The action of pinacidil in the isolated human bladder

Effect of the ATP-sensitive potassium channel opener ZM226600 on cystometric parameters in rats with ligature-intact, partial urethral obstruction

The activity of a recent K(ATP) channel opener, the N-(4-Phenylsulfonylphenyl)-3,3,3-trifluoro-2-hydroxy-2-methylpropionamide (ZM226600) was investigated on a female rat model of overactive bladder with outlet obstruction. Both ZM226600 and pinacidil instilled into the bladder (10(-7) M, 30 min) or following systemic administration (10, 100 nmol/kg e.v.) almost completely abolished bladder overactivity and improved residual volume and frequency of micturition. However, pinacidil affected arterial pressure. Oxybutynin instilled into the bladder (10(-7), 10(-6), 10(-5) M, 30 min) decreased detrusor overactivity by about 16%, 25% and 46% respectively, but also blocked micturition reflexes at highest doses tested. Oxybutynin reduced detrusor overactivity by about 50% and 80%, after systemic administration (10, 100 nmol/kg e.v.), but also blocked micturition reflexes at the highest dose tested. In conclusion, ZM226600 is more active than oxybutynin in reducing bladder overactivity, and it is devoid of vascular side effects observed with pinacidil. Its short duration of action (about 1 h) is probably the main problem to solve, in order to consider this compound a valid alternative to antimuscarinics in the therapy of bladder overactivity.

BL-1249 [(5,6,7,8-tetrahydro-naphthalen-1-yl)-[2-(1H-tetrazol-5-yl)-phenyl]-amine]: a putative potassium channel opener with bladder-relaxant properties

BL-1249 [(5,6,7,8-tetrahydro-naphthalen-1-yl)-[2-(1H-tetrazol-5-yl)-phenyl]-amine] produced a concentration-dependent membrane hyperpolarization of cultured human bladder myocytes, assessed as either a reduction in fluorescence of the voltage-sensitive dye bis-(1,2-dibutylbarbituric acid)trimethine oxonol (EC50 = 1.26 +/- 0.6 microM) or by direct electrophysiological measurement (EC50 = 1.49 +/- 0.08 microM). BL-1249 also produced a membrane hyperpolarization of acutely dissociated rat bladder myocytes. Voltage-clamp studies in human bladder cells revealed that BL-1249 activated an instantaneous, noninactivating current that reversed near E(K). The BL-1249-evoked outward K+ current was insensitive to blockade by glyburide, tetraethylammonium, iberiotoxin, 4-aminopyridine, apamin, or Mg2+. However, the current was inhibited by extracellular Ba2+ (10 mM). In in vitro organ bath experiments, BL-1249 produced a concentration-dependent relaxation of 30 mM KCl-induced contractions in rat bladder strips (EC50 = 1.12 +/- 0.37 microM), yet had no effect on aortic strips up to the highest concentration tested (10 microM). The bladder relaxation produced by BL-1249 was partially blocked by Ba2+ (1 and 10 mM) but not by apamin, iberiotoxin, 4-aminopyridine, glyburide, or tetraethylammonium. In an anesthetized rat model, BL-1249 (1 mg/kg i.v.) decreased the number of isovolumic contractions, without significantly affecting blood pressure. Thus, BL-1249 behaves as a potassium channel activator that exhibits bladder versus vascular selectivity both in vitro and in vivo. A survey of potassium channels exhibiting sensitivity to extracellular Ba2+ at millimolar concentration revealed that the expression of the K2P2.1 (TREK-1) channel was relatively high in human bladder cells versus human aortic cells, suggesting this channel as a possible candidate target for BL-1249.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Effects of ZD6169 and ZD0947, 2 potassium adenosine triphosphate channel openers, on bladder function of spinalized rats

PURPOSE

The use of K+ channel openers is emerging as an attractive possibility for treating bladder overactivity. We tested the efficacy of the 2 adenosine triphosphate dependent K channel openers ZD6169 and ZD0947 on detrusor hyperreflexia after spinal cord injury in rats.

MATERIALS AND METHODS

Included in this study were 72 adult Sprague-Dawley rats. Six animals served as normal controls, while 66 underwent spinal cord transection at the 10th thoracic vertebra. Two weeks after spinal cord injury 6 animals underwent filling cystometrography to confirm detrusor hyperreflexia, while another 12 served as control paraplegics. For each drug 24 animals were used and divided into 2 equal groups of 12. Group 1 received the drug in a dose of 3 mg./kg. daily, while group 2 received a dose of 0.3 mg./kg. daily. Each control paraplegic and treatment group was further subdivided into 2 subgroups of 6 rats. In subgroup 1 filling cystometrography was done 3 weeks after spinal cord injury, while in subgroup 2 it was done 4 weeks after spinal cord injury.

