bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of gastric contractions in response to tachykinins and bethanechol by extrinsic nerves
Authors: Holzer‐Petsche Ulrike
Published: July 2012

Extrinsic reflexes elicited by changes in gastric wall tension play an important role in regulating gastric tone. The present study investigated whether such reflexes modulate gastric contractions induced by close arterially administered neurokinin A (NKA), substance P (SP), SP‐methylester and bethanechol in anaesthetized rats.

Reflex pathways were acutely interrupted by either subdiaphragmatic vagotomy or prevertebral ganglionectomy. C‐fibre afferent nerve activity was abolished by pretreating rats with capsaicin 10 to 16 days before the experiments.

The order of potency in inducing gastric contractions was NKA > SP > bethanechol. SP‐methylester was markedly less effective than SP and its effects did not fit sigmoid dose‐response curves (DRCs). The maximal responses to NKA, SP, and bethanechol were similar, whilst the DRC for SP was significantly flatter than those for NKA or bethanechol. Pretreatment of the rats with the peptidase inhibitors phosphoramidon or captopril did not increase the contractile response to SP.

Prevertebral ganglionectomy had no significant effect on the DRCs for SP and NKA, whereas vagotomy shifted the DRCs for all three test substances to the left.

Capsaicin pretreatment did not change the DRC for NKA in rats with intact vagus but shifted that for bethanechol to the left. The leftward shift of the DRC for NKA caused by vagotomy was prevented in capsaicin‐pretreated rats whereas the vagotomy‐induced shift of the DRC for bethanechol remained unaltered. The shift of the DRC for SP seen in response to vagotomy was only slightly reduced by capsaicin pretreatment.

These data may be interpreted as demonstrating two neuronal mechanisms for modulating drug‐induced gastric contractions. First, the contractions themselves activate a vago‐vagal negative feedback involving capsaicin‐sensitive afferents. Second, NKA, and to a lesser degree SP, seem to induce a non‐vagal non‐splanchnic mechanism which via capsaicin‐sensitive afferent neurones reinforces tachykinin‐induced gastric contractions.
A receptor that is highly specific for extracellular ATP in developing chick skeletal muscle in vitro
Authors: Thomas Steven A. , Zawisa Mark J. , Lin Xi , Hume Richard I.
Published: July 2012

Extracellular adenosine 5′‐triphosphate (ATP) activated an early excitatory conductance followed by a late potassium conductance in developing chick skeletal muscle. A series of ATP analogues were tested for their ability to activate these two conductances. All compounds tested were either agonists for both responses or for neither. Furthermore, the potency of agonists was similar for the two responses.

The order of potency for agonists was ATP ≅ adenosine 5′‐O‐(3‐thio triphosphate) (ATP‐γ‐S) ≅ 2‐methylthio‐ATP (2‐CH3S‐ATP) > 2′‐deoxy‐ATP ≅ 3′‐deoxy‐ATP > adenosine 5′‐tetraphosphate (ATP‐OPO3) ≅ adenosine 5′‐diphosphate (ADP). Many other ATP analogues were not agonists.

Activation of the excitatory response did not require divalent cations. Furthermore, the concentration‐response relation of the excitatory response was similar when ATP was applied as the free anion of ATP (ATP4‐) or complexed with a divalent cation (M · ATP2‐).

Three antagonists of the ATP response were characterized. 8‐Br‐ATP was a weak antagonist, while 2′,3′‐dialdehyde‐ATP and DIDS (4,4′‐diisocyanatostilbene‐2,2′‐disulphonic acid) were potent irreversible inhibitors. The two conductances were equally affected by these antagonists.

These results suggest that both ATP responses are activated through the same receptor type, or two very similar receptors.
The effects of soman on the electrical properties and excitability of bullfrog sympathetic ganglion neurones
Authors: Heppner Thomas J. , Fiekers Jerome F.
Published: July 2012

The effects of soman (0.1–10 μm), an irreversible inhibitor of acetylcholinesterase (AChE), were examined on the electrical properties of ganglion neurones of the paravertebral sympathetic chain of the bullfrog, Rana catesbeiana.

Soman (10 μm) depolarized 29 of 35 (83%) ganglion neurones studied by 6.4 ± 0.65 mV within 10 min of application and reduced the cell input resistance in 9 of 11 neurones examined (82%) to 55 ± 5.3% of control.

Soman (10 μm) significantly reduced the maximum amplitude and the maximum rate of rise of the action potential and the duration, but not the amplitude, of the after‐hyperpolarization (AHP) following the action potential elicited by either direct or antidromic stimulation. The maximum rate of fall and the duration of the action potential were not significantly affected by soman. These actions of soman were independent of the agent‐induced depolarization. When examined by a single microelectrode voltage clamp, soman reduced the amplitude and the time constant of the current underlying the slow AHP, IAHs.

Soman (1–10 μm) produced an increase in neuronal excitability which was evidenced as either an increase in the number of action potentials or a decrease in the interspike interval in response to constant‐current depolarizing pulses. The soman‐induced increase in excitability occurred independently of both the agent‐induced depolarization and the decrease in input resistance, was reversible with washing, was not caused by an inhibition of the M‐current and was also recorded in dissociated sympathetic ganglion neurones.

The effects of soman on the membrane potential, input resistance and the duration of the AHP but not cell excitability were blocked by pretreatment with atropine (10 μm). Pretreatment with dihydro‐β‐erythroidine (DHβE) (10μm) was ineffective in blocking or reversing the effects of soman. These results suggest that the direct actions of soman on the electrical properties of these neurones are mediated by activation of muscarinic receptors.
Barbiturates inhibit ATP‐K+ channels and voltage‐activated currents in CRI‐G1 insulin‐secreting cells
Authors: Kozlowski R.Z. , Ashford M.L.J.
Published: July 2012

Patch‐clamp recording techniques were used to examine the effects of barbiturates upon the ATP‐K+ channel, and voltage‐activated channels present in the plasma membrane of CRI‐G1 insulin‐secreting cells.

