TRP Channel Agonists Activate Different Afferent Neuromodulatory Mechanisms in Guinea Pig Urinary Bladder

Activation of TRP channels expressed in urinary bladder afferent nerves and urothelium releases neurotransmitters that influence bladder function. Experiments were undertaken to examine the mechanisms underlying effects of TRPA1 (allyl isothiocyanate, AITC), TRPV1 (capsaicin, CAPS), and TRPC (oleoyl-2-acetyl-sn-glycerol, OAG) agonists on guinea pig bladder activity. Effects of these agonists were compared with effects of nitro-oleic acid (OA-NO2), an electrophilic nitro-fatty acid, known to activate TRPV1, TRPA1 or TRPC channels in sensory neurons. AITC (100 μM) increased (231%) area of spontaneous bladder contractions (SBCs) an effect reduced by a TRPA1 antagonist (HC3-03001, HC3, 10 μM) and reversed to inhibition by indomethacin (INDO, 500 nM) a cyclooxygenase inhibitor. The post-INDO inhibitory effect of AITC was mimicked (39% depression) by calcitonin gene-related peptide (CGRP, 100 nM) and blocked by a CGRP antagonist (BIBN, 25 μM). CAPS (1 μM) suppressed SBCs by 30% in 81% of strips, an effect blocked by a TRPV1 antagonist (diarylpiperazine, 1 μM) or BIBN. SBCs were suppressed by OA-NO2 (30 μM, 21% in 77% of strips) or by OAG (50 μM, 30%) an effect blocked by BIBN. OA-NO2 effects were not altered by HC3 or diarylpiperazine. OA-NO2 also induced excitation in 23% of bladder strips. These observations raise the possibility that guinea pig bladder is innervated by at least two types of afferent nerves: [1] Type A express TRPA1 receptors that induce the release of prostaglandins and excite the detrusor, [2] Type B express TRPV1, TRPA1 and TRPC receptors and release CGRP that inhibits the detrusor.

Head to head comparison of [99mTc]Tc(CO)3(NTA) and [99mTc]Tc-MAG3 in patients with suspected obstruction

Purpose 99mTc-tricarbonyl-nitrilotriacetic acid, [99mTc]Tc(CO)3(NTA), is a new 99mTc-renal radiopharmaceutical with a clearance equal to that of 131I-ortho-iodohippuran, [131I]I-OIH. Our purpose was to compare the performance of [99mTc]Tc(CO)3(NTA) and [99mTc]Tc-MAG3 in patients with suspected obstruction. Methods [99mTc]Tc(CO)3(NTA) was prepared with commercially available NTA ligand and CRS Isolink kit, and isolated by HPLC. Eighteen adult patients referred for diuretic renography received an intravenous injection of approximately 40 mg of furosemide 15 min prior to either [99mTc]Tc(CO)3(NTA) or [99mTc]Tc-MAG3 (mean activity of 47 ± 4.4 MBq). Data were acquired for 24 min followed by an anterior image of the liver and gall bladder and a measure of voided volume. Patients received a second furosemide injection equal to one third of the original dose followed fifteen minutes later by administration of the alternate tracer, mean activity of 320 ± 34 MBq. Clearances were measured using a camera-based technique. Results The clearance of NTA was greater than that of MAG3, 331 ± 146 versus 271 ± 105 mL/min/1.73 m2, respectively, p < 0.0001. The kidney to background ratio for NTA was greater than that of MAG3 for both left and right kidneys, p < 0.001; the 20 min/maximum count ratio was significantly less, p < 0.0001. There was no significant difference in the voiding volumes following NTA and MAG3 administration, 598 ± 237 mL versus 498 ± 170 mL, respectively, p = 0.07. Gall bladder activity was not observed with NTA but was present in 6/17 MAG3 studies. Images and renogram curves were comparable except for two patients where the NTA study excluded obstruction but the MAG3 study suggested an indeterminate or obstructed kidney. Conclusions Unlike MAG3, NTA is not eliminated via the hepatobiliary track. Moreover, NTA has a higher kidney to background ratio and more rapid clearance than MAG3. These advantages should allow more robust camera-based clearance measurements and may lead to better discrimination between obstructed and non-obstructed kidneys.