RESULTS

Three weeks after spinal cord injury detrusor hyperreflexia developed in all control paraplegic animals with a mean bladder capacity plus or minus standard deviation of 0.7 +/- 0.2 ml. and a mean voiding pressure of 59 +/- 14.2 cm. water. Detrusor hyperreflexia resolved in 66% of the animals that received ZD6169 for 1 week at either dose. For example, mean bladder capacity was 2.5 +/- 1.8 versus 1.8 +/- 1.2 ml. and mean voiding pressure was 42.1 +/- 15.9 versus 43.2 +/- 21.4 cm. water in animals that received 3 versus 0.3 mg./kg. daily, respectively. All animals that received a dose of 3 mg./kg. ZD0947 daily for 1 week showed no detrusor hyperreflexia with a mean bladder capacity of 2.7 +/- 1.8 ml. and mean voiding pressure of 34 +/- 8.5 cm. water, while at 0.3 mg./kg. daily 83% showed no detrusor hyperreflexia with a mean bladder capacity of 2.5 +/- 2.0 ml. and a mean voiding pressure of 41.5 +/- 13.8 cm. water. Each drug produced better urodynamic results when given for 2 weeks.

CONCLUSIONS

ZD6169 and ZD0947 are effective treatment for detrusor hyperreflexia after spinal cord injury and they may provide alternative treatment options for overactive bladder. Each drug has time and dose dependent response effects that reflect their wide range of efficacy. However, ZD0947 shows an efficacy profile that is relatively superior to that of ZD6169.

Pharmacologic management of urinary incontinence in women

This article summarizes current thought regarding the efficacy of various types of drug therapy for incontinence in women, borrowing liberally from similar previous presentations. Space limitations for this chapter necessitate some simplification and condensation of these subjects. References have generally been chosen because of their informational or review content and not because of originality or initial publication on a particular subject.

Effects of ZD6169, a KATP channel opener, on bladder hyperactivity and spinal c-fos expression evoked by bladder irritation in rats

Cystometrographic recording and immunocytochemical techniques were used to examine the effects of ZD6169, an ATP-sensitive K+-channel opener, and capsaicin, an afferent neurotoxin, on urinary bladder hyperactivity and immediate early gene expression in the spinal cord induced by acetic acid (0.25%) irritation of the bladder. Chemical irritation of the bladder of the rat increased the frequency of voiding reflexes by 8 fold and increased c-fos expression in neurons in the dorsal commissure (DCM), sacral parasympathetic nucleus (SPN) as well as the medial and lateral dorsal horn (MDH, LDH) of L6 and S1 segments of the spinal cord. Pretreatment with ZD6169 (30 nM) for 1 h reduced the effect of acetic acid on voiding frequency as reflected by an increase in the intercontraction interval (ICI, 137+/-48% increase, P<0.05). ZD6169 also decreased the number of Fos positive neurons in the L6 spinal cord, in the DCM (62.1+/-7.1% decrease), SPN (48.8+/-7%), MDH (50+/-7.3%) and LDH regions (38. 8+/-10.5%). Similar reductions were noted in the S1 spinal cord: 65. 1+/-10.8% in DCM, 53.8+/-11% in SPN, 56+/-10.4% in MDH and 25.3+/-18. 1% in LDH. Capsaicin pretreatment (125 mg/kg, s.c., 4 days prior to the experiments) also reduced bladder hyperactivity (550% increase in ICI) and decreased the numbers of acetic acid-induced Fos positive neurons 78.8+/-6.3% in DCM, 73+/-7.8% in MDH, 59.2+/-16% in LDH and 45.2+/-17% in SPN of L6 segment of the spinal cord. These results suggest that ZD6169 can influence bladder hyperactivity by suppressing the firing of capsaicin-sensitive C-fiber bladder afferents which are known to modulate the micturition reflex.

Pharmacologic options for the overactive bladder

OBJECTIVES

To review the current pharmacologic options for treatment of the overactive bladder and to describe potential therapies on the horizon.

METHODS

The literature on the clinical efficacy and safety of the currently available agents is described.

