Urodynamic studies after intrathecal administration of baclofen and morphine in dogs

Systemic and intrathecal baclofen produce bladder antinociception in rats

BACKGROUND

Baclofen, a clinically available GABAB receptor agonist, produces non-opioid analgesia in multiple models of pain but has not been tested for effects on bladder nociception.

METHODS

A series of experiments examined the effects of systemic and spinally administered baclofen on bladder nociception in female anesthetized rats. Models of bladder nociception included those which employed neonatal and adult bladder inflammation to produce bladder hypersensitivity.

RESULTS

Cumulative intraperitoneal dosing (1-8 mg/kg IP) and cumulative intrathecal dosing (10-160 ng IT) of baclofen led to dose-dependent inhibition of visceromotor responses (VMRs) to urinary bladder distension (UBD) in all tested models. There were no differences in the magnitude of the analgesic effects of baclofen as a function of inflammation versus no inflammation treatments. Hemodynamic (pressor) responses to UBD were similarly inhibited by IT baclofen as well as UBD-evoked excitatory responses of spinal dorsal horn neurons. The GABAB receptor antagonist, CGP 35,348, antagonized the antinociceptive effects of IT baclofen on VMRs in all tested models but did not affect the magnitude of the VMRs by itself suggesting no tonic GABAB activity was present in this preparation. Tolerance to a seven day continuous IT infusion of baclofen was not observed.

CONCLUSIONS

These data provide support for a clinical trial of baclofen as a non-opioid treatment of human bladder pain.

Effects of Dietary Vitamin E Supplementation in Bladder Function and Spasticity during Spinal Cord Injury

Traumatic spinal cord injury (SCI) results in debilitating autonomic dysfunctions, paralysis and significant sensorimotor impairments. A key component of SCI is the generation of free radicals that contributes to the high levels of oxidative stress observed. This study investigates whether dietary supplementation with the antioxidant vitamin E (alpha-tocopherol) improves functional recovery after SCI. Female adult Sprague-Dawley rats were fed either with a normal diet or a dietary regiment supplemented with vitamin E (51 IU/g) for eight weeks. The rats were subsequently exposed either to a contusive SCI or sham operation, and evaluated using standard functional behavior analysis. We report that the rats that consumed the vitamin E-enriched diet showed an accelerated bladder recovery and significant improvements in locomotor function relative to controls, as determined by residual volumes and Basso, Beatie, and Bresnaham BBB scores, respectively. Interestingly, the prophylactic dietary intervention did not preserve neurons in the ventral horn of injured rats, but it significantly increased the numbers of oligodendrocytes. Vitamin E supplementation attenuated the depression of the H-reflex (a typical functional consequence of SCI) while increasing the levels of supraspinal serotonin immunoreactivity. Our findings support the potential complementary use of vitamin E to ameliorate sensory and autonomic dysfunctions associated with spinal cord injury, and identified promising new cellular and functional targets of its neuroprotective effects.

Acute anal stretch inhibits NMDA-dependent pelvic-urethra reflex potentiation via spinal GABAergic inhibition in anesthetized rats

The impact of acute anal stretch on the pelvic-urethra reflex potentiation was examined in urethane-anesthetized rats by recording the external urethra sphincter electromyogram activity evoked by the pelvic afferent stimulation. Test stimulation (1 stimulation/30 s) evoked a baseline reflex activity with a single action potential that was abolished by gallamine (5 mg/kg iv). On the other hand, the repetitive stimulation (1 stimulation/1 s) induced spinal reflex potentiation (SRP) that was attenuated by intrathecal 6-cyano-7-nitroquinoxaline-2,4-dione (a glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionat receptor antagonist, 100 μM, 10 μl) and d-2-amino-5-phosphonovalerate [a glutamatergic N-methyl-d-aspartate (NMDA) antagonist, 100 μM, 10 μl]. Acute anal stretch using a mosquito clamp with a distance of 4 mm exhibited no effect, whereas distances of 8 mm attenuated and 12 mm abolished the repetitive stimulation-induced SRP. Intrathecal NMDA (100 μM, 10 μl) reversed the abolition on SRP caused by anal stretch. On the other hand, pretreated bicuculline [γ-aminobutyric acid (GABA) A receptor antagonist, 100 μM, 10 μl] but not hydroxysaclofen (GABAB receptor antagonist) counteracted the abolition on the repetitive stimulation-induced SRP caused by the anal stretch. All of the results suggested that anal stretch may be used as an adjunct to assist voiding dysfunction in patients with overactive urethra sphincter and that GABAergic neurotransmission is important in the neural mechanisms underlying external urethra sphincter activity inhibited by anal stretch.

