Effects of pregnancy on muscarinic receptor density and function in the rabbit urinary bladder.

The contractile response of the rabbit urinary bladder to field stimulation consists of both cholinergic and purinergic components. In general, approximately 60% of the contractile response to field stimulation is cholinergic and 40% is purinergic. Although the purinergic response represents a significant proportion of the initial (phasic) pressure response to field stimulation of the isolated whole bladder, it contributes only 10-15% of the ability of field stimulation to empty the bladder. The current study investigates the effects of pregnancy on the contractile responses of the isolated urinary bladder to cholinergic and purinergic stimulation. The results of these studies indicate that pregnancy induces substantial changes in the physiology and pharmacology of the urinary bladder. The following data are consistent with the theory that pregnancy substantially increases the relative purinergic component of the response to field stimulation (and presumably neuronal stimulation): (1) there was a significantly greater response of the bladders isolated from pregnant rabbits to low-frequency field stimulation; (2) atropine was more effective at inhibiting the pressure generation of bladders isolated from virgin female rabbits; (3) field stimulation was more effective at emptying bladders isolated from virgin female rabbits; (4) the response of the bladders from pregnant rabbits to bethanechol was significantly reduced, whereas the response to ATP was significantly increased. In addition to these effects of pregnancy on bladder physiology, pregnancy induced a 50% decrease in the muscarinic receptor density of the urinary bladder body, which correlated very well with the 50% decrease in the contractile response to bethanechol.     

Factors underlying the increased sensitivity to field stimulation of urinary bladder strips from streptozotocin-induced diabetic rats.

1. The responses of bladder strips from control, streptozotocin-diabetic, and sucrose-drinking rats to electrical field stimulation were investigated. Sucrose-drinking rats were included as additional controls because they have enlarged bladders as a result of non-diabetic diuresis. 2. Bladder strips from diabetic rats developed more spontaneous activity than those from the two control groups. Indomethacin reduced the amplitude and frequency of spontaneous contractions suggesting that they resulted from endogenous prostaglandin formation. Tetrodotoxin (TTX) had little effect, while alpha, beta-methylene ATP caused increases in spontaneous activity. 3. Bladder strips from diabetic rats responded to field stimulation with greater contractions than controls in the absence of antagonists as well as in the presence of atropine and alpha, beta-methylene ATP. Increasing TTX concentrations caused a step-wise depression of the contractile response to electrical stimulation which was not affected by preincubation with either atropine or alpha, beta-methylene ATP. 4. Atropine and indomethacin had no effect on strength-duration curves constructed to measure threshold contractile responses to five pulses stimulation. The curves were shifted to the right by both TTX and alpha, beta-methylene ATP, indicating that the responses were neurogenic in nature and at least partially, the result of stimulation of P2-purinoceptors. In the absence of drugs, bladder strips from diabetics responded at lower voltages and pulse widths than those of control and sucrose-drinking rats, suggesting that they were more excitable. 5. The response curve of bladder strips from diabetics to field stimulation at increasing voltage was shifted upwards and to the left compared to strips from control or sucrose-drinking rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Length-tension relationship of urinary bladder strips from streptozotocin-diabetic rats

Streptozotocin-induced diabetes mellitus or the consumption of 5% sucrose in place of drinking water cause an increase in rat urinary bladder capacity and mass. Length-tension curves were generated using bladder body strips isolated from control, diabetic, or sucrose-drinking rats to determine whether the length-tension relationship was altered by the bladder hypertrophy associated with diabetic and nondiabetic diuresis. In addition, we compared the data using three different methods of expression: (1) absolute grams tension developed; (2) grams tension/100 mg tissue, and (3) grams tension/mm2. The cross-sectional area of strips from diabetic rats was increased compared to the other two groups. The length-passive tension curves for all three groups increased with increasing tissue length to a plateau. No optimal resting length for generation of active tension was found. Strips from diabetic and sucrose-drinking rats reached the plateau at a slightly larger passive tension than did strips from control rats. In addition, strips from diabetic and sucrose-drinking rats generally developed a greater active tension than did strips from control rats depending on the method of data presentation used. The data suggest that the complex nonlinear arrangement of smooth muscle fibers in the bladder wall results in the unusual length-tension curves generated by urinary bladder strips (as compared to skeletal or vascular smooth muscle). This relationship would be of benefit in the urinary bladders of early-stage diabetic patients before neuropathy development, where the stretching of the bladder wall would allow accommodation without any compromise of bladder function. The data indicate that comparisons of bladder strip function from control and diabetic rats should be done at passive tensions of greater than or equal to 2 g to ensure that maximal active tension is generated.     

