bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociation of a ferric maltol complex and its subsequent metabolism during absorption across the small intestine of the rat
Authors: Barrand Margery A. , Callingham Brian A. , Dobbin Paul , Hider Robert C.
Published: July 2012

The fate and disposition of [59Fe]‐ferric [3H]‐maltol after intravenous administration were investigated in anaesthetized rats. Immediate dissociation of ferric iron from maltol took place in the circulation even with high doses of ferric maltol (containing 1 mg elemental iron). In plasma samples withdrawn within 1 min of injection and subjected to gel filtration, 59Fe eluted with the high molecular weight proteins whilst the tritium was associated with low molecular weight material.

The rates of elimination of 59Fe and of tritium from the plasma and their ultimate fate were very different. The half life for 59Fe in the plasma was around 70 min and 59Fe appeared mainly in the bone marrow and liver. There was an initial rapid exit of tritium from the plasma with a half life of around 12 min. This was followed either by a plateau or by a rise in tritium levels, involving entry of maltol metabolites into the circulation. These metabolites could be recovered in the urine.

Entry of 59Fe and of tritium into the blood plasma after intraduodenal administration of [59Fe]‐ferric [3H]‐maltol was also very different. At low doses of ferric maltol (containing 100 μg elemental iron), the tritium appeared in the plasma in highest amounts within seconds and then decreased whilst there was a slow rise in 59Fe levels. At higher doses of ferric maltol (containing 7 mg elemental iron), levels of 59Fe in the plasma were highest at 5 min and then fell whereas tritium levels rose steadily. Mucosal processing of 59Fe prevented further entry of iron at high dose into the circulation.

Initial rates of uptake of [3H]‐maltol into isolated intestinal fragments were measured over a range of concentrations and revealed that maltol alone could diffuse freely into the tissues whereas maltol complexed to iron showed saturable uptake kinetics similar to those seen with the iron itself.

After intestinal uptake, 59Fe and tritium were associated with different subcellular fractions, maltol itself being metabolized to the glucuronide conjugate within the intestinal mucosa.

It is concluded that dissociation of metal and ligand takes place before entry into the intestinal mucosa. Iron is then taken up on the endogenous carrier and processed in the normal way whilst maltol enters by diffusion, its rate of entry being limited by the degree of dissociation. It is subsequently metabolized by conjugation and eliminated rapidly from the body in the urine.
Regional heterogeneity in the contractile and potentiating effects of neuropeptide Y in rat isolated coronary arteries: modulatory action of the endothelium
Authors: Prieto Dolores , Benedito Sara , Simonsen Ulf , Nyborg Niels C. Berg
Published: July 2012

Neuropeptide Y (NPY) induced a concentration‐dependent contraction of isolated rings of proximal epicardial (PC) and distal intramural (DC) coronary arteries of the rat, with an EC50 of ca. 1 × 10−7 m. The NPY‐induced contraction at 3 × 10−7 m was significantly smaller in PC than DC arteries: 34% vs. 55% of the 125 mm K+‐induced response, respectively.

NPY (2 × 10−8 m) increased the sensitivity to noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) more in PC (4.2 and 2.8 fold, respectively) than in DC arteries (2.2 and 1.4 fold, respectively). The maximal contractile response to NA and 5‐HT was increased more in DC (43% and 29%, respectively) than in PC arteries (20% and 12%, respectively).

Removal of the endothelium increased the sensitivity and maximal response to NPY as well as the spontaneous myogenic tone in PC but not in DC arteries. NPY had no relaxing effect on PC and DC arteries submaximally contracted with 10−6 m prostaglandin F2α, suggesting that spontaneous rather than stimulated release of endothelium‐derived relaxing factor (EDRF) depresses the contractile action of NPY in PC arteries.

The results indicate a heterogeneity in the contractile and potentiating action of NPY in rat coronary arteries depending on size or location in the coronary circulation.
Deamination of newly‐formed dopamine in rat renal tissues
Authors: Fernandes M. Helena , Pestana Manuel , Soares‐da‐Silva P.
Published: July 2012

The present study has examined the formation of dopamine and 3,4‐dihydroxyphenylacetic acid (DOPAC) in slices of the rat renal cortex and the renal medulla loaded with exogenous l‐β‐3,4‐dihydroxyphenylalanine (l‐DOPA). The effects of pargyline and of two selective inhibitors of monoamine oxidase (MAO) types A and B, respectively Ro 41–1049 and Ro 19–6327, on the deamination of newly‐synthesized dopamine in kidney slices incubated with exogenous l‐DOPA were also tested. The assay of l‐DOPA, dopamine, noradrenaline and DOPAC was performed by means of h.p.l.c. with electrochemical detection.

Incubation of renal slices with exogenous l‐DOPA resulted in a concentration‐dependent accumulation of dopamine and DOPAC; the tissue levels of newly‐formed dopamine and DOPAC in slices of the renal medulla were 6–8% of those in cortical slices.

Pargyline (0.1 mm) produced a marked decrease (84% reduction) in the formation of DOPAC in kidney slices loaded with 1.0 mm l‐DOPA; this effect was accompanied by a 17% increase in the accumulation of dopamine. Similar effects were obtained at higher concentrations of pargyline (0.5 and 1.0 mm). At 5.0 and 10.0 mm pargyline, a marked decrease (46 and 76% reduction) in the accumulation of newly‐formed dopamine was observed.

The accumulation of dopamine and DOPAC was found to be time‐dependent in experiments in which tissues were incubated with 5 and 10 μm l‐DOPA for 5, 10, 20 and 30 min. Pargyline (0.1 mm) produced an increase in the accumulation of dopamine at all incubation periods and decreased the formation of DOPAC.

