ACTIVITY OF NONPEPTIDE TACHYKININ ANTAGONISTS ON NEUROKININ A INDUCED CONTRACTIONS IN DOG URINARY BLADDER

Prokinetic effects of the neurokinin NK2 receptor agonist [Lys5,MeLeu9,Nle10]-NKA(4-10) on bladder and colorectal activity in minipigs

The effects of the neurokinin NK2 receptor agonist [Lys⁵,MeLeu⁹,Nle¹⁰]-NKA_(4-10) (LMN-NKA) on bladder and colorectal function were examined in minipigs. In anesthetized animals, subcutaneous (SC) administration of 30-100 μg/kg increased peak bladder and colorectal pressures. Increases in bladder and colorectal pressure were inhibited by a 15 min pretreatment with the NK2 receptor antagonist GR 159897 (1 mg/kg intravenously (IV)). Bladder and colorectal pressures were also increased after IV (0.3 μg/kg), intranasal (IN; 100 μg/kg) and sublingual administration (SL; 5 mg/kg). There was a nonsignificant trend for hypotension (16 or 12% decrease in mean arterial pressure) after 100 μg/kg SC and 0.3 μg/kg IV, respectively, but not after 100 μg/kg IN or 5 mg/kg SL. In conscious minipigs, 30-300 μg/kg SC caused a dose-related increase in defecation that was accompanied by emesis in 38% of subjects receiving 300 μg/kg. Urination was increased after 100 μg/kg SC but not lower or higher doses. The peak plasma exposure (Cmax) after 100 μg/kg SC was 123 ng/mL, and area under the curve (AUC) was 1790 min * ng/mL. Defecation response rates (~82%) were maintained after SC administration of LMN-NKA (30 μg/kg) given 3 times daily over 5 consecutive days. Defecation rates were higher after a single dose of 100 μg/kg IN compared with vehicle, but this did not reach significance. After 7-10 mg/kg SL, 83% of animals urinated and defecated, and none had emesis. The data support the feasibility of developing a convenient and well-tolerated route of administration of LMN-NKA for human use. Minipigs may be a suitable species for toxicology studies with LMN-NKA due to the relatively low rate of emesis in this species.

Depressed contractile responses to neurokinin A in idiopathic but not neurogenic overactive human detrusor muscle

OBJECTIVE

The role of tachykinins such as neurokinin A in regulating bladder function is unclear, but NK2 receptors seem to mediate contraction in the human bladder and it has been suggested that these peptides may have a role in the pathophysiology of bladder dysfunction. The present study investigates neurokinin receptor-mediated contractility of detrusor muscle in the idiopathic overactive and neurogenic overactive bladder and investigates the neurokinin receptor subtypes involved.

METHODS

Human bladder was obtained from patients undergoing cystectomy (normal) or clam cystoplasty (idiopathic overactive) and from patients with spinal injuries (neurogenic overactive). Strips of isolated detrusor muscle were mounted in physiological Krebs-bicarbonate solution and cumulative concentration-response curves to 1 nM to 300 microM neurokinin A (NKA) were obtained in the absence and presence of neurokinin receptor antagonists, either the NK2 receptor-selective antagonist SR 48968 or the NK3 receptor-selective antagonist SB 223412.

