Preliminary observations on the mechanical and electrical activity of the rat ureter

Role of α- and β-adrenergic signaling in phenotypic targeting: significance in benign and malignant urologic disease

The urinary tract is highly innervated by autonomic nerves which are essential in urinary tract development, the production of growth factors, and the control of homeostasis. These neural signals may become dysregulated in several genitourinary (GU) disease states, both benign and malignant. Accordingly, the autonomic nervous system is a therapeutic target for several genitourinary pathologies including cancer, voiding dysfunction, and obstructing nephrolithiasis. Adrenergic receptors (adrenoceptors) are G-Protein coupled-receptors that are distributed throughout the body. The major function of α1-adrenoceptors is signaling smooth muscle contractions through GPCR and intracellular calcium influx. Pharmacologic intervention of α-and β-adrenoceptors is routinely and successfully implemented in the treatment of benign urologic illnesses, through the use of α-adrenoceptor antagonists. Furthermore, cell-based evidence recently established the antitumor effect of α1-adrenoceptor antagonists in prostate, bladder and renal tumors by reducing neovascularity and impairing growth within the tumor microenvironment via regulation of the phenotypic epithelial-mesenchymal transition (EMT). There has been a significant focus on repurposing the routinely used, Food and Drug Administration-approved α1-adrenoceptor antagonists to inhibit GU tumor growth and angiogenesis in patients with advanced prostate, bladder, and renal cancer. In this review we discuss the current evidence on (a) the signaling events of the autonomic nervous system mediated by its cognate α- and β-adrenoceptors in regulating the phenotypic landscape (EMT) of genitourinary organs; and (b) the therapeutic significance of targeting this signaling pathway in benign and malignant urologic disease. Video abstract.

The modulation of ureteral smooth muscle contractile responses by α1- and α2-adrenoceptor activation

PURPOSE

This study was performed to investigate the influence of α-adrenoceptor subtypes upon ureteral smooth muscle contractile responses.

METHODS

Rat ureters were challenged in vitro with noradrenaline (NA), the α₁-adrenoceptor agonist phenylephrine (PE), and the α₂-adrenoceptor agonist clonidine (CLON). The influences of the agonists on the magnitude and frequency of acetylcholine (ACh)-stimulated phasic contractile responses were recorded.

RESULTS

The magnitude of the phasic contractile responses effected by ACh was not significantly influenced by the adrenoceptor agonists, but the frequency of the response was significantly enhanced by all three agonists (p < 0.05). Idazoxan and prazosin abolished the rise in frequency effected by CLON and PE, respectively, whereas both antagonists in combination were required to abolish the increase in frequency effected by NA.

CONCLUSIONS

It has been demonstrated that α₁- and α₂-adrenoceptors modulate the contractile function of rat ureteral smooth muscle by increasing the frequency, but not the magnitude, of phasic contractile responses. The enhancement of contractile function by NA is mediated by mechanisms dependent upon both α₁- and α₂-adrenoceptors.

Pathophysiological aspects of ureterorenoscopic management of upper urinary tract calculi

PURPOSE OF REVIEW

Indications for ureterorenoscopy are expanding without hard scientific evidence to support its efficacy. Therefore, it is extremely important to focus on potential harmful effects of the procedure itself. This review explores how physiology of the upper urinary tract reacts to ureterorenoscopy, potentially translating into harmful effects, and how such pathophysiological processes may be minimized.

RECENT FINDINGS

Complications to ureterorenoscopy and postoperative pain seem to be related to intrarenal pressure and/or access. Mean intrarenal pressures in the range of 60-100 mmHg during ureterorenoscopy without access sheaths have been measured, thus by far exceeding the threshold for intrarenal backflow, potentially resulting in septic complications. Intrarenal pressure may be reduced by use of ureteral access sheaths, which, however, may cause ureteral damage due to the limited size of the ureter and strain-induced ureteral contractions (peristalsis). Different receptor types modulate this peristaltic activity. β-receptor agonists have been investigated in animal and human trials for the purpose of relaxing the ureter. In randomized, placebo-controlled trials in pigs and humans, usage of the β-receptor agonist isoproterenol in the irrigation fluid has shown a potential for reducing both intrarenal pressure and ureteral tone during ureterorenoscopy.