Ro 41–1049 (50, 100 and 250 nm) was found to produce a concentration‐dependent increase of newly‐formed dopamine (16–66% increase) and reduced DOPAC formation (44–89% reduction). Ro 19–6327 (50, 100 and 250 nm), was found not to affect the accumulation of newly‐formed dopamine, but significantly reduced the formation of DOPAC.

It is concluded that deamination of newly‐formed dopamine in kidney slices loaded with l‐DOPA constitutes an important mechanism of amine inactivation. The results presented also suggest that most of the MAO, located inside the compartment where the synthesis of dopamine occurs, is of the A type.
GABAB receptor modulation of the release of substance P from capsaicin‐sensitive neurones in the rat trachea in vitro
Authors: Ray N.J. , Jones A.J. , Keen P.
Published: July 2012

The role of γ‐aminobutyric acid (GABA) as an inhibitory transmitter in the central nervous system is well documented. Recently, GABAA and GABAB receptors have been identified in the peripheral nervous system, notably on primary afferent neurones (PAN). We have utilised a multi‐superfusion system to investigate the effect of selective GABA receptor agonists and antagonists on the release of substance P (SP) from the rat trachea in vitro.

GABA (1–100 μm) did not affect spontaneous release of SP‐like immunoreactivity (LI) but caused dose‐related inhibition of calcium‐dependent potassium (60 mm)‐stimulated SP‐LI release. The greatest inhibition of 77.7 ± 18.8% was observed at 100 μm.

The inhibitory effect of GABA was mimicked by the GABAB receptor agonist, (±)‐baclofen (1–100 μm), but not the GABAA receptor agonist, 3‐amino‐1‐propane‐sulphonic acid (3‐APS, 1–100 μm). Baclofen (100 μm) had no effect on SP‐LI release stimulated by capsaicin (1 μm).

The inhibitory effect of baclofen (30 μm) was significantly reduced by prior and concomitant exposure to the GABAB receptor antagonist, phacolofen (100 μm) but not the GABAA receptor antagonist, bicuculline (10 μm). Neither antagonist, alone, affected spontaneous or potassium‐stimulated SP‐LI release.

We conclude that activation of pre‐synaptic GABAB receptors on the peripheral termini of PANs in the rat trachea inhibits SP‐LI release and suggest that GABAB receptor agonists may be of value in the therapeutic treatment of asthma.
Comparison of endothelium‐dependent responses of monkey cerebral and temporal arteries
Authors: Toda Noboru , Kawakami Masahisa , Yamazaki Masaaki , Okamura Tomio
Published: July 2012

Endothelium‐dependency of vasodilator responses was compared in helical strips of monkey cerebral and superficial temporal arteries contracted with prostaglandin F2α. Acetylcholine produced an endothelium‐dependent relaxation in the temporal arteries, but did not consistently alter the tone of cerebral arteries.

Adenosine 5′‐triphosphate (ATP) produced a transient contraction followed by a relaxation in the temporal and cerebral arteries; removal of the endothelium partially attenuated the relaxation of the cerebral arteries and markedly suppressed the relaxation in the temporal arteries. The dependency of adenosine 5′‐diphosphate (ADP)‐induced relaxations on the endothelium was also greater in temporal arteries than in cerebral arteries.

Histamine‐induced relaxations in the temporal arteries were independent of the endothelium and were reversed to contractions by cimetidine. Cerebral arterial relaxations induced by histamine were partly dependent on the endothelium. Relaxations caused by substance P were reversed to contractions by removal of the endothelium in the temporal arteries, whereas the peptide did not consistently alter the tone of cerebral arteries.

The Ca2+ ionophore, A23187, relaxed the temporal and cerebral arteries to a similar extent; removal of the endothelium abolished these relaxations. Glyceryl trinitrate elicited similar relaxations of cerebral and temporal arteries, and these were independent of the endothelium.

These findings clearly indicate heterogeneity in the endothelium‐dependency of several vasodilator responses in monkey intra‐ and extracranial arteries, although the ability of these arteries to respond to A23187 and glyceryl trinitrate does not appear to differ. The heterogeneous responses observed so far could therefore be due to different distributions of receptors or to variation in receptor‐effector coupling in endothelial cells.
Haemodynamic responses to NG‐monomethyl‐l‐arginine in spontaneously hypertensive and normotensive Wistar‐Kyoto rats
Authors: Fozard John R. , Part Marie‐Louise
Published: July 2012

Nitric oxide (NO) is a major component of endothelium‐derived relaxing factor (EDRF) the synthesis of which from l‐arginine can be inhibited by NG‐monomethyl‐l‐arginine (l‐NMMA). To assess whether basal NO tone is different in experimental hypertension, the haemodynamic effects of l‐NMMA have been compared in anaesthetized spontaneously hypertensive (SH) and normotensive Wistar‐Kyoto (WKY) rats in which autonomic reflexes were blocked by ganglion blockade.

Bolus intravenous injections of l‐NMMA, 1–30 mg kg−1, but not d‐NMMA, 1–30 mg kg−1, induced dose‐related increases in mean arterial pressure and decreases in conductances in the renal, carotid, hindquarters and mesenteric vascular beds in both SH and WKY rats. Although the different vascular beds varied in their maximum responses to l‐NMMA, there were neither qualitative nor quantitative differences between the two rat strains in this respect.

The effects of l‐NMMA, 30 mg kg−1, i.v. on all parameters were rapidly and completely reversed by l‐arginine, 30 mg kg−1, i.v., in both SH and WKY rats.

