bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of propafenone on 45Ca movements and contractile responses in vascular smooth muscle
Authors: Carrón Rosalia , Pérez‐Vizcaino Francisco , Delpón Eva , Tamargo Juan
Published: July 2012

In rat isolated aorta the class Ic antiarrhythmic drug, propafenone, dose‐dependently inhibited the contractile responses induced by high K (80 mm) and noradrenaline (NA, 10−5 m), the IC50s being 2.5 ± 0.7 × 10−6 m and 8.7 ± 0.8 × 10−6 m, respectively. These inhibitory actions were also observed with propafenone added after the induced contractions.

Contractile responses induced by addition of Ca to 0 Ca high‐K solution were also inhibited by propafenone (IC50 = 2.5 ± 0.8 × 10−6 m). Moreover, propafenone inhibited the contractile responses elicited by NA in strips incubated in 0 Ca (IC50 = 1.9 ± 0.9 × 10−6 m).

Propafenone also inhibited (IC50 = 1.2 ± 0.4 × 10−5 m) the development of spontaneous mechanical activity in portal vein segments.

Propafenone, 5 × 10−6 m and 10−5 m, inhibited 45Ca uptake stimulated by high K or NA without altering 45Ca uptake in resting strips.

These results indicated that in rat isolated aortae and portal veins propafenone inhibited Ca entry through voltage‐operated channels and NA‐induced Ca uptake as well as Ca release from intracellular stores. As a consequence it would reduce the concentration of intracellular free Ca available at the contractile apparatus for vascular smooth muscle contraction.
IgE‐dependent activation of alveolar macrophages augments neurally mediated contraction of small airways
Authors: Tamaoki J. , Sakai N. , Kanemura T. , Yamawaki I. , Takizawa T.
Published: July 2012

We studied the effect of immunologically activated pulmonary alveolar macrophages (PAM) on functions of canine bronchiolar smooth muscle under isometric conditions in vitro.

PAM, stimulated with monoclonal anti‐dinitrophenyl (DNP) IgE antibody and DNP‐human serum albumin (DNP‐HSA), augmented the contractile responses of bronchioles to electrical field stimulation, whereas PAM treated with IgE antibody alone had no effect.

In contrast, the contractile responses to exogenously administered acetylcholine were not influenced by immunologically activated PAM.

The PAM‐induced increase in the contractile responses to field stimulation was inhibited by pretreatment of PAM with indomethacin and by addition of the thromboxane A2 (TxA2) receptor antagonist SQ 29548.

The release of TxA2 from PAM was increased by anti‐DNP IgE and DNP‐HSA, an effect that was prevented by indomethacin.

These results suggest that PAM may play a role in the development of antigen‐induced hyperreactivity of small airways through an IgE‐dependent release of TxA2 which potentiates prejunctionally the parasympathetic component of bronchiolar smooth muscle tone.
Receptors mediating tachykinin‐induced contractile responses in guinea‐pig trachea
Authors: Ireland S.J. , Bailey F. , Cook A. , Hagan R.M. , Jordan C.C. , Stephens‐Smith M.L.
Published: July 2012

The classification of tachykinin receptors in the guinea‐pig trachea has been investigated. This was of interest because, from previous studies, it was not clear whether the guinea‐pig trachea contains either a mixture of NK1 and NK2 receptors or, alternatively, a single type of novel tachykinin receptor.

In the present study, the guinea‐pig trachea was contracted by tachykinin agonists selective for NK1 receptors (substance P methylester (SPOMe) and GR73632) or NK2 receptors (GR64349) but not NK3 receptors (senktide).

Against SPOMe and GR73632, the NK1 antagonist, GR71251, behaved as a reversible competitive antagonist having apparent affinity (pKB 7.05 vs SPOMe) consistent with action at NK1 receptors. GR71251 (3 μm) did not antagonize responses to GR64349.

The NK2 antagonists L‐659,877 and Ac‐Leu‐Asp‐Gln‐Trp‐Phe‐Gly‐NH2 (R396) antagonized GR64349 although only R396 appeared to behave competitively (pKB 5.73). Neither L‐659,877 (30 μm) nor R396 (30 μm) blocked responses to SPOMe.

For L‐659,877 and R396, comparison was made between activity in guinea‐pig trachea and in preparations known to contain tachykinin receptors predominantly of the NK2 type. In the rabbit trachea, both L‐659,877 and R396 had effects similar to those in guinea‐pig trachea. In contrast, in the rat colon muscularis mucosae, both L‐659,877 and R396 appeared to behave competitively with pKB values against GR64349 of 7.83 and 6.90 respectively.

It is concluded that in guinea‐pig trachea, contractile responses can be induced by activation of both NK1 and NK2 receptors. The present data are discussed with reference to the proposed existence of subtypes of the NK2 receptor.
Epithelium‐dependent potentiation of anaphylactic contractions by β‐endorphin in tracheae isolated from actively sensitized guinea‐pigs
Authors: Van Oosterhout A.J.M. , Celeda L. , Delsman K.C. , de Wied D. , Nijkamp F.P.
Published: July 2012

It has been shown that opioid peptides modulate airway function. In the present study, the effect of β‐endorphin on antigen‐induced contractions of isolated tracheal rings from actively sensitized guinea‐pigs has been studied.

β‐Endorphin had a concentration‐dependent bimodal effect on anaphylactic contractions of the trachea. Low concentrations of β‐endorphin (10−10 and 10−8 m) significantly potentiated anaphylactic contractions, whereas higher concentrations (10−7 and 10−6 m) significantly suppressed anaphylactic contractions of guinea‐pig trachea.

β‐Endorphin in concentrations of 10−8 m and 10−7 m did not affect the responsiveness of the tracheal rings to histamine or leukotriene D4. This indicates that β‐endorphin does not influence the responsiveness of tracheal smooth muscle to anaphylactic mediators.

