scholarly journals Exploring prospects of β3-adrenoceptor agonists and inverse agonists for colon mobility control

2013 ◽  
Vol 3 (1) ◽  
pp. 5
Author(s):  
Maria Grazia Perrone ◽  
Marialessandra Contino ◽  
Antonio Scilimati
Keyword(s):  
Partial Agonist ◽  
Muscle Tension ◽  
Proximal Colon ◽  
Mobility Control ◽  
Rat Colon ◽  
Colon Motility ◽  
Pharmacological Characterization ◽  
Inverse Agonists ◽  
Male Wistar Rats ◽  
Adrenoceptor Agonists

Inverse agonists are useful active ingredient of drugs clinically used to treat diseases mainly involving receptors endowed with non-endogenous agonist induced activity (constitutive or basal activity). SP-1e and SP-1g are the first two potent and highly selective β3-adrenoceptor inverse agonists [EC50=181 nM (IA=- 64%) and 136 nM (IA=-73%), respectively], which their peculiar activity seems due to the absolute configurations of the two stereogenic centres present in each molecule. Rat proximal colon motility measurements allowed their further pharmacological characterization and pA2 values determination by Schild analysis (7.89 and 8.16, respectively). The purpose of our work is a further characterization of our novel β3-adrenoceptor agonists (SP-1a-d, SP-1f,1h) and inverse agonists (SP-1e and SP-1g) on rat proximal colon motility and a confirmation of their inverse agonist nature in a more complex system like the functional test on rat proximal colon. Male Wistar rats segment of the proximal colon were placed in organ baths containing Krebs solution. Muscle tension was recorded isotonically. Cumulative β3-AR agonists doses experiments were performed for each test compound: isoprenaline, BRL37344, SP-1a-d, SP-1f and SP-1h were dissolved in Krebs. The EC50 values of each agonists and pA2 of inverse agonists were determined. SP- 1a-d, SP-1f and SP-1h in rat colon have a muscle relaxing effect thus confirming their partial agonist activity found in CHO-K1 cell line. SP-1e and SP-1g behaved as antagonists with pA2 values of 7.89 and 8.16, respectively. In conclusion, experiments carried out by using isolated rat proximal colon allowed us to determine the pA2 values of the two β3-AR inverse agonists and add knowledge on the behavior of a novel set of compounds and their possible value as agents useful whenever is necessary to also control the colon motility.

Microradiographic Anatomy of the Explanted Rat Colon

1995 ◽  
Vol 36 (2) ◽  
pp. 210-214 ◽  
Author(s):  
F. Pomerri ◽  
G. Gasparini ◽  
A. Martin ◽  
W. Fries ◽  
E. Pagiaro ◽  
...  
Keyword(s):  
Distal Colon ◽  
Proximal Colon ◽  
Rat Colon ◽  
Sprague Dawley ◽  
Double Contrast ◽  
Colonic Wall ◽  
Sprague Dawley Rats ◽  
Contrast Technique ◽  
Isolated Aorta ◽  
Mucosal Folds

The colon of 32 healthy Sprague-Dawley rats was studied microradiographically. The colonic arterial distribution of 18 rats was examined after injecting barium sulfate into the isolated aorta. The mucosal surface in 9 rats was studied using double-contrast technique after colon explantation. In 5 animals arterial and mucosal studies were carried out simultaneously. The radiographic thickness of the colonic wall was measured using a comparative microscope. The specimens were observed, photographed and examined histologically. Unlike the cecum and distal colon which, when insufflated, do not have mucosal folds, the proximal colon exhibits folds in an oblique direction corresponding to that of the arteries, and the colonic wall in this region is thicker. Comparison between arterial and mucosal microradiographic anatomy and wall thickness enables the proposition of a simple nontopographic division of the rat colon into cecum, proximal colon and distal colon.

Flupirtine enhances NHE-3 mediated Na+ absorption in rat colon via an ENS-dependent mechanism

2021 ◽  
Author(s):  
Andrew J. Nickerson ◽  
Vazhaikkurichi M. Rajendran
Keyword(s):  
Immunofluorescence Microscopy ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Proximal Colon ◽  
Selective Inhibitor ◽  
Rat Colon ◽  
Pre Treatment ◽  
Apical Membranes ◽  
Microscopy Techniques ◽  
Dependent Mechanism