SUMMARY

Upper urinary tract physiology has unique features that may be pushed into pathophysiological processes by the unique elements of ureterorenoscopy: access and irrigation. Pharmacological ureteral relaxation during ureterorenoscopy deserves further attention with regard to reducing complications and postoperative pain.

Electrical propagation in the renal pelvis, ureter and bladder

Under normal conditions, following the passage of urine from the collecting duct, the urine is stored briefly in the renal pelvis before being transported through the ureter to the bladder where the urine is stored for a longer time (hours) before being voided through the urethra. The transport of urine from the renal pelvis to the bladder occurs spontaneously due to contractions of the muscles in the wall of the pelvis and ureter. Spontaneous contractions also occur in the detrusor muscle and are responsible for maintaining the bladder shape during the filling phase. These muscle contractions occur as result of electrical impulses, which are generated and propagated through different parts of the urinary tract. The renal pelvis and the ureter differ from the bladder in relation to the origin, characteristics and propagation of these electrical impulses. In the ureter, the electrical impulses originate mainly at the proximal region of the renal pelvis and are transmitted antegradely down the length of the ureter. The electrical impulses in the bladder, on the other hand, originate at any location in the bladder wall and can be transmitted in different directions with the axial direction being the prominent one. In this manuscript, an overview of the current state of research on the origin and propagation characteristics of these electrical impulses in the normal and pathological conditions is provided.

β-Adrenergic Receptor Subtypes in the Urinary Tract

Within the urinary tract, β-adrenergic receptors (AR) are found largely on smooth muscle cells but are also present, at least in the bladder, in the urothelium and on afferent nerves. Our understanding of β-AR subtype expression and function is hampered by a lack of well-validated tools, particularly with regard to β(3)-AR. Moreover, the β-AR subtypes involved in a specific function may differ between species. In the ureter, β-AR can modulate pacemaker activity and smooth muscle tone involving multiple subtypes. In the human bladder, β-AR promote urine storage. Bladder smooth muscle relaxation primarily involves β(3)-AR, and the agonists selective for this subtype are in clinical development to treat bladder dysfunction. While prostate and urethra also express β-AR, the overall physiological role in these tissues remains unclear.

Propagation of the electrical impulse in reversible unilateral ureteral obstruction as determined at high electrophysiological resolution

PURPOSE

We investigated the propagation of electrical impulses in a reversible, complete or partial unilateral ureteral obstruction model in vivo.

MATERIALS AND METHODS

In Wistar rats the left mid ureter was completely (8) or partially (7) occluded and released after 24 hours. We recorded electrical activity of the left and right ureter before, during and after obstruction at different stages up to 2 weeks after obstruction using a high resolution, 64 extracellular electrode probe.

RESULTS

Complete obstruction in the left proximal ureter caused an immediate increase in frequency from a mean ± SEM of 14.8 ± 1.3 to 18.6 ± 1.7 per minute (p <0.05), followed by a 1.4 ± 0.9 per minute decrease (p <0.001). Within the first 2 days after reversal velocity gradually decreased from 1.82 ± 0.12 to 0.79 ± 0.17 cm per second (p <0.001). Release of obstruction gradually restored frequency and velocity, which returned to baseline at 2 weeks. Generally the alterations in rats with complete and partial obstruction were similar but they were less marked in those with partial obstruction. Distal to the obstruction site the impulses disappeared (38%) or propagated retrograde (43%) at some stage in the post-obstruction period. These abnormal impulse propagations also gradually disappeared in the post-obstruction stage.

CONCLUSIONS

After complete or partial ureteral obstruction there were immediate, significant changes in the propagation of electrical impulses in the proximal and distal left ureter, which were generally less marked after partial than after complete obstruction. Reversal of obstruction resulted in the gradual disappearance of this abnormality in 2 weeks.

Propagation characteristics of the electrical impulse in the normal and obstructed ureter as determined at high electrophysiological resolution

OBJECTIVE

To investigate the propagation of the electrical impulses in a unilateral ureteric obstruction model using a high-resolution technique in vivo.

MATERIALS AND METHODS

In Wistar rats (n= 15), the left mid-ureter was occluded and the electrical activity was recorded from the proximal and distal part of the obstructed ureter and from the right ureter at different times up to 2 weeks post-obstruction using 64 extracellular electrodes.