Dual-phase 68Ga-PSMA-11 PET/CT may increase the rate of detected lesions in prostate cancer patients

Background: This study was conducted to compare the early static (3–6 min post-injection (p.i.)) and standard whole body (1 h, p.i.) 68Ga-PSMA-11 PET/CT imaging for detection of lesions in prostate cancer (PC) patients. Materials and methods: In this study, PC patients suspected of recurrence underwent 68Ga-PSMA-11 PET/CT. Early static images were acquired from the pelvis and the lower abdomen 3-5 minutes after radiotracer injection and, a routine whole body scan was performed from the skull to the mid-thigh 1 h after injection. Quantitative analysis (SUVmax) was evaluated in suspicious lesions. Results: Of 19 evaluated PC patients with a median age of 72 ± 1.66 years (range: 55–85 years) and prostate-specific antigen (PSA) of 1.72 ± 6.11 ng/ml (range: 0.1–100 ng/ml) (median ± SE), 16 showed positive in the whole body PET/CT. All of the patients with positive whole body scans due to pelvic involvement had positive early scan results. Totally, 22 lesions were detected in both early and delay scans in the pelvic which 16 were related to prostate involvement, 4 were related to lymph node involvement, and 2 were related to bone involvement. Moreover, in addition to the mentioned 22 lesions, early PET imaging successfully detected local recurrence in a patient who was negative on WB PET/ CT; this lesion was masked in the delay scan due to bladder activity. The median SUVmax values of the early and delay scans were 3.69 ± 1.07 (median ± SE) (range: 1.2–14.5) and 5.85 ± 1.69 (range: 3.1–23.4), respectively. ( p = 0.005). Conclusion: Early static 68Ga-PSMA-11 PET/CT imaging might discriminate metastases from urinary bladder activity. Therefore, early static imaging in combination with whole body 60-min p.i. imaging can improve the detection of local involvement pelvic disease.

Head to Head Comparison of 99mTc(CO)3(NTA) and 99mTc-MAG3 in Patients with Suspected Obstruction

Purpose 99mTc-tricarbonyl-nitrilotriacetic acid, 99mTc(CO)3(NTA), is a new 99mTc-renal radiopharmaceutical with a clearance equal to that of 131I-ortho-iodohippuran. Our purpose was to compare the performance of 99mTc(CO)3(NTA) and 99mTc-MAG3 in patients with suspected obstruction.Methods 99mTc(CO)3(NTA) was prepared with commercially available NTA and CRS Isolink kit, and isolated by HPLC. Eighteen adult patients referred for diuretic renography received an intravenous injection of approximately 40 mg of furosemide 15 min prior to either 99mTc(CO)3(NTA) or 99mTc-MAG3 (mean activity of 47 ± 4.4 MBq). Data were acquired for 24 minutes followed by an anterior image of the liver and gall bladder and a measure of voided volume. Patients received a second furosemide injection equal to one third of the original dose followed fifteen minutes later by administration of the alternate tracer, mean activity of 320 ± 34 MBq. Clearances were measured using a camera-based technique.Results The clearance of 99mTc(CO)3(NTA) was greater than that of 99mTc-MAG3, 331 ± 146 vs 271 ± 105 mL/min/1.73 m2, respectively, p < 0.0001. The kidney to background ratio for 99mTc(CO)3(NTA) was greater than that of 99mTc-MAG3 for both left and right kidneys, p < 0.001; the 20 min/maximum count ratio was significantly less, p < 0.0001. There was no significant difference in the voiding volumes following 99mTc(CO)3(NTA) and 99mTc-MAG3 administration, 598 ± 237 mL vs 498 ± 170 mL, respectively, p = 0.07. Gall bladder activity was not observed with 99mTc(CO)3(NTA) but was present in 6/17 99mTc-MAG3 studies. Images and renogram curves were comparable except for two patients where the 99mTc(CO)3(NTA) study excluded obstruction but the 99mTc-MAG3 study suggested an indeterminate or obstructed kidney.Conclusions Unlike 99mTc-MAG3, 99mTc(CO)3(NTA) is not eliminated via the hepatobiliary track. Moreover, 99mTc(CO)3(NTA has a higher kidney to background ratio and more rapid clearance than 99mTc-MAG3. These advantages should allow more robust camera-based clearance measurements and may lead to better discrimination between obstructed and non-obstructed kidneys.

