14 days. Ligand saturation binding studies for alpha adrenoceptors in the bladder base and proximal urethra were performed with [3H]dihydroergocryptine ([3H]DHE). Muscarinic cholinergic receptors (MChR) were assayed with [3H]quinuclidinyl benzilate ([3H]QNB) and beta adrenoceptors with [125I]iodocyanopindolol ([125I]CYP) on the detrusor smooth muscle. Castrated Group 2 animals showed no significant change in receptor density with either [3H]QNB or [125I]CYP in detrusor muscle, but did exhibit a significant reduction (59%) of alpha adrenoceptors in the bladder base-urethra. The testosterone treated castrate and testosterone treated non-operated animals had significant increases in the MChR density, but no change in the alpha adrenergic, or beta adrenergic receptor density as compared to untreated controls. Cumulative dose response contractile studies were performed with carbachol on detrusor muscle strips and with phenylephrine on bladder base strips in isolated organ baths. The contractile studies on muscles from Groups 1, 2 and 3 showed no change in the ED50 or maximal contractile strength between control, castration or testosterone treated castrated animals. The ratio of wet bladder weight as compared to total body weight between each of the treatment groups showed a slight increase in both of the testosterone treatment groups. It was concluded that castration down regulates the alpha adrenergic receptors of the bladder base, while testosterone treatment increases the density of MChRs, and increases the ratio of the bladder to total body weight. Although no contractile changes were observed in the bladder base tissue it is conceivable that longer chronic testosterone deficits might ultimately affect the bladder outlet resistance in the male because of the reduced alpha adrenergic receptor density.     

Functional and pharmacological effects of ureteral diversion

Urinary diversion is the final therapeutic approach in several bladder pathologies including selected cases of bladder cancer, neurogenic bladder, and painful bladder syndrome. While there have been a few experimental studies on the effects of urinary diversion and subsequent undiversion on bladder capacity, the pharmacological changes occurring with diversion and undiversion have not yet been investigated. Our primary objectives were to determine the functional and pharmacological alterations in the defunctionalized bladder and the effects of refunctionalization on these changes. Thirty-two male adult canines weighing 15 to 20 lb. were used for this study. Three groups of dogs were urine diverted for one, three, and six month durations (four dogs per group). Another three groups of dogs were urine diverted for one, three, and six months (four dogs per group); these dogs were then undiverted for three months. Six control animals received either one or two sham operations at one, three, and six months. In all groups the functional and contractile characteristics of the bladders were assessed by urodynamics and in vitro contractile studies; bladder weight and muscarinic receptor density were also measured. Intravesical capacities determined by in vivo cystometry were reduced significantly to 74%, 63%, and 47% of control values at one, three, and six months respectively after urinary diversion. Bladder capacity returned to above normal levels in bladders diverted and then subsequently undiverted. Similarly, the compliance and bladder weight of the diverted bladders were significantly less than control, while diverted bladders subsequently undiverted were similar to controls. Maximal bladder contractility in response to bethanechol stimulation was less in diverted bladders compared to control. This decrease in contractility was accompanied by a decrease in muscarinic receptor density. After undiversion maximal bladder contractility to bethanechol reached control levels; this was accompanied by a parallel increase in muscarinic receptor density to control values. There was no effect of diversion or undiversion on the maximal response of bladder strips to methoxamine stimulation. Thus, a bladder that has been diverted (defunctionalized) for a period of time showed decreases in capacity, compliance, and contractility to muscarinic stimulation along with a decrease in muscarinic receptor density. All of these parameters were restored after refunctionalization of the bladder.     

Evidence against the presence of spare muscarinic receptors in the rabbit urinary bladder

In a recent study by Anderson and Marks [1982], indirect evidence was presented for the existence of “150-fold muscarinic receptor excess” in the rabbit urinary bladder. This conclusion was based on the quantitative comparison of the ability of carbamylcholine to both directly contract bladder strips and to inhibit (quinuclidinyl benzilate) binding. In order to investigate the presence of “spare receptors” in the bladder directly, we have determined the effect of benzilylcholine mustard (a noncompetitive cholinergic inhibitor) on both bethanechol stimulation of muscle-strip contraction and on [³H]QNB binding (muscarinic receptor density). The results of these studies indicate that there is no significant “muscarinic receptor excess” in the rabbit urinary bladder.     