The results indicate that NO derived from l‐arginine exerts a powerful vasodilator tone in both anaesthetized, ganglion‐blocked SH and WKY rats. Although NO appears to contribute differentially to tone in the different vascular beds, there were no major differences between the two rat strains in this respect. Hence a reduced NO tone to the vasculature is unlikely to be a major factor contributing to the elevated blood pressure in the adult SH rat.
Convulsive thresholds in mice during the recovery phase from anaesthesia induced by propofol, thiopentone, methohexitone and etomidate
Authors: Lowson S. , Gent J.P. , Goodchild C.S.
Published: July 2012

Convulsive thresholds were measured with intravenous pentylenetetrazol in mice during the recovery phase after intravenous anaesthetic doses of propofol (10 and 20 mg kg−1), thiopentone (30 mg kg−1), methohexitone (10 mg kg−1), and etomidate 3 mg kg−1).

The convulsive threshold rose after each agent, indicating an anticonvulsant action for all the drugs tested; this declined to control values with initial half times of: 1.56 min (propofol 10 mg kg−1); 1.03 min (propofol 20 mg kg−1): 1.02 min (methohexitone); 3.35 min (etomidate); 13.7 min (thiopentone).

At no time during the recovery phase of any agent did the convulsive threshold fall below control values, which might indicate an epileptogenic effect of the drug.

The threshold was depressed below control values by intravenous administration of Ro 15–4513, a partial inverse agonist at the benzodiazepine receptor, thus indicating the ability of this pentylenetetrazol test to demonstrate a proconvulsant effect.

We conclude that the abnormal movements or convulsions associated with recovery from anaesthesia with short‐acting intravenous anaesthetics may not be the result of an intrinsic proconvulsant action of the drugs.
Inability of an opioid antagonist lacking negative intrinsic activity to induce opioid receptor up‐regulation in vivo
Authors: Morris B.J. , Millan M.J.
Published: July 2012

It has recently been suggested that opioid antagonists may be divided into those possessing negative intrinsic activity (e.g. naloxone) and those with neutral intrinsic activity (e.g. MR2266).

MR2266 was chronically administered to rats by subcutaneous infusion at a dose of 0.3 mg kg−1 h−1 for 1 week.

This dose reduced ingestive behaviour and blocked the antinociceptive effects of a κ‐agonist, indicating occupation of opioid receptors in vivo.

No supersensitivity could be detected to the antinociceptive actions of μ or κ agonists, either one or two days after cessation of treatment.

No up‐regulation of μ, δ or κ binding sites was observed.

Since naloxone induces both supersensitivity and receptor up‐regulation under equivalent conditions, the results suggest that negative intrinsic activity may be required for these phenomena to occur.
Effects of helospectin I on insulin and glucagon secretion in the mouse
Authors: Ahrén Bo
Published: July 2012

The helospectins are peptides structurally related to helodermin, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI) and secretin, which all potently stimulate glucagon secretion in the mouse. Therefore, the effects of helospectin I (0.1–0.8 nmol kg−1) on insulin and glucagon secretion under basal conditions and after stimulation with glucose (2.8 mmol kg−1) or the cholinoceptor agonist, carbachol (0.16 μmol kg−1), were examined in vivo in the mouse.

Helospectin I potently increased plasma levels of glucagon after its intravenous injection in mice. The increase was observed after only 2 min, and was evident also after 6 min.

In contrast, plasma insulin levels were not altered by helospectin I after 2 min, but slightly increased after 6 min. Plasma glucose levels were not altered by the peptide.

Carbachol‐induced glucagon secretion was markedly potentiated by helospectin I. In contrast, glucose‐ or carbachol‐stimulated insulin secretion was not affected by the peptide.

In conclusion, helospectin I markedly stimulates glucagon secretion in the mouse whereas the peptide has no direct action on insulin secretion. This pattern of effect of helospectin I is similar to that previously reported for helodermin, VIP, PHI and secretin in the mouse, i.e., for all peptides belonging to this superfamily of peptides.
Interactions between the vascular peptide endothelin‐1 and sensory neuropeptides in gastric mucosal injury
Authors: Whittle B.J.R. , Lopez‐Belmonte J.
Published: July 2012

The interactions between endogenous and exogenous sensory neuropeptides on gastric mucosal injury induced by endothelin‐1 (ET‐1) have been investigated in the anaesthetized rat.

Close intra‐arterial infusion of ET‐1 (4–20 pmol kg−1 min−1) dose‐dependently induced vasocongestion and haemorrhagic necrosis in the gastric mucosa.

Capsaicin‐pretreatment, two weeks earlier to deplete sensory neuropeptides from primary afferent neurones, augmented the mucosal damage induced by ET‐1, as assessed by both macroscopic and histological examination.

The damage induced by threshold doses of ET‐1 alone or in capsaicin‐pretreated rats was further enhanced by administration of indomethacin (5 mg kg−1, i.v.), indicating a modulatory influence of endogenous prostanoids.

Morphine administration (3 mg kg−1, i.v.), which can prevent neuropeptide release, augmented the damage induced by threshold doses of ET‐1, this effect being reversed by naloxone (1 mg kg−1, i.v.).

Concurrent local intra‐arterial infusion of rat α‐calcitonin gene‐related peptide (10–50 pmol kg−1 min−1) dose‐dependently reduced the mucosal injury induced by ET‐1.

These findings suggest interactions between ET‐1 and sensory neuropeptides, which may reflect an important influence of these peptide mediators in the regulation of mucosal integrity.
A selective effect of protein kinase C activators on noradrenaline release compared with subsequent contraction in canine isolated saphenous veins
Authors: Takata Yoshinobu , Ozawa Junko , Kato Hitoshi
Published: July 2012

Effects of protein kinase C (PKC) activators and inhibitors on both tritium overflow and subsequent contraction evoked by transmural nerve stimulation (TNS) were investigated in canine saphenous veins prelabelled with [3H]‐noradrenaline.

