Effect of [D-Phe6] bombesin (6-13) methylester, a bombesin receptor antagonist, towards bombesin-induced contractions in the guinea-pig and rat isolated urinary bladder

A Stress-Related Peptide Bombesin Centrally Induces Frequent Urination through Brain Bombesin Receptor Types 1 and 2 in the Rat

Stress exacerbates symptoms of bladder dysfunction including overactive bladder and bladder pain syndrome, but the underlying mechanisms are unknown. Bombesin-like peptides and bombesin receptor types 1 and 2 (BB1 and BB2, respectively) in the brain have been implicated in the mediation/integration of stress responses. In this study, we examined effects of centrally administered bombesin on micturition, focusing on their dependence on 1) the sympathoadrenomedullary system (a representative mechanism activated by stress exposure) and 2) brain BB receptors in urethane-anesthetized (1.0-1.2 g/kg, i.p.) male rats. Intracerebroventricularly administered bombesin significantly shortened intercontraction intervals (ICI) at both doses (0.1 and 1 nmol/animal) without affecting maximal voiding pressure. Bombesin at 1 nmol induced significant increments of plasma noradrenaline and adrenaline levels, which were both abolished by acute bilateral adrenalectomy. On the other hand, adrenalectomy showed no effects on the bombesin-induced shortening of ICI. Much lower doses of bombesin (0.01 and 0.03 nmol/animal, i.c.v.) dose-dependently shortened ICI. Pretreatment with either a BB1 receptor antagonist (BIM-23127; d-Nal-cyclo[Cys-Tyr-d-Trp-Orn-Val-Cys]-Nal-NH2; 3 nmol/animal, i.c.v.) or a BB2 receptor antagonist (BEA; H-d-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHEt; 3 nmol/animal, i.c.v.), respectively, suppressed the BB (0.03 nmol/animal, i.c.v.)-induced shortening of ICI, whereas each antagonist by itself (1 and 3 nmol/animal, i.c.v.) had no significant effects on ICI. Bombesin (0.03 nmol/animal, i.c.v.) significantly reduced voided volume per micturition and bladder capacity without affecting postvoid residual volume or voiding efficiency. These results suggest that brain bombesin and BB receptors are involved in facilitation of the rat micturition reflex to induce bladder overactivity, which is independent of the sympathoadrenomedullary outflow modulation.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Functional bombesin receptors in urinary tract of rats and human but not of pigs and mice, an in vitro study

AIMS

Bombesin receptors (BB receptors) and/or bombesin related peptides are expressed in the lower urinary tract, though their function and distribution in different species is largely unknown. This study examines whether BB receptor agonists can contract bladder smooth muscle in rats, mice, pigs and humans.

METHODS

Bladder strips were placed in tissue baths for in vitro contractility. Neuronally evoked contractions were elicited using electric field stimulation (EFS). Effects of the BB receptor agonists, neuromedin B (NMB; BB1 receptor agonist) and gastrin-releasing peptide (GRP; BB2 receptor agonist) on baseline tone and EFS-induced contractions were monitored.

RESULTS

In rat and human bladder strips, NMB and GRP (10(-11)-10(-6)M) increased EFS-induced contractions in a concentration dependent manner. In these species, NMB and GRP also increased baseline tension. In mouse and pig bladder strips, NMB and GRP (10(-8)-3×10(-6)M) had no effects on either parameter.

CONCLUSIONS

These data suggest that bombesin receptors BB receptor 1 and/or BB receptor 2 increase bladder contractions in rat and human. The site of action of these receptors may be pre- and/or post-synaptic, increasing release of transmitters or enhancing smooth muscle excitability, respectively. Thus, BB1 receptor and/or BB2 receptor may offer therapeutic targets for voiding dysfunction associated with impaired bladder contractility; however, species differences must be considered when studying these receptors. Part of this work was published in an abstract form at the SFN meeting New Orleans, 2012.

Exogenously administered bombesin and gastrin releasing peptide contract the female rat urethra in vivo and in vitro

BACKGROUND

Bombesin (BOM) and gastrin releasing peptide (GRP) have been located to the lower urinary tract. However, there is a paucity of data demonstrating the impact of these neuropeptides.

OBJECTIVES

The present study investigates the impact of BOM and GRP in the female Sprague-Dawley rats 225  g b.w. n = 37 urethras in vitro and in vivo. Intraurethral pressure was recorded by a catheter placed at the maximum pressure zone corresponding to the intrinsic urethral spincter.

MEASUREMENTS

In vitro, the intraurethral pressure was measured in response to the administration of BOM and GRP and noradrenaline from perfused intact urethral/bladder preparations. In vivo, changes in intraurethral pressure were conducted in anesthetized subjects and compared with the basal intraurethral pressure and sham controls.

