Tachykinin NK2 receptors in the hamster urinary bladder: in vitro and in vivo characterization

Abstract

We have characterized the contractile responses produced by stimulation of the tachykinin NK2 receptor in the hamster urinary bladder in vitro and in vivo. In isolated bladder strips, neurokinin A (NKA, pD2 7.40, Emax 71% of the response to 80 mM KCl) and the synthetic tachykinin NK2 receptor selective agonist [betaAla8]NKA(4-10) (pD2 7.48, Emax 77% of the response to KCl) both induced a concentration-dependent contraction, whereas the tachykinin NK1 and NK3 receptor selective agonists, [Sar9]substance P sulfone and senktide, respectively, produced a negligible contractile effect. The bicyclic peptide antagonists MEN 11420 and MEN 10627 behaved as competitive antagonists of the response to [betaAla8]NKA(4-10) with apparent pK(B) values of 9.3 and 9.7, respectively. Comparable apparent pK(B) values were estimated against NKA (pK(B) 9.2 and 9.4 for MEN 11420 and MEN 10627, respectively). Under isovolumetric recording of the intravesical pressure, the nicotinic receptor agonist DMPP (0.6 micromol/kg i.v.) produced a phasic contraction of the hamster bladder in vivo that was abolished by hexamethonium (110 micromol/kg i.v.) or by surgical ablation of pelvic ganglia. In vivo [betaAla8]NKA(4-10) (10 nmol/kg i.v.) induced a tonic-type sustained bladder contraction with superimposed high frequency and small amplitude (<12 mmHg) phasic contractions and, in about 70% of cases examined, a few high amplitude (>20 mmHg) phasic contractions. Hexamethonium abolished the high amplitude phasic contractions, indicating their reflex origin. In animals subjected to the ablation of pelvic ganglia, the urinary bladder response to [betaAla8]NKA(4-10) was comparable to that observed after administration of hexamethonium. Moreover, hexamethonium did not affect the contractile responses to [betaAla8]NKA(4-10) in ganglionectomized animals. MEN 10627 and MEN 11420 produced a dose-dependent and long-lasting inhibition of the contractile response to [betaAla8]NKA(4-10): the least effective doses of the two antagonists were 30 and 3 nmol/kg i.v. for MEN 10627 and MEN 11420, respectively. An almost complete and long-lasting inhibition of the response to the agonist was produced at doses of 10 and 100 nmol/kg i.v. of MEN 11420 and MEN 10627. In urethane-anaesthetized hamsters the non-stop intravesical infusion of saline (50 microl/min) produced repetitive micturition cycles which were abolished by hexamethonium (110 micromol/kg i.v.) or by surgical removal of the pelvic ganglia. MEN 11420 (100 nmol/kg) had no significant effect on the volume-evoked micturition reflex in anaesthetized hamsters. In conclusion, the hamster urinary bladder is a suitable preparation for studying the action of tachykinin NK2 receptor antagonists in vivo: in this species, the stimulation of tachykinin NK2 receptors induces bladder contractions. Blockade of tachykinin NK2 receptors does not appreciably modify the volume-evoked micturition reflex in this species.

Role of prostanoids in the contraction induced by a tachykinin NK2 receptor agonist in the hamster urinary bladder

“…induced a bladder contraction (13±0.14 mm Hg, n=17) that was reproducible when elicited at 60-min intervals (cf. Tramontana et al 1998). Dexketoprofen i.v.…”

“…Recently, we have characterized the response of the hamster urinary bladder to tachykinin NK 2 receptor stimulation in vitro and in vivo (Tramontana et al 1998). The aim of the present study was to assess the possible role played by prostanoids in this response and to examine some possible mechanism of prostanoids generation in response to selective tachykinin NK 2 receptor stimulation.…”

Mast cells mediate substance P-induced bladder inflammation through an NK1receptor-independent mechanism

“…Others have shown an increase in NK1R numbers, and distribution may underlie persistent pain such as that observed during chronic inflammation (1,9,55). In contrast, NK2Rs mediate detrusor muscle contraction in humans (63,95), dogs (56,71), hamsters (83), and mice (57), whereas NK3Rs have been found in the ganglia (35) and vascular smooth muscle (45), but they have yet to be identified in the urinary system (4).…”

The role of sensory neuropeptides in motor innervation of the hamster isolated urinary bladder

“…Evidence for this is that twitches are reduced by the selective tachykinin NK 2 receptor antagonist nepadutant (Catalioto et al 1998;Tramontana et al 1998) and potentiated by the hCGRP antagonist, according to the excitatory effect of neurokinin A and the inhibitory effect of CGRP. This is further evidence that peripheral sensory nerves may be stimulated at a wide range of frequencies (Maggi et al 1992b;Santicioli and Maggi 1994) including very low parameters of stimulation, as shown in this study where stimulation of sensory fibers has been obtained at a frequency of 0.05 Hz.…”

“…Apparently no excitatory substance is released by stimulation of the sensory nerve endings in this species: substance P-like immunoreactivity (SP-LI) has not been detected by radioimmunoassay in hamster urinary bladder (Maggi et al 1987). Notwithstanding, tachykinin NK 2 receptor agonists produce a potent contractile response (Watson et al 1983;Dion et al 1987;Tramontana et al 1998) and, in agreement with functional data, tachykinin NK 2 receptors have been demonstrated by binding studies (Van Giersbergen et al 1992;Guard et al 1993) and are abundantly expressed in the smooth muscle layer (Burcher and Buck 1986). The hamster isolated urinary bladder has been considered as a monoreceptorial organ for studying tachykinin NK 2 receptors (Dion et al 1987), and stimulation of the tachykinin NK 1 and NK 3 receptors with selective agonists did not produce contractile responses .…”