Pharmacology of the lower urinary tract

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the urinary bladder, urethra, and external urethral sphincter. This activity is in turn controlled by neural circuits in the brain, spinal cord, and peripheral ganglia. Various neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in the neural regulation of the lower urinary tract. Injuries or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce voiding dysfunctions such as urinary frequency, urgency, and incontinence or inefficient voiding and urinary retention. This chapter will review recent advances in our understanding of the pathophysiology of voiding disorders and the targets for drug therapy.

Dog model for studying detrusor instability secondary to acutely induced variable bladder outlet obstruction

BACKGROUND

Involuntary detrusor contractions often cause irritative symptoms such as urgency and incontinence. A dog model for acutely induced variable bladder outlet resistance was developed to investigate the possible role of prostatic afferent nerve fibers in the development and maintenance of detrusor instability.

METHODS

Fifty-eight mongrel dogs (weight range 19.5-36.5 kg) were divided into five groups: group I (n = 11) had surgically induced bladder outlet obstruction. Group II (n = 14) had urinary obstruction and bilateral sectioning of the lowest branches of the pelvic plexus supplying the prostate. Group III (n = 10) had prostate denervation only. Groups IV (n = 10) and V (n = 13) were sham-operated and controls, respectively. In the obstructed groups (I and II), an artificial urinary sphincter (length 4.5-6.0 cm) was placed around the bladder neck and connected to a reservoir placed subcutaneously to allow postoperative adjustments of urinary resistance. All dogs were evaluated at baseline and postoperatively at 1, 3, and 6 months with uroflowmetry, postvoid residual urine volume, cystometry as well as serum creatinine, and urinalysis.

RESULTS

Occurrences of detrusor instability were not associated with prostatic denervation input. The mean peak flow rates decreased significantly in the obstructed groups at all follow-ups, but did not change significantly in the nonobstructed groups. Postoperatively, the mean maximum bladder capacity was significantly decreased for groups I and II only. However, a significant correlation between maximum bladder capacity and maximum detrusor pressure could not be detected at any time point in any of the groups. Mean postvoid residual urine volume varied considerably in all groups over time. Creation of a urinary model of infravesical obstruction was associated with considerable problems.

CONCLUSIONS

In our dog model of bladder outlet obstruction, prostatic sensory nerve fibers appear not to be involved in detrusor instability. Surgical induction of a constant model of bladder outlet obstruction was difficult even in a large animal. The observations from the present study raise questions about the validity of obstructive urinary animal models.

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.

Long-term clinical, electrophysiological and urodynamic effects of chronic intrathecal baclofen infusion for treatment of spinal spasticity

Seventeen patients with severe disabling spinal spasticity were selected and treated by chronic intrathecal baclofen infusion using an implanted programmable pump. Nine patients were tetraparetic, seven were paraplegic and one paraparetic. Patients were regularly followed for 5 to 69 months (mean 37.5 months). The clinical efficacy of baclofen was estimated by means of evaluation of: hypertonia, spasms, pain and functional disability. All patients experienced significant amelioration of quality of life secondary to reduction of hypertonia, spasms and pain related to contractures. Neurogenic pain improved in 3 cases and remained unchanged in 3 others. In patients whose motor functions were partially preserved, various degrees of motor improvement were detected. Electrophysiological recordings of Polysynaptic flexion reflexes (FR) were obtained to control conditions, and under intrathecal baclofen, in order to quantify the spinal excitability responsible for spontaneous or induced spasms. Flexion reflex threshold was increased and amplitude proved to be very significantly reduced by chronic baclofen infusion in all our patients. Twelve patients with neurogenic bladder dysfunction were also evaluated by a clinically oriented questionnaire and by quantitative urodynamic recordings, before and after pump implantation. In patients with normal micturition, this was not changed by intrathecal baclofen. In patients with spastic bladder, intrathecal baclofen produced a decrease of detrusor hypertonia and hyperactivity in 50% of cases, with reduction of leakage and increase in functional bladder capacity.