RESULTS

In vitro, the increase in intraurethral pressure induced by BOM was 23.6 ± 3.2  cmH(2) O, exceeding the pressure evoked with NA by 10.7  cmH(2) O whereas GRP induced 10.7 ± 1.6  cmH(2) O, an increase of 3.3 cmH(2) O but less than the NA evoked intraurethral pressure by 2.2  cmH(2) O. Incubation with scopolamine (1 µM), phentolamine (1  µM), pancuronium (1  µM), and indomethacin (1  µM) did not produce any significant difference in the contractile responses to BOM or GRP. In vivo, the mean basal pressure was 22.9 ± 1.4  cmH(2) O. The intraurethral pressure evoked by BOM was 29.7  cmH(2) O (21.3  ±  1.3 to 51.0  ±  1.6  cmH(2) O), and for GRP, the evoked intraurethral pressure was 33.8  cmH(2) O (22.3  ±  1.9 to 56.2  ±  30  cmH(2) O).

CONCLUSIONS

BOM and GRP may contribute to the control of continence by their contractile action on the sphincters of the lower urinary tract outflow region.

Characterization of putative GRP- and NMB-receptor antagonist's interaction with human receptors

The mammalian bombesin (Bn) peptides neuromedin B (NMB) and gastrin-releasing peptide (GRP) actions are mediated by two receptors (NMB-receptor, GRP-receptor) which are widely distributed in the GI tract and CNS. From primarily animal studies NMB/GRP-receptor activation has physiological/pathophysiological effects in the CNS and GI tract including stimulating of growth of cancers and normal tissues. Whereas these Bn-receptors' effects have been extensively studied in nonhuman cells and animals, little is known of the physiological/pathological role(s) in humans, largely due to lack of potent antagonists. To address this issue we compared NMB/GRP-receptor affinity/potency of 10 chemical classes of putative antagonists (35 compounds) for human Bn-receptors by performing binding studies or assessing abilities to activate hGRP/hNMB-receptor [assessing phospholipase C activation] in four different cells containing native Bn-receptors or transfected receptors. From binding studies 23 were GRP-receptor-preferring, 4 were NMB-receptor, and 8 nonselective. For the hGRP-receptor-preferring analogues none showed hGRP-receptor agonist activity, but 13 were full or partial hNMB-receptor agonists at hNMB-receptors. For hNMB-receptor-preferring analogues none were agonists. Analogue #24 ([(3-Ph-Pr(6)), His(7), d-Ala(11), d-Pro(13), Psi(13-14), Phe(14)]Bn(6-14)NH2) and analogue #7 [d-Phe(6), Leu(13), Psi(CH(2)NH), Cpa(14)]Bn(6-14) were the most potent (0.2-1.4nM) and selective (>10,000-fold) for the hGRP-receptor with analogue #7.5 [d-Tpi(6), Leu(13), Psi(CH2NH), Leu(14)]Bn(6-14)[RC-3095] (0.2-1.4nM) slightly less selective. Analogue #34 (PD168368) had the highest affinity for hNMB-receptor (1.32-1.58nM) and the greatest selectivity (2298-6952-fold) for the hNMB-receptor. These results demonstrate numerous putative hGRP/hNMB-receptor antagonists identified in nonhuman cells and/or animals have agonist activity at the hNMB-receptor, limiting their potential usefulness. However, a number were identified which were potent/selective for human Bn-receptors and should be useful for investigating their roles in human physiological/pathophysiological conditions.

International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states

The mammalian bombesin receptor family comprises three G protein-coupled heptahelical receptors: the neuromedin B (NMB) receptor (BB(1)), the gastrin-releasing peptide (GRP) receptor (BB(2)), and the orphan receptor bombesin receptor subtype 3 (BRS-3) (BB(3)). Each receptor is widely distributed, especially in the gastrointestinal (GI) tract and central nervous system (CNS), and the receptors have a large range of effects in both normal physiology and pathophysiological conditions. The mammalian bombesin peptides, GRP and NMB, demonstrate a broad spectrum of pharmacological/biological responses. GRP stimulates smooth muscle contraction and GI motility, release of numerous GI hormones/neurotransmitters, and secretion and/or hormone release from the pancreas, stomach, colon, and numerous endocrine organs and has potent effects on immune cells, potent growth effects on both normal tissues and tumors, potent CNS effects, including regulation of circadian rhythm, thermoregulation; anxiety/fear responses, food intake, and numerous CNS effects on the GI tract as well as the spinal transmission of chronic pruritus. NMB causes contraction of smooth muscle, has growth effects in various tissues, has CNS effects, including effects on feeding and thermoregulation, regulates thyroid-stimulating hormone release, stimulates various CNS neurons, has behavioral effects, and has effects on spinal sensory transmission. GRP, and to a lesser extent NMB, affects growth and/or differentiation of various human tumors, including colon, prostate, lung, and some gynecologic cancers. Knockout studies show that BB(3) has important effects in energy balance, glucose homeostasis, control of body weight, lung development and response to injury, tumor growth, and perhaps GI motility. This review summarizes advances in our understanding of the biology/pharmacology of these receptors, including their classification, structure, pharmacology, physiology, and role in pathophysiological conditions.

