Peter Zvara

Erectile dysfunction in mice lacking the large-conductance calcium-activated potassium (BK) channel

Penile erection is dependent on the nitric oxide (NO)/cGMP‐dependent protein kinase I (PKGI) pathway. One important target of PKGI in smooth muscle is the large‐conductance, calcium‐activated potassium (BK) channel, which upon activation hyperpolarizes the smooth muscle cell membrane, causing relaxation. Relaxation of arterial and corpus cavernosum smooth muscle (CCSM) is necessary to increase blood flow into the corpora cavernosa that leads to penile tumescence. We investigated the functional role of BK channels in the corpus cavernosum utilizing a knock‐out mouse lacking the Slo gene (Slo−/−) responsible for the pore‐forming subunit of the BK channel. Whole‐cell currents were recorded from isolated CCSM cells of Slo+/+ and Slo−/− mice. Iberiotoxin‐sensitive voltage‐ and [Ca2+]‐activated K+ currents, the latter activated by local transient calcium releases (calcium sparks), were present in Slo+/+ CCSM cells, but absent in Slo−/− cells. CCSM strips from Slo−/− mice demonstrated a four‐fold increase in phasic contractions, in the presence of phenylephrine. Nerve‐evoked relaxations of precontracted strips were reduced by 50%, both in strips from Slo−/− mice and by blocking BK channels with iberiotoxin in the Slo+/+ strips. Consistent with the in vitro results, in vivo intracavernous pressure exhibited pronounced oscillations in Slo−/− mice, but not in Slo+/+ mice. Furthermore, intracavernous pressure increases to nerve stimulation, in vivo, were reduced by 22% in Slo−/−mice. These results indicate that the BK channel has an important role in erectile function, and loss of the BK channel leads to erectile dysfunction.

Erectile dysfunction in mice lacking in large conductance calcium-activated (BK) channel

Penile erection is dependent on the nitric oxide (NO)/cGMP‐dependent protein kinase I (PKGI) pathway. One important target of PKGI in smooth muscle is the large‐conductance, calcium‐activated potassium (BK) channel, which upon activation hyperpolarizes the smooth muscle cell membrane, causing relaxation. Relaxation of arterial and corpus cavernosum smooth muscle (CCSM) is necessary to increase blood flow into the corpora cavernosa that leads to penile tumescence. We investigated the functional role of BK channels in the corpus cavernosum utilizing a knock‐out mouse lacking the Slo gene (Slo−/−) responsible for the pore‐forming subunit of the BK channel. Whole‐cell currents were recorded from isolated CCSM cells of Slo+/+ and Slo−/− mice. Iberiotoxin‐sensitive voltage‐ and [Ca2+]‐activated K+ currents, the latter activated by local transient calcium releases (calcium sparks), were present in Slo+/+ CCSM cells, but absent in Slo−/− cells. CCSM strips from Slo−/− mice demonstrated a four‐fold increase in phasic contractions, in the presence of phenylephrine. Nerve‐evoked relaxations of precontracted strips were reduced by 50%, both in strips from Slo−/− mice and by blocking BK channels with iberiotoxin in the Slo+/+ strips. Consistent with the in vitro results, in vivo intracavernous pressure exhibited pronounced oscillations in Slo−/− mice, but not in Slo+/+ mice. Furthermore, intracavernous pressure increases to nerve stimulation, in vivo, were reduced by 22% in Slo−/−mice. These results indicate that the BK channel has an important role in erectile function, and loss of the BK channel leads to erectile dysfunction.

Pad weight testing in the evaluation of urinary incontinence.

To present the teaching module “Pad Weight Testing in the Evaluation of Urinary Incontinence.” This teaching module embodies a presentation, in combination with this manuscript. This manuscript serves as a scientific background review; the evidence base made available on ICS website to summarize current knowledge and recommendations.

Ablation of canine prostate using transurethral intraprostatic absolute ethanol injection

OBJECTIVES Despite extensive research involving numerous treatments for benign prostatic hyperplasia (BPH), the ideal modality has yet to be discovered. This study evaluated chemoablation of the prostate using transurethral intraprostatic absolute ethanol injection (AEI) in an in vivo canine model. METHODS Eight mongrel dogs, 7 to 10 years old, underwent transurethral intraprostatic AEI with various ethanol volumes (10 to 26 mL/animal, mean 19.9). Injection was performed using a 20-gauge, passive deflection, hollow-core needle, introduced cystoscopically by way of a perineal urethrotomy. Oral antibiotics were administered perioperatively. Blood alcohol levels were determined. The canines were kept alive for 1 hour (n = 1), 7 days (n = 2), and 21 days (n = 5) after the treatment. The dogs were observed twice daily for a minimum of 30 minutes to determine continence. At least one spontaneous voiding was recorded at each observation. Before the dogs were sacrificed, the prostate and surrounding tissues were harvested, with gross and microscopic examination performed by a single pathologist. RESULTS Seven and 21 days after AEI, the prostates demonstrated necrosis and cavity formation. Deep injection resulted in cavity formation in a subcapsular location. Superficial injection resulted in cavity formation that was confluent with the urethra and resulted in a widened urethral lumen. No complications directly related to AEI were seen, and systemic absorption of ethanol was minimal. CONCLUSIONS AEI can effectively ablate prostatic tissue in canines with minimal systemic absorption. No disruption of the prostatic capsule or injury to the bladder urothelium and urethral sphincter was identified. Human studies of intraprostatic AEI for BPH adenomatous tissue chemoablation are ongoing at our institution.