In the presence of the non‐selective opioid receptor antagonist naloxone, 10−8 m β‐endorphin still potentiated the anaphylactic contractions of the trachea. In addition, an equimolar concentration of des‐Tyr1‐β‐endorphin, a fragment of β‐endorphin without opioid‐like activity, also potentiated anaphylactic contractions. The potentiation of anaphylactic contraction by 10−8 m β‐endorphin is not therefore mediated by classical opioid‐receptors.

In the presence of naloxone, 10−7 m, β‐endorphin did not suppress anaphylactic contractions of the trachea. Thus, the suppression of anaphylactic contraction is mediated via a classical opioid‐receptor.

In epithelium‐denuded tracheae, both 10−8 and 10−7 m β‐endorphin suppressed the anaphylactic contractions, whereas 10−8 and 10−7 m des‐Tyr1‐β‐endorphin did not affect anaphylactic contractions. It is concluded that the potentiation of the anaphylactic contraction in intact trachea is epithelium‐dependent whereas the suppression of the anaphylactic contraction is epithelium‐independent.
Time‐dependent synergistic interactions between the vasodilator neuropeptide, calcitonin gene‐related peptide (CGRP) and mediators of inflammation
Authors: Buckley T.L. , Brain S.D. , Rampart M. , Williams T.J.
Published: July 2012

The action of the long lasting neuropeptide vasodilator, calcitonin gene‐related peptide (CGRP), in potentiating oedema formation and neutrophil accumulation was investigated in the dorsal skin of the rabbit, in vivo. Combinations of agents under test were administered by intradermal (i.d.) injection. Oedema formation and neutrophil accumulation were then measured by quantitative radiolabel techniques.

CGRP (1 × 10−11 mol per site) potentiated neutrophil accumulation induced by zymosan activated plasma, (used as a source of C5a des Arg), N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP) and leukotriene B4 (LTB4). In contrast CGRP did not induce neutrophil accumulation when injected alone.

Oedema formation induced by a series of chemically distinct mediators of increased microvascular permeability; bradykinin, platelet activating factor (PAF), FMLP and zymosan‐activated plasma; measured 0–30 min after i.d. injection was potentiated by CGRP (1 × 10−11 mol per site).

Oedema formation induced by zymosan activated plasma and FMLP but not bradykinin and PAF, was also significantly potentiated by CGRP when oedema was measured 30–60 min after i.d. injection. The potentiation of oedema induced by zymosan activated plasma measured 30–60 min after i.d. injection was not observed in the presence of the shorter acting prostanoid vasodilator prostacyclin (PGI2, 3 × 10−10 mol per site).

These results suggest that CGRP, as a consequence of its sustained vasodilator activity could have prolonged potentiating effects on neutrophil accumulation and oedema formation in inflammatory conditions.
Kinetics of (+)‐tubocurarine blockade at the neuromuscular junction
Authors: Le Dain Alexander C. , Madsen Barry W. , Edeson Robert O.
Published: July 2012

Although (+)‐tubocurarine (Tc) is classically considered to be a competitive antagonist at the neuromuscular junction, kinetic details of the interaction remain unclear.

We studied the competitive action of Tc on the nicotinic receptor at the frog neuromuscular junction using a quantitative analysis of the generation phase of miniature endplate currents (m.e.p.cs) recorded in Ringer solution (20°C) under voltage clamp (–90 mV) in the absence or presence of 1–5 μm Tc. Under control conditions four neurotransmission parameters were estimated by non‐linear regression using a mathematical model of synaptic transmission incorporating transmitter release, diffusion, hydrolysis, receptor binding and channel gating. These parameters were then used in a further regression to estimate binding rate constants for Tc at the same endplate. Allowance was made for open channel block by Tc, which under the conditions of this study was only a small component of total blockade.

The results suggest that Tc binds to the two agonist recognition sites on the nicotinic receptor with equal affinity (stoichiometric KDs of 2.2 and 8.8 μm), and that most of the functional blockade at concentrations up to 5 μm is due to occupancy of only one site.

The association rate constant for Tc binding to sites on the nicotinic acetylcholine receptor appears to be very fast (k+ D = 8.9× 108 m−1 s−1) and comparable to that for acetylcholine (ACh).

In the brief time during which an m.e.p.c. is generated (≅ 200 μs), reversal of Tc blockade by transiently high concentrations of ACh seems to be kinetically limited.
Pressor effects following microinjection of 5‐HT1A receptor agonists into the raphe obscurus of the anaesthetized rat
Authors: Dreteler Gea H. , Wouters Wout , Saxena Pramod R. , Ramage Andrew G.
Published: July 2012

The effects of electrical stimulation and microinjections (90 nl) of the 5‐HT1A receptor agonists, flesinoxan and 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT), and glutamate into the raphe obscurus on blood pressure, heart rate and phrenic nerve activity (central inspiratory drive) were investigated in rats anaesthetized with α‐chloralose.

Electrical stimulation of the raphe obscurus caused a rise in blood pressure which was associated with bradycardia, while glutamate (2.7 nmol) caused only a rise in blood pressure.

Flesinoxan (1.3 nmol) and 8‐OH‐DPAT (0.7 nmol) increased blood pressure by 9 ± 1 and 14 ± 2 mmHg, respectively and did not affect heart rate. For both agonists the effect on blood pressure was shown to be dose‐dependent; again no effect on the heart rate was observed over the dose‐ranges chosen.

Microinjections of the non‐selective 5‐HT1A receptor antagonists, (±)‐pindolol (2.7 nmol) or methiothepin (5.2 nmol), into the raphe obscurus prevented the increase in blood pressure caused by microinjection of flesinoxan. However, (±)‐pindolol caused a sustained rise in blood pressure of 15 ± 1 mmHg while methiothepin caused a transient rise in blood pressure. Neither drugs affected heart rate. The ability of methiothepin to attenuate the pressor effect of flesinoxan was found to be partially reversed after 30 min.

It is suggested that activation of 5‐HT1A receptors within the raphe obscurus can cause sympathoexcitation.
Radioligand binding to muscarinic receptors of bovine aortic endothelial cells
Authors: Brunner Friedrich , Kukovetz Walter R.
Published: July 2012

Muscarinic receptors on endothelial cells of bovine thoracic aorta were characterized by binding assays in which (−)‐[3H]‐N‐methyl quinuclidinyl benzilate ([3H]‐NMeQNB) was used as radioligand.

