Disuse as cause of supersensitivity in the rat urinary bladder

Hypertrophy changes the muscarinic receptor subtype mediating bladder contraction from M3 toward M2

Major pelvic ganglion electrocautery (MPGE) and spinal cord injury in the rat induce bladder hypertrophy and a change in muscarinic receptor subtypes mediating bladder contraction from predominantly M3 to a combination of M2 and M3. To determine whether this is a result of bladder hypertrophy or denervation, we studied the following groups: sham-operated controls, urinary diversion (DIV), MPGE together with urinary diversion (DIV-DEN), bilateral MPGE (DEN), bladder outlet obstruction (BOO), and MPG decentralization (MPGDEC). The degree of bladder denervation was determined by the maximal carbachol response normalized to the response to electric field stimulation. Receptor subtype density was determined by immunoprecipitation. The affinity of subtype-selective muscarinic antagonists for inhibition of carbachol-induced contractions was used to determine the subtype-mediating contraction. DEN, MPG-DEC, and BOO bladders were hypertrophic whereas DIV bladders were atrophic compared with sham operated. Bladder contraction in sham-operated, DIV, and DIV-DEN was mediated by the M3 receptor subtype, whereas the M2 subtype participated in contraction in the DEN, MPG-DEC, and BOO groups. The hypertrophied bladders had an increase in total and M2 receptor density while all experimental groups showed a reduction in M3 receptor density. Thus bladder hypertrophy, independent from bladder denervation, causes a shift in the muscarinic receptor subtype mediating bladder contraction from M3 toward M2.

Morphometric analysis of smooth muscle in the exstrophy-epispadias complex

PURPOSE

In bladder exstrophy and to a lesser extent in epispadias the muscular tissue in the bladder wall may often be replaced by collagen. The aim of our study was to assess the relative changes of smooth muscle versus connective tissue in patients with the exstrophy-epispadias complex.

MATERIALS AND METHODS

Nine full thickness detrusor biopsies from children with the exstrophy-epispadias complex were analyzed. Biopsies were stained with the Masson trichrome method to differentiate muscular tissue from collagen. At x50 magnification using image software for computerized morphometry the areas of smooth muscle and collagen were measured and expressed as a percent. As controls, detrusor biopsies from 8 children with unilateral obstructive megaureter or ectopic ureter were analyzed using the same method.

RESULTS

The average rates of smooth muscle in children with the exstrophy-epispadias complex were 7, 19.3 and 31.5%, respectively, in newborns, and before and after bladder neck reconstruction. In controls the rate averaged 56.5%.

CONCLUSIONS

The ratio of smooth muscle-to-connective tissue increases from the newborn period to puberty in the exstrophy-epispadias complex. After staged reconstruction is completed this ratio remains below normal, although it is increased. Such a change may represent a histological marker of the inadequate volume increase of some of these bladders.

Effect of urinary diversion on the recovery of micturition reflexes after spinal cord injury in the rat

Patients with suprasacral spinal cord injury usually exhibit severe lower urinary tract dysfunction, which is generally attributed to loss of supraspinal input to the spinal micturition centers. However, some of the dysfunction may also arise secondary to bladder overdistension during the initial period of bladder areflexia. This study evaluated the consequences of bladder overdistension by performing urinary diversion in spinalized (T8-T10) rats. Bladder function was evaluated in urethane-anesthetized control and spinalized animals approximately 24 days after diversion. Chronically spinalized diverted and nondiverted rats exhibited similar micturition dysfunction: bladder/sphincter dyssynergia, incomplete voiding and ineffective (nonvoiding) bladder contractions. These data indicate that neither the condition of the bladder (such as chronic overdistension or bladder hypertrophy) nor afferent input from the bladder to the spinal cord dictates the development of reflex micturition and micturition dysfunction after spinal cord injury, suggesting that the dysfunction is intrinsic to spinal micturition reflex pathways.

Comparison of urinary bladder function in sexually mature and immature male and female rats

Although studies exist using both male and female rats, there are virtually no studies that compare male and female bladder function. In this initial study, in-vivo and in-vitro urinary bladder function was investigated in two age groups of male and female rats (sexually immature and sexually mature). These studies compare in-vivo micturition behavior (water intake, urine output, frequency and volume per micturition); and in-vitro whole bladder function (bladder volume/pressure relationships, the ability of the in-vitro bladders to generate pressure and empty in response to bethanechol and field stimulation). The results can be summarized as follows: 1) The 24 hour water intake, urine output, and volume per micturition for the mature male rats was significantly greater than that of the mature females with no significant differences among the immature females, mature females, or immature males. 2) There were no significant differences in the frequency of micturition between the 4 groups. 3) Although the average plateau pressures (cystometrograms) of the immature and mature female bladders were greater than that of the immature and mature male bladders, the compliance was similar for all groups. 4) The maximum pressure response of the mature female bladder was significantly greater than pressures generated by bladders in the other three groups; there were no age or sex related differences in the bethanechol log ED50 values. 5) There were no age or sex-related differences in the bethanechol log ED50 values or maximal expulsion responses. 6) Field stimulated bladders from mature animals generated significantly greater intravesical pressures than bladders from immature animals, but, there were no significant differences in maximal pressures attained between mature male and female bladders nor between immature male and female bladders. In conclusion, micturition behavior, and the maximal pressure response to bethanechol changed dramatically with sexual maturity. These results are consistent with the idea that estrogen and other hormones may have a marked influence on bladder function and micturition behavior.

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.

Muscarinic receptor density in the rat urinary bladder after denervation, hypertrophy and urinary diversion

Parasympathetic denervation of the urinary bladder results in supersensitivity to muscarinic agonists and in bladder hypertrophy. In the present study, the effects of denervation on the muscarinic receptors in the rat bladder were investigated, using a receptor binding technique with (-)3H-QNB as radioligand. The density of muscarinic receptors was increased in denervated, hypertrophied bladders but it was decreased, below that in control bladders, when the development of hypertrophy was prevented by urinary diversion. A decreased receptor density was also found in innervated bladders after urinary diversion, whereas the receptor density was unaffected by hypertrophy alone. Competition experiments with methacholine revealed no changes in the agonist binding properties of the receptors. When the present data are combined with those in previous functional studies, it seems unlikely that the muscarinic receptors in the bladder are involved in the development of supersensitivity. It is suggested that the density of muscarinic receptors in the bladder may be related to the bladder function.

Unilateral denervation of the rat urinary bladder and reinnervation: a predominance for ipsilateral changes

Unilateral removal of the pelvic ganglion affected the bladder-half on the denervated side more profoundly than that on the non-denervated side. At an early stage (3-7 days) the former was heavier, had a lower choline acetyltransferase activity, developed less tension to nerve stimulation and, in course of time, became more sensitized to methacholine in vitro than the latter. At a late stage (30-60 days) the nerve-evoked contractile responses on the denervated side had increased, which was almost wholly attributed to the atropine-sensitive part of the contraction, but the recovery was not complete. On the non-denervated side the nerve-evoked responses were not significantly changed. It was calculated that in the normally innervated bladders 25-30% of the cholinergic nerves of each half were of contralateral origin. The figure was lower (18%) for the nerves mediating the atropine-resistant response.