Effects of Potassium Channel Modulators Cromakalim, Tetraethylammonium and Glibenclamide on the Contractility of the Isolated Human Ureter

Effects of a non-selective COX inhibitor and selective COX-2 inhibitors on contractility of human and porcine ureters in vitro and in vivo

BACKGROUND AND PURPOSE

Anti-inflammatory drugs are used in the treatment of acute renal colic. The aim of this study was to investigate the effects of selective COX-2 inhibitors and the non-selective COX inhibitor diclofenac on contractility of human and porcine ureters in vitro and in vivo, respectively. COX-1 and COX-2 receptors were identified in human ureter and kidney.

EXPERIMENTAL APPROACH

Human ureter samples were used alongside an in vivo pig model with or without partial ureteral obstruction. COX-1 and COX-2 receptors were located in human ureters by immunohistochemistry.

KEY RESULTS

Diclofenac and valdecoxib significantly decreased the amplitude of electrically-stimulated contractions in human ureters in vitro, the maximal effect (Vmax) being 120 and 14%, respectively. Valdecoxib was more potent in proximal specimens of human ureter (EC50=7.3 x 10(-11) M) than in distal specimens (EC50=7.4 x 10(-10) M), and the Vmax was more marked in distal specimens (22.5%) than in proximal specimens (8.0%) in vitro. In the in vivo pig model, parecoxib, when compared to the effect of its solvent, significantly decreased the maximal amplitude of contractions (Amax) in non-obstructed ureters but not in obstructed ureters. Diclofenac had no effect on spontaneous contractions of porcine ureter in vivo. COX-1 and COX-2 receptors were found to be expressed in proximal and distal human ureter and in tubulus epithelia of the kidney.

CONCLUSIONS AND IMPLICATIONS

Selective COX-2 inhibitors decrease the contractility of non-obstructed, but not obstructed, ureters of the pig in vivo, but have a minimal effect on electrically-induced contractions of human ureters in vitro.

Physiology and pharmacology of the human ureter: basis for current and future treatments

INTRODUCTION

This article sets out to be a review regarding agents that affect contraction and relaxation of the ureter in order to establish a basis for current and future treatments for upper urinary tract obstruction.

MATERIAL AND METHODS

A complete review of the English literature using MEDLINE was performed between 1960 and 2007 on ureter physiology and pharmacology with special emphasis on signal transduction mechanisms involved in the contractile regulation of the human ureter.

RESULTS

Activation of muscarinic and adrenergic receptors increases the amplitude of ureteral contractions. The sympathetic nerves modulate the contractions by alpha-adrenoceptors and relaxation by beta-adrenoceptors. The purinergic system is important in sensory/motor functions and ATP is an important non-adrenergic non-cholinergic (NANC) agent causing contraction. Nitric oxide (NO) is a major inhibitory NANC neurotransmitter causing relaxation. Serotonin causes contraction. Prostaglandin-F(2)alpha contracts whereas prostaglandin-E(1)/E(2) relaxes the ureter. Phosphodiesterases (PDE) and the Rho-kinase pathway have recently been identified in the human ureter. PDE-IV inhibitors, K(+) channel openers, calcium antagonists, alpha(1)-adrenoceptor antagonists and NO donors seem to be promising drugs in relieving obstruction and facilitating stone passage.

CONCLUSIONS

Further understanding of the ureteral function and pharmacology may lead to the discovery of promising new drugs that could be useful in relieving ureteral colic, facilitating spontaneous stone passage, preparing the ureter for ureteroscopy as well as acting adjunctive to extracorporeal shock-wave lithotripsy.

Myocytes, myometrium, and uterine contractions

The pregnant uterus is unique because of the dramatic functional changes that occur in the peripartum period. To promote the concept that we have a relatively poor understanding of the physiology of parturition, we will posit 10 facts that are so obvious and so clearly accepted as facts that they probably are not even facts at all. (1) The laboring uterus undergoes peristalsis to dilate the cervix, deliver the fetus, and expel the placenta. (2) The human uterus is composed of longitudinal and circular layers of smooth muscle. (3) The functional cells of the uterus are the myocytes, which are a homogeneous cell type responsible for the generation of contraction forces, passage of action potentials, and control of contractility. (4) The phasic contractions of the uterus are typical for visceral smooth muscle. (5) The primary, and perhaps only, role of gap junctions is to allow passage of action potentials through the tissue. (6) Action potential propagation as the mechanism for global communication (over many centimeters throughout the uterus) is sufficient to recruit all regions and all myocytes of the uterus. (7) Slow waves pace the contractions of human myometrium. (8) Calcium-activated potassium channels are responsible for repolarization of the membrane potential that terminates each contraction. (9) Chloride channels are not important in uterine electrophysiology. (10) With enough computing power, it would be straightforward to build a closed model of human labor, given our current understanding of the components of myometrium. This manuscript discusses each point to stimulate questions for future investigation.