Binding of [3H]‐NMeQNB to crude membranes of freshly isolated endothelial cells was atropine‐displaceable and of high affinity (KD = 0.48 nm) to a single class of sites (maximum binding capacity: 14 ± 3 fmol mg−1 protein). Stereospecificity of the binding sites was demonstrated in experiments in which [3H]‐NMeQNB binding was inhibited by dexetimide in the nanomolar range (KI = 0.63 nm) and by levetimide, its stereoisomer in the micromolar range (KI = 3.2 μm) (selectivity factor: ∼5000).

Drug competition curves indicated a single class of binding sites for antagonists and the following apparant affinities (KI, nm): methyl atropine: 1.1; 4‐diphenylacetoxy N‐methyl piperidine methyl bromide (4‐DAMP): 3.4; pirenzepine: 16; 11‐[2‐(diethylamino‐methyl)‐1‐piperidinyl‐acetyl]‐5,11‐dihydro‐6H‐pyrido(2,3‐b)1,4‐benzodiazepine‐6‐one (AF‐DX 116): 2.500. Competition of acetylcholine with [3H]‐NMeQNB was best described by two affinity sites (or states) (KH = 0.82 μm, KL = 1.6 μm). In the presence of guanylimido diphosphate [Gpp(NH)p] (100 μm), acetylcholine affinity (IC50) was slightly, but significantly reduced (factor ∼4).

Binding of [3H]‐NMeQNB to freshly harvested intact cells was also atropine‐displaceable, stereospecific (selectivity factor: ∼3500) and of high affinity (KD = 0.35 nm). The maximum binding capacity (9 ± 2 fmol mg−1 total cell protein) was comparable to that of membranes and corresponded to ∼900 binding sites per endothelial cell. Binding to enzymatically harvested and cultured endothelial cells, or membranes derived therefrom, showed no atropine‐displaceable binding.

The results suggest that (1) bovine aortic endothelial cells contain muscarinic binding sites with all necessary criteria of functional muscarinic receptors; (2) the receptor most closely corresponds to the M1 subtype and is of comparatively very low density, and (3) cultured endothelial cells lose their receptors during isolation or culture procedures.
Mechanisms underlying the differential sensitivity to a1‐adrenoceptor activation in the bisected rat vas deferens
Authors: Sallés Joan , Badia Albert
Published: July 2012

The factors underlying the different responsiveness of the prostatic and epididymal portions of rat vas deferens to α1‐adrenoceptor stimulation were investigated.

The α1‐adrenoceptors in membranes of both halves of rat vas deferens were labelled with [3H]‐prazosin and the affinities of agonists and antagonists for these receptors were determined. In saturation studies, the Bmax and KD values for [3H]‐prazosin in membranes of both portions were the same.

In competition studies, the inhibition curves for phentolamine were biphasic and consistent with the presence of both α1a‐ and α1b‐adrenoceptor subtypes. The proportions of binding sites with high and low affinity for phentolamine in both halves of rat vas deferens were similar and in good agreement with the percentages of binding sites for WB‐4101 and phentolamine previously reported in the whole rat vas deferens.

The phenylethylamines displaced [3H]‐prazosin with a shallow inhibition curve. The data are compatible with the assumption of two affinity states for the binding sites. For the imidazoline compounds no such distinct affinity states could be demonstrated.

The affinity for, and the relative intrinsic efficacy on postsynaptic α1‐adrenoceptors of both portions of rat vas deferens were studied for noradrenaline, phenylephrine and methoxamine by irreversible inactivation of the α1‐adrenoceptors by phenoxybenzamine. The parameters for partial agonists were determined by comparing the responses to the partial agonist to those of a full agonist in the same tissue. Homogeneous estimates of the equilibrium dissociation constants (Ka) were obtained, indicating that these agonists bind to the receptors of both tissues in an identical manner. Further, estimation of the intrinsic efficacy of agonists relative to noradrenaline, indicated no differences between the two halves of rat vas deferens.

Ka values for agonist activation of the functional α1‐adrenoceptors were compared with KI values for agonist inhibition of specific [3H]‐prazosin binding. The Ka values were well correlated with the low affinity KI values for phenylethylamines in both portions of rat vas deferens, suggesting that the initial event in signal transduction by α1‐adrenoceptors is the binding to the low affinity state of the receptor.

There was a non‐linear relationship between response and receptor occupancy in both halves of rat vas deferens but the occupancy‐response coupling was more efficient in the epididymal than in the prostatic portion. This fact may account for the differences observed in the functional responses.
Effects of captopril on membrane current and contraction in single ventricular myocytes from guinea‐pig
Authors: Bryant S.M. , Ryder Kathryn O. , Hart G.
Published: July 2012

Single guinea‐pig ventricular myocytes were voltage‐clamped and cell length was measured with a photodiode array.

Captopril (1 × 10−5 m) reduced both peak early current and active shortening in response to a depolarizing clamp pulse along a similar time course.

From a holding potential of around −45 mV peak early inward current was reduced by 37 ± 9% (P < 0.001) on exposure to captopril. The early current‐voltage relationship was shifted outwards by captopril indicating a reduction in membrane conductance through the L‐type calcium channel (ICa).

The amplitude of cell shortening in response to depolarizing voltage steps was reduced but the voltage‐dependence of contraction after captopril was unchanged.

A small negative shift of the potential at which ICa was half‐activated was observed after captopril. There was no change in the voltage‐dependence of the inactivation variable or in the time‐dependence of repriming for ICa.

The actions of captopril on ICa and developed shortening were dose‐dependent and took place in the same proportion when ICa was increased by isoprenaline.

These results are discussed in relation to the effects of captopril on ICa and contraction and to its clinical usage.
Strychnine‐induced potassium current in isolated dorsal root ganglion cells of the rat
Authors: Aibara K. , Oonuma M. , Akaike N.
Published: July 2012

Effects of strychnine (Str) on the dissociated dorsal root ganglion (DRG) cells of the rat have been investigated in whole‐cells configuration by a conventional patch‐clamp technique.