Thiopentone inhibited ATP‐K+ channel activity when applied to cell‐attached patches or the intracellular or extracellular surface of cell‐free patches. Secobarbitone and pentobarbitone were also effective inhibitors of ATP‐K+ channels in cell‐free patches, whereas phenobarbitone was ineffective.

The diabetogenic agent, alloxan, which is structurally related to the barbiturates also produced an inhibition of ATP‐K+ channel activity in outside‐out patches.

Whole‐cell ATP‐K+ currents were used to quantify the effects of the barbiturates: concentration‐inhibition curves for thiopentone, secobarbitone and pentobarbitone resulted in IC50 values of 62, 250 and 360 μm respectively. Phenobarbitone at a concentration of 1 mm was virtually ineffective.

Calculation of the apparent membrane concentrations for these drugs indicate that for a given degree of ATP‐K+ channel inhibition a similar concentration of each barbiturate is present in the membrane. This suggests that hydrophobicity plays a primary role in their mechanism of action. The pH‐dependence and additive nature of barbiturate block also indicates a membrane site of action.

Thiopentone, (100 μm) was also found to inhibit differentially voltage‐activated whole‐cell currents. The relative potency of thiopentone at this concentration was 0.64, 0.38 and 0.12 for inhibiting Ca2+, K+ and Na+ currents respectively when compared with its ability to inhibit the ATP‐K+ channel.
CP‐93,129, a potent and selective 5‐HT1B receptor agonist blocks neurogenic plasma extravasation within rat but not guinea‐pig dura mater
Authors: Matsubara Toshio , Moskowitz Michael A. , Byun Barkjang
Published: July 2012

Pretreatment with CP‐93,129 blocked plasma extravasation in rat dura mater induced by electrical trigeminal ganglion stimulation when administered at ≥140 nmol kg−1, i.v. but did not affect plasma leakage in guinea‐pig at 460 or 1400 nmol kg−1. Sumatriptan, a 5‐HT1D‐like receptor agonist, blocked plasma extravasation in the guinea‐pig model when administered at 7 nmol kg−1. In as much as CP‐93,129 binds with micromolar affinities to 5‐HT1A, 5‐HT1C, 5‐HT1D, and 5‐HT2 recognition sites, and with nanomolar affinity to the 5‐HT1B receptor subtype, blockade of plasma extravasation in the rat dura mater may be mediated by 5‐HT1B receptors whereas the 5‐HT1D receptor may be more relevant to the guinea‐pig.
Effect of acute and subchronic nicotine treatment on cortical efflux of [3H]‐d‐aspartate and endogenous GABA in freely moving guinea‐pigs
Authors: Beani Lorenzo , Tanganelli Sergio , Antonelli Tiziana , Ferraro Luca , Morari Michele , Spalluto Piero , Nordberg Agneta , Bianchi Clementina
Published: July 2012

The [3H]‐d‐aspartate preloading of the parietal cortex of freely moving guinea‐pigs equipped with epidural cups makes it possible to investigate drug effects on the efflux of this radiolabel, assumed as a marker of the glutamatergic structures underlying the cup. In the same model, the efflux of [3H]‐γ‐aminobutyric acid ([3H]‐GABA) and endogenous GABA can be measured.

Nicotine, 0.9–3.6 mg kg−1, s.c., or 3–5 μg, i.c.v., increased the efflux of [3H]‐d‐aspartate but reduced that of GABA.

These effects were mediated through mecamylamine‐sensitive receptors but the ganglionic blocking agent was devoid of any primary activity.

The inhibition of GABA efflux induced by nicotine 3.6 mg kg−1, s.c., was abolished by methysergide 2 mg kg−1, i.p. and was reduced by naloxone 3 mg kg−1 i.p. pretreatment, suggesting the involvement of tryptaminergic and opioid systems. In contrast, muscarinic and catecholamine antagonists were ineffective.

Chronic treatment with nicotine (3.6 mg kg−1, twice daily for 16 days) reduced the facilitatory effect of [3H]‐d‐aspartate and abolished the inhibition of endogenous GABA efflux.

A slight increase in the number of nicotinic binding sites (by use of [3H]‐nicotine as ligand) was found in the neocortex of chronically treated guinea‐pigs.

The higher degree of tolerance to chronic nicotine treatment shown by GABA as compared with [3H]‐d‐aspartate efflux suggests that adaptative changes of the inhibitory neuronal pools prevail. This may contribute to the reinforcing and addictive properties of nicotine.
Nitric oxide synthase in cultured endocardial cells of the pig
Authors: Schulz R. , Smith J.A. , Lewis M.J. , Moncada S.
Published: July 2012

Endocardial cells release factors which regulate myocardial contractility and guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) levels. One of these factors is indistinguishable from endothelium‐derived relaxing factor (EDRF).

The effluent from pig heart endocardial cells cultured on microcarrier beads caused the relaxation of a pig coronary artery ring denuded of endothelium. This relaxation was enhanced by a combination of superoxide dismutase and catalase and was attenuated by haemoglobin, which binds nitric oxide (NO), and by inhibitors of NO synthase, NG‐monomethyl‐l‐arginine (l‐NMM A) or NG‐nitro‐l‐arginine.

A Ca2+‐, l‐arginine‐ and NADPH‐dependent enzyme activity which generated NO was detected by a specific spectrophotometric assay in cytosol prepared from endocardial cells. The formation of NO was inhibited in a concentration‐dependent manner by l‐NMMA (but not d‐NMMA) and this could be partially reversed upon addition of excess l‐arginine.

Like endothelial cells from the blood vessels, the endocardial cells possess the ability to synthesize NO, which may act to regulate myocardial contractility.
Inhibition of the release of endothelium‐derived relaxing factor in vitro and in vivo by dipeptides containing NG‐nitro‐l‐arginine
Authors: Thiemermann Christoph , Mustafa Marina , Mester P. Achim , Mitchell Jane A. , Hecker Markus , Vane John R.
Published: July 2012

We have shown that dipeptides containing NG‐nitro‐l‐arginine (NO2Arg) inhibit the biosynthesis of endothelium‐derived relaxing factor (EDRF) in vitro and in vivo.