Activation of PKC by stepwise increasing concentrations (0.01 nm–1 μm) of 12‐O‐tetradecanoylphorbol 13‐acetate (TPA), phorbol 12,13‐dibutyrate (PDBu) or mezerein caused a significant and concentration‐dependent enhancement of the tritium overflow evoked by TNS, while the activators failed to affect the corresponding contraction except with the highest concentration of PDBu when the contraction was significantly reduced. Phorbol, which is inactive on PKC, had no effects on the tritium overflow and contraction induced by TNS.

PKC inhibitors, polymyxin B (1 and 10 μm) and the isoquinolinesulphonamide, H‐7 (1 μm), inhibited significantly the phorbol ester‐potentiated tritium overflow evoked by TNS with no effects on the contraction. H‐7 and the related inhibitor H‐8 at 10 μm reduced significantly both responses to TNS in the presence of TPA, while they suppressed only the TNS‐induced contraction in the absence of TPA.

None of the PKC activators or inhibitors affected the spontaneous tritium overflow.

PDBu (0.01 and 0.1 μm) elevated resting tension of the veins more effectively than TPA and mezerein.

These results suggest that PKC may modulate electrically stimulated noradrenaline release from adrenergic nerve endings of the canine saphenous veins and the PKC activators may act more selectively on presynaptic than postsynaptic sites, but have no apparent effect on postjunctional noradrenergic mechanisms.
Bradykinin stimulates production of inositol (1,4,5) trisphosphate in cultured mesangial cells of the rat via a BK2‐kinin receptor
Authors: Bascands J.L. , Emond C. , Pecher C. , Regoli D. , Girolami J.P.
Published: July 2012

Using [125I‐Tyr0]‐BK, as radiolabelled ligand, and various agonists and antagonists of bradykinin (BK) we identified a single class of specific BK2‐binding sites in mesangial cell membranes (Bmax = 73 fmol mg−1 protein and Kd = 3.7 nm).

Following the addition of 0.1 μm BK, inositol (1,4,5) trisphosphate (IP3) formation increased within 20 s from a basal level of 64 to a maximal value of 175 pmol mg−1 protein.

Incubation in a Ca2+‐free medium did not change IP3 production but a 5 min preincubation with 1 mm EGTA completely prevented the BK‐induced IP3 formation, suggesting that IP3 formation is partly dependent on extracellular calcium.

The BK2 antagonist d‐Arg‐Hyp3‐d‐Phe7‐BK (10 μm) but not the BK1 antagonist (des‐Arg9‐Leu8‐BK) abolished IP3 production in response to 0.1 μm BK. Pretreatment of mesangial cells with pertussis toxin was without effect on BK‐induced IP3 formation, whereas phorbol 12‐myristate 13‐acetate significantly enhanced (by 25%) BK‐induced IP3 formation.

The present data demonstrate that inositol phosphate breakdown in rat mesangial cells can be mediated via activation of a BK2‐kinin receptor and is under negative control of protein‐kinase C.
Blood pressure and vascular reactivity changes in spontaneously hypertensive rats fed fish oil
Authors: Yin K. , Chu Z.M. , Beilin L.J.
Published: July 2012

To examine possible mechanisms of antihypertensive effects of feeding fish oil rich in n‐3 fatty acids, we have studied vascular reactivity of aortic rings and perfused mesenteric resistance vessels of spontaneously hypertensive rats (SHR) given such a diet.

In two experiments, rats were fed a semi‐synthetic diet containing either ‘fish oil’ (10 and 20% by weight) or hydrogenated coconut oil (control) (10 and 20%) for 4 weeks.

Blood pressure rose significantly less in the fish oil group than in controls in both experiments.

Aortic rings from control rats showed endothelium‐dependent relaxations to low concentrations of acetylcholine (ACh) but relaxed less at higher concentrations. In contrast, rings from the fish oil group had relaxations which increased through the range of concentrations used. Indomethacin (10 μm) also increased the relaxation responses seen in rings from control rats, suggesting that fish oil inhibits a contractile cyclo‐oxygenase product. This contractile substance may be thromboxane A2 (TxA2) or its endoperoxide precursor, prostaglandin H2 (PGH2) as aortic incubates and serum levels of TxB2 (the stable product of TxA2) were greatly reduced in fish oil‐fed rats, and the decrease of relaxant responses to high concentrations of ACh were also blocked by a TxA2/PGH2 receptor blocker (SQ 29548).

In contrast to aortic rings, perfused preconstricted mesenteric resistance vessels of control rats relaxed to ACh in a similar fashion to tissues from fish oil‐fed rats. However, in this preparation, fish oil feeding enhanced relaxations to sodium nitroprusside (SNP) and contractile responses to noradrenaline were less than controls. After removal of endothelium with 0.05% saponin, contractile responses to noradrenaline increased in both groups but responses from fish oil‐treated rats were still attenuated. This suggests that fish oil feeding alters reactivity of mesenteric resistance vessels at the level of the smooth muscle.

The results indicate that fish oil feeding may reduce blood pressure by decreasing vascular smooth muscle reactivity to noradrenaline in resistance vessels. The effect may be enhanced by inhibition of an endothelium‐derived cyclo‐oxygenase product, such as TxA2 or PGH2 in conduit vessels.
5‐HT3 receptor agonism may be responsible for the emetic effects of zacopride in the ferret
Authors: Middlefell Vicki C. , Price Tracey L.
Published: July 2012

The racemic 5‐HT3 receptor antagonist, zacopride (10–100 μg kg−1, i.m.) evoked an emetic response in ferrets. This property appeared to reside totally in the S‐enantiomer which also produced emesis over the same dose range. This emesis could be prevented by pretreatment with ondansetron (1 mg kg−1, i.m.) or by R‐zacopride (100 μg kg−1, i.m.). In urethane‐anaesthetized ferrets, S‐zacopride (0.3 μg kg−1, i.v.) evoked a profound Bezold‐Jarisch reflex which was blocked by both ondansetron (30 μg kg−1, i.v.) and by R‐zacopride (100 μg kg−1, i.v.). These results suggest that, in the ferret, S‐zacopride possesses 5‐HT3 receptor agonist properties which may be responsible for the emetic effect. In contrast R‐zacopride does not appear to possess 5‐HT3 receptor agonist properties in this species.
Bioassay of nitric oxide released upon stimulation of non‐adrenergic non‐cholinergic nerves in the canine ileocolonic junction
Authors: Boeckxstaens Guy E. , Pelckmans Paul A. , Ruytjens Isabelle F. , Bult Hidde , De Man Joris G. , Herman Arnold G. , Van Maercke Yvan M.
Published: July 2012