γ‐Aminobutyric acid (GABA)‐induced Cl− current (ICl) increased sigmoidally with increasing concentration. The half‐maximal response (Ka) was 3 × 10−5 m and the Hill coefficient was 1.5. Both Str and bicuculline inhibited the GABA‐induced ICl in a concentration‐dependent manner.

Str itself could elicit the current at concentrations over 10−5 m, at which concentrations the GABA response was completely suppressed. The concentration‐response curve for the Str‐induced current was bell‐shaped, and a nearly maximum response occurred at 3 × 10−4 m. A transient ‘hump’ current appeared immediately after the wash‐out of external solution containing high concentrations of Str over

× 10−4 m.

The Str‐induced outward current and a transient ‘hump’ current were augmented by the removal of extracellular K+ and were suppressed by the substitution of intracellular K+ for Cs+. But the current was not sensitive to extracellular Na+, Ca2+ and Cl−.

The reversal potential of Str‐induced current (EStr) was −75 mV, which was close to the K+ equilibrium potential (EK = −76.3 mV). The change of EStr for a ten fold change in extracellular K+ concentration was 58 mV, indicating that the membrane behaves like a K+ electrode in the presence of Str. The reversal potential of the ‘hump’ current was also close to EK.

The Str‐induced outward current was antagonized by K+ channel blockers such as Ba2+, tetraethylammonium (TEA)‐chloride, and 4‐aminopyridine (4‐AP) in a concentration‐dependent manner.

The Str‐induced K+ current was not affected by internal perfusion of bis(γ‐aminophenoxy)ethane‐N,N,N′,N‐tetraacetic acid (BAPTA), indicating that the Str response does not result in the activation of K+ conductance by the intracellular Ca2+.
Calcitonin gene‐related peptide and human epicardial coronary arteries: presence, release and vasodilator effects
Authors: Franco‐Cereceda A.
Published: July 2012

In the present study, the levels of calcitonin gene‐related peptide (CGRP)‐like immunoreactivity (‐LI) in human cardiopulmonary tissue were determined in combination with studies on CGRP‐LI release from the left anterior descending coronary artery (LAD) and functional effects of CGRP on coronary arterial tone.

The highest levels of CGRP‐LI were found in the LAD followed in declining order by the bronchus, right atrium, pulmonary artery, lung and left ventricle.

Exposure to capsaicin evoked a clear‐cut increase in CGRP‐LI outflow, suggesting release from isolated large specimen of the LAD. This release was Ca2+‐dependent and was markedly attenuated by incubation with the mitochondrial Ca2+‐inhibitor, ruthenium red. Exposure to potassium also released CGRP‐LI in a Ca2+‐dependent fashion from the LAD.

In functional experiments on human epicardial coronary arteries with an inner diameter of 0.4 to 0.8 mm, human CGRP alpha and beta relaxed the potassium‐precontracted arteries equipotently. Substance P (SP) also relaxed these precontracted arteries but the relaxation could be prevented by incubation with methylene blue, an inhibitor of endothelium derived relaxing factor (EDRF)‐mechanisms, which did not influence the effect of CGRP.

Capsaicin evoked a ruthenium red‐sensitive relaxation of the potassium‐precontracted arteries. However, ruthenium red did not affect the relaxations induced by CGRP or SP. Furthermore, the capsaicin effect was not influenced by methylene blue.

It is concluded that CGRP‐LI is present in human cardiopulmonary tissue and can be released upon exposure to high concentrations of capsaicin as well as potassium. CGRP causes relaxation of arteries independently of EDRF activation and closely resembles the vasodilator effects of capsaicin. This supports the view that the coronary vasodilatation observed upon sensory nerve activation is mediated by CGRP. Ruthenium red inhibits capsaicin‐induced CGRP‐LI release and functional effects and may thus serve as an experimental tool in evaluating the function of capsaicin‐evoked stimulation of peripheral nerve terminals.
Characterization of the palytoxin‐induced sodium conductance in frog skeletal muscle
Authors: Ecault Eudes , Sauviat Martin‐Pierre
Published: July 2012

The effects of palytoxin (PTX) on transmembrane potentials and currents of frog skeletal muscle were analyzed by intracellular microelectrode techniques and the double sucrose‐gap voltage clamp method.

PTX irreversibly depolarized the membrane. The depolarization was Na‐sensitive.

Under voltage clamp, PTX induced an inward resting current which did not inactivate, was inhibited by external Na+ removal and was a function of external Na concentration.

This resting current could be carried either by Na+, Li+, K+ or by guanidinium according to the permeability sequence K+ < Li+ < Na+ < Gua+.

The PTX‐induced current was only weakly sensitive to tetrodotoxin. It was reversibly and dose‐dependently inhibited by amiloride with a one to one stoichiometry and a KD of 0.3 mm.

Acidic pH partially inhibited the current induced by PTX which was also highly sensitive to external Cd2+ and La3+. The inhibitory sequence for divalent cations was: Mg2+ < Ca2+ = Ba2+ = Mn2+ < Cd2+; with La3+ > Cd2+.

The amplitude of the PTX‐induced Irest was markedly reduced in the absence of external Ca2+.

PTX induced a Na+ resting conductance in frog skeletal muscle. The size of the channel induced by PTX is larger than the guanidinium ion. External membrane Ca2+ might be a cofactor involved in the mode of action of PTX.
Influence of lorcainide on microsomal Na+, K+‐ATPase in guinea‐pig isolated heart preparations
Authors: Almotrefi Abdulrahman A. , Dzimiri Nduna
Published: July 2012

The effects of lorcainide on the myocardial Mg2+‐dependent, Na+ and K+‐activated adenosine triphosphatase (Na+, K+‐ATPase) were compared in guinea‐pig heart preparations with those of ouabain, a specific inhibitor of the enzyme activity.