In anaesthetized rats, intravenous administration at 1–30 mg kg−1 of the methyl ester of NO2Arg, NO2‐Arg‐l‐phenylalanine (NO2Arg‐Phe), l‐alanyl‐NO2Arg (Ala‐NO2Arg) or NO2Arg‐l‐arginine (NO2Arg‐Arg) produced dose‐related increases in mean arterial blood pressure (MABP) which were unaffected by d‐arginine (d‐Arg; 20 mg kg−1 min−1 for 15 min), but prevented by co‐infusions of l‐arginine (l‐Arg; 20 mg kg−1 min−1 for 15 min) or by their parent dipeptides.

NO2Arg methyl ester, NO2Arg‐Phe methyl ester or Ala‐NO2Arg methyl ester (10 mg kg−1, i.v.) also inhibited the reduction in MABP caused by the endothelium‐dependent vasodilator, acetylcholine (30 μg kg−1 min−1 for 3 min), but not those induced by glyceryl trinitrate (20 μg kg−1 min−1 for 3 min) or iloprost (6 μg kg−1 min−1 for 3 min) which act directly on the vascular smooth muscle.

Moreover, NO2Arg methyl ester, NO2Arg‐Phe methyl ester or NO2Arg‐Arg methyl ester (100 μm) inhibited the acetylcholine‐induced relaxation of rabbit aortic strips, and NO2Arg‐Phe methyl ester (30 μm) blocked the stimulated (bradykinin, 30 pmol) release of EDRF from bovine aortic endothelial cells grown on microcarrier beads.

In endothelial cells grown in l‐Arg‐deficient medium, l‐Arg‐containing dipeptides such as l‐Arg‐l‐Phe, l‐Ala‐l‐Arg or l‐Arg‐l‐Arg increased both the basal and stimulated release of EDRF. Moreover, the l‐Arg containing dipeptides, but not their NO2Arg analogues, were rapidly cleaved by these cells.

Thus, dipeptides containing NO2Arg can directly interfere with the biosynthesis of EDRF in vitro and in vivo. Moreover, the potentiation of EDRF release from endothelial cells deprived of l‐Arg by dipeptides containing l‐Arg suggests that such peptides may serve as an additional or alternative substrate for the biosynthesis of EDRF.
Regional coronary haemodynamic effects of two inhibitors of nitric oxide synthesis in anaesthetized, open‐chest dogs
Authors: Richard Vincent , Berdeaux Alain , la Rochelle Christophe Drieu , Giudicelli Jean‐François
Published: July 2012

The role of endothelial nitric oxide synthesis from l‐arginine in the regulation of coronary vascular tone and myocardial tissue perfusion was evaluated in anaesthetized, open‐chest dogs. Coronary blood flow was measured with an electromagnetic flow probe placed around the left circumflex coronary artery. Coronary vascular resistance was calculated from mean arterial blood pressure and mean coronary blood flow, whereas regional myocardial tissue flow was determined by use of the radioactive microspheres technique.

NG‐monomethyl l‐arginine (l‐NMMA) and NG‐nitro‐l‐arginine methyl ester (l‐NAME), administered directly into the left circumflex artery, induced a small increase in arterial blood pressure and an increase in coronary vascular resistance. However, myocardial tissue perfusion, assessed by the microspheres technique (whether subendocardial, subepicardial, or transmural), was unaffected by l‐NMMA or l‐NAME.

Acetylcholine, administered intracoronarily, induced an increase in left circumflex coronary blood flow and a decrease in coronary vascular resistance, without affecting systemic haemodynamics. This coronary vasodilator effect of acetylcholine was markedly inhibited by l‐NMMA and l‐NAME, the latter being a more potent antagonist than the former.

These results indicate that the endothelial l‐arginine pathway is largely responsible for the coronary vasodilator effect of acetylcholine. However, although basal release of nitric oxide from l‐arginine apparently contributes to the regulation of resting coronary vascular tone, blockade of this pathway does not affect myocardial tissue perfusion, possibly because of compensatory mechanisms occurring at the level of small arterioles and/or capillaries.
The role of the l‐arginine‐nitric oxide pathway in relaxation of the opossum lower oesophageal sphincter
Authors: Tøttrup A. , Knudsen M.A. , Gregersen H.
Published: July 2012

The role of the l‐arginine‐nitric oxide pathway in lower oesophageal sphincter (LOS) relaxation and oesophageal peristalsis was investigated.

Twenty four adult opossums were anaesthetized and the right vagus nerve was isolated in the neck and sectioned. Electrical stimulation, applied to the peripheral end of the nerve, resulted in a frequency‐dependent relaxation of the LOS, and peristaltic and non‐peristaltic contractions in the oesophageal body.

Nω‐nitro‐l‐arginine (l‐NNA, 10−8–10−5mol kg−1), an inhibitor of the l‐arginine‐nitric oxide pathway, inhibited LOS relaxation in a dose‐dependent manner, but did not affect resting LOS pressure. At the highest dose of l‐NNA no relaxation of the LOS was elicited in response to vagal stimulation. The effect of l‐NNA, (10−5mol kg−1) was fully reversed by infusion of 10−4mol kg−1 l‐arginine. Peristaltic velocity and amplitude of contractions in the oesophageal body were unaffected by l‐NNA.

Infusion of sodium nitroprusside reduced LOS pressure to zero, and the drug was equally potent in control animals (–log ED50: 8.1 ± 0.2 mol kg−1) and in animals pretreated with l‐NNA (–log ED50: 8.2 ± 0.3 mol kg−1). This suggests that the effect of l‐NNA was not directly on guanylate cyclase.

A significant elevation of blood pressure was recorded after administration of l‐NNA (10−5mol kg−1).

It is suggested that the l‐arginine‐nitric oxide pathway plays an important functional role for relaxation of the LOS, but not for oesophageal peristalsis. Whether the active substance is nitric oxide or a related nitroso‐compound remains to be settled.
Ca2+ion sequestration by guinea‐pig tracheal cartilage: its influence on trachealis reactivity to KCl
Authors: Gupta Paul , Markham Anthony , Morgan Rae M.
Published: July 2012

The contractile response of guinea‐pig isolated trachealis to KCl has been studied in the presence and absence of cartilage.