The potency of KUL-7211, a selective ureteral relaxant, in isolated canine ureter: comparison with various spasmolytics

We compared the potency of a selective ureteral relaxant KUL-7211 (beta(2)/beta(3)-adrenoceptor agonist; (-)-2-[4-(2-{[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino}ethyl)phenyloxy]acetic acid) with those of various spasmolytics on contractions in isolated canine ureteral preparations. Drug effects were evaluated on the tonic contraction induced by KCl (80 mM) and on spontaneous, 1x10(-5) M phenylephrine-, and 1x10(-6) M PGF(2alpha)-induced rhythmic contractions in isolated canine ureteral preparations using a functional experimental technique. The potencies (pD(2) value) of the following drugs were compared: KUL-7211, tamsulosin (an alpha(1A/1D)-adrenoceptor antagonist), prazosin (an alpha(1)-adrenoceptor antagonist), verapamil (a Ca(2+)-channel blocker), butylscopolamine (a nonselective muscarinic antagonist), and papaverine (a phosphodiesterase inhibitor). The rank order of relaxing potencies against KCl-induced tonic contraction was KUL-7211 (6.60)>tamsulosin(5.90)>verapamil(5.70)>papaverine(4.88)>prazosin (4.54). The rank order of potencies for reductions in spontaneous rhythmic contractions was KUL-7211 (6.80)>verapamil(6.12)>papaverine(5.05). Conversely, high concentrations of the two alpha-adrenoceptor antagonists (tamsulosin and prazosin) and of butylscopolamine enhanced the spontaneous contractions, although at low concentrations (up to 1x10(-6) M) they had no significant effects. For suppression of spasmogen-induced rhythmic contractions, the rank order of potencies was, against phenylephrine-induced contractions: KUL-7211 (6.95)>tamsulosin(6.26)>prazosin(5.68)>verapamil(5.64)>papaverine (5.03), and against PGF(2alpha)-induced contractions: KUL-7211 (7.05)>verapamil(6.70)>papaverine (5.27). Our results suggest that in dogs, the beta(2)/beta(3)-adrenoceptor agonist KUL-7211 is the most efficacious ureteral relaxant among the spasmolytics tested against various contractions. Possibly, KUL-7211 might be useful for promoting stone passage and relieving ureteral colic in urolithiasis patients.

Involvement of Rho-kinase in the contractile mechanism of human ureteral smooth muscle

AIM

Even though many agents have been implicated as modulators of ureteral contractile activity, the exact mechanisms that control human ureteral smooth muscle contractility have yet to be clearly defined. Recently, Rho-kinase has been reported to be involved in the contractile mechanism of smooth muscles in various organs. In the present study, we sought to investigate whether or not Rho-kinase is expressed in the human ureteral smooth muscle, and to study its role regarding human ureteral smooth muscle contractility.

METHODS

Ureteral samples were obtained from human adult subjects undergoing radical nephrectomy. Immunohistochemistry and Western blotting were performed to determine the presence of Rho-kinase in human ureter. Functional studies were performed with human ureteral strips suspended in organ bath, and the effects of Y-27632, a specific inhibitor of Rho-kinase, on baseline tensions, spontaneous contractions, and electrical field stimulation (EFS)-induced contractions were analyzed.

RESULTS

The results of immunohistochemistry and immunoblotting study indicated that Rho-kinase is present in human ureteral smooth muscle. In functional analysis, Y-27632 was shown to decrease the baseline tension. And, both spontaneous and EFS-induced contractile responses of human ureteral strips were attenuated by Y-27632 in dose-dependent manners.

CONCLUSIONS

For the first time, the results of the present study indicate that Rho-kinase is present in human ureteral smooth muscle and may play an important role in the intricate mechanism of human ureteral contractility and tone.