Both ouabain and lorcainide inhibited the microsomal Na+, K+‐ATPase activity in a concentration‐dependent fashion. Their inhibitory effective ranges were 0.05–100 μm and 0.15–125 μm respectively, and the concentrations for half maximal inhibition (IC50 values) were 2.1 ± 0.3 and 33.5 ± 7.3 μm, respectively.

In a second series of experiments, the combined effects of the two drugs on the enzyme activity were studied. In these experiments, lorcainide produced a concentration‐dependent potentiation of the inhibitory effects of ouabain on Na+, K+‐ATPase activity.

The present study demonstrates that lorcainide is a potent inhibitor of myocardial Na+, K+‐ATPase.
Chemosensitive cardiopulmonary afferents and the haemodynamic response to simulated haemorrhage in conscious rabbits
Authors: Evans Roger G. , Ludbrook John
Published: July 2012

We set out to test whether the signal from the heart that initiates the decompensatory phase of acute central hypovolaemia in conscious rabbits is conveyed by chemosensitive afferents.

Haemorrhage was simulated by inflating an inferior vena caval cuff so that cardiac output fell at a constant rate of 8% of its baseline level per min. After sham or vehicle treatments the haemodynamic response had two phases. In the first, sympathoexcitatory, phase systemic vascular conductance fell in proportion to cardiac output so that mean arterial pressure fell by only 13 mmHg. When cardiac output had fallen by ∼50% a second, sympathoinhibitory, phase supervened. There was an abrupt rise of systemic vascular conductance and an abrupt fall of mean arterial pressure, to ∼40 mmHg.

The sympathoinhibitory phase was prevented by injection of the δ‐opioid antagonist ICI 174864 (100–300 nmol) or the μ‐opioid agonist H‐Tyr‐d‐Ala‐Gly‐MePhe‐NH(CH2)2OH (DAMGO) (100–300 pmol) into the fourth cerebral ventricle.

5‐HT3 receptors on myocardial or pulmonary afferents were excited by injection of ascending doses of phenylbiguanide (6.25–400 μg) into the left or right atrium respectively. Neuronal‐type nicotinic cholinoceptors in the epicardium were excited by injecting ascending doses of nicotine bitartrate (6.25–400 μg) into the pericardial sac. Each of these treatment regimens caused a reproducible, dose‐dependent, fall in mean arterial pressure. Intravenous injection of the 5‐HT3 antagonist MDL 72222 (1.0 mg kg−1) markedly attenuated the responses to phenylbiguanide. Intrapericardial injection of the neuronal‐type nicotinic cholinoceptor antagonist mecamylamine HCl (0.1 mg kg−1) abolished the effects of intrapericardial nicotine. Neither of these treatments affected the haemodynamic response to simulated haemorrhage.

Injection into the fourth ventricle of ICI 174864 (100–300 nmol) or DAMGO (100–300 pmol) had no effects on the dose‐response relationships for phenylbiguanide or nicotine.

We conclude that the cardiac afferents responsible for initiating the sympathoinhibitory phase of simulated haemorrhage in conscious rabbits do not correspond to the populations of phenylbiguanide‐sensitive cardiopulmonary afferents, nor to the population of nicotine‐sensitive epicardial afferents. We also conclude that the reflex haemodynamic responses to atrial phenylbiguanide and intrapericardial nicotine do not depend on an endogenous δ‐opioid receptor mechanism in the brainstem, and are not affected by exposure of the brainstem to exogeneous DAMGO.
Modulation by endothelium of the responses induced by endothelin‐1 and by some of its analogues in rat isolated aorta
Authors: Topouzis S. , Huggins J.P. , Pelton J.T. , Miller R.C.
Published: July 2012

The contractile effects of endothelin‐1 and various analogues were studied in rat isolated aortic rings. The potency order of the peptides studied was endothelin‐1 > sarafotoxin S6b > [Ala3,11]endothelin‐1 > [Ala1,15]endothelin‐1. [Ala1,3,11,15]endothelin‐1 was neither agonist nor antagonist.

The concentration of endothelin‐1 required to induce contractions equal to 50% of those induced by 1 μm noradrenaline was reduced from 5.8 nm when the vascular endothelium was present to 1.4 nm after it had been mechanically removed.

Contractions elicited by [Ala3,11]endothelin‐1, [Ala1,15]endothelin‐1 and sarafotoxin S6b were not modulated by the endothelium.

Endothelin‐1 increased the tissue content of guanosine 3′,5′‐cyclic monophosphate (cyclic GMP) in rat aortic segments with endothelium by about 4 fold, suggesting that it increased the release of endothelium‐derived relaxing factor. Sarafotoxin S6b did not reduce, or significantly increase, tissue cyclic GMP levels and therefore had little effect on EDRF release.

The concentration of sodium nitroprusside required to relax half‐maximally aortae denuded of endothelium was 430 nm if the aortae had been precontracted with 10 nm endothelin‐1 and 35 nm if 10 nm sarafotoxin S6b was used as the spasmogen. This indicates that differential sensitivities of the smooth muscle to cyclic GMP cannot explain differences between responses to endothelin‐1 and sarafotoxin S6b in the presence of. endothelium.

It is concluded that endothelin‐1 contractions of rat aorta are modified by the endothelium, probably by enhancing the release of endothelium‐derived relaxing factor (EDRF) and not by affecting the sensitivity of the smooth muscle to EDRF. This suggests that a stimulated release of an adequate amount of EDRF is necessary to modulate contractile responses to these peptides.
Peristalsis evoked by 5‐HT and renzapride: evidence for putative 5‐HT4 receptor activation
Authors: Craig Douglas A. , Clarke David E.
Published: July 2012

The effect of 5‐hydroxytryptamine and renzapride was studied on the peristaltic reflex elicited in vitro in the guinea‐pig ileum. Both agents evoked the reflex at subthreshold intraluminal pressures (50% of threshold) and were blocked by ICS 205–930 (3 μm), but not ondansetron (5 μm). This novel finding suggests strongly that the prokinetic action of renzapride and gut motility stimulating action of 5‐hydroxytryptamine are mediated via agonism at the putative 5‐HT4 receptor.
Coronary vasoconstriction in the conscious rabbit following intravenous infusion of l‐NG‐nitro‐arginine
Authors: Humphries R.G. , Carr R.D. , Nicol A.K. , Tomlinson W. , O'Connor S.E.
Published: July 2012