Dissection of cartilage from the trachealis resulted in both a rightward displacement of the concentration‐response curve to KCl (EC50 value: intact strip, 26.9 ± 3.7 mm n = 5; dissected strip, 38.7 ± 2.6 mm n = 5; P < 0.05), and a reduction in the contractile response to KCl (30 mm) observed in a nominally Ca2+‐free medium.

Removal of cartilage from the trachealis did not alter the responsiveness of the tissue to CaCl2 (2.5 mm) when added to K+depolarized tissues.

Muscle‐denuded cartilage rings were prepared by surgical removal of the trachealis muscle. Autoradiographic studies, and a direct comparison of Ca2+(2.5 mm) uptake with that of sorbitol (2.5 mm) showed that cartilage per se had a high capacity to accumulate Ca2+ions by a process which was resistant to iodoacetate (100 μm), diflunisal (100 μm) and boiling.

The uptake of 45Ca into isolated cartilage was unaltered by the addition of orthovanadate (500 μm), verapamil (10 μm), diltiazem (10 μm) or Bay K 8644 (10 μm), but was significantly reduced (P < 0.05) in the presence of LaCl3 (1–10 mm).

We conclude, like previous studies, that cartilage may supply a pool of Ca2+ions to airway smooth muscle during the generation of tension in a noninally Ca2+‐free medium, and that LaCl3 may provide an experimental tool to elucidate further the role of non‐muscle Ca2+‐depots in smooth muscle contraction.
Substance P modulates the time course of nicotinic but not muscarinic catecholamine secretion from perfused adrenal glands of rat
Authors: Zhou Xin‐Fu , Marley Philip D. , Livett Bruce G.
Published: July 2012

Substance P (SP) and acetylcholine (ACh) are contained within the splanchnic nerve terminals in the adrenal gland and can be released in response to stress. In the rat, the release of ACh brings about secretion of catecholamines (CA) by acting on nicotinic and muscarinic receptors on the adrenal chromaffin cells.

In the present study, we have used a rat isolated adrenal gland preparation to investigate the effects of SP, perfused at different concentrations, on CA secretion evoked by 10−5m nicotine and 10−4m muscarine.

In the first 10 min stimulation period (S1), in the absence of SP, nicotine (10−5m) evoked substantial and equal secretion of noradrenaline (NA) and adrenaline (Ad). In a second 10 min stimulation period (S2), carried out 18 min after S1, the nicotinic response was desensitized. In contrast, the muscarinic response, which preferentially evoked Ad secretion in S1 (Ad/NA: 8.7/1), was well maintained in S2.

SP present in S1 had no effect on desensitization of the subsequent nicotinic response in S2.

At low concentrations (10−7–10−10m), SP changed the time course of nicotine‐induced CA secretion during S1 by enhancing CA secretion in the first 4 min and inhibiting CA secretion thereafter. The maximal effect occurred at 10−9m SP.

At a higher concentration (10−5m), SP inhibited total nicotinic CA secretion throughout S1 and produced a biphasic secretion of CA (depressed in the presence of SP and enhanced after wash out of SP). Pre‐exposure of adrenal glands to SP (10−9to 10−5m) for 10 min produced marked inhibition of the nicotine‐induced CA secretion.

In contrast to the effect of SP on the nicotinic response, SP from 10−9to 10−5m had no effect on muscarinic CA secretion.

This difference in sensitivity of the nicotinic and muscarinic responses to SP points to a diversity of mechanisms available for control of adrenal catecholamine secretion. In addition to the ability of SP to increase or decrease the total amount of adrenal CA secretion, dependent on the concentration of SP, the present study shows that SP can change the time‐course of nicotinic CA secretion. These results with the rat adrenal gland perfused in vitro suggests both a quantitative and temporal role for SP as a novel modulator of adrenal CA secretion.
The effects of neuropeptide Y on myocardial contractility and coronary blood flow
Authors: Awad Sonia J. , Einstein Rosemarie , Potter Erica K. , Richardson Desmond P.
Published: July 2012

This study was designed to assess the effects of exogenous neuropeptide Y (NPY) on cardiac contractility and coronary blood flow (CBF) in anaesthetized dogs and to evaluate the effect of NPY on the responses to sympathetic and parasympathetic stimulation and to inotropic agents.

Bolus doses of NPY (500 μg), administered via the femoral vein, increased mean arterial pressure. The pressor effect was associated with reductions in heart rate, CBF and cardiac contractility.

The effects of NPY (500 μg) on contractility and CBF were compared with that of vasopressin (VP) (1 unit). For similar reductions in CBF, NPY and VP had similar negative inotropic effects. Thus, it is likely that the negative inotropic response to NPY is not due to a direct effect of NPY on the heart muscle but is largely due to coronary vasoconstriction.

In the presence of NPY (500 μg, i.v.), there was an inhibition of the positive inotropic response to stimulation of the left cardiac sympathetic nerve (2 or 5 Hz, 0.05 ms). NPY also inhibited the negative inotropic response and chronotropic response to vagal stimulation (2, 3 or 5 Hz, 0.05 ms).

Dose‐response curves were obtained for the inotropic, chronotropic and pressor responses to cumulative infusions of noradrenaline (n = 6) and dobutamine (n = 6). NPY had no effect on these dose‐response curves.

The effect of NPY on the responses to salbutamol and impromidine was assessed. NPY did not alter the positive inotropic, chronotropic or depressor responses to these agonists.