Inhibition of human and pig ureter motility in vitro and in vivo by the K(+) channel openers PKF 217-744b and nicorandil

The relaxing property of the K(+) channel opener and nitric oxide donor nicorandil and the new K(+) channel opener PKF 217-744b was investigated on isolated human ureteral tissue in vitro and in intact ureters of anesthetized pigs in vivo. In addition, nicorandil and its antagonists, glibenclamide and methylene blue, were tested on isolated pig ureter tissue in vitro. Nicorandil decreased the frequency of spontaneous contractions in isolated pig ureter rings. This effect was antagonized by glibenclamide and methylene blue suggesting that the nicorandil induced relaxation of the ureter is mediated by activation of ATP-sensitive K(+) channels and involvement of soluble guanylate cyclase. Moreover, nicorandil and PKF 217-744b reduced the amplitude of electrically induced contractions in isolated human ureter rings. Calculations of EC(50) values showed that PKF 217-744b [EC(50) = 4.83 x 10(-8) M] was more potent than nicorandil [EC(50) = 4.38 x 10(-5) M]. Both drugs reduced the contraction frequency of the pig ureter after intravenous and topical administration in vivo. Intravenous, but not topical, administration of nicorandil and PKF 217-744b significantly decreased arterial blood pressure but did not affect the heart rate. The in vitro findings suggest that K(+) channel opening and nitric oxide release mediate the effect of nicorandil. Our in vivo results indicate that PKF 217-744b and nicorandil are promising drugs for clinical application in patients with acute stone colic to relieve obstruction and facilitate stone passage or to relax the ureter before ureteroscopy.

Systemic and topical drug administration in the pig ureter: effect of phosphodiesterase inhibitors alpha1, beta and beta2-adrenergic receptor agonists and antagonists on the frequency and amplitude of ureteral contractions

PURPOSE

We searched for compounds that are pharmacologically active on ureteral motility for treating ureteral colic to ease retrograde access into the ureter and improve the clearance of stones or stone particles from the ureter. The effects of the alpha1-adrenergic receptor agonist phenylephrine, the nonselective beta and beta2-adrenergic receptor agonists isoproterenol and fenoterol, and the phosphodiesterase inhibitors papaverine (nonspecific) and rolipram (type IV) on the frequency and amplitude of ureteral contractions when administered intravenously or topically were investigated in pigs.

MATERIALS AND METHODS

A total of 52 pigs were anesthetized. A double lumen 6Fr catheter was inserted through each renal pelvis and into the ureter, allowing perfusion of saline or drug solution into the renal pelvis and the recording of contractions from the mid portion of the ureter.

RESULTS

The alpha1 and beta-adrenergic receptors of the ureter are not tonically activated by endogenous epinephrine or norepinephrine. Phenylephrine administered intravenously at a dose of 0.01 to 3 mg./kg. and topically at 0.1 to 3 mg./ml. per minute increased contraction frequency 10 and 4-fold, respectively, and contraction amplitude 2-fold each in a dose dependent manner. Arterial blood pressure increased markedly during intravenous administration of phenylephrine but was minimally affected during topical application. The phenylephrine effects were reversed by the antagonist prazosin. Isoproterenol administered intravenously at a dose of 0.01 to 10 mg./kg. and topically at 0.1 to 200 microg./ml. per minute decreased contraction frequency to 13% and 31% of controls, respectively. Contraction amplitude was not affected by intravenous administration but decreased to 59% of controls when applied topically. These effects were also observed with a slight delay in the saline perfused contralateral ureter. The heart rate also increased, suggesting absorption of the drug by the urothelium. The isoproterenol effects were blocked by the antagonist propranolol. Fenoterol administered intravenously at a dose of 0.1 to 30 microg./kg. and topically at 0.003 to 1 mg./ml. per minute decreased contraction frequency to 14% and 10% of controls, and contraction amplitude to 84% and 65%, respectively. These effects on the drug perfused ureter were also observed on the contralateral saline perfused ureter but to a lesser extent. The fenoterol effects were blocked by the antagonist propranolol. Papaverine administered intravenously at a dose of 0.001 to 3 mg./kg. decreased contraction frequency to 33% of controls. Topically administered papaverine as well as intravenous and topically administered rolipram had no relevant effect on ureteral motility.

CONCLUSIONS

Intravenous phenylephrine increases, and isoproterenol and fenoterol decrease the frequency and amplitude of ureteral contractions in the pig. The same effects are observed with the topical administration of phenylephrine, which causes a significant local but not systemic side effect. Topical administration of isoproterenol and fenoterol produced local as well as systemic effects, suggesting absorption by the urothelium. However, to our knowledge a drug that relaxes ureteral peristalsis in pigs without causing systemic side effects has not yet been identified.