Effects of partial outlet obstruction of the rat urinary bladder on micturition characteristics, DNA synthesis and the contractile response to field stimulation and pharmacological agents

Effects of long-term partial outflow obstruction on bladder function in the rat

The effects of chronic partial outflow obstruction in rats were investigated. The urethra of male rats was partially obstructed for 3 or 6 months and bladder function was compared with that of age-matched controls. Bladder function was studied in vivo by infusion cystometry and in vitro by measuring the response of bladder muscle strips to stimulation. Cystometrograms of outflow-obstructed bladders were categorized into three types: type 1 was equivalent to a normal bladder; type 2 was characterized by large capacity, enhanced voiding pressure, and some residual urine; type 3 had the largest capacity, an impaired voiding pressure, and considerable residual volume (overflow-type of incontinence). The type 3 bladder was the most frequently observed type in rats obstructed for 6 months. Bladder weight increased significantly in rats with outflow obstruction. When five in vivo cystometric parameters (pressure at which micturition was induced, capacity, maximum voiding pressure, voided urine volume, and residual urine volume) were analyzed according to duration of obstruction, only two parameters (capacity and residual urine volume) in rats obstructed for 6 months differed significantly from those in age-matched controls. Evaluation of these values according to cystometric type showed a significant deterioration in four of five parameters in type 3 bladders. Contractile responses of the bladder in vitro to field stimulation, bethanechol, ATP, and KCI were significantly impaired in those obstructed for 3 or 6 months. When in vitro responses were analyzed according to the classification of cystometric type, deterioration of contractility was confirmed in both types 2 and 3 bladders. The present animal model of outflow obstruction can serve as a model of benign prostatic hyperplasia in humans.

Effect of slow and rapid cystometry on in vitro rat urinary bladder DNA synthesis

1. Partial outflow obstruction induces marked changes in detrusor contractile function and morphology. One common finding in all experimental animal models of partial outflow obstruction is a significant increase in bladder mass. 2. Previous studies have demonstrated that partial outlet obstruction induces a rapid and substantial increase in [3H]thymidine incorporation into virtually all cellular elements of the bladder. 3. The present study was designed to investigate the [3H]thymidine uptake and localization induced by exposure of the in vitro whole rat bladder model to various intravesical pressures and rates of intravesical infusion. 4. The results are as follows: (a) There were no differences in DNA concentration between control and other groups. (b) Slow infusion induced a mild increase in DNA synthesis ([3H]thymidine incorporation) at 0.5 ml and a significantly greater level of DNA synthesis at 1.6 ml. (c) [3H]thymidine incorporation was significantly increased by exposure to 7.5 cm H2O, 15 cm H2O, and 30 cm H2O. (d) Exposure to 60 cm H2O and 90 cm H2O did not initiate an increase in [3H]thymidine incorporation. (e) Autoradiography showed that all tissue elements (urothelium, connective tissue, smooth muscle) participated in the response.

3H-thymidine uptake by the rat urinary bladder after partial outflow obstruction

Partial outflow obstruction induces marked changes in detrusor contractile function and morphology. One common finding in all experimental animal models of outflow obstruction is a significant increase in bladder mass. It is not clear which tissue compartments undergo hypertrophy, hyperplasia, or both. The present study was designed to evaluate the time-related changes in 3H-thymidine uptake and distribution within each tissue compartment induced by partial outflow obstruction using autoradiography. Partial outlet obstruction in rats induced a mild 2-fold increase in mass over a 14 day period. DNA synthesis increased significantly at 1 day following surgery, and remained increased through 7 days. DNA synthesis returned to control levels by 14 days. Distribution studies (using autoradiography) demonstrated a marked increase in the number of labelled urothelium cells at 1 and 3 days after obstruction. Sham surgery also initiated an increase in the number of labelled cells in the urothelium at 1 day. Although both sham and obstructive surgeries induced substantial increases in the labelling of cells within the connective tissue components, the magnitude of the increase in labelled connective tissue cells of the obstructed bladders was greater than that of the sham group. The number of labelled smooth muscle cells of the obstructed bladder increased significantly at 3, 5, and 7 days. However, there were no changes in smooth muscle incorporation of 3H-thymidine by the sham groups. In conclusion, partial outflow obstruction induced time-dependent increases in bladder wall proliferation. The urothelium and connective tissue were the compartments first affected, followed by smooth muscle.

Effect of partial outflow obstruction on rat detrusor contractility and intracellular free calcium concentration

Partial outlet obstruction induces significant alteration in detrusor contractility. A mild obstruction can result in increased contractile force, whereas severe obstruction results in marked contractile dysfunction. The cellular mechanisms mediating these alterations in the contractile response are presently not known. In the current study, we have investigated the effect of both mild and severe partial outlet obstruction on detrusor contractility and correlated the contractile response to field stimulation, bethanechol, adenosine triphosphate (ATP), and KCl with the level of intracellular free calcium using FURA-2 fluorescence. Our results are as follows. Severe obstruction induced a significantly greater increase in bladder weight than mild obstruction. In general, mild outlet obstruction induced an increase in the contractile responses to field stimulation, bethanechol, ATP, and KCl, whereas severe outlet obstruction induced a decrease to field stimulation and ATP. In general, the stimulated increase in intracellular free calcium paralleled the contractile response. The results indicate that the alterations in the contractile response to field stimulation and pharmacological stimulation induced by partial outlet obstruction may be mediated by altered calcium translocation and intracellular release.

Effect of partial outlet obstruction of the rat urinary bladder on the response to alterations in the concentrations of potassium and calcium

1. The contractile response of the 7 day obstructed bladder to field stimulation was significantly increased from that of the control bladder. 2. In the presence of 1.8 mM calcium (normal Tyrode's solution) the contractile response of control bladders to low-frequency field stimulation was significantly enhanced by increasing the potassium concentration from 2.5 to 7.5 or 12.5 mM. 3. Increasing the potassium concentration had no effect on the response of the obstructed bladder to low-frequency field stimulation. 4. Increasing the extracellular calcium concentration enhanced detrusor contractility in a dose-dependent manner in both control and obstructed bladders. 5. The magnitude of the effect of increasing the extracellular calcium concentration were greater in the obstructed bladder than in the control bladder. 6. These results suggest that calcium transporting mechanisms of the cell membrane and intracellular calcium storage and mobilization may be significantly affected by partial outflow obstruction.