RESULTS

According to the guidelines issued by the Agency for Health Care Policy and Research (AHCPR), anticholinergic agents should be the first-line pharmacologic therapy for patients with detrusor instability. Oxybutynin is the anticholinergic of choice for this indication, whereas propantheline is the second-line therapy. Although calcium antagonists have been investigated, the one such drug introduced for the treatment of overactive bladder (terodiline) was withdrawn from the market because of a risk of cardiac arrhythmia. Studies of potassium channel openers have found either a lack of clinical efficacy or an unacceptable level of side effects. Alpha-adrenergic antagonists may be useful for decreasing bladder overactivity in patients who have autonomous bladders as the result of conditions such as spinal cord injury. Tricyclic antidepressants (particularly imipramine) may be effective in decreasing bladder contractility, although the AHCPR guidelines caution that these drugs should be reserved for use in carefully evaluated patients. Future developments in the treatment of detrusor overactivity are likely to occur in 3 categories: drugs that affect peripheral excitatory mechanisms, drugs that inhibit afferent mechanisms, and drugs that affect more central actions at either the ganglionic, spinal cord, or supraspinal level.

CONCLUSIONS

Although pharmacologic management of the overactive bladder has progressed little in the past 10 years, the future may hold the promise of more effective therapies.

A myogenic basis for the overactive bladder

OBJECTIVES

This article summarizes evidence supporting the conclusion that the spontaneous rises in pressure that occur in the overactive bladder, particularly in detrusor instability (DI), regardless of etiology, are myogenic.

METHODS

The evidence quoted has been obtained by several groups of investigators and includes electrophysiologic studies of detrusor myocytes, tension studies of strips of smooth muscle, in vivo experiments on animal models, and light and electron microscopic studies of the structure of the bladder wall.

RESULTS

The results of these studies demonstrate changes in the properties, structure, and innervation of the detrusor. These changes are consistent with the hypothesis that partial denervation of the detrusor may be responsible for altering the properties of the smooth muscle, leading to increased excitability and increased ability of activity to spread between cells, resulting in coordinated myogenic contractions of the whole detrusor.

CONCLUSIONS

It is suggested that alterations in the properties of the detrusor myocytes are a necessary prerequisite for the production of the unstable pressure rises seen in DI of any origin.

Smooth muscle of the bladder in the normal and the diseased state: pathophysiology, diagnosis and treatment

The smooth muscle of the normal bladder wall must have some specific properties. It must be very compliant and able to reorganise itself during filling and emptying to accommodate the change in volume without generating any intravesical pressure, but whilst maintaining the normal shape of the bladder. It must be capable of synchronous activation to generate intravesical pressure at any length to allow voiding. The cells achieve this through spontaneous electrical activity combined with poor electrical coupling between cells, and a dense excitatory innervation. In the diseased state, alterations of the smooth muscle may lead to failure to store or failure to empty properly. The diseased states discussed are bladder instability and diabetic neuropathy. Bladder instability is characterised urodynamically by uninhibitable rises in pressure during filling, and is seen idiopathically and in association with bladder outflow obstruction and neuropathy. In diabetic neuropathy, many of the smooth muscle changes are a consequence of diuresis, but there is evidence for alterations in the sensory arm of the micturition reflex. In the unstable bladder, additional alterations of the smooth muscle are seen, which are probably caused by the patchy denervation that occurs. The causes of this denervation are not fully established. Nonsurgical treatment of instability is not yet satisfactory; neuromodulation has some promise, but is expensive, and the mechanisms poorly understood. Pharmacological treatment is largely through muscarinic receptor blockade. Drugs to reduce the excitability of the smooth muscle are being sought, since they may represent a better pharmacological option.

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.

Potassium channel openers for treatment of bladder hyperactivity

The potassium (K+) channel openers induce hyperpolarization by ATP-sensitive K+ channels. This group of compounds has been demonstrated to effectively relax the human detrusor and reduce bladder hyperactivity in obstructed rats. In patients with overactive bladders, oral administration and intravenous infusion of different K+ channel openers were without significant effect on urodynamic variables. In conscious dogs, a new K+ channel opener was found to increase bladder compliance with reduced micturition frequency. K+ channel openers have an interesting potential for the treatment of bladder hyperactivity, but development of new selective compounds with further clinical experience are demanded.

Potassium channel activation: a potential therapeutic approach?

The physiological role of K+ channel opening by endogenous substances (e.g., neurotransmitters and hormones) is a recognised inhibitory mechanism. Thus, the identification of novel synthetic molecules that 'directly' open K+ channels has led to a new direction in the pharmacology of ion channels. The existence of many different subtypes of K+ channels has been an impetus in the search for new molecules demonstrating channel and, thus, tissue selectivity. This review focuses on the different classes of openers of K+ channels, the intracellular mechanisms involved in the execution of their effects, and potential therapeutic targets.