The release and the nature of the inhibitory non‐adrenergic non‐cholinergic (NANC) neurotransmitter was studied in the canine ileocolonic junction. A circular muscle strip of the canine ileocolonic junction served as donor tissue in a superfusion bioassay in which rings of rabbit aorta with the endothelium removed served as detector tissue.

The ileocolonic junction released a labile factor with vasodilator activity upon stimulation of non‐adrenergic non‐cholinergic (NANC) nerves in response to electrical impulses and the nicotinic receptor agonist 1,1‐dimethyl‐4‐phenylpiperazinium (DMPP). This release was respectively frequency‐ and concentration‐dependent.

The release was reduced by the blocker of neuronal conductance, tetrodotoxin, and by the inhibitor of the nitric oxide (NO) biosynthesis NG‐nitro‐l‐arginine. The biological activity was enhanced by superoxide dismutase and eliminated by haemoglobin. Hexamethonium abolished only the release in response to DMPP.

Injection of adenosine 5′‐triphosphate (ATP) or vasoactive intestinal polypeptide (VIP) onto the cascade induced relaxations of the rabbit aorta but they were different from those induced by NO or the transferable factor.

Based on organ bath experiments in which the reactivity of different parts of the circular smooth muscle layer of the ileocolonic junction was investigated, a muscle strip of superficial circular muscle with submucosa was chosen as the detector strip in the bioassay cascade.

The ileocolonic junction dose‐dependently relaxed in response to nitroglycerin and NO. NO was much more potent in the rabbit aorta than in the canine ileocolonic junction. Equivalent amounts of the transferable factor, endothelium‐derived relaxing factor and NO, as assessed by the relaxation of the rabbit aorta, failed to affect the ileocolonic junction.

In conclusion, our results demonstrate the release of a transferable vasorelaxant factor in response to NANC nerve stimulation which behaves pharmacologically like NO but not like ATP or VIP. Therefore, we suggest that NO or a NO releasing substance is the inhibitory NANC neurotransmitter in the canine ileocolonic junction.
Adenosine‐induced dilatation of the rabbit hepatic arterial bed is mediated by A2‐purinoceptors
Authors: Mathie R.T. , Alexander B. , Ralevic V. , Burnstock G.
Published: July 2012

This study was carried out in order to identify the receptor responsible for adenosine‐induced dilatation of the hepatic arterial vascular bed.

Livers of 10 New Zealand White rabbits were perfused in vitro with Krebs‐Bülbring buffer via the hepatic artery and the portal vein at constant flows of 26 and 77 ml min−1 100 g−1 liver respectively. The tone of the preparation was raised by the presence of noradrenaline in the perfusate (concentration: 10−5 m).

Dose‐response curves for adenosine and its analogues 5′‐N‐ethyl‐carboxamido‐adenosine (NECA), the 2‐substituted NECA analogue CGS 21680C, and R‐ and S‐N6‐phenyl‐isopropyl‐adenosine (R‐ and S‐PIA) were obtained after their injection into the hepatic arterial supply.

The order of vasodilator potency of these agents was: NECA > CGS 21680C > adenosine > R‐PIA > S‐PIA. Their potency, expressed relative to that of adenosine, was in the approximate ratio 10:3:1:0.3:0.1, consistent with that resulting from activation of P1‐purinoceptors of the A2 sub‐type (which mediate vasodilatation due to adenosine).

The P1‐purinoceptor antagonist 8‐phenyltheophylline (10−5 m) caused significant attenuation of the vasodilatation to adenosine and analogues.

It is concluded that adenosine‐induced dilatation of the hepatic arterial vascular bed is mediated by P1‐purinoceptors of the A2 sub‐type.
Evidence for prejunctional inhibitory muscarinic receptors on sympathetic nerves innervating guinea‐pig trachealis muscle
Authors: Pendry Yvonne D. , Maclagan Jennifer
Published: July 2012

Relaxation responses induced by stimulation of the postganglionic sympathetic nerve trunk were studied in the isolated, fluid‐filled, innervated tracheal tube preparation of the guinea‐pig.

The thromboxane‐mimetic U46619, prostaglandin F2α and histamine each caused concentration‐dependent increases in the intraluminal pressure (ILP) of the fluid‐filled tracheal tube, reflecting contraction of the trachealis muscle. Sympathetic nerve stimulation in the presence of the spasmogens caused relaxations which increased with increasing ILP. Relaxant responses evoked in the presence of these three spasmogens were comparable at any given ILP.

Muscarinic agonists caused concentration‐dependent increases in ILP, pilocarpine being more potent than acetylcholine. Sympathetic nerve‐induced relaxations were reduced in the presence of pilocarpine and acetylcholine when compared to those obtained at the same ILP in the presence of U46619. This inhibitory effect of muscarinic agonists on sympathetic nerve‐induced responses was concentration‐dependent.

Exogenously applied noradrenaline opposed the contractile effect of U46619 and acetylcholine to a similar extent, indicating that a comparable degree of postjunctional functional antagonism exists between the sympathetic neurotransmitter noradrenaline and both spasmogens.