Influence of the bathing medium on the contractile responses of the rabbit urinary bladder.

This study examined contractile responses of the in vitro rabbit whole-bladder preparation to field stimulation, bethanechol and KCl in Tyrode's solution and minimum essential medium (MEM). We found frequency-dependent increases in intravesical pressure in bladders incubated in Tyrode's solution and MEM. However, bladders incubated in MEM consistently responded with greater increases in intravesical pressure compared to those incubated in Tyrode's solution. Similarly, there were frequency-dependent increases in the rate of pressure generation in bladders incubated in Tyrode's solution and MEM, and bladders incubated in MEM responded with greater rates of pressure generation than those incubated in Tyrode's solution at frequencies of 1, 2 and 4 Hz. In addition, there were significant increases in intravesical pressure generated in response to administration of 500 mmol/l bethanechol and 186.4 mmol/l KCl in bladders incubated in MEM compared to Tyrode's solution but no changes in the rate of pressure generation. The influence of L-methionine, one of the constituents of MEM, on the responses of whole bladders to nerve stimulation was also investigated. L-methionine at concentrations of 0.1 and 1.0 mmol/l had no effects on the increase in intravesical pressure or rate of pressure generation following nerve stimulation. It is speculated that the increases in contractile responsiveness of bladders incubated in MEM are related to the combination of amino acids, vitamins and other constituents of the cell culture medium.     

The ability of insulin treatment to reverse or prevent the changes in urinary bladder function caused by streptozotocin-induced diabetes mellitus

1. The effects of insulin treatment on in vivo and in vitro urinary bladder function in streptozotocin-diabetic rats were investigated. 2. Diabetes of 2 months duration resulted in decreases in body weight and increases in fluid consumption, urine volume, frequency of micturition, and average volume per micturition; effects which were prevented by insulin treatment. 3. Insulin treatment also prevented the increases in contractile responses of bladder body strips from diabetic rats to nerve stimulation, ATP, and bethanechol. 4. Diabetes of 4 months duration also resulted in decreases in body weight, and increases in fluid consumption, urine volume, frequency of micturition, and average volume per micturition, effects which were reversed by insulin treatment for the final 2 months of the study. 5. Insulin treatment reversed the increases in contractile responses of bladder body strips from diabetic rats to nerve stimulation, ATP, and bethanechol. 6. The data indicate that the effects of streptozotocin-induced diabetes on urinary bladder function are both prevented and reversed by insulin treatment.     

Effect of anoxia on in vitro bladder function.

Previous studies have demonstrated that the ability of the in vitro whole bladder to empty in response to bethanechol administration was inhibited by anoxia while its ability to generate pressure decreased only slightly. One question was not addressed by these early studies: Is the anoxic effect selective for receptor-mediated contractile stimulation (as opposed to non-receptor-mediated contractile stimulation)? The present study was designed to compare the effect of anoxia on the ability of the in vitro bladder to generate pressure, sustain pressure, and empty in response to field stimulation (FS), bethanechol and KC1 administration. Each New Zealand white rabbit was anesthetized with pentobarbital and the bladder removed. The bladder was mounted as a whole-bladder preparation in a 300-ml isolated bath containing Tyrode's solution at 37 degrees C and equilibrated with 95% O2, 5% CO2. Anoxia was produced by changing the gas mixture to 95% nitrogen, 5% CO2. The effect of anoxia on the response to FS, bethanechol, and KCl was determined at different times after the initiation of anoxia. The results of these studies can be summarized as follows. (1) Anoxia induced a time-dependent decrease in the rate of pressure generation, the magnitude of pressure generation, and the percent volume emptied in response to FS and bethanechol. (2) At all time periods of anoxia, the ability of the bladder to empty was inhibited to a significantly greater degree than either the rate of magnitude of pressure generation (for both FS and bethanechol administration).(ABSTRACT TRUNCATED AT 250 WORDS)     

Developmental aspects of bladder contractile function: sensitivity to extracellular calcium.