Our results indicate that NPY has direct, postsynaptic vasoconstrictor activity and the reduction in myocardial contractility and heart rate are due to a combination of coronary vasoconstriction, baroreceptor reflex activation and presynaptic inhibition of transmitter release from sympathetic nerves. The well‐documented inhibitory effect of NPY on the chronotropic response to parasympathetic stimulation was confirmed and similar inhibition of the inotropic response to both sympathetic and parasympathetic stimulation was demonstrated. Since there was no modulation of the inotropic effects of exogenous α‐ and β‐ adrenoceptor or H2‐receptor agonists, it is concluded that the effects of NPY on myocardial contractility are exerted presynaptically.
Effects of lemakalim on changes in Ca2+concentration and mechanical activity induced by noradrenaline in the rabbit mesenteric artery
Authors: Ito Shinichi , Kajikuri Junko , Itoh Takeo , Kuriyama Hirosi
Published: July 2012

Effects of (−)‐cromakalim (lemakalim) on tension and Ca2+mobilization induced by noradrenaline (NA) were investigated by measuring intracellular Ca2+concentration ([Ca2+]i), isometric tension and production of inositol‐1,4,5‐trisphosphate (IP3) in smooth muscle strips of the rabbit mesenteric artery.

In thin smooth muscle strips, 10 μm NA produced a large phasic, followed by a small tonic increase in [Ca2+]i, which correlated well with the evoked phasic and tonic contractions, respectively. Lemakalim (0.1–10 μm) lowered the resting [Ca2+]i without a decrease in the resting tension, and also inhibited the increased [Ca2+]i and tension induced by 10 μm NA, all in a concentration‐dependent manner. Glibenclamide (1 μm) inhibited these actions of lemakalim.

In Ca2+‐free solution containing 2 mm EGTA, NA (10 μm) transiently increased [Ca2+]i, tension and synthesis of IP3. Lemakalim (over 0.01 μm) inhibited these actions of NA in Ca2+‐free solution containing 5.9 mm K+, but not in Ca2+‐free solution containing 128 mm K+. These actions of lemakalim were prevented by glibenclamide (1 μm). Lemakalim (1 μm) did not modify the increases in [Ca2+]i and tension induced by 10 mm caffeine.

In β‐escin‐skinned strips, 10 μm NA increased [Ca2+]i in Ca2+‐free solution containing 50 μm EGTA, 3 μm guanosine triphosphate (GTP) and 2 μm Fura 2 after the storage sites were loaded by application of 0.3 μm Ca2+for 2 min, suggesting that Ca2+is released from intracellular storage sites following activation of the α‐adrenoceptor. Lemakalim (1 μm) did not inhibit the Ca2+release from storage sites induced by NA.

We conclude that lemakalim inhibits NA‐induced Ca2+release due to inhibition of NA‐induced IP3 production in a manner dependent on the membrane potential and causes inhibition of the phasic contraction induced by NA.
Mechanism of action of platelet activating factor in the pulmonary circulation: an investigation using a novel isotopic system in rabbit isolated lung
Authors: Seale J.P. , Nourshargh S. , Hellewell P.G. , Williams T.J.
Published: July 2012

Rabbit isolated lungs were perfused via the pulmonary artery with Tyrode solution containing 4.5% Ficoll and 0.1% bovine serum albumin at a constant rate of 20 ml min−1. Lung perfusate was drawn for alternating 5 min periods from two reservoirs, one containing 125I‐albumin and the other unlabelled albumin to wash out the intravascular label. Microvascular 125I‐albumin leakage was determined from the count remaining at the end of the washout phase with an external gamma scintillation probe. In addition, perfusion pressure was monitored continuously. Each experiment comprised 6 cycles over a total period of 60 min.

Infusion of platelet activating factor (PAF, 3 nmol min−1 for 10 min) resulted in microvascular 125I‐albumin leakage, whereas lyso‐PAF was without effect. During PAF infusions there was also an increase in perfusion pressure. Both the permeability and pressor effects of PAF were inhibited by the PAF antagonist L‐652731.

Infusion of the thromboxane analogue U‐46619 (0.6 nmol min−1 for 10 min) caused an increase in perfusion pressure but protein accumulation was not significantly different from that observed with control infusions.

Bolus injections of PAF (1 nmol) caused increases in perfusion pressure which were reduced by indomethacin, dazmegrel and BW 755C. Bolus injections of PAF, repeated at 30 min intervals caused reproducible pressor responses; however, repeated injections at 60 min intervals resulted in augmented responses. This augmentation did not occur in the presence of indomethacin.

Retrograde perfusion of PAF via the pulmonary vein induced increased perfusion pressure and microvascular 125I‐albumin leakage. The observed increase in leakage when compared with forward perfusion suggests that PAF produces predominantly arteriolar constriction i.e. proximal to the site of leakage during forward perfusion.

These results indicate that PAF is a vasoconstrictor in the rabbit pulmonary circulation and augmented responses occur with repeated injections at 60 min intervals. Cyclo‐oxygenase inhibition abolished this vascular hyperresponsiveness induced by PAF. PAF also caused protein accumulation in the lungs. Both these actions of PAF appear to be receptor‐mediated because they were inhibited by PAF antagonists. Another pulmonary vasoconstrictor, U‐46619 did not cause protein accumulation suggesting that the extravasation of protein with PAF is not merely secondary to changes in vascular tone.
Characterization of nitric oxide synthases in non‐adrenergic non‐cholinergic nerve containing tissue from the rat anococcygeus muscle
Authors: Mitchell Jane A. , Sheng Hong , Förstermann Ulrich , Murad Ferid
Published: July 2012

Tissue homogenates prepared from rat anococcygeus muscle converted l‐arginine to l‐citrulline indicating the presence of nitric oxide (NO) synthase. NO synthase activity was also found in crude and partially‐purified soluble and particulate fractions prepared from the homogenates. Both soluble and particulate NO synthase were dependent on NADPH, 5,6,7,8‐tetrahydrobiopterin and calcium, and inhibited by NG‐nitro‐l‐arginine. Tissue homogenates or crude cytosolic and membrane fractions from rat vas deferens, which does not contain NO releasing non‐adrenergic non‐cholinergic neurones, had no NO synthase activity.
Investigation into species variants in tachykinin NK1 receptors by use of the non‐peptide antagonist, CP‐96,345
Authors: Beresford I.J.M. , Birch P.J. , Hagan R.M. , Ireland S.J.
Published: July 2012

The affinity of the non‐peptide antagonist CP‐96,345 for tachykinin NK1 receptors has been estimated in a range of species by use of both radioligand binding and functional assays. CP‐96,345 was 30–120 fold less active at NK1 receptors in rat and mouse than in the other species examined, including man. These results demonstrate the existence of species variations in NK1 receptors.
Neuropeptide Y (NPY) metabolism by endopeptidase‐2 hinders characterization of NPY receptors in rat kidney
Authors: Price J.S. , Kenny A.J. , Huskisson N.S. , Brown M.J.
Published: July 2012

Despite the observation of pharmacological responses to neuropeptide Y (NPY) in mammalian kidneys, there are species differences in the ease with which specific NPY binding sites can be demonstrated; we have investigated whether this can be explained by differential metabolism of NPY by a membrane‐bound peptidase.