RESULTS

In the left ureter, impulses propagated in an antegrade direction at a frequency of 15.5 ± 1.3/min and a velocity of 1.6 ± 0.1 cm/s. Immediately post-obstruction, the proximal part showed an increase in frequency (19.1 ± 2.5/min; P < 0.05) followed by a gradual decrease (at 2 weeks: 2.5 ± 1.2/min; P < 0.001). The velocity of these impulses decreased gradually (at 2 weeks: 0.5 ± 0.1 cm/s; P < 0.05). Distally, the antegrade propagations gradually disappeared and, at 1 week, 33% of ureters showed retrograde impulses and 67% displayed no electrical activity. The frequency of both antegrade and retrograde impulses distal to the obstruction dropped immediately after obstruction so that, at 1 day, it was 1.0 ± 0.3 and 1.5 ± 0.2/min, respectively (P < 0.01 for both). The velocity of these antegrade and retrograde impulses showed a significant rise throughout the post-obstruction period. The right ureter showed only a transient increase in frequency from 18.7 ± 2.7 to 30.3 ± 6.1/min (P < 0.05).

CONCLUSIONS

Using this high-resolution technique, it is concluded that, after ureteric obstruction, there were immediate and significant changes in the propagation of electrical impulses in the proximal and distal left ureter and in the right ureter, all of which behaved differently. This data may provide a better insight into the electrophysiological function of the normal and obstructed ureter.

Pharmacological effect on pyeloureteric dynamics with a clinical perspective: a review of the literature

We searched to review experimental and clinical trials concerning the capabilities of impacting on the ureteric and pelvic activity by means of pharmacological stimulation. Ureteropyeloscopy may cause high renal pelvic pressure. The normal pressure is in the range of 5-15 mmHg whereas pressure of 410 mmHg has been measured during endoscopy. The threshold pressure for intrarenal reflux is about 35 mmHg. Studies in animals have revealed that high renal pelvic pressures may cause permanent damage to the renal parenchyma. Furthermore, it has been demonstrated that elevated pressures may entail an increased risk of several complications related to endourological procedures including bleeding, perforation and infection. In other words, means by which intrarenal pressure could be lowered during endourological procedures might be beneficial with respect to clinical outcomes. In vitro experiments support the existence of different receptors in the ureter and renal pelvis. The ureteric and pelvic responses to the corresponding neurotransmitters have been determined. It seems that alpha-adrenergic and cholinergic agents are stimulating whereas beta-adrenergic agents inhibit ureteric activity. The effect may depend on the mode of administration. Drugs exerting advantageous effects in the pyeloureter may cause undesirable systemic side effects when administered intravenously. In animal studies, renal pelvic pressure can be significantly lowered by topical administration of beta-adrenergic agonists without systemic side effects. In vivo human studies are necessary to clarify the exact dose-response relationship and the degree of urothelial absorption of a drug before clinical use may be adopted.

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.

Propagation of impulses in the guinea-pig ureter and its blockade by calcitonin gene-related peptide (CGRP)

The guinea-pig ureter was placed in a three-compartment organ bath to enable the application of electrical stimuli or drugs to its renal end (R-site), the middle region (M-site) or the bladder end (B-site) while recording mechanical activity at the R- and B-sites. All experiments were performed in ureters pre-exposed to capsaicin (10 microM for 15 min) to prevent the release of sensory neuropeptides from afferent nerves. Electrical field stimulation (EFS, 5-25 ms pulse width, 20 V) produced a phasic contraction at the site of stimulation ('direct' response to EFS) which propagated to the other end of the ureter. Section of the ureter at the M-site abolished the propagated response to EFS; after section, EFS applied at the M-site induced a phasic contraction at both the R- and B-sites. Likewise, the application of KCl at the M-site produced phasic contractions at both the R- and B-sites. Tetrodotoxin (1 microM), nifedipine (1 microM) or Bay K 8644 (1 microM) applied at the M-site had no influence on the direct or propagated responses to EFS; nifedipine (10 microM) applied at the M-site abolished the propagated responses without affecting the direct responses to EFS. Bay K 8644 (1 microM) applied at the R-site produced a marked enhancement of the direct response (EFS applied at R-site) while having no effect on the amplitude of the propagated response to EFS.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-blocking agent facilitating the spontaneous passage of ureteral stones

Based on data from neurophysiological studies, the author checked the action of a beta-blocking agent facilitating spontaneous stone passage from the ureter. Experience has shown that, compared with the control group, the beta-receptor-blocking agents proved to be useful in the facilitation of a spontaneous discharge of stones located in the lower part of the ureter.

