This Month in Investigative Urology

Article Outline

• Nephrectomy by Combined Transvesical and Transgastric Approach
• Real-Time Fiberoptic Imaging of Cavernous Nerves
• Can Desmopressin Be Used in Elderly Patients With Nocturnal Polyuria?
• Effects of a New Selective Prostacyclin Receptor Antagonist on the Micturition Reflex
• Copyright

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Nephrectomy by Combined Transvesical and Transgastric Approach 

Natural orifice transluminal endoscopic surgery (NOTES) is being studied as a potentially less invasive alternative to conventional laparoscopy for intra-abdominal surgery. Lima et al (page 2648) from Braga, Portugal assessed the feasibility of a combined transgastric and transvesical approach for performing nephrectomy in a porcine model. With a uteroscope a transvesical 5 mm entry port was established in the peritoneal cavity, and a flexible gastroscope was passed orally into the peritoneal cavity by a gastrotomy. Right or left nephrectomy was performed with instruments introduced via the transvesical and transgastric routes. Four right and 2 left nephrectomies were performed through a transgastric and transvesical combined approach, thus the procedure is technically feasible in a porcine model.

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Real-Time Fiberoptic Imaging of Cavernous Nerves 

A critical intraoperative variable for the return of tumescence following radical prostatectomy is preservation of the cavernous nerves. Boyette et al (page 2694) from Charlottesville, Virginia developed a technique that would allow high resolution, in vivo real-time imaging of the cavernous nerves. Cavernous nerves were labeled by injecting a fluorescent retrograde nerve tracer into the corpus cavernosum of male rats. In vivo real-time video sequences of fluorescently labeled cavernous nerves were recorded. The screening trial indicated that the B subunit of cholera toxin conjugated to AlexaFluor^™ 488 provided optimal imaging after 9 days of retrograde transport. Toxicity studies showed that maximal intracavernous pressure responses did not differ between labeled and unlabeled nerves. Tracer injection did not increase apoptosis in cavernous tissue and laser exposure did not increase lipid peroxidation in nerves. In vivo real-time imaging of the cavernous nerves is possible with no measurable toxicity, allowing the maintenance of erection. This novel imaging modality may allow urologists to identify cavernous nerves during pelvic surgery.

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Can Desmopressin Be Used in Elderly Patients With Nocturnal Polyuria? 

While there are some well-defined pathophysiological causes related to nocturia the major proportion is unrelated to diseases known to interfere with renal regulation of body water homeostasis. The circadian rhythm of urine production changes considerably with age, with the prevalence of nocturia increasing gradually. Monosymptomatic polyuric nocturia is a consequence of aging, and Hvistendahl et al (page 2671) from Aarhus, Denmark investigated the physiological differences between nonpolyuric and polyuric nocturia in the elderly. Elderly and young healthy volunteers were hospitalized for 48 hours. Before admittance and during hospitalization fluid intake was standarized. The first 24 hours were at baseline conditions. On the second night participants were given a single oral dose of desmopressin. During the subsequent 48 hours urine output and plasma arginine vasopressin levels were determined. There was an age related change in the circadian rhythm of arginine vasopressin secretion which was associated with the presence or absence of nocturnal polyuria. Elderly patients with nocturnal polyuria had an inverted rhythm in urine output which was restored after a single dose of desmopressin. Compensatory diuresis following the induction of temporary antidiuresis was markedly postponed in elderly participants.

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Effects of a New Selective Prostacyclin Receptor Antagonist on the Micturition Reflex 

Prostaglandins are products of cyclooxygenase metabolism of arachidonic acid that have been shown to modulate the micturition reflex by regulating detrusor smooth muscle contraction and afferent sensitization. Of the multiple prostaglandin subtypes produced in the human bladder, prostacyclin (PGI₂) is the most abundant. PGI₂ levels are increased in the spinal cord in response to spinal cord injury, and recent studies have shown that the novel selective prostaglandin receptor antagonist RO3244019 decreases bladder hyperreflexia. Based on these findings it was postulated that PGI₂ may facilitate bladder reflexes by modulating sensory neurotransmission.

Cefalu et al (page 2683) from Palo Alto, California investigated the role of prostacyclin in the afferent modulation of the micturition reflex using the novel selective prostacyclin receptor antagonist RO3244019 in rat models of bladder function. In the anesthetized isovolumetric bladder contraction and volume induced micturition reflex (Refill) models the effects of RO3244019 and chronic capsaicin desensitization were compared. In the citric acid induced detrusor overactivity model the effects of RO3244019 and the cyclooxygenase inhibitor indomethacin were evaluated. The prostacyclin receptor antagonist RO3244019 decreased bladder contraction frequency and increased the micturition threshold in the anesthetized isovolumetric bladder contraction model and Refill models, respectively, and increased the micturition voiding interval in the conscious citric acid induced detrusor overactivity model. Additionally, RO3244019 remained effective for increasing the micturition threshold in the Refill model even following chronic capsaicin desensitization. Taken together these data suggest that PGI₂ may have a facilitory role in the micturition reflex by modulating the threshold for the activation of capsaicin sensitive and insensitive bladder sensory afferents.