Short term functional effects of bladder outlet obstruction in the cat

Experimental bladder outlet obstruction in cats was produced by surgical placement of a silastic cuff around the urethra. Two sizes of cuff were used to produce either moderate or severe obstruction. The following is a summary of the short-term effects on bladder function. Obstruction induced a significant increase in the in vivo voiding pressure, in proportion to severity of the obstruction. There were no significant differences between control and obstructed cats in bladder mass, response of the isolated whole bladder to field stimulation or bethanechol, response of isolated bladder strips to field stimulation, bethanechol and ATP, or muscarinic receptor density in the bladder body. Although there were no differences in bladder mass between control and obstructed bladders, the hydroxyproline concentration of the severely obstructed bladders was significantly reduced. Creatine phosphate concentration was also significantly reduced in obstructed bladders. Although all whole cat bladder preparations displayed spontaneous contractile activity during in vitro cystometry, the obstructed bladders had a greater amplitude and frequency of spontaneous contractions with a lower volume threshold. In addition, the obstructed bladders had a greater tetrodotoxin-resistant contractile response to field stimulation. These results suggest that the obstructed cat bladder can compensate for increased outlet resistance without induction of bladder hypertrophy or significant functional changes, as seen in both rat and rabbit.     

The effects of acute overdistention of the rabbit urinary bladder

The effects of in vivo acute overdistention on both the metabolic state and the in vitro contractile responses of the rabbit urinary bladder were studied. Intracellular adenosine triphosphate (ATP) was used as an indicator of the metabolic states. The responses of isolated strips of bladder body and base to bethanechol, methoxamine, and isoproterenol were used to assess pharmacologic response. The results of acute overdistention for one hour can be summarized as follows: (1) There was no significant decrease in the intracel Mar stores of high-energy phosphate (ATP). (2) The cholinergic-induced contractile response of the bladder body was significantly decreased. After one week of recovery, the cholinergic response returned to control levels. (3) There was a moderate shift in the dose-response of the bladder base to methoxarnine. After one week of recovery, the response to methoxamine returned to control levels. It is concluded that overdistention produces an immediate dysfunction in the contractile system of the bladder that is not secondary to a reduction in intracellular ATP and is reversible within one week following overdistention.     

Effect of partial outlet obstruction on contractility: Comparison between severe and mild obstruction

Detrusor dysfunction is one of the most common problems in patients with outflow obstruction secondary to benign prostatic hyperplasia. These patients complain of various symptoms, including urinary frequency, urge incontinence, difficulty in voiding, and retention. The severity of the symptoms is dependent on the stage of disease and/or severity of the obstruction. We compared the changes in the rat detrusor function following both mild and severe models of partial outlet obstruction in the rat. Outflow obstructions were created by ligation of the urethra over which a catheter was placed. The size of the catheter determined whether the severity of obstruction was mild or severe (1.70 mm for mild obstruction and 1.09 mm for severe obstruction). Changes in the bladder weight, length-tension relationships, and the contractile response to field stimulation, pharmacologic agonists, and KCl were studied in bladders isolated from 1 and 2 week obstructed rats. Bladder weights of all obstructed rats increased significantly. The weight of the severe obstructed rats were significantly greater than rats subjected to mild obstruction. In general, passive length-tension curves of obstructed rats were shifted to right. The magnitude of the active tension induced by high KCl was higher in the mild obstruction and lower in the severe obstruction. The maximum response to KCl of mild obstruction was generated at greater lengths than for the other groups. In general, the contractile responses of the mild obstructed bladder body to field stimulation, bethanechol, KCl, and ATP, and of the bladder base to field stimulation, KCl, and methoxamine, were significantly increased when compared to the responses of the control bladder body and base. However in the severe obstructed bladder, the responses to field stimulation, KCl, ATP, and methoxamine were significantly reduced from the responses of the control strips; the response to bethanechol was similar for control and the severe obstructed groups. In conclusion, the severity of outlet obstruction significantly altered the contractile response of the bladder. Mild obstruction induced a mild increase in bladder mass, which was associated with significant increases to all forms of stimulation. Severe outflow obstruction induced a substantial increase in bladder mass and a significantly greater reduction in the response to field stimulation than the response to bethanechol (which was unchanged).     