The urinary bladders of 1-day and 1-week-old rabbits generate higher intravesical pressures in response to bethanechol and field stimulation than bladders isolated from mature 8-week-old rabbits. Yet the density of cholinergic receptors in the rabbit bladder does not change with maturation (1 day to 8 weeks). In an effort to better understand the molecular mechanisms by which newborn rabbit bladders generate greater pressures than the bladders of adult rabbits, we studied the effect of maturation on the relationship between extracellular calcium and contraction. Our results showed quite clearly that (1) at physiologic concentrations of calcium (2.5 mumol/l), isolated bladder strips of 1-day- and 1-week-old rabbits contracted in response to bethanechol to 98% of their maximal tension as opposed to 68% for their 8-week-old counterparts, (2) the ED50 (for calcium) for the 1-day and 1-week bladders was 0.4 mmol/l whereas the ED50 for the adult bladder strips was 2.2 mmol/l, and (3) the neonatal bladders demonstrated a much greater sensitivity to diltiazem than the adult bladders. The contractile response to calcium of the neonatal bladders was significantly inhibited by 1 mumol/l diltiazem whereas the 8-week-old bladders showed no inhibition at this concentration. In a second series of experiments, the effect of extracellular calcium on concentration was correlated with the intracellular concentration of free calcium using the calcium fluoride FURA-2 and surface spectrofluorometry. These studies confirmed that the increased contractile response of the neonatal bladder strips to calcium or cholinergic agonists was associated with an increase in the maximal intracellular free calcium concentration.     

Muscarinic stimulation of the mouse isolated whole bladder: physiological responses in young and ageing mice

1 Peripheral autonomous bladder activity is an incompletely understood property that may be important both in normal bladder function and in functional problems of the lower urinary tract. We describe how a muscarinic agonist, arecaidine, influences intravesical pressure and intramural bladder contractions in the isolated mouse and how response varies in ageing mice. 2 A group of 12 mice aged 3-4 months was compared with an 'ageing' group of 12 mice age 28-34 months. Bladders were microsurgically removed and mounted in whole organ tissue baths. The effects of the muscarinic agonist arecaidine on intravesical pressure and intramural contractions were performed at different bladder volumes. 3 In normal mice, arecaidine elicited tonic and phasic contractions, the latter showing a more substantial increase in amplitude with bladder distension. Localized 'micromotion' contractions were seen in the bladder wall, with regional differences arising after exposure to arecaidine. A background release of acetylcholine was inferred from the pressure increase induced by the cholinesterase inhibitor physostigmine. 4 Both micromotion activity and the phasic component of the arecaidine response were substantially reduced in ageing mice; the tonic component was preserved in the same specimens. 5 We conclude that the enhanced pressure fluctuations seen at high bladder volumes may act as a peripheral determinant of bladder capacity, and that changes in such activity may contribute to altered functional capacity and lower urinary tract symptoms in ageing individuals.     

Systemic capsaicin treatment impairs the micturition reflex in the rat.

Filling the urinary bladder via a urethral cannula and preventing its voiding in anaesthetized rats led to rhythmic contractions of the detrusor muscle, which lasted for more than 1 h. This rhythmic activity ceased about 30 min after a s.c. injection of 50 mg kg-1 capsaicin. The contractile response of the detrusor to topically applied capsaicin was lost after systemic administration of the toxin, whereas no change in the sensitivity to acetylcholine was observed. Urinary bladders of normal rats had a capacity of about 1 ml. Bladders of rats treated with capsaicin as neonates held a volume of more than 5 ml without contracting. Such bladders were insensitive to topically applied capsaicin but they contracted to acetylcholine as strongly as the bladders of control rats. During an observation period of 3 days control rats gained weight at night and lost weight by day. Rats treated with capsaicin as neonates showed little fluctuation in body weight. Such rats hardly excreted any urine by day although at night they excreted as much as controls. A water load of 5 ml 100 g-1 was excreted by control rats within 3 h. Rats treated with capsaicin as neonates excreted only half as much. In addition, 50% of the water load was excreted far later by capsaicin treated rats than by controls. Few changes were observed in rats treated with capsaicin as adults. It is concluded that all primary afferent fibres mediating the sensation of a full bladder are capsaicin-sensitive. An additional effect of capsaicin on renal mechanisms cannot be excluded.     