RESULTS

NKA evoked concentration-dependent contraction of normal, idiopathic, and neurogenic overactive detrusor strips. In idiopathic overactive detrusor muscle, NKA-induced contraction was significantly reduced relative to normal detrusor (0.031 +/- 0.005 mg/g, n = 11 versus 0.193 +/- 0.039 mg/g, n = 7). Sensitivity to the peptide was also significantly (p < 0.01) reduced in idiopathic overactive detrusor, with mean pEC50 values (concentration producing 50% maximal response) of 6.62+/-0.16 (n = 11) compared to 7.47+/-0.19 (n = 7) in normal detrusor. In contrast, NKA-induced responses of neurogenic overactive detrusor were similar to those in normal detrusor, with a mean maximum contraction of 0.199 +/- 0.036 mg/g (n = 10) and mean pEC50 value of 7.85+/-0.16 (n = 10). NKA curves in all groups were shifted to the right by the NK2 receptor-selective antagonist SR 48968 with high affinity, pK(B) values being similar in normal, idiopathic, and neurogenic overactive detrusor (8.85 + 0.08, n = 14; 8.97 +/- 0.13, n = 12; 8.73 +/- 0.12, n = 8, respectively). In contrast the NK3 receptor-selective antagonist SB 223412 had a minimal effect on NKA responses and affinity values were low (pK(B) 5.81 +/- 0.11, n = 12 in normal; 5.75 +/- 0.08, n = 12 in idiopathic overactive, and 5.77 +/- 0.13, n = 11 in neurogenic overactive).

CONCLUSION

These data indicate that NKA-induced responses are impaired in detrusor muscle from idiopathic overactive human bladder, but not in detrusor muscle from neurogenic overactive bladder. The NK2 receptor subtype appears to mediate NKA responses in the normal, idiopathic overactive, and neurogenic overactive detrusor. This is important evidence suggesting a difference between the bladder pathophysiology observed in idiopathic versus neurogenic overactive detrusor.

Investigation of neurokinin-2 and -3 receptors in the human and pig bladder

OBJECTIVE

To investigate the role of neurokinin (NK)-2 and -3 receptors in mediating the contraction of detrusor muscle strips from human and pig, to determine whether the pig is a good model for the study of tachykinin receptors in the human bladder, as the biological actions of tachykinins, e.g. substance P and NKA are mediated via three distinct receptor subtypes, NK-1, -2 and -3.

MATERIALS AND METHODS

Strips of detrusor muscle were obtained from the bladder dome and neck of female pigs and from patients undergoing cystectomy. Cumulative concentration-response curves to NKA were obtained in the absence and presence of either the NK-2 receptor-selective antagonist SR48968 or the NK-3 receptor-selective antagonist SB223412.

RESULTS

NKA produced concentration-dependent contractions in the human and pig detrusor muscle; the curves were shifted to the right by SR48968, with high affinity (pKB 8.9, 8.3 and 8.0 in the human, pig dome and pig neck, respectively), whereas SB223412 had a minimal effect (pKB 5.8, 5.8 and 6.3, respectively).

CONCLUSION

These data confirm that the NK-2 receptor subtype mediates NKA-induced contraction of the human and pig detrusor muscle. The NK-3 receptor appears to have no role in detrusor contraction of either species. The results also provide evidence that the NK-2 receptor in human and pig are the same, and the latter may be an appropriate species to study tachykinin-induced contractions in human bladder.

New agents for the medical treatment of interstitial cystitis

Interstitial cystitis (IC) is a painful, sterile, disorder of the urinary bladder characterised by urgency, frequency, nocturia and pain. IC occurs primarily in women but also in men with recent findings indicating that chronic, abacterial prostatitis may be a variant of this condition. The prevalence of IC has ranged from about 8 - 60 cases/100,000 female patients depending on the population evaluated. About 10% of patients have severe symptoms that are associated with Hunner's ulcers on bladder biopsy; the rest could be grouped in those with or without bladder inflammation. Symptoms of IC are exacerbated by stress, certain foods and ovulatory hormones. Many patients also experience allergies, irritable bowel syndrome (IBS) and migraines. There have been various reports indicating dysfunction of the bladder glycosaminoglycan (GAG) protective layer and many publications showing a high number of activated bladder mast cells. Increasing evidence suggests that neurogenic inflammation and/or neuropathic pain is a major component of IC pathophysiology. Approved treatments so far include intravesical administration of dimethylsulphoxide (DMSO) or oral pentosanpolysulphate (PPS). New treatments focus on the combined use of drugs that modulate bladder sensory nerve stimulation (neurolytic agents), inhibit neurogenic activation of mast cells, or provide urothelial cytoprotection, together with new drugs with anti-inflammatory activity.