Recent studies in our lab have shown that the KV7 channel activator, flupirtine, inhibits colonic epithelial Cl- secretion through effects on submucosal neurons of the enteric nervous system (ENS). We hypothesized that flupirtine would also stimulate Na+ absorption as a result of reduced secretory ENS input to the epithelium. To test this hypothesis, unidirectional 22Na+ fluxes were measured under voltage-clamped conditions. Pharmacological approaches using an Ussing-style recording chamber, combined immunofluorescence microscopy techniques were used to determine the effect of flupirtine on active Na+ transport in the rat colon. Flupirtine stimulated electroneutral Na+ absorption in partially seromuscular stripped colonic tissues, while simultaneously inhibiting short circuit current (ISC; i.e., Cl- secretion). Both of these effects were attenuated by pre-treatment with the ENS inhibitor, tetrodotoxin. The NHE-3-selective inhibitor, S3226, significantly inhibited flupirtine-stimulated Na+ absorption whereas the NHE-2-selective inhibitor HOE-694 did not. NHE-3 localization near the apical membranes of surface epithelial cells was also more apparent in flupirtine-treated colon versus control. Flupirtine did not alter epithelial Na+ channel (ENaC)-mediated Na+ absorption in distal colonic tissues obtained from hyperaldosteronaemic rats and had no effect in the normal ileum, but did stimulate Na+ absorption in the proximal colon. Finally, the parallel effects of flupirtine on ISC (Cl- secretion) and Na+ absorption were significantly correlated with each other. Together, these data indicate that flupirtine stimulates NHE-3-dependent Na+ absorption, likely as a result of reduced stimulatory input to the colonic epithelium by submucosal ENS neurons.

scholarly journals I8-arachnotocin–an arthropod-derived G protein-biased ligand of the human vasopressin V2 receptor

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Leopold Duerrauer ◽  
Edin Muratspahić ◽  
Jasmin Gattringer ◽  
Peter Keov ◽  
Helen C. Mendel ◽  
...  
Keyword(s):  
G Protein ◽  
Partial Agonist ◽  
Receptor Subtypes ◽  
Signaling System ◽  
Pharmacological Characterization ◽  
Metaseiulus Occidentalis ◽  
Physiological Relevance ◽  
V2 Receptor ◽  
Second Messenger Signaling ◽  
The Individual

AbstractThe neuropeptides oxytocin (OT) and vasopressin (VP) and their G protein-coupled receptors OTR, V1aR, V1bR, and V2R form an important and widely-distributed neuroendocrine signaling system. In mammals, this signaling system regulates water homeostasis, blood pressure, reproduction, as well as social behaviors such as pair bonding, trust and aggression. There exists high demand for ligands with differing pharmacological profiles to study the physiological and pathological functions of the individual receptor subtypes. Here, we present the pharmacological characterization of an arthropod (Metaseiulus occidentalis) OT/VP-like nonapeptide across the human OT/VP receptors. I8-arachnotocin is a full agonist with respect to second messenger signaling at human V2R (EC50 34 nM) and V1bR (EC50 1.2 µM), a partial agonist at OTR (EC50 790 nM), and a competitive antagonist at V1aR [pA2 6.25 (558 nM)]. Intriguingly, I8-arachnotocin activated the Gαs pathway of V2R without recruiting either β-arrestin-1 or β-arrestin-2. I8-arachnotocin might thus be a novel pharmacological tool to study the (patho)physiological relevance of β-arrestin-1 or -2 recruitment to the V2R. These findings furthermore highlight arthropods as a novel, vast and untapped source for the discovery of novel pharmacological probes and potential drug leads targeting neurohormone receptors.

Effect of chronic metabolic acidosis on net electrolyte transport in rat colon

1989 ◽  
Vol 256 (6) ◽  
pp. G1036-G1040 ◽  
Author(s):  
G. M. Feldman
Keyword(s):  
Metabolic Acidosis ◽  
Distal Colon ◽  
Distal Segment ◽  
Proximal Colon ◽  
Electrolyte Transport ◽  
Rat Colon ◽  
Chronic Metabolic Acidosis ◽  
In Situ Perfusion ◽  
Arterial Blood ◽  
Acute Correction

Rats fed NH4Cl (5 meq.100 g body wt-1.day-1) for one week developed chronic metabolic acidosis and had an arterial blood pH and plasma HCO3- concentration of 7.27 +2- 0.02 and 16.2 +/- 0.8 meq/l, respectively; control animals had values of 7.36 +/- 0.01 and 22.4 +/- 0.5 meq/l, respectively. Net electrolyte transport was measured in proximal and distal colonic segments by in situ perfusion. In proximal colon, chronic metabolic acidosis increased HCO3- absorption from 3.3 +/- 0.8 to 6.4 +/- 0.6 mu eq.min-1.g-1 but did not alter Na+ absorption. In distal colon, although Na+ transport was unaffected, chronic acidosis reduced HCO3- secretion from -6.9 +/- 0.8 to -4.4 +/- 0.7 mu eq.min-1.g-1 and increased voltage from -18.9 +/- 2.0 to -51.1 +/- 4.2 mV. To evaluate the dependence of these effects on altered arterial pH and HCO3- concentration, NaHCO3 was infused intravenously, raising pH and HCO3- concentration to 7.53 +/- 0.04 and 23.9 +/- 1.7 meq/l, respectively. Although acute correction of chronic metabolic acidosis reduced HCO3- absorption in proximal colon, it did not affect HCO3- secretion or voltage in the distal segment, suggesting that proximal and distal colon respond differently to chronic metabolic acidosis. These results also suggest that chronic metabolic acidosis alters the mechanisms of ion transport in distal colon.