Intravenous infusion of l‐NG‐nitro‐arginine, an inhibitor of endothelial nitric oxide (NO) synthesis, produced vasoconstriction in the coronary, cerebral, renal and duodenal vascular beds of the conscious rabbit. In this study, using radiolabelled microspheres, we provide in vivo evidence for a basal NO‐dependent vasodilator tone in the coronary vascular bed.
Relationship between lipolysis and cyclic AMP generation mediated by atypical β‐adrenoceptors in rat adipocytes
Authors: Hollenga Ch. , Brouwer F. , Zaagsma J.
Published: July 2012

The nature of the β‐adrenoceptor(s) mediating adenylyl cyclase activation in rat adipocyte ghosts by (−)‐isoprenaline and the lipolytically selective β‐adrenoceptor agonist, BRL 37344, was investigated by use of the β1‐selective antagonist, CGP 20712A. The results were compared with lipolysis in adipocytes.

While in lipolysis BRL 37344 was a full and 10 times more potent agonist than (−)‐isoprenaline, in adenylyl cyclase activation similar pD2 values for both agonists were found. BRL 37344 was only a partial agonist on rat adipocyte adenylyl cyclase, with an intrinsic activity of 0.62.

With CGP 20712A small rightward shifts of the (−)‐isoprenaline concentration‐response curve (CRC) were observed at concentrations up to 10 μm, while at 100 μm and 1 mm clear rightward shifts occurred. The BRL 37344 CRC was not shifted with antagonist concentrations up to 10 μm. Only at 100 μm and 1mm CGP 20712A were rightward shifts observed.

CGP 20712A concentrations of 10 μm and 100 μm depressed the maximum of the (−)‐isoprenaline CRC to 89 and 60%, while the BRL 37344 CRCs retained the control maximum effect (62% of (−)‐isoprenaline). Only at 1 mm CGP 20712A, was the CRC of BRL 37344 depressed, while the (−)‐isoprenaline maximum was diminished further.

It was concluded that as with lipolysis, (−)‐isoprenaline acts both through typical β1‐ and atypical β3‐adrenoceptors for activation of adenylyl cyclase, while BRL 37344 acts solely through atypical β3‐adrenoceptors.

The results also demonstrate that the relationship between adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) and lipolysis is different for BRL 37344 and (−)‐isoprenaline. Although the maximum activation of adenylyl cyclase by BRL 37344 is only 62% of that by (−)‐isoprenaline, the distance between the lipolysis and adenylyl cyclase CRCs is much larger in the case of BRL 37344, indicating a larger transduction reserve for this agonist.
Differences in the K+‐channels opened by cromakalim, acetylcholine and substance P in rat aorta and porcine coronary artery
Authors: Bray Katharine , Quast Ulrich
Published: July 2012

The effects of acetylcholine and substance P on the efflux of 86Rb+ and 42K+ from rat aorta and pig coronary artery, respectively, were compared with those of the K+ channel opening agent, cromakalim.

In rat aorta preloaded with 86Rb+ and/or 42K+, acetylcholine produced transient, concentration‐dependent increases in the efflux rate coefficients of these tracers (maximum ≅ 35%). These effects were abolished by endothelial cell removal.

Donor/acceptor experiments with rat aorta suggested that at least some of the efflux of 86Rb+ seen in the presence of acetylcholine was not derived from the endothelium, but came from the smooth muscle itself.

Acetylcholine (10 μm)‐induced 86Rb+ efflux was reduced by tetraethylammonium (TEA, 10 mm) to 33% and ouabain (300 μm) to 54% of control. Preincubation with Ba2+ (100 μm) did not significantly inhibit acetylcholine‐induced efflux.

Acetylcholine‐induced 42K+/86Rb+ efflux was unaffected by preincubation with glibenclamide (10 μm). In contrast, the 42K+/86Rb+ efflux induced by cromakalim was inhibited by glibenclamide (50 nm) by 50%.

Acetylcholine (0.3–10 μm)‐induced inhibition of phenylephrine (1 μm)‐induced tone was abolished by endothelial cell removal but unaffected by glibenclamide. Cromakalim‐induced relaxations were endothelium‐independent and were inhibited by glibenclamide in a concentration‐dependent manner.

lG‐monomethyl l‐arginine (l‐NMMA, 250 μm) produced a significant (37 ± 14%) inhibition of acetylcholine‐induced 86Rb+ efflux whereas DG‐monomethyl l‐arginine was without effect. In the tissue bath l‐NMMA inhibited relaxations produced by acetylcholine (0.3–10 μm), but was without effect on responses to cromakalim.

In the pig coronary artery, substance P induced an endothelium‐dependent efflux of 86Rb+ and 42K+, which was unaffected by preincubation with glibenclamide (10 μm) or l‐NMMA (250 μm).

The present study shows that acetylcholine and substance P each open K+‐channels in arterial smooth muscle. However, the insensitivity of the stimulated 86Rb+/42K+ efflux to inhibition by glibenclamide suggests that the K+‐channel opened by these agents is different from the K+‐channel opened by cromakalim. In addition, the inability of l‐NMMA to inhibit fully the acetylcholine‐ and substance P‐stimulated 86Rb+ efflux suggests that in rat aorta and pig coronary artery the endothelium‐derived hyperpolarizing factor(s) (EDHF) is different from endothelium‐derived relaxing factor (EDRF).
Heterogeneity of thromboxane A2 (TP‐) receptors: evidence from antagonist but not agonist potency measurements
Authors: Tymkewycz Paulina M. , Jones R.L. , Wilson N.H. , Marr C.G.
Published: July 2012

Thromboxane A2 (TP‐) receptors in human, rat and rabbit platelets and in smooth muscle of guinea‐pig trachea, rat aorta and rabbit aorta have been characterized by measurement of the potencies of agonists and antagonists having considerable variations in chemical structure.