Functional development of the rat urinary bladder after pre- or postpubertal castration

Experiments were done to evaluate the role of sex hormones in the functional development of the rat urinary bladder. Rats were orchiectomized or ovariectomized at 30 (prepubertal) or 70 (postpubertal) days of age and bladders were removed 1 month later. An additional group of immature male and female rats was used in which the bladders were removed at 30 days of age. There were only minor differences in contractile responses of bladder strips from any group to electrical field stimulation, ATP, carbachol, or KCl compared to age-matched controls. There were no differences in responses of bladder strips from immature females or males to the adrenergic agonists, isoproterenol, norepinephrine, or methoxamine. Bladders from the pre- and postpubertally castrated rats and their controls relaxed fully in response to isoproterenol, but strips from prepubertally castrated rats relaxed significantly less in response to norepinephrine than those from other groups. Approximately one half of the bladder strips from prepubertally castrated rats failed to relax by at least 50% in response to norepinephrine; these same strips responded to methoxamine with exaggerated contractions. Our data indicate that the normal development of rat bladder alpha-adrenergic responsiveness is adversely altered by prepubertal castration. We postulate that this may result from an alteration in the relative expression of alpha(1)-adrenergic receptor subtypes.     

The effects of parasympathetic blocking agents on bladder electromyograms and function in conscious and anaesthetized cats

Voiding induced in conscious cats by infusion of sterile saline into the bladder via a chronically implanted bladder catheter was stable over many months. Artefact-free recordings of electrical activity obtained from the bladder neck and dome of these preparations during bladder filling and voiding showed characteristic voiding electromyograms but did not permit a functional differentiation. Both voiding and the associated electromyogram were abolished by the ganglion blocking agent, pentolinium. Hyoscine or methyl atropine did not affect the electromyogram but impaired the ability of cats to empty their bladders completely. In anaesthetized cats, ganglion blocking agents prevented a rise in bladder pressure during sacral ventral root stimulation but a hyoscine-sensitive bladder contraction was seen following the period of stimulation. Further stimulation during this post-stimulus rise in intravesical pressure revealed a hyoscine-sensitive stimulus-bound relaxation. Sacral ventral root stimulation relaxed the bladder neck/proximal urethra particularly in the presence of sympathetic tone.     

Intravesical antisense therapy for cystitis using TAT-peptide nucleic acid conjugates

The present study investigated the potential of intravesical instillation for localized reduction of NGF (nerve growth factor) expression in the urinary bladder. Overexpression of NGF has been linked to the pathogenesis of interstitial cystitis (IC). A minimum free energy algorithm was used to predict suitable regions in mRNA of rat betaNGF, which can be targeted for an antisense approach. The candidate antisense oligos were evaluated for their ability to reduce NGF expression in vitro by cotransfecting HEK293 cells with NGF cDNA. A single oligonucleotide ODN sequence was chosen for testing in an acute cystitis model in rat induced by cyclophosphamide. Overexpression of NGF is known to mediate inflammation of bladder in this model. For improved stability, antisense ODN was replaced with antisense peptide nucleic acid (PNA) and its penetration into bladder was facilitated by tethering TAT peptide sequence. Rat bladders were instilled with either antisense or its scrambled control prior to cystitis induction. Cystometrograms performed on rats under urethane anaesthesia exhibited bladder contraction frequency that was significantly decreased in the antisense treated rats than rats treated with the control. NGF immunoreactivity was also decreased in the urothelium of the antisense treated bladders. Our findings demonstrate the feasibility of using TAT-PNA conjugates for intravesical antisense therapy.     

Functional effects of imipramine on the rabbit urinary bladder: an in-vitro study

Imipramine is a tricyclic antidepressant that has been demonstrated to be useful in the treatment of certain voiding dysfunctions. Imipramine has a variety of pharmacological effects including direct antimuscarinic activity, inhibition of catecholamine reuptake, direct muscle relaxant, and calcium antagonism. Using the in-vitro whole bladder model we have studied the effect of imipramine on the rate and magnitude of both intravesical pressure generation and bladder emptying in response to field stimulation. The results can be summarized as follows: at concentrations as low as 1 mumol/l imipramine causes a significant inhibition of volume expulsion without significantly affecting pressure generation. Imipramine produced a dose-dependent inhibition of both pressure development and percent volume emptying; however, it was substantially more potent in inhibiting the ability of the bladder to empty than to generate pressure.     

