Intravesical instillation of a calcium entry blocker and its effects on detrusor contractility: in vitro and vivo experiments

Effects of verapamil on bladder instability induced by partial outflow obstruction in rat

BACKGROUND

Overactivity of the detrusor due to benign prostatic hyperplasia may be induced by hyperpermeability of the smooth muscle cell membrane to calcium. We investigated the effect of verapamil, a calcium channel blocker, on detrusor function in outflow obstructed and control rat bladders.

METHODS

Verapamil was injected intravenously via a catheter inserted into the internal jugular vein in doses of 0.5, 1.0, 2.0, 4.0, and 10.0 mg/kg in rat bladders with and without partial outflow obstruction under urethane anaesthesia. The intravesical pressure was monitored continuously. We measured the tidal voided urine volume, the voiding pressure, the pressure at which micturition was induced, and the end-point pressure of micturition.

RESULTS

The tidal voided urine volume was significantly decreased in the obstructed bladders before administration of verapamil. Verapamil had similar effects in cystometric parameters in obstructed and control bladders. Verapamil increased the tidal voided urine volume, the pressure at which micturition was induced, and the end-point pressure of micturition, and reduced the voiding in obstructed and control bladders. Verapamil at doses of 4.0 mg/kg or higher induced significant arrhythmia.

CONCLUSIONS

Verapamil reduced the contractile force of the bladder and increased the capacity and residual urine volume in both normal and obstructed bladders. Thus, although calcium channel blockers such as verapamil may be effective in treating a hyperactive bladder, they may have adverse cardiovascular effects.

Effects of alterations in potassium and calcium concentrations on the pressure generated in rat whole bladder in vitro

BACKGROUND

Various physiologic systems maintain the ionic equilibrium essential for normal neuron and smooth muscle function. These systems are impaired by nonphysiologic concentrations of extracellular cations. This study investigated the effects of altered extracellular concentrations of potassium and calcium on the in vitro pressure generation in the whole bladder of rats.

METHODS

Pressure increases in response to field stimulation, as well as low and high doses of bethanechol, were determined in a Krebs solution containing a normal amount of potassium, and in excess of 10 mmol/L and 20 mmol/L of potassium. Each of these solutions had calcium concentrations, that were low (0.8 mmol/L), normal (2.5 mmol/L), or high (7.5 mmol/L).

RESULTS

The response to field stimulation was significantly decreased at the 20-mmol/L concentration of potassium in the presence of the different concentrations of calcium. The response to field stimulation increased as the extracellular concentration of calcium increased. The pressure increase caused by a low dose of bethanechol was significantly enhanced by elevations in the concentrations of both potassium and calcium. There was no difference in the response to a high dose of bethanechol in the presence of the various concentrations of potassium and calcium.

CONCLUSION

These findings indicated that changes in the cationic equilibrium that result in blocking of the neuronal sodium channels, as well as increasing the level of intracellular bound calcium in smooth muscle, alter bladder function in vitro.

Urodynamic effects of intravesical instillation of terodiline in healthy volunteers and in patients with detrusor hyperactivity

The effects of intravesical instillation of terodiline on urodynamic parameters were investigated in 8 healthy volunteers (10(-4) M.) and in 34 patients with detrusor hyperactivity (10(-5) M.) of neurogenic (22) or nonneurogenic (12) origin. The volunteers were investigated with conventional medium-fill cystometry, while in the patients a modified cystometric technique with slow intermittent filling was used. The reproducibility of the procedure was verified in 17 patients. Instillation of terodiline had no effect on the normal bladders nor were any improvements found in the nonneurogenic patients. In 12 patients in the neurogenic group treated with terodiline instillation the bladder capacity increased significantly (p < 0.05) from 289 +/- 32 to 413 +/- 55 ml. Within this group 5 patients were responders. It is suggested that pathophysiological changes may explain the difference between the neurogenic and nonneurogenic groups, and that the number of responders within the neurogenic group may be increased by an optimal drug preparation and increased dosage. Intravesical administration of terodiline may offer an alternative treatment in selected patients with detrusor hyperreflexia.