The selective M2 muscarinic antagonists, gallamine and methoctramine, altered neither the postjunctional contractile action of acetylcholine nor its inhibitory effect on sympathetic nerve‐induced relaxations. In addition, the inhibitory effect of acetylcholine was not modified by concentrations of pirenzepine known to block M1 muscarinic receptors.

The postjunctional contractile action of acetylcholine and its inhibitory effect on sympathetic neurotransmission were antagonized by atropine, by the M3 muscarinic antagonist hexahydrosiladiphenidol and by higher concentrations of pirenzepine.

These results suggest that in the guinea‐pig trachea, muscarinic cholinoreceptor agonists inhibit sympathetic neurotransmission via activation of muscarinic receptors located on the sympathetic nerve endings. These inhibitory prejunctional muscarinic heteroreceptors are of the M3 subtype.
Characterization of endogenous noradrenaline release from intact and epithelium‐denuded rat isolated trachea
Authors: Racké Kurt , Bähring Astrid , Brunn Gernot , Eisner Mathias , Wessler Ignaz
Published: July 2012

Overflow of endogenous noradrenaline (NA) from the in vitro incubated rat trachea evoked by two periods of electrical field stimulation (S1, S2, at 3 or 15 Hz) or by high potassium (60 mm) was determined by high performance liquid chromatography (h.p.l.c.) with electrochemical detection.

In the presence of the neuronal uptake inhibitor desipramine, the α2‐adrenoceptor antagonist, yohimbine, enhanced the overflow of NA evoked by stimulation at 3 Hz by about 100% suggesting the presence of presynaptic inhibitory autoreceptors on the sympathetic nerves innervating the trachea.

When desipramine and yohimbine were present throughout the experiments, the overflow of NA evoked by the second period of electrical stimulation (S2) was significantly smaller than that evoked by the first (S1). This decline of overflow was prevented when the NA precursor, tyrosine, was additionally present throughout the experiments.

After removal of the epithelium, the tissue content of NA was reduced by about 30%, suggesting that part of the NA may be present and released within the epithelium. However, the overflow of NA evoked by stimulation at 3 Hz or 15 Hz was reduced by 70–80%, indicating that the epithelium may additionally exert a permissive role on the release of NA within the airways, possibly by suppressing inhibitory factors.

Stimulation by high potassium (60 mm for 10 min) caused a large overflow of NA (about 45% of the tissue NA), both from epithelium‐free and epithelium‐denuded tracheae. Thus the ‘endogenous inhibition’ of NA release after removal of the epithelium is surmountable when a high potassium stimulus is applied.

An enhanced muscarinic inhibition of NA release in epithelium‐denuded tracheae may not be responsible for the reduction in NA overflow, since the muscarinic receptor antagonist, scopolamine, did not significantly affect the overflow of NA evoked by 3 or 15 Hz, either in the presence or the absence of the epithelium.

The muscarinic receptor agonist, oxotremorine, inhibited the overflow of NA evoked by stimulation at 3 Hz almost completely, an effect antagonized by scopolamine, demonstrating specific, inhibitory muscarinic receptors.

Since damage to the epithelium is known to occur in obstructive bronchial disease, the present experiments suggest that an impaired sympathetic (broncho‐relaxant) neurotransmission could be involved in the pathogenesis of bronchoconstriction.
Possible dependence of pressor and heart rate effects of NG‐nitro‐l‐arginine on autonomic nerve activity
Authors: Wang Yong‐Xiang , Pang Catherine C.Y.
Published: July 2012

The effects of NG‐nitro‐l‐arginine (l‐NNA) on mean arterial pressure (MAP) and heart rate (HR) were investigated in conscious rats.

Intravenous bolus cumulative doses of l‐NNA (1–32 mg kg−1) dose‐dependently increased MAP. Both mecamylamine and phentolamine increased MAP responses to l‐NNA, angiotensin II and methoxamine. Propranolol, reserpine, atropine and captopril did not affect MAP response to l‐NNA.

A significant negative correlation of HR and MAP responses to l‐NNA was obtained in control rats but not in rats pretreated with reserpine or mecamylamine. Significant negative correlations also occurred in the presence of atropine, propranolol, phentolamine or captopril.

A single i.v. bolus dose of l‐NNA (32 mg kg−1) raised MAP to a peak value of 53 ± 3 mmHg and the effect lasted more than 2 h; the rise and recovery of MAP were accompanied by significant decrease and increase in HR, respectively. While both phentolamine and mecamylamine increased peak MAP response to l‐NNA, mecamylamine abolished the biphasic HR response and phentolamine potentiated the bradycardic component of HR.

Blockade of the autonomic nervous and renin‐angiotensin systems did not attenuate the pressor effects of l‐NNA. However, the biphasic HR response to l‐NNA is mediated via modulation of autonomic nerve activities.
Further evidence for the existence of NK2 tachykinin receptor subtypes
Authors: Patacchini Riccardo , Astolfi Mara , Quartara Laura , Rovero Paolo , Giachetti Antonio , Maggi Carlo Alberto
Published: July 2012

We have evaluated the biological activity of a number of neurokinin A (4–10), (NKA (4–10)) analogues in the endothelium‐deprived rabbit isolated pulmonary artery (RPA) and hamster isolated trachea (HT), two tissues rich in different NK2 receptor subtypes.

MDL 28,564, a pseudopeptide selective for NK2 receptor sites, behaved as a full agonist in the RPA, while in the HT it competitively antagonized NKA or [βAla8]‐NKA (4–10) contractile effects.

The peculiar behaviour of MDL 28,564 in the RPA and HT may be explained neither by a difference in receptor reserve between the two organs (the reserve being three times greater in RPA than in the HT) nor by a different affinity for the two receptor subtypes (identical dissociation constants, pKA or pKB, calculated in the RPA and in the HT). On the other hand, MDL 28,564 displayed a very different intrinsic efficacy for the two receptor subtypes.