Ureteral urine transport: changes in bolus volume, peristaltic frequency, intraluminal pressure and volume of flow resulting from autonomic drugs

An experimental model which permits independent changes in ureteral peristalic frequency and bolus volume was employed to explore the effects of autonomic agonists on ureteral bolus volume, peristaltic frequency, intraluminal pressure and flow volume in the dog. Norepinephrine caused an increase in ureteral peristaltic frequency, an elevation in intraureteral baseline and contractile pressure and a decrease in bolus volume, with a resultant decrease in the rate of fluid transport. Isoproterenol caused a decrease in ureteral peristaltic frequency, and a fall in intraureteral baseline and contractile pressure, or it completely abolished peristalsis and bolus formation. These changes were accompanied by an increase in the rate of fluid transport. Acetylcholine caused an increase in ureteral peristaltic frequency, an elevation of intraureteral baseline pressure but no change in contractile pressure, and a small decrease in bolus volume with a resultant small decrease in the rate of fluid transport. These data suggest that the autonomic nervous system may affect urine transport through the ureter by not only regulating peristaltic frequency but also by influencing bolus volume.

Effects of noradrenaline, isoproterenol and acetylcholine on ureteral resistance

Resistance to fluid flow in the canine ureter can be divided into two categories. The higher resistance is recorded at flow rates less than or equal to 2.16 ml./min. At these rates the ureter is able to completely coapt its walls so that urine is transported in individual boluses. The lower resistance is recorded at flow rates greater than or equal to 5.40 ml./min. At these rates the ureteral walls remained open and urine is transported as a column of fluid. Noradrenaline causes a marked increase in ureteral resistance at low flow rates and a small but statistically significant increase in ureteral resistance at high flow rates. Acetylcholine increases resistance only at the low flow rates. Isoproterenol significantly decreases resistance at both low and high flow rates. These findings are consistent with ureteral resistance to fluid flow being composed of two components. One is the ureteral peristaltic contraction which plays a principal role in urinary bolus transport at low flows; the other is ureteral wall tonus, which plays an important role in the transport of columns of urine by the ureter, which does not coapt its walls, at the higher flow rates.

Conduction velocity of peristaltic waves in the in vivo ureter: application of a new diameter gauge

The conduction velocity of peristaltic movements of the canine ureter was measured under anaesthesia with a new type of diameter gauge using an image sensor. The peristaltic velocity was 34.1 +/- 6.2 mm/sec in 10 experiments. Noradrenaline at a low dosage of 1 microgram/kg i.v. reduced the resting diameter, increased the conduction velocity to 47--56 mm/sec, and approximately doubled the frequency of contraction. The application of acetylcholine also caused an increase in both frequency and conduction velocity (42--46 mm/sec). A plot of the conduction velocity against the mean period of peristaltic contraction was hyperbolic in shape.

A contribution to the study of kinetics of ureteral urine passage in children

For the assessment of ureteral urine passage in children sequential scintigraphy with an analyzing system was used. Through the proper division of the time of examination into short time intervals the information on the areal distribution of urine was obtained, dependent on time. After demarcation of the spheres of interest by light-pen, the level of radioactivity was followed continually in a form of curves. Information for the assessment of etiopathogenesis of the disease was selected from the memory system of the device. Through the radioisotope examination also the dynamic changes have been recorded, not visible in excretion urograms, or only presumable from them. The method of examination described can help to assess the functional importance of morphological findings.

Acetylcholine content of and release from isolated pelviureteral tract

Measurements were taken for the acetylcholine content of animal and human pelviureteral muscle and for the release of acetylcholine at rest and during field stimulation of the isolated renal pelvis and ureter. Release was frequency-dependent, with the maximum output obtained at 10 Hz. The release of acetylcholine from reserpine-pretreated and piperoxan-treated tissues remained unchanged, but tetrodotoxin (1.10(-6) g/ml) and noradrenaline (2.10(-6) g/ml) significantly reduced the output.