Effect of extracellular Ca2+ on cholinergic, KCl and phorbol ester-mediated phosphoinositide turnover and guinea pig urinary bladder contraction

The effect of extracellular Ca2+ ([Ca2+]o) on cholinergic, KCl and phorbol ester-mediated detrusor contractions was related to phosphoinositide (PI) breakdown in guinea pig urinary bladder. Carbachol (1.0 mM) elicited a 20-fold increase in inositol phosphate (IP) accumulation both in presence and absence of [Ca2+]o yielding the same EC50 value (approximately 12 microM). In contrast, carbachol-induced detrusor contractions were reduced by 35% without [Ca2+]o, but maximal efficacy was restored with Ca2+ replenishment. In absence of [Ca2+]o, repeated cholinergic stimulation yielded contractions only if tissues were intermittently equilibrated in [Ca2+]o. High K+ and PDBu evoked [Ca2+]o-dependent contractions. Ca2+ channel antagonists and divalent metal cations inhibited high K+ more potently than carbachol-mediated contractions. Together, these findings suggest multiple sources of Ca2+ for urinary bladder contraction, where voltage-sensitive responses depend primarily on [Ca2+]o and PI-linked muscarinic responses involved Ca2+ mobilization from intracellular stores as well. Clinical agents used for the treatment of urinary incontinence inhibited both carbachol-induced PI turnover and muscle contraction with the same rank order of potency both in presence and absence of [Ca2+]o. These findings suggest that the cholinergic mechanism of action of these agents involves the PI-Ca2+ effector system.

Effect of nifedipine on the contractile responses of the isolated rat bladder

The effect of the calcium channel blocker nifedipine on the motor transmission in isolated preparations of rat detrusor smooth muscle has been studied. Nifedipine blocked the major part (75 to 80%) of the contractile response to electrical field stimulation, while atropine only blocked 20 to 25%. In preparations pretreated with atropine, the response to electrical field stimulation was completely abolished by nifedipine. The converse was also true; in preparations pretreated with nifedipine the response was fully blocked by atropine. The nifedipine-resistant response was greatly potentiated by the anticholinesterase eserine. The blocking action of nifedipine on motor transmission was partially antagonised by raising Ca2(+)-concentration. Acetylcholine concentration-response curve was shifted to the right by nifedipine. It is concluded that the non-cholinergic motor neurotransmitter evokes contraction of the rat detrusor smooth muscle by activating external Ca2(+)-transport channels whereas the cholinergic contraction is mediated partly or wholly by alternative mechanisms.

In vitro intravesical instillation of anticholinergic, antispasmodic and calcium blocking agents (rabbit whole bladder model)

The systemic side effects accompanying oral pharmacotherapy of neurogenic bladder dysfunction present significant drawbacks to this type of therapy. In these studies we investigated the effect of intravesical administration of anticholinergic, antispasmodic and calcium blocking agents on pressure response mediated by field stimulation and bethanechol. We used the rabbit in vitro whole bladder model for these experiments. The bladder from a mature male NZW rabbit was mounted in an organ bath as a whole bladder preparation. After control field stimulation and bethanechol stimulation, 20 ml. of saline containing the specific drug being evaluated was instilled into the bladder. At 30 minute intervals, the responses to field stimulation and bethanechol were determined. Two hours after instillation of 100 microM of each specific drug, the inhibition of the contractile response to bethanechol and field stimulation (as % inhibition) was as follows: oxybutynin (95%/64%), verapamil (85%/81%), atropine (68%/31%), diltiazem (47%/39%), and imipramine (44%/47%). Atropine and oxybutynin suppressed the contractile response of the bladder to bethanechol to a much greater extent than that to field stimulation, while verapamil, diltiazem and imipramine suppressed the contractile response to bethanechol and field stimulation to approximately the same extent. Two hours after drug instillation, the intravesical solution was washed out and replaced with saline, but the recovery of the bladder contraction was slow and incomplete. The results of this study suggest that the use of self-intravesical instillation to suppress bladder contractility should be a good therapeutic approach for patients with neurogenic bladder, especially those who are already managed by intermittent catheterization.

