Response to isoproterenol of rabbit detrusor strips following exposure to NSAIDs

Potential for control of detrusor smooth muscle spontaneous rhythmic contraction by cyclooxygenase products released by interstitial cells of Cajal

Interstitial cells of Cajal (ICCs) have been identified as pacemaker cells in the upper urinary tract and urethra, but the role of ICCs in the bladder remains to be determined. We tested the hypotheses that ICCs express cyclooxygenase (COX), and that COX products (prostaglandins), are the cause of spontaneous rhythmic contraction (SRC) of isolated strips of rabbit bladder free of urothelium. SRC was abolished by 10 μM indomethacin and ibuprofen (non-selective COX inhibitors). SRC was concentration-dependently inhibited by selective COX-1 (SC-560 and FR-122047) and COX-2 inhibitors (NS-398 and LM-1685), and by SC-51089, a selective antagonist for the PGE-2 receptor (EP) and ICI-192,605 and SQ-29,548, selective antagonists for thromboxane receptors (TP). The partial agonist/antagonist of the PGF-2α receptor (FP), AL-8810, inhibited SRC by ∼50%. Maximum inhibition was ∼90% by SC-51089, ∼80–85% by the COX inhibitors and ∼70% by TP receptor antagonists. In the presence of ibuprofen to abolish SRC, PGE-2, sulprostone, misoprostol, PGF-2α and U-46619 (thromboxane mimetic) caused rhythmic contractions that mimicked SRC. Fluorescence immunohistochemistry coupled with confocal laser scanning microscopy revealed that c-Kit and vimentin co-localized to interstitial cells surrounding detrusor smooth muscle bundles, indicating the presence of extensive ICCs in rabbit bladder. Co-localization of COX-1 and vimentin, and COX-2 and vimentin by ICCs supports the hypothesis that ICCs were the predominant cell type in rabbit bladder expressing both COX isoforms. These data together suggest that ICCs appear to be an important source of prostaglandins that likely play a role in regulation of SRC. Additional studies on prostaglandin-dependent SRC may generate opportunities for the application of novel treatments for disorders leading to overactive bladder.

Tachykinin-independent activity of capsaicin on in-vitro lamb detrusor

The capsicum alkaloid capsaicin is an afferent fibre exciter. In the vesical bladder, capsaicin acts by releasing peptides stored in afferent fibres. The aim of this work was to verify the activity of capsaicin on in-vitro lamb urinary bladder and to ascertain whether this alkaloid evokes peptide release. Capsaicin relaxed about 80% of the lamb detrusor muscle preparations tested and contracted about 20%. Whereas neurokinin A and substance P antagonists, administered alone or together, left the contractile responses to capsaicin unchanged, atropine and tetrodotoxin totally inhibited contraction. Ruthenium red and indometacin abolished contractions and relaxation. The substance P and neurokinin A antagonists and the NO-synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) left relaxation unchanged; conversely, the calcitonin gene-related peptide antagonist alpha h-CGRP (8-37) abolished this response. These results suggest that capsaicin relaxes lamb detrusor muscle not through tachykinins but by releasing CGRP from afferent fibres. Our observation that indometacin blocks the capsaicin response in in-vitro lamb urinary bladder also suggests a role of prostanoids.

Response to isoprenaline of rabbit detrusor muscle following exposure to 5, 8, 11, 14 eicosatetraynoic acid. Role of prostanoids on beta-adrenergic-evoked response

1. Incubation with indomethacin or ibuprofen causes a fall in basal tone and inhibits isoprenaline-evoked response in rabbit detrusor muscle strips. To ascertain whether this is due to cyclo-oxygenase inhibition, we investigated the influence on beta-adrenoceptor response of 5, 8, 11, 14 eicosatetraynoic acid (ETYA) which, unlike nonsteroidal anti-inflammatory drugs, has no action in vitro other than cyclo-oxygenase inhibition. 2. Incubation of detrusor strips with ETYA (7 or 14 microM) for 60 min significantly reduced tissue response to isoprenaline by an extent similar to that induced by indomethacin, but only slightly affected basal tone. 3. In tissues preincubated with indomethacin, the addition of PGE2 or PGE1 to restore basal tone, completely re-established isoprenaline-evoked responses. 4. Our findings in rabbit detrusor strips show that inhibition of cyclo-oxygenase and of prostanoid production is the main mechanism involved in lowered beta-adrenoceptor evoked response. 5. In addition, these findings strengthen the conviction that ibuprofen and indomethacin act largely through mechanisms other than inhibition of prostanoid production.