The novel peptides MEN 10,295 ([Trp7, βAla8]‐NKA‐(4–10)) and MEN 10,296 ([Tyr5, Trp7, βAla8]‐NKA‐(4–10)) behaved as weaker agonists than MDL 28,564 in the RPA, but retained appreciable agonist activity also in the HT.

The novel peptides: MEN 10,282 ([Tyr5, d‐Trp6,8, Trp9, Arg10]‐NKA‐(4–10)), MEN 10,449 ([diI‐Try5, d‐Trp6,8,9, Arg10]‐NKA‐(4–10)) and the cyclic hexapeptide L 659,877 (cyclo [Leu‐Met‐Gln‐Trp‐Phe‐Gly]) behaved as competitive antagonists against NKA contractile effects both in the RPA and HT. MEN 10,282 and MEN 10,449 were unable to distinguish between the NK2 receptor subtypes, having almost the same affinity in the two organs. On the other hand L 659,877 was about 15 times more potent in the HT than in the RPA.

These results provide further evidence for NK2 receptors heterogeneity and are useful in outlining pharmacological features of the two subtypes present in the RPA and HT.
Effect of a 7‐day treatment with idazoxan and its 2‐methoxy derivative RX 821001 on α2‐adrenoceptors and non‐adrenoceptor idazoxan binding sites in rabbits
Authors: Portillo M. , Reverte M. , Langin D. , Senard J.M. , Tran M.A. , Berlan M. , Montastruc J.L.
Published: July 2012

The present study investigates the influence of a 7‐day treatment with 2 mg kg−1, s.c., twice daily of RX 821002 (an α2‐adrenoceptor antagonist which binds only to α2‐adrenoceptors) or idazoxan (α2‐antagonist which binds to α2‐adrenoceptors and also to non‐adrenoceptor idazoxan binding sites: NAIBS) on α2‐adrenoceptor (labelled with [3H]‐RX 821002) and NAIBS (labelled with [3H]‐idazoxan) number in three tissues (adipocytes, colocytes and platelets) in the rabbit.

Acute administration of RX 821002 or idazoxan increased plasma non‐esterified fatty acids (NEFA) and catecholamine levels with no change in plasma glucose levels.

The 7‐day treatment with RX 821002 or idazoxan failed to influence food intake, total body weight or perirenal adipose tissue weight.

RX 821002 and idazoxan increased the number of [3H]‐RX 821002 binding sites in adipose tissue with no change in colocytes or platelets.

RX 821002 and idazoxan failed to modify [3H]‐idazoxan binding sites on adipocytes and colocytes. No significant [3H]‐idazoxan binding was detected on rabbit platelets.

The results show that a 7‐day treatment with α2‐antagonists induces an up‐regulation in adipocyte α2‐adrenoceptors. In contrast, this phenomenon does not involve all the tissues since colocytes and platelets escape the effects of α2‐antagonists. The data suggest a differential regulation of α2‐adrenoceptors according to their location.

The fact that NAIBS did not vary suggests that α2‐adrenoceptors and NAIBS are two different entities. Finally, since RX 821002 and idazoxan exert similar effects after either acute or chronic treatment, it is suggested that NAIBS are not involved in the control of catecholamine release or in NEFA or glucose metabolism.
Evidence against a role for dopamine D1 receptors in the myocardium of the pig
Authors: Van Woerkens L.J. , Duncker D.J. , Den Boer M.O. , McFalls E.O. , Sassen L.M.A. , Saxena P.R. , Verdouw P.D.
Published: July 2012

We investigated the presence of dopamine D1 receptors in the myocardium of anaesthetized pigs using intravenous infusions of dopamine, alone and after α‐ and β‐adrenoceptor blockade and intracoronary infusions of the selective D1 receptor agonist, fenoldopam.

Intravenous infusion of dopamine (2.5, 5 and 10 μg kg−1 min−1 for 10 min, n = 6) caused dose‐dependent changes in heart rate (from 94 ± 6 to 132 ± 10 beats min−1, P < 0.05), the maximal rate of rise of left ventricular pressure (LVdP/dtmax; from 2280 ± 170 to 4800 ± 410 mmHgs−1, P < 0.05), mean arterial blood pressure (from 87 ± 5 to 62 ± 3 mmHg) and systemic vascular resistance (from 40 ± 4 to 28 ± 2 mmHg l−1 min, P < 0.05). The increases in heart rate and LVdP/dtmax were abolished when dopamine was infused after α‐ and β‐adrenoceptor blockade. The vasodilator response was, however, only minimally affected.

Intravenous infusions of dopamine decreased coronary vascular resistance from 0.90 ± 0.06 to 0.53 ± 0.07 mmHg ml−1 min 100 g (P < 0.05). This action of dopamine was not observed when dopamine was infused after blockade of the α‐ and β‐adrenoceptors.

Pretreatment with α‐ and β‐adrenoceptor blockade had no effect or only slightly attenuated the dopamine‐induced decrease in vascular resistance of the brain, kidneys, adrenals and small intestine.

In 7 animals, intracoronary doses of 0.04, 0.1, 0.2 and 0.4 μg kg−1 min−1 of fenoldopam had no effect on coronary venous oxygen content, local myocardial oxygen consumption, coronary blood flow or coronary vascular resistance. However, systemic effects were observed at the highest two doses, as manifested by a drop in mean arterial blood pressure from 82 ± 4 to 72 ± 4 mmHg (P < 0.05) due to peripheral vasodilatation (e.g. cerebral vascular bed). Heart rate, LVdP/dtmax, regional myocardial segment length shortening and left ventricular end‐diastolic pressure were not affected at these doses. In 2 animals the infusion rate was increased to 4 μg kg−1 min−1, but again there was no evidence for coronary vasodilatation.