Identification and characterisation of functional bombesin receptors in human astrocytes

Reverse transcription polymerase chain reaction (RT-PCR) demonstrated the presence of bombesin BB2 receptor mRNA but not bombesin BB1 receptor or bombesin BB3 receptor mRNA in cultured human astrocytes. Neuromedin C hyperpolarised human astrocytes in whole-cell current and voltage clamp recordings and increased the intracellular free Ca(2+) ion concentration ([Ca(2+)](i)) in single astrocytes. Treatment with neuromedin C caused larger and more frequent increases in [Ca(2+)](i) than those triggered by neuromedin B, with 96% and 78% of cells responding, respectively. The stimulatory effects of neuromedin C were inhibited significantly by treatment with U73122 or the bombesin BB2 receptor antagonist [D-Phe(6), des-Met(14)]bombesin-(6-14) ethylester. A Fluorometric Imaging Plate Reader (FLIPR) was used to measure [Ca(2+)](i) in cell populations. Neuromedin C was approximately 50-fold more potent than neuromedin B in elevating [Ca(2+)](i) in astrocytes and Chinese hamster ovary (CHO) cells expressing human bombesin BB2 receptors (hBB2-CHO). However, in CHO cells expressing the bombesin BB1 receptor hBB1-CHO, neuromedin B was 32-fold more potent than neuromedin C. [D-Phe(6), des-Met(14)]bombesin-(6-14) ethylester was a partial agonist in hBB1-CHO cells (E(max)=55%) but was a noncompetitive antagonist in both hBB2-CHO cells and astrocytes. These studies report the first identification of functional bombesin receptors on cultured human astrocytes and have demonstrated that the bombesin BB2 receptor contributes significantly to astrocyte physiology.

Tachykinin NK1 receptor subtypes in the rat urinary bladder

1. Following the recent proposal that the selective agonist septide, ([pGlu6,Pro9]SP(6-11)), acts on a novel tachykinin receptor distinct from the 'classical' NK1 receptor, the aim of the study was to investigate the possible heterogeneity of tachykinin NK1 receptors in the rat urinary bladder. 2. The synthetic tachykinin receptor agonists, septide (pD2 7.87) and [Sar9]substance P (SP) sulphone (pD2 7.64) produced concentration-dependent contractions of the rat isolated urinary bladder. 3. The NK1 receptor antagonists GR82,334, (+/-)-CP96,345, and RP67,580 competitively antagonized (slopes of Schild plot not significantly different from unity) the response to septide with the rank order of potency (pKB values in parentheses): RP 67,580 (7.57) > GR 82,334 (7.01) > (+/-)-CP 96,345 (6.80). The same antagonists were significantly less potent when tested against [Sar9]SP sulphone, while maintaining the same rank order of potency: RP 67,580 (7.00) > GR 82,334 (5.93) > (+/-)-CP 96,345 (< 6). The antagonists did not affect the concentration-response curve to bombesin. 4. To exclude the involvement of the NK2 receptor, a second series of experiments was performed in the presence of the potent nonpeptide NK2 receptor antagonist, SR 48,968. SR 48,968 (1 microM) produced a rightward shift of the concentration-response curve to the NK2 receptor selective agonist, [beta Ala8]neurokinin A (NKA) (4-10). SR 48,968 did not significantly modify the response to SP, NKA, neurokinin B (NKB), neuropeptide K (NPK), neuropeptide gamma (NP gamma), SP(4-11), SP(6-11), septide or [Sar9]SP sulphone. 5. In the absence or presence of SR 48,968, RP 67,580 antagonized in a competitive manner the response to septide, [Sar9]SP sulphone, SP(4-11) and SP(6-11): pKB values obtained in the absence and presence of SR 48,968 were not significantly different for any of these four agonists.6. RP 67,580 antagonized the response to SP and NKA both in the absence and presence of SR 48,968.In both cases, the slopes of the Schild plots were significantly different from unity. Mean dose-ratios produced by RP 67,580 in the presence of SR 48,968 were larger than those measured without NK2receptor blockade for both SP and NKA.7. RP 67,580 (3 MicroM) did not antagonize the response to NKB in the absence of SR 48,968. In the presence of SR 48,968, RP 67,580 acted as a competitive antagonist of NKB-induced contractions with apKB value (7.63) not significantly different from that measured towards septide. In the present of SR48,968, RP 67,580, GR 82,334 and (+/-)-CP 96,345 antagonized the response to NKB with a rank order of potency identical to that measured towards septide or [Sar9]SP sulphone.8. In the absence of SR 48,968, RP 67,580 (3 MicroM) produced a small shift of the concentration-response curve to neuropeptide K and was ineffective toward neuropeptide T. In the presence of SR 48,968 a clear shift of the curve to both agonists was observed.9. These findings are compatible with the idea that a septide-sensitive tachykinin receptor may exist in the rat urinary bladder. The septide-sensitive receptor is recognized by NK1 receptor antagonists with higher affinity than the 'classical' NK1 receptor recognized by [Sar9]SP sulphone. Our data suggest that NKB, after NK2 receptor blockade, is a more suitable ligand than SP for activation of the 'septidesensitive'receptor. While the final proof for the existence of possible NK1 receptor subtypes must await confirmation at the molecular level, the present findings provide strong pharmacological evidence that either NK, receptor subtypes or a novel type of tachykinin receptor exist in the rat urinary bladder.