On each washed platelet system, eight prostanoids induced maximal irreversible aggregation (full agonists) and the potency ranking was EP 171 > STA2 > 9,11‐azo PGH2 > 9,11‐endoxy‐10a‐homo PGH2 > U‐46619 (standard) > PGH2 = 16‐p‐fluorophenoxy‐ω‐tetranor PGF2α > 16,16‐dimethyl PGF2α. Correlations between the three platelet preparations for both absolute and relative potencies were good. On human platelets, STA2, at concentrations above that required for maximum aggregation, exerted an inhibitory effect which was independent of its interaction with the TP‐receptor.

Five prostanoids, EP 109, EP 167, EP 204, PTA2 and 16,20‐methano PTA2, exhibited partial agonist activity on the platelet and smooth muscle preparations. There was good agreement between absolute potencies on the six preparations; on platelets potency was assessed from shape change measurements, since aggregation, when present, always showed a very shallow concentration‐response relationship. The magnitude of the maximum response induced by each compound decreased in the order listed above, to the extent that 16,20‐methano PTA2 could be treated as a pure antagonist.

With U‐46619 as agonist, the pA2 values of seven antagonists were found to be very similar on human and rat platelets. The potency ranking was EP 169 > AH 23848 > EP 092 > ONO 11120 > EP 115 = 16,20‐methano PTA2 > BM 13177. There was a similar trend on rabbit platelets but pA2 values were 1.0–1.5 log units smaller; the exception was BM 13177 which had similar affinities. The antagonism produced by EP 169 and AH 23848 was surmountable on rabbit platelets but not on human and rat platelets.

None of the antagonists was highly potent on the rabbit aorta (pA2 values < 7.5 by Schild analysis). Affinities on the guinea‐pig trachea and the rat aorta were higher and in the same range as those obtained for human and rat platelets. However the correlations of pA2 values between any pair of smooth muscle preparations and between any pair of platelet/smooth muscle preparations were either weak or not significant (P > 0.05).

The excellent agreement for both full and partial agonist potencies between the six preparations provides no evidence for TP‐receptor subtypes and further suggests that the agonist recognition sites of the TP‐receptors could be very similar, if not identical, in nature. In contrast, the different antagonist affinities found in this and other published studies indicate heterogeneity of TP‐receptors. However, classification into TP1‐, TP2‐receptors, etc. on the basis of the limited antagonist data available does not appear appropriate at this time.
Adenosine‐5′‐O‐(2‐thiodiphosphate) is a potent agonist at P2 purinoceptors mediating insulin secretion from perfused rat pancreas
Authors: Bertrand G. , Chapal J. , Puech R. , Loubatières‐Mariani M.M.
Published: July 2012

The effects of a P2 purinoceptor agonist, adenosine 5′‐O‐(2‐thiodiphosphate) (ADP‐β‐S) have been studied on insulin secretion and flow rate of the isolated perfused pancreas of the rat.

In the presence of a moderately stimulating glucose concentration (8.3 mm), ADP‐/7‐S (4.95–495 nm) evoked a biphasic insulin response in a concentration‐dependent manner. A comparison of relative potency between ADP‐β‐S and adenosine 5′‐triphosphate (ATP) showed that ADP‐β‐S was 100 times more potent than ATP. On the other hand, in the presence of a non stimulatory glucose concentration (4.2 mm), ADP‐β‐S (165 nm) did not modify the basal insulin secretion.

ADP‐β‐S, at concentrations effective on insulin secretion and also at higher concentrations (1.65 and 16.5 μm), provoked an increase of the pancreatic flow rate in a concentration‐dependent manner.

Our results show that ADP‐β‐S is a potent insulin secretory P2 purinoceptor agonist. As it is resistant to hydrolysis it might be useful in studying the effect of activation of the P2 purinoceptor of β cells on insulin secretion in vivo.
The use of 4‐diphenylacetoxy‐N‐(2‐chloroethyl)‐piperidine (4‐DAMP mustard) for estimating the apparent affinities of some agonists acting at muscarinic receptors in guinea‐pig ileum
Authors: Barlow R.B. , McMillen Louise S. , Veale M.A.
Published: July 2012

4‐Diphenylacetoxy‐N‐(2‐chloroethyl)‐piperidine (4‐DAMP mustard), which is known to block muscarinic M3 receptors in preference to muscarinic M2 receptors, was used to estimate the apparent affinity constants of some agonists acting at muscarinic receptors in guinea‐pig ileum. Estimates for carbachol and n‐pentyl‐trimethyl ammonium iodide were similar to published values obtained in similar conditions: those for n‐hexyl‐trimethyl ammonium iodide were slightly lower.

The results for the agonists, n‐pentyl‐ and n‐hexyl‐trimethyl ammonium iodides and for the partial agonist, n‐heptyl‐trimethyl ammonium iodide were not as regular as was suggested by Stephenson, though there is an overall increase in apparent affinity with chain length.

Estimates of apparent affinity may be affected by hexamethonium, usually present in experiments on ileum. Its absence had little effect on the results with carbachol but reduced the estimates obtained with n‐pentyl trimethyl ammonium, which has strong nicotinic effects compared with its muscarinic effects. On ileum treated with tetrodotoxin the values for n‐pentyl trimethyl ammonium were similar to those obtained in the presence of hexamethonium (0.28 mm): slightly higher estimates of affinity were obtained in the presence of indomethacin (2.8 μm). The nicotinic effects of n‐pentyl ammonium may involve the release of prostaglandins.

The estimates of apparent affinity did not depend on the method used to calculate them as the ‘null’ method and the ‘operational’ method give similar answers. Estimates of the transducer‐ratio for the partial agonist, n‐heptyl‐trimethyl ammonium iodide, were numerically the same as those of its efficacy.