Comparison of the effects of several potassium-channel openers on rat bladder and rat portal vein in vitro

1. The ability of several K-channel openers to inhibit KCl-induced contractions of rat bladder detrusor and spontaneous mechanical activity in rat portal vein was examined. 2. Lemakalim, pinacidil, Ro 31-6930, RP 49356, P1060 and S 0121 dose-dependently relaxed rat detrusor, precontracted with 20 mM KCl. With the exception of pinacidil, concentrations of these agents below 30 microM did not inhibit 80 mM KCl-included contractions. Pinacidil (10 microM) produced a small, but significant (P < 0.05) relaxation of 80 mM KCl-induced mechanical activity. Minoxidil sulphate and BRL 38226 produced some relaxation of 20 mM but not 80 mM KCl-induced contractions. 3. Glibenclamide (0.3-3 microM) antagonized the relaxant effects of lemakalim, pinacidil, Ro 31-6930, RP 49356, P1060 and S 0121 in a competitive manner (pA2 values 6.3-6.6). The effects of minoxidil sulphate and BRL 38226 were fully antagonized by 3 microM glibenclamide. 4. Lemakalim, pinacidil, S 0121, BRL 38226 and minoxidil sulphate were each approximately 8 times more potent as inhibitors of the spontaneous contractions of rat portal vein than KCl-induced contractions of the rat detrusor. Minoxidil sulphate was approximately 30 times more potent in the rat portal vein than in the bladder. This may indicate that either minoxidil sulphate is acting at different recognition sites in these two tissues, or that this compound has an additional mechanism of action in the portal vein. 5. With the exception of minoxidil sulphate, all the compounds tested stimulated 86Rb efflux and 42K efflux from preloaded rat detrusor strips. The stimulated 86Rb efflux was qualitatively but not quantitatively similar to the stimulated 42K efflux. Minoxidil sulphate stimulated 42K efflux from rat portal vein but not from rat bladder. 6. It is concluded that all the compounds tested cause relaxation of rat detrusor predominantly by Kchannel opening. Selectivity for bladder rather than vascular smooth muscle was not shown by any compound.

The effects of potassium channel openers on isolated pregnant human myometrium before and after the onset of labor: potential for tocolysis

OBJECTIVE

Our purpose was to investigate the effects and pharmacologic properties of potassium channel openers in isolated pregnant human myometrium.

STUDY DESIGN

Biopsy specimens of myometrium obtained from 67 women during pregnancy and labor were used for isometric recording under physiologic conditions.

RESULTS

Levcromakalim and pinacidil, two prototype potassium channel openers, are potent inhibitors of spontaneous and induced (0.5 nmol/L oxytocin and 10 mumol/L phenylephrine) contractions in isolated human pregnant myometrium, obtained before and after the onset of labor. The sulfonylurea glibenclamide is an apparent competitive antagonist of this inhibition. No antagonism was observed with the sulfonylurea tolbutamide. Both potassium channel openers significantly inhibited contractility evoked by low (10 and 20 mmol/L) but not high (40 and 80 mmol/L) concentrations of extracellular potassium chloride.

CONCLUSION

These findings suggest that the relaxant ability of levcromakalim and pinacidil in human pregnant myometrium is because of potassium channel activation. This introduces a potential new approach for tocolysis.

Inhibitory effect of cromakalim in human detrusor muscle is mediated by glibenclamide-sensitive potassium channels

The effects of cromakalim, a potassium channel activating drug, and glibenclamide, a relatively selective antagonist of ATP-sensitive potassium channels, have been investigated on isolated detrusor muscle from human bladder. Specimens of human bladder were cut into strips and suspended in an organ bath filled with modified Tyrode solution for measurement of isometric contractile force. Concentration-response curves to acetylcholine were constructed before and after pretreatment with cromakalim and cromakalim plus glibenclamide. The concentration-response curves to acetylcholine were displaced to the right, and the maximal response to acetylcholine was significantly inhibited by cromakalim in a concentration-dependent manner. The inhibitory effect of cromakalim on acetylcholine-induced contraction was significantly reduced by glibenclamide. Following sustained contraction induced by 20 mM. KCl, the cumulative addition of cromakalim to the organ bath produced a concentration-dependent relaxation. However, in strips precontracted with 60 mM. KCl, the addition of cromakalim in concentrations as high as 10(-5) M. did not induce relaxation. The relaxation induced by cromakalim in strips precontracted with 20 mM. KCl was significantly inhibited by glibenclamide. These results suggest that the inhibitory effect of cromakalim in human bladder involves activation of glibenclamide-sensitive potassium channels.