Effect of diltiazem and pinacidil on the response of the rabbit urinary bladder to repetitive stimulation and in vitro ischemia

The effect of repetitive stimulation, in the presence and absence of diltiazem or pinacidil, on the contractile responses of isolated strips of rabbit bladder detrusor to field stimulation and carbachol, after 2 hr of incubation in a medium that serves as an in vitro model of ischemia (oxygen and substrate depleted Tyrode's solution), was determined. Our results are summarized as follows: a) The magnitude of the contractile dysfunctions after in vitro ischemia was enhanced by repetitive stimulation. b) Pre-incubation of isolated strips of detrusor with diltiazem (50 microM) inhibited the contractile responses to field stimulation (FS) and carbachol by 43 and 50%, respectively. Pinacidil (100 microM) inhibited the contractile responses to FS and carbachol by 37 and 32%, respectively. c) Neither diltiazem nor pinacidil protected the bladder strips against the effects of 2 hr of incubation in in vitro ischemia medium. However, d) both pinacidil and diltiazem reduced the level of contractile dysfunctions induced by repetitive stimulation. In conclusion, the contractile response to FS was significantly more sensitive to in vitro ischemia and repetitive stimulation than was the contractile response to carbachol. Both diltiazem and pinacidil protected the contractile responses to FS and carbachol from the degenerative effects of repetitive stimulation, but not from the effects of in vitro ischemia.     

Effect of acute complete obstruction on the rabbit urinary bladder

Studies on the effect of partial bladder outlet obstruction demonstrate that significant alterations in urinary bladder structure and function occur within 24 hours of the creation of the obstruction. These studies suggest that many of the functional and structural alterations following partial outlet obstruction may result from the initial overdistension which occurs within the first 24 hours. In these present studies, we investigated the time course of the effect of complete obstruction of the rabbit urinary bladder on the contractile response to bethanechol and field stimulation and on the muscarinic receptor density. Male White New Zealand rabbits were divided into five groups: controls, four, eight, 20, and 24 hours of complete obstruction. The results demonstrated that there was a significant decrease in both the contractile response to muscarinic stimulation and muscarinic receptor density at four hours following outlet obstruction (at a time when there was no bladder overdistension). The receptor density and contractile response to stimulation further decreased over the 24 hour period. These studies indicate that the initial decrease in muscarinic receptor density and contractile response to muscarinic stimulation may be mediated in part by the high level of spontaneous contractile activity induced by ligation of the urethra.     

The effect of noradrenaline on the contractile response of the urinary bladder. An in vitro study in man and cat

In this study, bladder muscle strips from the detrusor of man and cat were used to evaluate the modulating effects of adrenergic agonist and antagonists on the field stimulation induced contractile response. Noradrenaline (NA) inhibited and phentolamine enhanced the contraction in a dose-dependent manner. Propranolol did not influence the field stimulation response. When a study of the combined effect of adrenergic drug influence was performed, the NA-induced inhibition was partly reversed by propranolol but a further increase of the contractile response compared to the control was seen, when phentolamine was added. No species differences were found. The conclusion drawn from these results is, that the inhibiting effect of NA on the contractile response is mediated via alpha- and beta-adrenergic receptors. The former could be located on the short parasympathetic intramural neurons while the latter probably are located on muscle cells.     