In vivo inhibitory effects of stimulation at the central end of the pelvic nerve severed from urinary bladder on urinary bladder contraction in rats

Two- or five-Hz electrical stimulation of the central end of the left pelvic nerve severed from the urinary bladder in rats inhibited bladder contraction induced by intravesical infusion of Tyrode's solution. Inhibition of bladder motility by 2-Hz nerve stimulation appeared after pretreatment with strychnine (0.3 mg/kg, i.v.), naloxone (1 mg/kg, i.v.) and picrotoxin (1 mg/kg, i.v.). Hypogastric nerve stimulation, however, did not affect bladder contraction. These results suggest the presence of an inhibitory mechanism on the pelvic motoneuron activated by contralateral pelvic nerve stimulation in rats.     

Atropine and micturition responses by rats with intact and partially innervated bladder.

1 Micturition responses by a group of 17 rats wee recorded during a water diuresis. During a 2 h period, uniform volumes of urine were passes at regular intervals; the mean of the voiding responses by each animal was consistent from one water loading period to another. Residual urine volumes were physiologically insignificant. 2 Atropine treatment did not compromise seriously micturition by water-loaded rats. Treated animals micturated more frequently; the mean volume was 68% of control. The residual urine volume was equal to that of controls. 3 Several week after the surgical removal of half the motor innervation of the bladder, there was no significant effect on micturition. Mean voiding volumes were not different from those of controls; residual urine volumes were the same as before denervation. 4 After half the innervation of the bladder had been destroyed. The effect of atropine on micturition was enhanced. Volumes passes were 50% of control; large residual volumes remained when micturition was over. Only in this group could bladder distension be found. 5 It is concluded that functional responses of the rat urinary bladder are not only resistant to atropine but also to the sizeable reduction in the number of neuroeffector units in the bladder itself. The functional reserve of the rat bladder musculature is remarkably high when assessed by its ability to empty adequately.     

Content and contractile effect of arginine vasopressin in rat urinary bladder

The contractile response of normal male rat urinary bladders to exogenous arginine vasopressin (AVP) and the AVP content of normal and denervated bladders were investigated. In isolated detrusor strips, the maximal response to AVP was about 12% of the contraction elicited by KCl (124 mM), and the EC50 value was 1.03 +/- 0.13 x 10(-8) M. The response to transmural nerve stimulation was not affected by the presence of AVP. Addition of an AVP receptor antagonist strongly reduced the response to exogenous AVP, but did not affect contractions in response to nerve stimulation. In normal bladders, the concentration of immunoreactive (ir) AVP was 29 +/- 6.0 x 10(-15) mol/g. Three days after denervation the bladders had increased 2.4-fold in weight. At this time, the concentration of irAVP was not different from the control value, but the total content had increased significantly. Characterization of bladder irAVP by reverse-phase HPLC revealed that 66.5% of the total immunoreactivity eluted in the position of synthetic AVP. The results suggest a non-neuronal localization of bladder irAVP.     

Different effect of anticholinergic agents and potassium channel openers on urinary bladder response to pelvic nerve stimulation in anaesthetized dogs

1 Effects of the anticholinergic agents atropine, oxybutynin and terodiline, and the potassium channel openers YM934 (2-(3,4-dihydro-2,2-dimethyl-6-nitro-2H-1,4-benzoxazin-4-yl) pyridine N-oxide) and cromakalim were examined on urinary bladder response to pelvic nerve stimulation in pentobarbital-anaesthetized dogs. 2 Pelvic nerve stimulation (PNS) produced a frequency-dependent increase in intravesical pressure in anaesthetized dogs. The response to PNS was abolished by topical tetrodotoxin, and markedly inhibited by intravenous hexamethonium, suggesting a neurogenic origin for the in vivo contractile response. 3 Atropine (0.3–3 mg kg^?1 i.v.) and the anti-neurogenic bladder agents, oxybutynin (1–10 mg kg^?1 i.v.) and terodiline (1–10 mg kg^?1 i.v.) dose-dependently decreased the amplitude of the peak intravesical pressure response to PNS. At either frequency of PNS, these agents inhibited the response to a similar degree. 4 The potassium channel openers YM934 (1–10 μg kg^?1 i.v.) and cromakalim (3–30 μg kg^?1 i.v.) dose-dependently decreased the amplitude of the peak intravesical pressure response to PNS. The inhibitory effects of these drugs were more potent at lower than at higher frequencies of PNS. 5 These data suggest that the inhibitory effects of potassium channel openers on urinary bladder response to PNS are different from those of anticholinergic agents. The preferential inhibitory effect of potassium channel openers on detrusor smooth muscle contraction at lower frequencies of PNS may represent new potential for the treatment of neurogenic bladder.     