Clinical pharmacology of potassium channel openers

Opening of K+ channels in cell membranes with resulting increase in K+ conductance, shifts the membrane potential in a hyperpolarizing direction towards the K+ equilibrium potential. Hyperpolarization reduces the opening probability of ion channels involved in membrane depolarization and excitation is reduced. K+ channel openers are believed to hyperpolarize smooth muscle cells by a direct action on the cell membrane. The best known members of the group are cromakalim, nicorandil and pinacidil, but several new compounds are being evaluated. In addition, it has recently been shown that also clinically well-known drugs like, e.g. diazoxide and minoxidil exhibit K+ channel opening properties. Nicorandil and new compounds containing nitro groups have a dual mechanism of action, also activating guanylate cyclase, an effect that contributes to their cardiovascular effect profile. K+ channel openers have a wide range of effects. Some of their properties and actions are summarized, and their present applications and/or potential for future application, in e.g. hypertension, angina pectoris, asthma, bladder instability, and several other disorders are discussed. It is concluded that K+ channel openning represents an interesting pharmacological principle with many potential clinical applications. However, most available drugs do not seem to have a sufficient tissue selectivity to be useful therapeutic alternatives. Before the potential of the new members of the group on clinical trials can be properly evaluated, clinical experiences are needed.

Effects of pinacidil on detrusor instability in men with bladder outlet obstruction

In a double-blind, crossover study the effect of the potassium channel opener pinacidil (N''-cyano-N'4-pyridyl-N-1,2,2-trimethylpropylguanidine monohydrate) at 25 mg. per day was evaluated in 10 patients with detrusor instability and bladder outlet obstruction. Nine patients completed the study: in 7 pinacidil was without significant effect on urodynamic variables and in 2 detrusor instability was not found at the end of the pinacidil period. Maximum urinary flow, frequency and nocturia were unchanged during pinacidil treatment, compared to the initial test and the placebo period. There was a significant decrease in standing blood pressure but heart rate was stable throughout the study. No patient experienced distinct symptomatic improvement or side effects during pinacidil treatment. The results suggest that pinacidil at the dosage given is not effective for treatment of unstable detrusor contractions associated with bladder outflow obstruction.

The efflux of 86Rb and [3H]5-HT from human platelets during continuous perfusion: effects of potassium-induced membrane depolarization and thrombin stimulation

In order to study the ionic efflux or granule release from human platelets following pulse exposure to various stimuli, a method for continuous perfusion of platelets was developed. The method was applied to compare the effects of membrane depolarization and thrombin stimulation on the release of 86Rb and [3H]5-HT. Washed and preloaded human platelets were placed on a membrane filter in a temperature controlled polypropylene chamber, and subsequently perfused with buffer. After an initial washout period the efflux of 86Rb or [3H]5-HT reached steady, low levels. K+ induced concentration dependent increases in 86Rb efflux, corresponding to a depolarization of the membrane potential, whereas the efflux of [3H]5-HT was unaltered. Thrombin induced concentration dependent increases in the efflux of both 86Rb and [3H]5-HT. Pretreatment with K+ 12 or 30 mM did not alter the [3H]5-HT efflux induced by thrombin 0.1 U ml-1. Scanning electron micrographs of platelets on the filter showed that the unstimulated platelets had regular shape, whereas after addition of thrombin there was formation of pseudopods and minor aggregates. The effect of potassium-induced membrane depolarization on platelet aggregation was also studied. High concentration of K+ did not induce aggregation or shape change during 2 or 10 minutes of incubation. K+ had little or no effect on aggregation induced by ADP 2 microM or thrombin 0.4 U ml-1. The results from release experiments and aggregation tests argue against an immediate coupling between membrane potential and platelet reactivity.