The effect of pregnancy and contractile activity on bladder muscarinic receptor subtypes.

In the rabbit bladder, pregnancy and prolonged bladder contractions decrease both muscarinic receptor density and contractile response, whereas newborns show enhanced muscarinic contractile response. Although the M(2) receptor predominates in rabbit bladder, we and others have shown that the affinity of a series of subtype selective muscarinic antagonists for inhibition of muscarinic agonist-induced contractions is most consistent with the pharmacologically defined M(3) receptor directly mediating smooth muscle contraction. Bladders from fetal rabbits, gravid rabbits, and male rabbits exposed to 4 hr of induced spontaneous contractions were used to determine whether changes in receptor density and contractility are due to a selective decrease in either the M(2) or M(3) muscarinic receptor subtype. To determine organ specificity, the heart and uterus were also studied. Gravid rabbits of 3 weeks' gestation and their fetal rabbits were studied. In male rabbits, bladder contractions were induced for 4 hr by ligating the catheterized penis at its base. Muscarinic receptor density and subtype distribution were determined by radioligand binding and immunoprecipitation. Receptor density was 24% lower in gravid bladder body, unchanged in gravid bladder base, 54% lower in gravid uterus, 115% higher in fetal bladders, and 34% lower after induced bladder contractions. Immunoprecipitation showed greater M(2) receptors than M(3) in all tissues studied, whereas M(l) and M(4) receptors were undetectable. There was no difference from control in the ratio of M(2) to M(3) receptor in any tissues except that a greater proportion of M(3) receptors was found in male vs. female bladders. Changes in contractile response to cholinergic stimulation in the gravid, fetal, and experimental detrusor instability model are associated with changes in total receptor density and not solely with changes in the M(3) receptor subtype that mediates bladder smooth muscle contraction. Neurourol. Urodynam. 18:511-520, 1999.     

Comparative physiology and biochemistry of rat and rabbit urinary bladder

OBJECTIVE: To compare directly the biochemistry and contractile responses of rat and rabbit bladder to different stimuli. Materials and methods Sexually mature male New Zealand White rabbits and Sprague Dawley rats were compared. Each bladder was excised while the animal was anaesthetized; longitudinal bladder strips were cut and then mounted in an organ bath. Tension (2 g) was placed on all strips and each underwent field stimulation (FS) for a total of 20 s at 1-32 Hz, 1 ms and 80 V and was exposed to carbachol (100 micromol/L), ATP (2 mmol/L) and KCl (120 mmol/L). The tension was monitored continually using a polygraph and data stored digitally in a computer. The responses to each stimulus were determined as the maximum tension generated, maximum rate of tension generation and duration to a maximum response. The Ca2+- ATPase activity of the rat and rabbit bladder was determined. Bladder pressures were then predicted from the strip data using Laplace's law and compared with published values. RESULTS: Contractile responses (per unit tissue mass) of rat bladder strips were significantly greater than those of rabbit bladder strips at all frequencies of FS and to carbachol, KCl and ATP. The rate of contractile force generated by rat bladder strips in response to all stimuli were significantly greater than that generated by rabbit strips. Rabbit bladder strips took significantly longer to generate maximum tension than did rat bladder strips in response to pharmacological stimuli. In response to FS, rat strips took significantly longer than rabbit strips to generate maximum tension. Although the predicted rat bladder pressures were significantly greater than those for rabbit, the predicted pressures for both the rat and rabbit were significantly lower than the pressure responses of the isolated whole bladder model. The contractile data correlated well with the Ca2+-ATPase activity data; rat bladder had seven times the enzyme activity of rabbit bladder. CONCLUSION: Per unit mass, rat bladder is capable of generating more than five times the tension of rabbit bladder. Similarly, the rate of tension generation by rat bladder is three to five times greater than that by rabbit bladder. The duration to maximum tension generated in response to FS compared with pharmacological stimuli was affected by the inherent difference in the rate of contractile response to electrical activation compared with agents which diffuse through tissue, and by the difference in size between rat and rabbit bladder smooth muscle cells.     