Effect of atropine and terbutaline on motor activity of the continent caecal reservoir for urine

The effects of muscarinic receptor blockade (atropine) and of beta-adrenoceptor stimulation (terbutaline) on the motor activity of the continent caecal reservoir for urine were studied in 12 patients during continuous filling of the reservoir. Basal pressure was low at high level filling, but pressure waves with amplitudes of 40 to 50 cm H2O occurred every other minute. The reservoir's functional adaptation, revealed as a diminished amplitude of pressure waves and evident soon after its construction, remained stable at long-term follow-up. Subcutaneously injected atropine or terbutaline did not influence the basal pressure but increased the volume at which the first pressure wave appeared and decreased the wave amplitude and frequency at high filling levels. Intra-reservoir instillation of these drugs did not alter the dynamic behaviour of the reservoir. In selected patients, orally administered anticholinergic drugs or beta 2-adrenoceptor agonists may be useful in the management of hyperactivity in a colonic segment used as a continent reservoir or bladder substitute.

Effects of intravesical instillation of verapamil in patients with detrusor hyperactivity

The effects of verapamil instilled intravesically were investigated in patients with detrusor hyperactivity of neurogenic and non-neurogenic origin. An intermittent, well reproducible cystometric technique with stepwise infusion of fluid was used. Verapamil produced a significant increase of the bladder capacity in patients with detrusor hyperreflexia, but not in patients with detrusor instability. The drug had no significant influence on any other cystometric parameter. It is suggested that pathophysiological differences between hyperactivity of neurogenic and non-neurogenic origin may be responsible for the difference observed. The possible diagnostic and/or therapeutic importance of the present findings remains to be established.

The effect of nifedipine on spontaneous, drug-induced and reflexly-activated contractions of the rat urinary bladder: evidence for the participation of an intracellular calcium store to micturition contraction

1. The effect of nifedipine on spontaneous and stimulated motility of the rat urinary bladder has been investigated in vitro (isolated detrusor strips) and in vivo (micturition reflex). 2. Nifedipine inhibited tone and spontaneous activity of the isolated rat bladder, its effect being greater in indomethacin-treated preparations. Nifedipine suppressed the KCl induced phasic and tonic contraction and inhibited by 60-80% the carbachol- or ATP- induced contractions. Nifedipine reduced by about 70% amplitude of the nerve-mediated bladder contractions. 3. Exposure to Ca free medium containing EDTA suppressed tone and spontaneous activity of the rat bladder. In these conditions the response to KCl or ATP was rapidly abolished while a response to carbachol was still evident even after a long exposure to the Ca free medium. 4. In vivo, nifedipine affected reflex micturition e.g. increased volume threshold and slightly reduced amplitude of micturition contraction. In addition, nifedipine reduced voiding efficiency e.g. increased residual volume after micturition. These effects were evident following ligation of the ureters because in normal conditions nifedipine induced a marked diuresis which masked its effect on volume threshold. 5. These findings indicate that in the rat urinary bladder Ca from both intra- and extracellular pools is mobilized during spontaneous or stimulated contractions. Mobilization of an intracellular Ca pool by cholinomimetics or other neurotransmitter(s) may be responsible for the nifedipine-resistant component of the voiding contraction in vivo.

Identification and characterization of muscarinic cholinergic receptors in the human urinary bladder and parotid gland

The binding characteristics of [3H]quinuclidinyl benzilate (QNB) to muscarinic sites in isolated plasma membrane fractions of the human urinary bladder and parotid gland were studied. QNB binding to both preparations was of high affinity and low capacity. Mean values for the apparent dissociation constants (Kd) for binding to membrane preparations from the urinary bladder and parotid glands were 22 and 34 pM and the Bmax values 234 and 456 fmol/mg protein, respectively. Significance of difference between Kd and Bmax values from the two tissues was at the level of P less than 0.005 and P less than 0.05, respectively. QNB binding was inhibited by muscarinic receptor antagonists with varying degree of effectiveness. The mean values for the inhibition constant (Ki) were significantly lower for oxybutynin, amitriptyline, and pirenzepine but higher for secoverine in preparations of the urinary bladder than of the parotid gland. The mean Ki values for quinidine and verapamil were lower in the urinary bladder than that in the parotid gland. Carbachol exhibited a marked selectivity for the urinary bladder (about 30-fold) compared with the parotid gland. The present data obtained in two human tissues that are highly cholinergic in their innervation give support to the argument for heterogeneity of the muscarinic cholinergic receptors.