Mechanism of synaptic inhibition by noradrenaline acting at α 2 -adrenoceptors

1988 ◽  
Vol 234 (1274) ◽  
pp. 85-114 ◽  
Keyword(s):  
Time Course ◽  
Partial Agonist ◽  
Single Cells ◽  
Inward Rectification ◽  
Synaptic Potential ◽  
High Concentration ◽  
Agonist Action ◽  
Neuronal Inhibition ◽  
Adrenoceptor Agonists ◽  
Pipette Tip

The actions of agonists at α 2 -adrenoceptors were investigated on single cells of the submucous plexus of the guinea pig small intestine. Intracellular recordings were made from neurons in vitro , and noradrenaline and other agonists were applied by adding them to the superfusion solution. The actions of noradrenaline released from terminals of sympathetic nerves was also studied by stimulating the nerves and recording the inhibitory postsynaptic current; this current can be mimicked by brief applications of noradrenaline from a pipette tip positioned within 50 μm of the neuron. The α 2 -adrenoceptor-bound noradrenaline with an apparent dissociation constant of 15 μM, determined by the method of partial irreversible receptor inactivation: clonidine and 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14304) had dissociation con­stants of 36 nM and 2.5 μM respectively. Noradrenaline and UK 14304 caused maximal hyperpolarizations, or outward currents; clonidine was a full agonist in only 4 of 35 cells, a partial agonist in 25 cells, and without effect in 4 cells. Clonidine acted as a competitive antagonist of noradrenaline in those cells in which it lacked agonist action; its dissociation equilibrium constant determined by Schild analysis was about 20 nM. The potassium conductance increased by the α 2 -adrenoceptor agonists, whether they were applied exogenously or released by stimulation of presynaptic nerves, showed marked inward rectification. The neurons showed inward rectification also in the absence of agonist; both types of rectification were eliminated by rubidium (2 mM), barium (3–30 μM) and caesium (2 mM). When the recording electrodes contained the non-hydrolysable derivative of guanosine 5′-triphosphate (GTP), guanosine 5′- O -(3-thiotriphosphate, GTP-γ-S), the effects of applied α 2 -adrenoceptor agonists did not reverse when they were washed from the tissue, imply­ing that GTP hydrolysis is necessary for the termination of agonist action. Pretreatment with pertussis toxin abolished the inhibitory synaptic potential (IPSP) and agonist-induced hyperpolarizations. Phorbol 12, 13-dibutyrate, forskolin, cholera toxin and sodium fluoride did not affect the responses to α 2 -adrenoceptor agonists. The synaptic hyperpolarization resulting from sympathetic nerve stimulation, or the hyperpolarization evoked by a brief (3–5 ms) application of noradrenaline, began after a latency of about 30 and 60 ms respectively. The decline of the synaptic current was exponential with time constant about 300 ms: when a high concentration of the antagonist idazoxan was applied suddenly (by applying pressure to a pipette tip positioned near the neuron), a steady-state hyperpolarization evoked by superfusion with noradrenaline was terminated with a similar time-course. This result suggests the decline of the synaptic response may be determined by the dissociation rate of noradrenaline; it is also possible that an intermediate biochemical process may underlie the decay of the synaptic potential. Many of the features of the response to noradrenaline are noted to be the same as for inhibitory synaptic potentials caused by acetylcholine acting on the cardiac type of M 2 muscarinic receptor. It is proposed that synaptically released noradrenaline binds to the α 2 receptor and brings about neuronal inhibition by activating a GTP binding protein within the membrane, which in turn leads to an increased opening of inwardly rectifying potassium channels.