This work illustrates the use of 4‐DAMP mustard as a tool for measuring the apparent affinity of agonists acting at muscarinic M3 receptors.
Comparison of the effects of several potassium‐channel openers on rat bladder and rat portal vein in vitro
Authors: Edwards G. , Henshaw M. , Miller M. , Weston A.H.
Published: July 2012

The ability of several K‐channel openers to inhibit KCl‐induced contractions of rat bladder detrusor and spontaneous mechanical activity in rat portal vein was examined.

Lemakalim, pinacidil, Ro 31–6930, RP 49356, P1060 and S 0121 dose‐dependently relaxed rat detrusor, precontracted with 20 mm KCl. With the exception of pinacidil, concentrations of these agents below 30 μm did not inhibit 80 mm KCl‐included contractions. Pinacidil (10 μm) produced a small, but significant (P < 0.05) relaxation of 80 mm KCl‐induced mechanical activity. Minoxidil sulphate and BRL 38226 produced some relaxation of 20 mm but not 80 mm KCl‐induced contractions.

Glibenclamide (0.3–3 μm) antagonized the relaxant effects of lemakalim, pinacidil, Ro 31–6930, RP 49356, P1060 and S 0121 in a competitive manner (pA2 values 6.3–6.6). The effects of minoxidil sulphate and BRL 38226 were fully antagonized by 3 μm glibenclamide.

Lemakalim, pinacidil, S 0121, BRL 38226 and minoxidil sulphate were each approximately 8 times more potent as inhibitors of the spontaneous contractions of rat portal vein than KCl‐induced contractions of the rat detrusor. Minoxidil sulphate was approximately 30 times more potent in the rat portal vein than in the bladder. This may indicate that either minoxidil sulphate is acting at different recognition sites in these two tissues, or that this compound has an additional mechanism of action in the portal vein.

With the exception of minoxidil sulphate, all the compounds tested stimulated 86Rb efflux and 42K efflux from preloaded rat detrusor strips. The stimulated 86Rb efflux was qualitatively but not quantitatively similar to the stimulated 42K efflux. Minoxidil sulphate stimulated 42K efflux from rat portal vein but not from rat bladder.

It is concluded that all the compounds tested cause relaxation of rat detrusor predominantly by K‐channel opening. Selectivity for bladder rather than vascular smooth muscle was not shown by any compound.
Interference of BN 52021, an antagonist of PAF, with different forms of active anaphylaxis in the guinea‐pig: importance of the booster injection
Authors: Desquand Stéphanie , Lefort Jean , Dumarey Claude , Vargaftig B. Boris
Published: July 2012

BN 52021, an antagonist of platelet activating factor (PAF), was inactive against bronchoconstriction in guinea‐pigs sensitized with low amounts of ovalbumin (OA) injected twice, at a 14 day interval and challenged i.v. 7 days later.

Serum IgG titers increased for 7 weeks after the booster injection at day 14 and returned to low levels at day 96.

Administered by the intratracheal (i.t.) route at 1 mg, BN 52021 failed to inhibit bronchoconstriction induced by the i.t. administration of OA to guinea‐pigs tested 7, 28, 56 and 84 days after the booster injection, even when the titers of circulating IgG had declined with time. BN 52021 was also inactive against bronchoconstriction in guinea‐pigs boosted at day 98 and tested 7 days later and against contractions and thromboxane (Tx) B2 and histamine release induced by OA‐challenged parenchymal lung strips from the boosted guinea‐pigs.

Sensitized unboosted guinea‐pigs displayed reduced IgG serum titers. Used 21 or 70 days after the sensitizing injection, they did develop bronchoconstriction upon the i.t. instillation of OA, which was blocked by BN 52021. The latter also inhibited OA‐induced contractions of lung parenchymal strips from these unboosted guinea‐pigs.

When boosted and non‐boosted guinea‐pigs received OA i.t. and bronchoalveolar lavage fluid was collected 10 min later, the number of eosinophils increased markedly in boosted, but not in non‐boosted guinea‐pigs.

The booster injection of antigen thus modifies the response of the lung and PAF appears to be relevant for antigen‐induced bronchoconstriction in unboosted animals, but loses its major role following the booster injection.
Effects of antagonists on quisqualate and nicotinic receptor‐mediated currents of midbrain neurones in culture
Authors: Bijak M. , Jarolimek W. , Misgeld U.
Published: July 2012

The action of non‐N‐methyl‐d‐aspartate (non‐NMDA) and nicotinic antagonists on excitatory postsynaptic currents (e.p.s.cs) and on quisqualate (Quis)‐ and nicotine‐gated currents was studied by use of whole‐cell recording in dissociated culture of the rat midbrain.

6‐Cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; 0.1 μm) and kynurenic acid (0.1 mm) attenuated network‐generated and miniature e.p.s.cs while mecamylamine (100 μm) and hexamethonium (400 μm) had no effect. Acetylcholine (ACh) enhanced or suppressed e.p.s.cs. The suppressing effect of ACh was blocked by atropine (0.1–10 μm).

ACh (50–1000 μm) and quisqualate (Quis, 0.1–20 μm) induced inward currents with the same reversal potential as e.p.s.cs.

Application of Quis and α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) in a low concentration (0.5 and 5 μm, respectively) evoked a maintained current which was attenuated by CNQX (1 μm) and kynurenic acid (0.5 mm) but not by mecamylamine (100 μm).

Higher concentrations of Quis (5–20 μm) and AMPA (50–100 μm) evoked a transient and a maintained current component. Kynurenic acid (1 mm) reduced the transient but not the maintained component. CNQX (5–10 μm) increased the maintained component without reducing the transient one; 20 μm CNQX reduced both components.

ACh‐induced transient current was mimicked by nicotine and reversibly and dose‐dependently blocked by mecamylamine. Atropine (10 μm), hexamethonium (400 μm) as well as CNQX (100 μm) and kynurenic acid (1 mm) did not affect the current.

Hexamethonium (50–400 μm) voltage‐dependently depressed the maintained current elicited by both Quis and ACh.

In conclusion, although the antagonists examined here seem to discriminate between non‐NMDA and nicotinic receptor‐mediated e.p.s.cs, they vary considerably in respect of their mode of action when tested on Quis, AMPA and ACh‐induced currents.