Muscarinic stimulation of the rat isolated whole bladder: pathophysiological models of detrusor overactivity

1 Hypotheses as to the pathophysiological basis of bladder detrusor muscle overactivity (DO) have identified both central nervous and peripheral mechanisms as likely contributory factors. In this paper, we describe peripheral autonomous bladder activity in two animal models of DO and discuss how the differences observed between the two models support the likelihood that clinical DO has a multifactorial basis. 2 A total of 12 adult female Sprague-Dawley rats underwent obstruction or sham operation for 1 or 4 weeks. Six adult female spontaneously hypertensive rats (SHR) were compared with normal Wistar controls. Bladders were microsurgically removed and mounted in whole organ tissue baths. Recordings of intravesical pressure in response to the muscarinic receptor agonist arecaidine were performed under standardized conditions. 3 In the partially obstructed rat bladder, the amplitude of pressure fluctuations elicited by the muscarinic agonist arecaidine was significantly increased compared with sham-operated animals. The tonic component of the response was no different for the two groups. No difference from controls was apparent in the SHR. 4 We conclude that alterations in autonomous bladder activity in the obstructed rat model suggest that peripheral functional changes contribute to the pathophysiological abnormality. In contrast, the fundamental abnormality in the SHR appears to be at a more central level. The observations support the supposition that lesions at widely separate sites can give rise to apparently similar abnormalities of lower urinary tract function.     

The in vitro rabbit whole bladder as a model to investigate the urothelial transport of anticancer agents: The ONCOFID-P paradigm

Intravesical instillation of BCG or anticancer agents after transurethral resection is currently considered a standard of therapy. However, this approach is basically empirical; none of the anticancer agents used in this setting was specifically formulated for intravesical therapy. Moreover, concern is raised by the kinetic features of water soluble drugs, because of poor transport across the mucosal barrier, or of liphophylic compounds, for the increased risks of systemic toxicity. A need exists to improve the pre-clinical and clinical approaches used at present to test anticancer agents undergoing specific development for intravesical use. We used in vitro rabbit whole bladders as a new pre-clinical model to investigate the kinetics of locally administered anticancer agents. In this study, we investigated the rate of urothelial transport of a novel paclitaxel derivative, Oncofid-P. Male New Zealand albino rabbits were used. Bladders were rapidly explanted, filled with vehicle alone or vehicle containing graded concentrations of Oncofid-P, and kept for various times under standardized incubation conditions. At the end of experiments, drug concentrations were assessed by high-pressure-liquid-chromatography technique in the intravesical and external bath solutions, as well as in bladder wall homogenates. We found that less than 1% of the drug additioned to the intravesical solution is recovered within the bladder wall in the form of paclitaxel; experiments carried out collecting different areas from the same bladders showed that Oncofid-P is uniformly distributed over the internal surface of bladder mucosa. Isolated rabbit bladders may be a useful pre-clinical model to investigate the rate of transport of chemotherapeutic agents administered by intravesical route. In this paradigm, Oncofid-P displays a kinetic profile that is predictive of local activity over the whole urothelial surface, and low or absent systemic absorption.     

Development factors in the contractile response of the rabbit bladder to both autonomic and non-autonomic agents.

Previous work in this laboratory has demonstrated that the bladders of 1-day-old and 1-week-old rabbits generate higher pressures in whole-bladder preparations than bladders from mature 8-week-old rabbits. In addition, the density of cholinergic receptors does not change during this maturation period. The present study was designed to determine if the increased responsiveness of the neonatal bladder was specific for cholinergic stimulation. Using bladder strips, we have demonstrated that the newborn bladders generated much greater tension in response to ATP, serotonin, histamine, and substance P. The response of the 1-day-old bladder smooth muscle to these contractile agents was at least double the response of the 8-week-old bladders. However, the response of all age groups to bethanechol was approximately the same, and the response to KCl was only 40% greater in the 1-day-old bladders as compared to the adult. These current studies indicate that the newborn bladder responds to a variety of nonadrenergic, noncholinergic agonists to a significantly higher degree than the adult bladder, and that maturation is accompanied by substantial changes in the pharmacology of the bladder.