Aging effects on contractility of longitudinal and circular detrusor and trigone of rat bladder.

PURPOSE: Aging is associated with bladder dysfunction, including difficult voiding and urinary leakage. Voiding involves reduction in the bladder lumen in all dimensions brought about by contraction of the meshwork of longitudinal, circular and oblique layers of detrusor smooth muscles. Most in vitro physiological studies of the effects of aging on bladder function used the longitudinal detrusor. To understand the region specific effects of aging on bladder function the contractile responses of longitudinal and circular detrusor, and trigone segments of the bladder from young and old rats were monitored. MATERIALS AND METHODS: These studies were performed using male Fisher 344 rats 6 months (young) and 27 months (old) old obtained through the National Institute on Aging. Each rat was anesthetized and the bladder was isolated. From each bladder a strip of longitudinal detrusor, circular detrusor and trigone was isolated and mounted in an in vitro multi-muscle chamber containing normal physiological solution at 37C. Isometric contractions of the 3 bladder strips were monitored after electrical field stimulation, 120 mM. potassium and 1 to 1,000 microM. bethanechol using a digital oscilloscope. RESULTS: In longitudinal detrusor from old rats there was no significant difference in the contractions evoked by electrical stimulation or high potassium but there was a significant reduction in contractions evoked by bethanechol compared with the responses of longitudinal detrusor from young rats. In circular detrusor from old rats there was a significant increase in contractions evoked by electrical stimulation and a slight increase in contractions produced by high potassium but no significant change in contractions evoked by bethanechol compared with the responses of circular detrusor from young rats. In trigone from old rats there was a significant decrease in contractions evoked by electrical stimulation, high potassium and bethanechol compared with young trigone. CONCLUSIONS: The reduction in contractions evoked by bethanechol suggests an age related reduction in muscarinic receptors in the longitudinal detrusor of aged rats. An increase in contractions evoked by electrical stimulation without a change in contractions evoked by bethanechol suggests a decrease in compliance caused by an increase in collagen in the circular detrusor of aged rats. A general decline in all contractile responses, including those evoked by high potassium, suggests reduced membrane depolarization in the trigone of aged rats. The effect of aging is specific to different regions and functional components of the bladder, probably due to changes in muscarinic receptors, collagen and depolarization.     

Correlation between the structure and function of the rabbit urinary bladder following partial outlet obstruction

PURPOSE: To understand the relationship between contractile and structural changes in the obstructed bladder, rabbit bladder was partially obstructed for up to 70 days and alterations in tension response to field stimulation and carbachol were compared with alterations in ultrastructure and innervation of detrusor smooth muscle (SM). The effect of partial outlet obstruction on the physiological responses to field stimulation (FS) (nerve mediated contraction) and carbachol (receptor mediated contraction) were correlated with the structure and innervation of the detrusor smooth muscle (SM) of the same animal during a 70 day period. MATERIALS AND METHODS: 28 rabbits were subjected to 1 to 70 days of mild partial outlet obstruction. Sham operated rabbits were euthanized at 7, 14, 28, and 70 days post-obstruction. At each time period, isolated strips of bladder body were mounted in individual baths and the contractile response to FS and carbachol determined. Three additional strips from each bladder were fixed for electron microscopy. RESULTS: Bladder mass increased rapidly during the first 7 days after obstruction, was constant for the next 7 days, and then continued to increase gradually. Dysfunction of the contractile response to FS was noted as early as 3 days and progressively increased over the 70-day study period. The decrease in the response to FS increased at a significantly faster rate than the decrease in the contractile response to carbachol. In ultrastructure studies, at 3 and 7 days post-obstruction the majority of SM cells displayed the characteristics of hypertrophy. At 28 days some SM cells displayed loosely packed myofilaments and an irregular distribution of sarcoplasmic dense bodies. At 70 days swollen mitochondria were present in all cell types of the bladder wall. Evidence of axonal degeneration was first observed at 7 days post-obstruction and became more extensive thereafter. No evidence of mitotic figures, nerve growth cones or regenerating SM cells was observed. CONCLUSIONS: Prolonged partial bladder outflow obstruction is accompanied by a progressive decrease in contractility of SM. The present study describes the structural damage that occurs in the bladder wall in response to partial outlet obstruction and correlates these observations with the contractile dysfunction with which it is associated. Furthermore, mitochondrial damage in vessels and fibroblasts is suggestive of bladder wall ischemia.     