Pharmacological Characterization of a Highly Selective and Potent Partial Agonist of the MT2 Melatonin Receptor

Pharmacology ◽  
2014 ◽  
Vol 93 (5-6) ◽  
pp. 244-252 ◽  
Author(s):  
Taku Sakurai ◽  
Tatsuki Koike ◽  
Masaharu Nakayama
Keyword(s):  
Partial Agonist ◽  
Melatonin Receptor ◽  
Pharmacological Characterization

Evidence for age-associated reduction in acetylcholine release and smooth muscle response in the rat colon

1994 ◽  
Vol 267 (4) ◽  
pp. G515-G522 ◽  
Author(s):  
D. Roberts ◽  
D. Gelperin ◽  
J. W. Wiley
Keyword(s):  
Calcium Channels ◽  
Acetylcholine Release ◽  
Calcium Influx ◽  
Muscle Tension ◽  
Calcium Ionophore ◽  
Rat Colon ◽  
Neural Pathways ◽  
Dependent Manner ◽  
Ach Release ◽  
Age Dependent

The effect of aging was examined on cholinergically mediated contractions and acetylcholine (ACh) release in isolated colonic segments from Fischer (F344 x BN) F1 rats, 4-8 mo (postpubertal) and 22-28 mo (senescent) of age. This species demonstrates age-dependent slowing of colonic transit. Muscle tension response to electrical stimulation of cholinergic neural pathways and application of ACh was significantly decreased in preparations from senescent compared with postpubertal animals. We focused on the hypothesis that aging was associated with reduced ACh release that resulted from decreased calcium influx through membrane calcium channels. Aging did not affect either the synthesis of [3H]ACh from [3H]choline or the percentage of 3H released in the form of [3H]ACh. However, elevated KCl-evoked release of [3H]ACh was significantly reduced in tissue from senescent compared with postpubertal animals. Treatment with the calcium ionophore ionomycin increased [3H]ACh release in tissue from senescent animals to near postpubertal levels. However, increasing extracellular calcium concentration ([Ca2+]o) from 1.2 to 5 mM did not increase the amount of transmitter release in tissue from senescent animals to the levels observed with 1.2 mM [Ca2+]o in postpubertal tissue. The neuronal calcium channel antagonist omega-conotoxin GVIA inhibited acetylcholine release in a concentration-dependent manner with half-maximal inhibitory values of 1.8 and 8.2 nM for senescent and postpubertal preparations, respectively. In summary, age-dependent reduction in ACh release was observed in the rat colon myenteric plexus that may, in part, be associated with decreased calcium influx via membrane calcium channels.

Pharmacological characterization of 5-hydroxytryptamine receptor types in the guinea-pig proximal colon

2008 ◽  
Vol 5 (4) ◽  
pp. 239-246 ◽  
Author(s):  
M. R. BRIEJER ◽  
L. M. A. AKKERMANS ◽  
A. L. MEULEMANS ◽  
R. A. LEFEBVRE ◽  
J. A. J. SCHUURKES
Keyword(s):  
Guinea Pig ◽  
Proximal Colon ◽  
Pharmacological Characterization

Peptide-regulated guanylate cyclase pathways in rat colon: in situ localization of GCA, GCC, and guanylin mRNA

1993 ◽  
Vol 265 (2) ◽  
pp. G394-G402 ◽  
Author(s):  
Z. Li ◽  
M. F. Goy
Keyword(s):  
In Situ Hybridization ◽  
Mrna Expression ◽  
Natriuretic Peptide ◽  
Proximal Colon ◽  
Bacterial Toxin ◽  
Surface Epithelium ◽  
Rat Colon ◽  
Hybridization Technique ◽  
In Cells

Guanylate cyclases play a role in both physiological and pathological secretion in the mammalian intestine. Agents that raise guanosine 3',5'-cyclic monophosphate (cGMP) levels, such as atrial natriuretic peptide (ANP), guanylin (an endogenous intestinal peptide), or Escherichia coli heat-stable enterotoxin type a (STa; a bacterial toxin), enhance electrolyte secretion and the accumulation of luminal fluid. Although secretion in all parts of intestine is sensitive to changes in cGMP metabolism, an increasing body of evidence suggests that these responses are particularly important in proximal colon. To date, three peptide-sensitive membrane-bound guanylate cyclases [types A, B, and C (GCA, GCB, and GCC, respectively)] have been cloned from mammalian tissues. GCA responds to ANP, GCB to C-type natriuretic peptide, and GCC to guanylin and STa. Expression of these receptor/cyclase genes has not previously been investigated at the cellular level in the colon. Nucleotide probes specific for GCA, GCB, GCC, and guanylin were generated by polymerase chain reaction. These probes were used to evaluate colonic cyclase and guanylin mRNA expression in the rat. GCB mRNA is not detectable in this tissue either by in situ hybridization or by Northern blot analysis. In contrast, GCA, GCC, and guanylin mRNAs are all conspicuously expressed. With the in situ hybridization technique, GCA mRNA expression is seen in cells in the lamina propria. GCC mRNA expression is seen in epithelial cells throughout colonic crypts, and also, although at a slightly lower level, in cells of the surface epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

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