[Effects of anesthesia on postoperative micturition and urinary retention]

Postoperative micturition difficulties, considered as minor complications, have a high incidence. Acute urinary retention can follow all types of anaesthetics or operations. Surgical trauma to the pelvic nerves or to the bladder, postoperative oedema around the bladder neck, and pain-induced reflex spasm of the external and internal urethral sphincters may play a role in the development of urinary retention. Acute urinary retention is the most common complication of surgery for benign anorectal disease. The incidence of urinary retention is more likely to occur in old male patients. Preoperative urinary symptoms are not a prerequisite for developing postoperative urinary retention, although they are considered to be a risk factor. The type of anaesthetic, postoperative pain and its management may have little effect on the occurrence of postoperative urinary dysfunction. Studies on the urodynamic effects of various anaesthetic agents are rare. The parasympatholytic drugs increase bladder capacity, decrease the rate of bladder contractions and cause downward trends in urethral resistance. The barbiturates and halothane produce similar effects on urethral resistance. The anaesthetic agents decrease the intrabladder pressure and inhibit the micturition reflex. Halothane decreases bladder contractions and increases its capacity measured by the cystometrogram. Urinary retention is a side effect of opioids, particularly after intrathecal or epidural administration. Epidural morphine relaxes the detrusor muscle with a corresponding increase in the maximal bladder capacity. Spinal opioids influence the function of the lower urinary tract, by direct spinal action on the sacral nociceptive neurons and autonomic fibres, as well as by an effect on supraspinal centres. Naloxone increases detrusor pressure, decreases bladder capacity, and causes a need to void. Urinary retention is less common after a short-acting (lidocaine 5%) than after a long-acting agent (bupivacaine 0.5%). After spinal anaesthesia, detrusor strength and the ability to void restarts with the return of sacral sensation to pinprick. A single episode of bladder overdistention can result in significant morbidity. Overfilling of the bladder can stretch and damage the detrusor muscle, leading to atony of the bladder wall, so that recovery of micturition may not occur when the bladder is emptied. On the other hand, the excessive use of an indwelling catheter can lead to urinary tract infection, urethral stricture and prolonged hospital stay. Short-term prophylactic catheterisation is recommended in patients with obstructive symptoms. Patients at risk for urinary retention should be stimulated to void and provided a quiet environment in which to do so. They should be encouraged to seat, stand or ambulate as early as possible. The alpha 1 adrenergic receptor blocking agents have been used for treatment of organic or functional urinary retention. It is essential to make sure the bladder empties regularly in the postoperative period, especially in day-case surgery or in patients receiving opioid analgesia or after epidural anaesthesia.

Voiding dysfunction in patients with spastic paraplegia: urodynamic evaluation and response to continuous intrathecal baclofen

Patients with hereditary spastic paraplegia (HSP), a degenerative central nervous system disorder characterized by progressive lower extremity spasticity, frequently experience symptoms of voiding dysfunction. Urodynamic evaluation of patients with HSP has not been reported, and the etiology of voiding dysfunction remains unexplained. We present our evaluation of three men (ages 42-62 years) with this rare syndrome. Urgency of urination was a uniform and dominant complaint, and two patients regularly experienced urge incontinence. Other symptoms included frequency (n = 3), nocturia (n = 3), and diminished force of stream (n = 1). Postvoid residual volumes were less than 25 ml in all patients. On urodynamic evaluation the two patients with urge incontinence displayed cystometric evidence of involuntary detrusor contractions. Pelvic floor EMG recordings suggested detrusor-sphincter dyssynergia (DSD). In addition, one patient exhibited markedly diminished bladder compliance (1.0 ml/cm H2O) and capacity (50 ml). All patients reported marked symptomatic improvement when treated with continuous intrathecal baclofen. Evaluation during baclofen treatment revealed increases in bladder compliance and capacity, with apparent resolution of DSD in one patient. Voiding symptoms in these patients most likely arise from a neurogenic etiology; however, a contributory role for chronic outlet obstruction from striated muscle spasticity may also exist.

Effects of acute bolus and chronic continuous intrathecal baclofen on genitourinary dysfunction due to spinal cord pathology

A prospective, blinded study was done to examine the effects of acute bolus and chronic continuous intrathecal baclofen on genitourinary function in 10 patients with severe spasticity due to spinal cord pathology. Genitourinary function was assessed by symptom questionnaires and urodynamic studies performed after a bolus dose of baclofen and 6 to 12 months after continuous intrathecal baclofen. Results were compared to placebo for acute bolus testing or to pre-continuous intrathecal baclofen values. In all patients with irritative voiding and urge incontinence uninhibited bladder contractions were eliminated. Of 3 patients with an indwelling urethral catheter for incontinence due to detrusor hyperreflexia 1 was converted to intermittent self-catheterization. Whereas bladder capacity, compliance, sensation and voiding pressures were not different after continuous intrathecal baclofen, when a mean of all patients was compiled, a 72% increase in capacity and 16% improvement in compliance were observed in subjects without cervical spinal cord pathology. Detrusor-sphincter dyssynergia was abolished in 40% of the patients. Continuous intrathecal baclofen may represent a novel approach to the management of patients with a neurogenic bladder who have decreased bladder compliance and detrusor hyperreflexia not controlled by oral medications.