Bladder underactivity induced by prolonged pudendal afferent activity in cats

The purpose of this study was to determine the effects of pudendal nerve stimulation (PNS) on reflex bladder activity and develop an animal model of underactive bladder (UAB). In six anesthetized cats, a bladder catheter was inserted via the urethra to infuse saline and measure pressure. A cuff electrode was implanted on the pudendal nerve. After determination of the threshold intensity (T) for PNS to induce an anal twitch, PNS (5 Hz, 0.2 ms, 2 T or 4 T) was applied during cystometrograms (CMGs). PNS (4-6 T) of 30-min duration was then applied repeatedly until bladder underactivity was produced. Following stimulation, control CMGs were performed over 1.5-2 h to determine the duration of bladder underactivity. When applied during CMGs, PNS (2 T and 4 T) significantly ( P < 0.05) increased bladder capacity while PNS at 4 T also significantly ( P < 0.05) reduced bladder contraction amplitude, duration, and area under contraction curve. Repeated application of 30-min PNS for a cumulative period of 3-8 h produced bladder underactivity exhibiting a significantly ( P < 0.05) increased bladder capacity (173 ± 14% of control) and a significantly ( P < 0.05) reduced contraction amplitude (50 ± 7% of control). The bladder underactivity lasted more than 1.5-2 h after termination of the prolonged PNS. These results provide basic science evidence supporting the proposal that abnormal afferent activity from external urethral/anal sphincter could produce central inhibition that underlies nonobstructive urinary retention (NOUR) in Fowler’s syndrome. This cat model of UAB may be useful to investigate the mechanism by which sacral neuromodulation reverses NOUR in Fowler’s syndrome.

The long-lasting post-stimulation inhibitory effects of bladder activity induced by posterior tibial nerve stimulation in unanesthetized rats

Tibial nerve stimulation (TNS) is one of the neuromodulation methods used to treat an overactive bladder (OAB). However, the treatment mechanism is not accurately understood owing to significant differences in the results obtained from animal and clinical studies. Thus, this study was aimed to confirm the response of bladder activity to the different stimulation frequencies and to observe the duration of prolonged post-stimulation inhibitory effects following TNS. This study used unanesthetized rats to provide a closer approximation of the clinical setting and evaluated the changes in bladder activity in response to 30 min of TNS at different frequencies. Moreover, we observed the long-term changes of post-stimulation inhibitory effects. Our results showed that bladder response was immediately inhibited after 30 min of 10 Hz TNS, whereas it was excited at 50 Hz TNS. We also used the implantable stimulator to observe a change in duration of the prolonged post-stimulation inhibitory effects of the TNS and found large discrepancies in the time that the inhibitory effect lasted after stimulation between individual animals. This study provides important evidence that can be used to understand the neurophysiological mechanisms underlying the bladder inhibitory response induced by TNS as well as the long-lasting prolonged post-stimulation effect.

Blockade of Acid-Sensing Ion Channels Increases Urinary Bladder Capacity With or Without Intravesical Irritation in Mice

We conducted this study to examine whether acid-sensing ion channels (ASICs) are involved in the modulation of urinary bladder activity with or without intravesical irritation induced by acetic acid. All in vivo evaluations were conducted during continuous infusion cystometry in decerebrated unanesthetized female mice. During cystometry with a pH 6.3 saline infusion, an i.p. injection of 30 μmol/kg A-317567 (a potent, non-amiloride ASIC blocker) increased the intercontraction interval (ICI) by 30% (P &lt; 0.001), whereas vehicle injection had no effect. An intravesical acetic acid (pH 3.0) infusion induced bladder hyperactivity, with reductions in ICI and maximal voiding pressure (MVP) by 79% (P &lt; 0.0001) and 29% (P &lt; 0.001), respectively. A-317567 (30 μmol/kg i.p.) alleviated hyperreflexia by increasing the acid-shortened ICI by 76% (P &lt; 0.001). This dose produced no effect on MVP under either intravesical pH condition. Further analysis in comparison with vehicle showed that the increase in ICI (or bladder capacity) by the drug was not dependent on bladder compliance. Meanwhile, intravesical perfusion of A-317567 (100 μM) had no effect on bladder activity during pH 6.0 saline infusion cystometry, and drug perfusion at neither 100 μM nor 1 mM produced any effects on bladder hyperreflexia during pH 3.0 acetic acid infusion cystometry. A-317567 has been suggested to display extremely poor penetrability into the central nervous system and thus to be a peripherally active blocker. Taken together, our results suggest that blockade of ASIC signal transduction increases bladder capacity under normal intravesical pH conditions and alleviates bladder hyperreflexia induced by intravesical acidification and that the site responsible for this action is likely to be the dorsal root ganglia.