NPY receptors were identified on cell membranes isolated from the rabbit kidney (KD = 97 ± 16 pm, Bmax = 290 ± 30 fmol mg−1protein), and this preparation did not degrade [125I]‐NPY. However, a similar preparation of cell membranes from the rat kidney exhibited a much lower apparent receptor affinity (IC50 approximately 30 nm); these membranes rapidly degraded [125I]‐NPY to fragments which did not bind NPY receptors in either tissue.

[125I]‐NPY binding sites were revealed in the rat kidney when degradation was inhibited by insulin B chain. Chelating agents also inhibited degradation, but interfered with receptor binding. Binding sites could not be demonstrated in sections of rat kidney, even in the presence of insulin B chain.

The difference in degradative activity between rat and rabbit renal cell membranes, inhibition of degradation by chelating agents and insulin B chain, and insensitivity to phosphoramidon suggest that the enzyme responsible was endopeptidase‐2, and this was confirmed by comparing the hydrolysis of [125I]‐NPY by purified enzyme with rat renal tissue. Activity of this enzyme explains the difficulties encountered demonstrating receptors in the rat kidney.

Renal cell membranes from the mouse digested [125I]‐NPY in a similar manner and this may be due to the closely related enzyme, meprin. NPY degradation has not previously been reported. The results suggest that NPY should be added to the list of peptides sensitive to these enzymes.
The relationship of KCl‐ and prostaglandin F2α‐mediated increases in tension of the porcine coronary artery with changes in intracellular Ca2+measured with fura‐2
Authors: Balwierczak Joseph L.
Published: July 2012

Changes in intracellular free Ca2+concentration ([Ca2+]i) were measured simultaneously with changes in muscle tension by use of the fluorescent Ca2+indicator, fura‐2, in coronary arterial rings of the Pig.

Changes in [Ca2+]i were measured by monitoring the ratio of fluorescence due to excitation at 340 nm (F340) to that at 380 nm (F380).

Increases in tension of the porcine coronary artery induced by prostaglandin F2α (PGF2α) (2–30 μm) and KCl (25–70 mm) were accompanied by increases in the F340/F380 fluorescence ratio of fura‐2.

KCl‐induced increases in muscle tension, equivalent to those produced by PGF2α, were observed to occur in the presence of a higher [Ca2+]i.

Nearly complete relaxation of KCl‐induced contractions by sodium nitroprusside (SNP) was accompanied by only a partial reversal of the increase in [Ca2+]i that occurred during contraction.

Complete relaxation of the PGF2α‐contracted coronary artery by cromakalim (BRL 34915) was accompanied by a nearly complete reversal of the increase in [Ca2+]i caused by the contractile agent.

The contractile state of smooth muscle is not an indicator of [Ca2+]i. The [Ca2+]itension relationship is dependent upon the type of pharmacological agent that is used to change muscle tension.
Inhibition of the tocolytic activity of atrial natriuretic factor by progesterone and potentiation by progesterone receptor antagonist RU486 in rats
Authors: Potvin W. , Mulay S. , Varma D.R.
Published: July 2012

The influence of progesterone on the activity of atrial natriuretic factor (ANF) on rat myometrial motor activity was determined in vitro.

ANF inhibited the tension development by myometrium from cycling or oestrogen‐treated rats in a dose‐dependent manner; maximal inhibition was 100%.

Injections of progesterone into rats inhibited the tocolytic activity of ANF in a dose‐ and time‐dependent manner. The tocolytic effects of ANF were completely abolished by 3 daily injections of 1 mg kg−1progesterone.

Pregnancy‐related increase in plasma progesterone was accompanied by a corresponding decrease in the tocolytic effects of ANF; myometria from gestational day 10 to 21 were completely refractory and those from earlier gestational age and immediate postpartum were responsive to ANF to varying degrees.

Treatment of pregnant rats with the progesterone antagonist, RU486, caused abortions and vaginal bleeding, decreased plasma progesterone concentrations and restored the tocolytic activity of ANF. Tocolytic activity of ANF on virgin rat myometria was potentiated by RU486.

Progesterone also inhibited the effects of ANF on myometria from ovariectomzed rats.

Tocolytic activity of isoprenaline was not modified by progesterone, pregnancy, RU486 or ovariectomy.

It is concluded that progesterone antagonizes myometrial effects of ANF by an oestrogen‐independent mechanism and the pregnancy‐induced refractoriness to the tocolytic effects of ANF is caused by progesterone.
Adenosine receptors and nucleoside transport sites in cardiac cells
Authors: Parkinson F.E. , Clanachan A.S.
Published: July 2012

Potential mechanisms responsible for the prominent depression of atrioventricular conduction by adenosine have been investigated in guinea‐pig heart.

Adenosine A1 receptors and nucleoside transport (NT) sites were identified and enumerated in cardiac myocytes, atrioventricular conduction cells and coronary endothelial cells in 10 μm sections by autoradiographical analysis of the binding of the A1 selective antagonist 8‐cyclopentyl‐1,3‐[3H]‐dipropylxanthine ([3H]‐DPCPX) and the NT ligand [3H]‐nitrobenzylthioinosine ([3H]‐NBMPR), respectively.

Atrioventricular conduction cells were identified by acetylcholinesterase histochemistry and endothelial cells by von Willebrand factor immunohistochemistry.