The effects of short-term in-vivo ischemia on the contractile function of the rabbit urinary bladder

The proper functioning of any smooth muscle requires adequate perfusion with oxygen and nutrients. Ischemia compromises both these factors and results in dysfunction, the extent depending on the degree and duration of ischemia. This study determined the effects of one, two and four weeks in vivo ischemia on the capacity, compliance and contractile function of the rabbit urinary bladder. Morphological changes were also studied with light microscopy. Different degrees of ischemia were achieved as follows. In the unilateral group the vesical artery was tied on one side and the animals were sacrificed at one week or two weeks. In the bilateral group the vesical arteries on both sides were tied and the animals were sacrificed one week later. In the bilateral staged group the vesical artery was tied on one side and after one week the contralateral artery was ligated, and the animals sacrificed one week after the second procedure. Muscle strips were studied for contractile response, with a distinction being made between the ipsilateral and contralateral side of vessel ligation in the unilateral group. The results were as follows. 1) In the unilateral group there was a 72% reduction in the contractile response of the dome of the bladder to bethanecol on the side of vessel ligation and a 32% reduction on the contralateral side. The response to methoxamine on the base was reduced by 44%, with no difference between the ipsilateral and contralateral side. 2) Bilateral vessel ligation resulted in a 97% reduction in contractile response to bethanechol on the dome and a 75% in the response of the base to methoxamine. 3) Staged bilateral ligation resulted in a 69% reduction in the contractile response of the dome to bethanechol and a 18% reduction in the response of the base to methoxamine. Ischemia caused a marked reduction in the compliance and capacity of the bladder in all the three groups, with the most marked changes in the bilateral group. Multiple spontaneous contractions were noted in the three groups during the filling phase of the cystometrograms. Histological features correlated well with the functional changes in the different groups.     

Response of the fetal sheep bladder to urinary diversion

PURPOSE: In adults urinary diversion results in bladder atrophy and a rapid decrease in contractile function. Little is known about the effects of urinary diversion on bladder development. In this regard we characterized the responses of fetal sheep bladder strips obtained from animals that underwent urinary diversion. MATERIALS AND METHODS: Urinary diversion was performed on fetal sheep after 90 days of gestation (term 147 days) and bladder tissue was obtained 2 weeks later. Contractile and relaxant responses of full-thickness bladder strips were tested. RESULTS: Bladders from fetal sheep subjected to urinary diversion weighed significantly less than control fetal bladders. Histological studies demonstrated marked connective tissue infiltration and the reorganization of smooth muscle elements. Carbachol stimulated a tonic contraction, while field stimulation administered during the tonic contraction elicited a phasic relaxation or a biphasic response, consisting of an initial relaxation and then a phasic contraction in control and diverted bladders. Contractile responses of defunctionalized strips to carbachol were significantly less than those of control bladder strips. Contractile responses of defunctionalized bladder strips to field stimulation at 1 Hz. were significantly greater than those of control strips. Responses of the 2 sets of fetal bladder strips to higher frequencies were similar, as were the contractile responses to adenosine triphosphate and KCl. Field stimulated relaxations in the presence of carbachol stimulated contraction of defunctionalized bladder strips were significantly greater than those of control strips, while the relaxant responses of each set of fetal bladder strips to isoproterenol and nitroprusside were similar. CONCLUSIONS: Urinary diversion in normal fetal sheep resulted in marked structural changes, reduced carbachol stimulation and increased field stimulation relaxation.