K(+)-channel openers for relaxation of isolated penile erectile tissue from rabbit

The effects of the K(+)-channel openers (KCOs) cromakalim (BRL 34915) and pinacidil were investigated and compared with those of papaverine on isolated corpus cavernosum from rabbit. Preparations were mounted in organ baths and isometric tension was recorded. Spontaneous contractile activity was effectively abolished by the KCOs tested, cromakalim being the most potent of them. The KCOs concentration-dependently and effectively depressed electrically induced contractions and also contractions induced by exogenously applied noradrenaline and by low (less than or equal to 20 mM) concentrations of K+. Cromakalim was three to four times more potent than pinacidil. Pinacidil and cromakalim were shown to cause increases in the efflux of 86Rb from preloaded cavernous tissue. Papaverine also effectively depressed spontaneous contractile activity, and contractions evoked by electrical stimulation and noradrenaline. It had a potency 19 to 36 times lower than that of cromakalim. However, papaverine did not increase 86Rb efflux from preloaded tissue. The results show that cromakalim and pinacidil effectively relax penile erectile tissue, probably by the opening of K(+)-channels and subsequent hyperpolarization. Further investigations on human material seems motivated in order to elucidate if the principle of K(+)-channel opening offers any therapeutic advantages to other drugs in the diagnosis and treatment of penile erectile dysfunction.

Effects of pinacidil on isolated human corpus cavernosum penis

Intracavernous injection of vasoactive agents causing vasodilatation is widely recognized in the diagnosis and treatment of erectile dysfunction. However, papaverine, the drug most commonly used for this purpose, may produce priapism and fibrotic lesions, and alternatives without these disadvantages are desirable. In this study we investigated the effects of pinacidil, a vasodilator drug supposed to act through the opening of K+ channels, on isolated human corpus cavernosum penis. Besides abolishing spontaneous contractile activity, pinacidil effectively relaxed preparations precontracted by noradrenaline 10(-6) M and inhibited contractions induced by electrical field stimulation of nerves. Furthermore, pinacidil depressed contractions induced by low-K+ solutions (less than or equal to 20 mM) and concentration-dependently increased the efflux of 86Rb from preloaded tissue. The results suggest that pinacidil is effective in relaxing isolated human erectile tissue, probably by way of increased K+ permeability and subsequent hyperpolarization. Clinical testing seems justified in order to find out if K(+)-channel openers can be used in the pharmacological treatment of impotence.

Effects of cromakalim (BRL 34915) and pinacidil on normal and hypertrophied rat detrusor in vitro

Normal and hypertrophied rat detrusor were investigated in vitro with regard to effects of the K(+)-channel openers pinacidil and cromakalim. Both drugs abolished spontaneous contractile activity and induced a relaxation of normal and hypertrophied detrusor preparations. In both types of preparation, contractions elicited by K+, carbachol or electrical field stimulation were depressed in the presence of the K(+)-channel openers. Responses induced by K+ or electrical stimulation were more reduced in the hypertrophied than in the normal detrusor. Both K(+)-channel openers increased the efflux of 86Rb+ in a concentration-dependent way and this increase was similar in normal and hypertrophied detrusor. If applicable to man, this data suggest that K(+)-channel openers may be effective in the treatment of bladder instability secondary to outflow obstruction.

Effects of pinacidil and cromakalim (BRL 34915) on bladder function in rats with detrusor instability

Normal rats as well as rats with bladder hypertrophy secondary to outflow obstruction were investigated cystometrically before and after administration of the potassium channel openers pinacidil or cromakalim one mg./kg. orally. In normal rats cromakalim decreased micturition pressure by 15 +/- 6%. A diminished micturition pressure was also seen after pinacidil (by 18 +/- 8%) but this did not achieve statistical significance. Further, no clear-cut effects on bladder capacity, residual volume, basal bladder pressure, threshold pressure, bladder compliance or on bladder wall tension were seen in this group of rats neither in the presence of pinacidil nor cromakalim. Rats with bladder hypertrophy exhibited a significant bladder instability during cystometrical investigations. The mean amplitude of the spontaneous bladder contraction exceeded 20 cm. H2O prior to micturition. Administration of pinacidil and cromakalin decreased the spontaneous contractions to 26 +/- 12% and 22 +/- 7%, respectively, of that seen in the absence of the drugs. Furthermore, pinacidil decreased micturition pressure by 61 +/- 12%. Also cromakalim decreased micturition pressure (by 27 +/- 13%) but this effect did not achieve statistical significance. After both pinacidil and cromakalim these rats tended to develop residual urine. In accordance with the results in normal rats pinacidil and cromakalim showed no effects on bladder capacity, basal bladder pressure, threshold pressure, bladder compliance or on bladder wall tension in rats with bladder hypertrophy. The findings of an almost complete disappearance of spontaneous bladder contractions in rats with bladder instability and a remaining voiding ability after administration of pinacidil or cromakalim suggest that potassium channel openers may be a therapeutic alternative in the treatment of bladder instability associated with outflow obstruction.