DIFFERENTIAL EXPRESSION OF BLADDER NEUROTROPHIC FACTOR mRNA IN MALE AND FEMALE RATS AFTER BLADDER OUTFLOW OBSTRUCTION

PURPOSE We validated a male rat model of bladder outflow obstruction and compared the expression of bladder neurotrophic factor mRNA in male and female rats 6 weeks after bladder outlet obstruction. MATERIALS AND METHODS We examined the proximal urethra in male Wistar rats. Urethral lumen reducing ligatures were placed in 15 females and 19 males, while 10 male and 10 female controls underwent sham surgery. Awake cystometry was performed 6 weeks after surgery. Ribonuclease protection assay was used to measure changes in bladder neurotrophic factor mRNA expression in the 2 sexes. RESULTS Average bladder capacity in rats with bladder outlet obstruction increased 3-fold in males and 4.4-fold in females compared with controls, while bladder weight increased 2.2 and 4.3-fold, respectively. Filling and threshold pressure increased significantly and nonvoiding bladder contractions were recorded in 100% of female and 80% of male rats with bladder outlet obstruction. An 8-fold increase in bladder brain derived neurotrophic factor mRNA was noted in each sex after obstruction. A 2-fold increase in bladder nerve growth factor mRNA after obstruction was only observed in females. CONCLUSIONS This male rat model of bladder outlet obstruction was created by placing lumen reducing ligatures at the urethrovesical junction. The dramatic increase in bladder brain derived neurotrophic factor mRNA expression and differential expression of nerve growth factor mRNA in male and female rats with bladder outlet obstruction suggest that additional neurotrophic factors may contribute to the lower urinary tract neuroplasticity associated with bladder outlet obstruction and this contribution may be gender dependent.

Intraprostatic ethanol chemoablation via transurethral and transperineal injection

To further assess the safety and feasibility of prostatic chemoablation with ethanol and to address previous concerns associated with transperineal injection using a canine model.

A Preliminary Report on the Use of Functional Magnetic Resonance Imaging with Simultaneous Urodynamics to Record Brain Activity During Micturition

PURPOSE We mapped brain activity during micturition using functional magnetic resonance imaging with simultaneous recording of urodynamic properties during slow bladder filling and micturition. MATERIALS AND METHODS We evaluated 12 healthy female volunteers 20 to 68 years old. Eight subjects could urinate while supine. Meaningful data were obtained on 6 of these subjects. Brain activity was recorded continuously during bladder filling and micturition. Functional magnetic resonance imaging measurements made during the micturition phase were used for the final analysis. RESULTS Using group statistics we identified clusters of brain activity in the parahippocampal gyrus, anterior cingulate gyrus, inferior temporal gyrus and inferior frontal gyrus during micturition. At the individual level we also observed activation in the upper pontine region, thalamus and posterior cingulum. In subjects unable to void brain activation was documented in the frontal lobe and posterior cingulate gyrus but not in the pons, thalamus or anterior cingulate gyrus. In 5 subjects we identified a relevant pattern of brain activity during the terminal portion of the filling phase when the patient reported a strong desire to urinate. CONCLUSIONS This new protocol allows for the localization of brain structures that are active during micturition. Data suggest that additional validation studies are needed. Future studies will test modifications that include more detailed monitoring of bladder sensation, stratifying subjects based on age and gender, and increasing the number of data points by adding subjects and the number of micturitions recorded in a single subject.

A role for pituitary adenylate cyclase activating polypeptide (PACAP) in detrusor hyperreflexia after spinal cord injury (SCI).

Abstract:  Intrathecal administration of the PAC1 receptor antagonist, PACAP6‐38 (10 nM), significantly (P≤ 0.05) reduced intermicturition, threshold and micturition pressures in chronic (3–6 weeks) spinal cord injured rats but intravesical administration (100–300 nM) was without effect. Intrathecal PACAP6‐38 reduced the number and amplitude of nonvoiding bladder contractions observed after spinal cord injury (SCI). PACAP may contribute to detrusor hyperreflexia induced by SCI and PACAP antagonists may be a novel approach to reduce detrusor hyperreflexia after SCI.

Brain activity during bladder filling and pelvic floor muscle contractions: a study using functional magnetic resonance imaging and synchronous urodynamics.

To map the brain activity during bladder filling by functional magnetic resonance imaging using a refined scanning protocol including synchronous urodynamics and pelvic floor muscle contractions.

Caffeine ingestion causes detrusor overactivity and afferent nerve excitation in mice.

PURPOSE We examined the effect of caffeine (Sigma®) on voiding patterns in mice and characterized potential changes in bladder function and sensory signaling. MATERIALS AND METHODS A total of 12 mice were fed high dose (150 mg/kg) caffeine daily for 2 weeks. Micturition frequency and volume were recorded at baseline and at the end point. The effects of chronic low dose (10 mg/kg) caffeine on voiding patterns were examined in 7 mice, which were subsequently studied using awake cystometry. In a separate study to characterize the effects of acute caffeine consumption on bladder function and sensory signaling cystometry was performed in 6 mice. Bladder extracellular multifiber afferent signaling was recorded at baseline and 1 hour after feeding low dose caffeine. In a separate group of mice baseline cystometrograms were done using normal saline, followed by a caffeine filling solution. RESULTS Compared to pretreatment conditions, daily oral high dose caffeine resulted in a significant increase in average micturition frequency and a decreased average volume per void. In animals fed low dose caffeine cystometry demonstrated a statistically significant increase in filling and threshold bladder pressure compared to caffeine naïve animals. Acute low dose caffeine ingestion resulted in a significant increase in filling pressure, an increased frequency of nonvoiding bladder contractions, a decrease in cystometric capacity and a 7.2-fold increase in the average firing rate of afferent nerves during filling. Caffeine administered intravesically had no effect on cystometric parameters. CONCLUSIONS Oral caffeine administration results in detrusor overactivity and increased bladder sensory signaling in the mouse.