Site‐specific binding of [3H]‐DPCPX, when expressed as grains per cell nucleus was significantly higher (30 fold) in conduction cells than in surrounding myocytes. [3H]‐DPCPX site density on endothelial cells in adjacent coronary vessels was not significantly different from myocytes.

In contrast, autoradiography of [3H]‐NBMPR sites in these areas indicated that, relative to myocytes, conduction cells and endothelial cells were significantly enriched (2 fold and 4.5 fold, respectively) in NT sites.

The pronounced dromotropic effect of adenosine in guinea‐pig heart is correlated with a higher density of adenosine A1 receptors in atrioventricular conduction cells than in myocytes. The NT capacity of these cells, as estimated by [3H]‐NBMPR binding site density, is not increased in proportion to A1 receptors.
Comparison of the electrophysiological effects of Org 7797, disopyramide, mexiletine and propafenone in anaesthetized dogs with myocardial infarcts
Authors: Campbell J.K. , Marshall R.J. , Winslow E.
Published: July 2012

The electrophysiological effects of intravenously administered Org 7797 were compared with those of disopyramide (class Ia), mexiletine (Ib) and propafenone (Ic) in anaesthetized dogs with 5–6 day‐old left ventricular myocardial infarcts.

Org 7797 (0.5 mg kg−1) slowed conduction at all levels of the myocardium as shown by increases in St‐A, AH, HV and QRS intervals, very modestly prolonged atrial and ventricular refractory periods and slightly shortened ventricular repolarization. Sinus node recovery time was increased whilst the RR interval was unchanged. A higher dose (2 mg kg−1) prolonged RR and rendered 5 out of 8 dogs unable to follow an atrial pacing stimulus of mean cycle length 322 ms.

Electrophysiological changes induced by propafenone (2 mg kg−1) were qualitatively similar to those of Org 7797 (0.5 mg kg−1).

Electrophysiological changes induced by mexiletine (2 mg kg−1) were small or insignificant. The most noticeable effect was a modest increase in the St‐A interval and a slight shortening of ventricular repolarization. A higher dose (8 mg kg−1) additionally slowed conduction in the His‐Purkinje system and in the ventricular myocardium.

Disopyramide (2 and 5 mg kg−1) prolonged all cardiac intervals including JTc, QTc and QT during pacing and prolonged cardiac refractory periods.

It was concluded that the electrophysiological profile of Org 7797 is more like that of the Ic agent propafenone than that of the class Ia and Ib drugs, disopyramide and mexiletine.
The presence of five cyclic nucleotide phosphodiesterase isoenzyme activities in bovine tracheal smooth muscle and the functional effects of selective inhibitors
Authors: Shahid Mohammed , van Amsterdam Ronald G.M. , de Boer Jacob , ten Berge Ronald E. , Nicholson C David , Zaagsma Johan
Published: July 2012

The profile of cyclic nucleotide phosphodiesterase (PDE) isoenzymes and the relaxant effects of isoenzyme selective inhibitors were examined in bovine tracheal smooth muscle. The compounds examined were the non‐selective inhibitor 3‐isobutyl‐1‐methylxanthine (IBMX), zaprinast (PDE V selective), milrinone and Org 9935 (4,5‐dihydro‐6‐(5,6‐dimethoxy‐benzo[b]thien‐2‐yl)‐5‐methyl‐1(2H)‐pyridazinone; both PDE III selective), rolipram (PDE IV selective) and Org 30029 (N‐hydroxy‐5,6‐dimethoxy‐benzo[b]‐thiophene‐2‐carboximidamide HCl a dual PDE III/IV inhibitor).

Ion exchange chromatography showed three main peaks of PDE activity. The first peak was stimulated by Ca2+/calmodulin (PDE I), the adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) hydrolytic activity of the second peak was stimulated by guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) (PDE II) whilst that of the third peak was not significantly modified by any regulator (PDE IV). Calmodulin affinity chromatography revealed the additional presence of cyclic GMP‐specific PDE (PDE V) in the first peak. A clearly distinct peak of cyclic GMP‐inhibited PDE (PDE III) was not observed. However, Org 9935 inhibited the third activity peak more effectively in the presence, than in the absence, of rolipram (3 μmol l−1), indicating the presence of PDE III activity.

Rolipram was the most potent inhibitor of PDE IV. The mean −log50IC50values for rolipram, IBMX, milrinone, Org 30029, Org 9935 and zaprinast were 5.9 ± 0.1, 4.9 ± 0.1, 4.7 ± 0.1, 4.6 ± 0.1 and 4.6 ± 0.1, respectively.

Rolipram was a potent relaxant of both histamine (1 μmol1−1) and methacholine (0.03 μmol1−1) precontracted preparations; (pD2values; histamine 7.1 ± 0.1, methacholine 6.8 ± 0.2 and 4.5 ± 0.1, biphasic relaxation). IBMX also relaxed all preparations (pD2values; histamine 5.6 ± 0.1, methacholine 5.6 ± 0.1) whilst zaprinast (pD2values; histamine 5.2 ± 0.1, methacholine 4.4 ± 0.3), milrinone (pD2values; histamine 5.2 ± 0.1, methacholine 4.3 ± 0.3) and Org 9935 (pD2values; histamine 4.1 ± 0.1, methacholine 4.1 ± 0.2) did not completely relax preparations at concentrations up to 100 μmol1−1. Org 30029 (pD2values; histamine 6.2 ± 0.1, methacholine 5.4 ± 0.1) was a more effective relaxant than can be explained on the basis of PDE IV inhibition alone.

We conclude that bovine tracheal smooth muscle contains five distinct PDE isoenzymes. PDE IV appears to be more important in the modulation of tissue function than PDE III and PDE V.
Thermogenic and lipolytic effect of yohimbine in the dog
Authors: Galitzky Jean , Vermorel Michel , Lafontan Max , Montastruc Paul , Berlan Michel
Published: July 2012

Lipid mobilization during a hypocaloric diet may be enhanced by a pharmacological approach using α2‐adrenoceptor antagonists since these drugs are known to increase sympathetic tone and stimulate lipolysis. Studies were undertaken in the dog in order to evaluate the effects of oral yohimbine administration (α2‐adrenoceptor antagonist) on heat production, metabolic, endocrinological and cardiovascular parameters.