We conclude that the intravenous infusion of dopamine after α‐ and β‐adrenoceptor blockade and the intracoronary infusion of fenoldopam provided no evidence for a major role of D1 receptors in the coronary circulation of pigs. The absence of any effect of the employed doses of fenoldopam on LVdP/dtmax and on regional myocardial segment length shortening also indicates that fenoldopam does not exhibit any inotropic action in this species.
Different mechanisms of action of agents acting on β‐adrenoceptors in barium‐stimulated and electrically‐stimulated rat vas deferens
Authors: Diaz‐Toledo Alejandro , Jurkiewicz Aron
Published: July 2012

The relaxation induced by β‐adrenoceptor agonists in rat vas deferens was examined under two different experimental conditions: on electrically‐induced twitch responses (35 V, 3 ms, 0.07 Hz), and on contractions induced by single doses of barium chloride (300 μm). The experiments were performed in vasa of reserpine‐treated rats, after blockade of α‐adrenoceptors and extraneuronal uptake with dibenamine (10 μm, 30 min), and neuronal uptake with cocaine (10 μm).

When twitch responses were used, the values of pD2, interpolated from cumulative concentration‐response curves for isoprenaline (Iso), adrenaline (Ad), and noradrenaline (NA) showed a rank order of potency consistent with the presence of β2‐adrenoceptors (Iso > Ad ≫ NA).

When twitch responses were used, the non‐selective β‐antagonist, propranolol, caused a concentration‐dependent parallel shift to the right of Iso concentration‐response curves. Similar shifts were obtained by use of the β2‐antagonist, isopropylmethoxamine (IMA), and higher doses of the β1‐antagonist, practolol, according to the expectations from receptor occupation theory. Practolol presented the lowest value of pKB, 5.03, corroborating the presence of β2‐adrenoceptors.

When twitch responses were used, and Ad or NA employed instead of Iso, the antagonists produced shifts of concentration‐response curves which were smaller than expected from theory, precluding the determination of pKB values. This indicates that other mechanisms are involved besides an interaction with a single population of postsynaptic β2‐adrenoceptors.

When barium chloride was used instead of twitch responses, although the potencies of Iso and Ad were increased respectively by about 30 fold and 5 fold, the rank order of potency was still consistent with an interaction with β2‐adrenoceptors. In addition, the antagonists produced parallel and concentration‐dependent shifts of the curves of all the agonists, as expected from receptor theory. The values of pKB for a given antagonist were not modified by interchanging the agonists used, indicating a typical interaction with a single population of β2‐adrenoceptors. When compared to the field‐stimulated vas, the values of pKB for propranolol and IMA against isoprenaline were respectively 1.3 and 0.6 log units larger. These results suggest the β‐adrenoceptor agents act by different mechanisms of action in barium‐stimulated and electrically‐stimulated vas.

It is suggested that when barium is used, the effects of agents acting on β‐adrenoceptors are mediated only by postsynaptic β2‐receptors, while other complicating factors, probably nerve‐dependent presynaptic mechanisms, may be involved with electrical stimulation.
Ruthenium‐red inhibits CGRP release by capsaicin and resiniferatoxin but not by ouabain, bradykinin or nicotine in guinea‐pig heart: correlation with effects on cardiac contractility
Authors: Franco‐Cereceda Anders , Lou Ya‐Ping , Lundberg Jan M.
Published: July 2012

The possible influence of ruthenium‐red (RR) on contractility and outflow of calcitonin gene‐related peptide (CGRP)‐like and neuropeptide Y (NPY)‐like immunoreactivity (LI) from the heart of the guinea‐pig induced by capsaicin, resiniferatoxin, nicotine, ouabain or bradykinin was studied in vitro.

In the isolated right atrium, exposure to capsaicin evoked an increase in contractile rate and tension simultaneously with an enhanced outflow of CGRP‐LI, indicating release from the atria. Repeated administration of capsaicin induced tachyphylaxis. Incubation with RR markedly attenuated the capsaicin‐evoked release of CGRP‐LI while no clear‐cut effects were seen on contractile tension or rate.

In the isolated whole heart, perfusion with capsaicin induced an increased outflow of CGRP‐LI and stimulated heart rate, while a negative inotropic effect was observed. A second administration of capsaicin to the same preparations failed to influence the CGRP‐LI outflow and in these experiments the positive chronotropic effect was absent while the negative inotropic action remained unchanged. Capsaicin‐perfusion in the presence of RR failed to induce any increased outflow of CGRP‐LI from the hearts or changes in contractile activity. However, after 1 h of rinsing with Tyrode solution repeated capsaicin perfusion in the absence of RR caused a clear‐cut (60% of control) release of CGRP‐LI and contractile responses were restored.

Perfusion with resiniferatoxin evoked a RR‐sensitive, clear‐cut increased CGRP‐LI output without any effects on contractile force or heart rate. Repeated administration of resiniferatoxin induced tachyphylaxis with respect to outflow. Capsaicin perfusion after resiniferatoxin did not influence cardiac rate, force or CGRP‐LI outflow suggesting development of cross‐tachyphylaxis.

Perfusion with RR did not influence the outflow of CGRP‐LI or contractility changes evoked by perfusion with nicotine, ouabain or bradykinin. In addition, the release of NPY‐LI by nicotine remained unchanged in the presence of RR. Furthermore, the positive chronotropic effect of human CGRP alpha remained intact in the presence of RR.

It is concluded that RR selectively inhibits capsaicin‐ and resiniferatoxin‐induced excitation of cardiac sensory nerves as revealed by inhibition of both CGRP‐LI release and the cardiostimulatory action of capsaicin. RR also seems to protect the cardiac capsaicin‐sensitive fibres from the development of tachyphylaxis to capsaicin. Finally, RR prevents the capsaicin‐evoked negative inotropic effect which is not related to activation of sensory nerves.