Acute oral yohimbine (0.25 or 0.40 mg kg−1) provoked an increase in plasma non‐esterfied fatty acids. The drug increased sympathetic nervous system activity as indicated by the increased level of plasma noradrenaline. These effects persisted during the entire experimental period (4 h). The increase in plasma noradrenaline level was two fold higher with the higher dose of yohimbine (0.4 mg kg−1). The plasma adrenaline level was increased only with the higher dose.

Yohimbine transiently increased plasma insulin and the effect was dose‐dependent.

Yohimbine (0.25 mg kg−1) enhanced heart rate and arterial blood pressure.

The effect of yohimbine on oxygen consumption, carbon dioxide and heat production was determined by indirect calorimetry. The drug (0.25 mg kg−1) increased O2 consumption and CO2 and heat production 30 min after its administration and the effect persisted over the experimental period. The respiratory quotient, rather low in the fasting animals, remained unchanged.

The present work indicates that thermogenesis and lipid mobilization are enhanced during fasting in the dog by α2‐adrenoceptor blockade. Yohimbine also induced a transient increase in plasma insulin level and increased heart rate and blood pressure. The lipid mobilization plus the action on thermogenesis observed after yohimbine draw attention to the putative interest of α2‐antagonists in the pharmacological treatment of obesity during restricted calorie intake.
Alkaline phosphatase prevents platelet stimulation by thromboxane‐mimetics
Authors: Hatmi Mohamed , Haye Bernard , Gavaret J. Michel , Vargaftig B. Boris , Jacquemin Claude
Published: July 2012

The effects of alkaline phosphatase on platelet aggregation, secretion and thromboxane B2 (TxB2) generation induced by the full dose‐range of common platelet agonists were studied in human platelet‐rich plasma and washed platelets.

Platelet aggregation and adenosine 5′‐triphosphate (ATP) secretion induced by threshold and supramaximal concentrations of arachidonate and stable TxA2 and prostaglandin endoperoxide‐mimetics (compounds U46619 and EP171) were abolished in the presence of alkaline phosphatase (0.5–1 u ml−1), even though the synthesis of TxB2 persisted. In contrast, platelet aggregation by PAF‐acether and by supramaximal concentrations of thrombin as well as the primary wave of aggregation by adenosine diphosphate (ADP) and adrenaline were unaffected by alkaline phosphatase under conditions where the secondary wave of aggregation by ADP was blocked.

Alkaline phosphatase, unlike prostacyclin, failed to raise the adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) content of the platelets. Also, the pretreatment of platelets by inorganic phosphate or by ATP plus creatine phosphate/creatine phosphokinase reversed the inhibitory effect of alkaline phosphatase.

Experiments performed in the guinea‐pig in vivo showed that alkaline phosphatase was effective on thrombocytopenia induced by arachidonate.

Our results provide the first direct evidence for a specific inhibitory effect of alkaline phosphatase at a site sensitive to TxA2 and prostaglandin endoperoxides and suggest that its phosphorylation/dephosphorylation state may play an important role in modulating platelet activation. These results also suggest the presence of ecto‐protein kinases on membrane platelets.
Heterogeneity of endothelin‐sarafotoxin receptors mediating contraction of pig coronary artery
Authors: Harrison Vanessa J. , Randriantsoa Adolphe , Schoeffter Philippe
Published: July 2012

The contractile effects of endothelin‐1, endothelin‐3, sarafotoxin 6b and sarafotoxin 6c were studied in endothelium‐denuded rings of pig coronary artery. Endothelin‐1, sarafotoxin 6b and sarafotoxin 6c produced monophasic concentration‐response curves (mean EC50 values 6.7, 14.8 and 1.6 nm), whereas the concentration‐response curve to endothelin‐3 was biphasic (mean EC50 values 9.6 nm and 0.32 μm). The maximal effect of sarafotoxin 6c was about one third of that reached by the other peptides. The higher sensitivity component of the curve to endothelin‐3 was abolished in the presence of sarafotoxin 6c (0.3 μm), while the EC50 value for the other component remained unchanged. Sarafotoxin 6c (0.3 μm) failed to alter the EC50 values of endothelin‐1 and sarafotoxin 6b. These data strongly suggest the presence of at least two endothelin‐sarafotoxin receptors mediating contraction of pig coronary artery, one with the profile of the endothelin ETA receptor subtype, the other recognizing sarafotoxin 6c and endothelin‐3, but not endothelin‐1 and sarafotoxin 6b, being thus different from the ETB receptor subtype.
Adenine nucleotide‐induced inhibition of binding of sulphonylureas to their receptor in pancreatic islets
Authors: Schwanstecher M. , Löser S. , Brandt Ch. , Scheffer K. , Rosenberger F. , Panten U.
Published: July 2012

The effects of the Mg complex of adenosine 5′‐triphosphate (MgATP) on binding of sulphonylureas to microsomes obtained from mouse pancreatic islets were examined.

MgATP inhibited the binding of both glibenclamide and tolbutamide to microsomes.

Binding of [3H]‐glibenclamide inhibited by MgATP was not further diminished by Mg2+‐bound adenosine 5′‐(β,γ‐imidotriphosphate) (AMP‐PNP) or free adenosine 5′‐diphosphate (ADP). Higher concentrations of MgAMP‐PNP induced a partial reversal of the inhibitory effect of MgATP on [3H]‐glibenclamide binding.

The apparent dissociation constant (K'D) for binding of [3H]‐glibenclamide remained constant when the MgATP concentration was increased from 100 to 500 μm.

Extracellular ADP did not markedly stimulate insulin release from mouse pancreatic islets.

It is concluded that sulphonylureas and cytosolic nucleotides exert their inhibitory effects on the K‐ATP‐channels of β‐cells by binding to different sites. The binding properties of the sulphonylurea receptor seem to be modulated by protein phosphorylation.