bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of a new and potent cholecystokinin antagonist on motor responses of the guinea‐pig intestine
Authors: Barthó Loránd , Holzer Peter , Lembeck Fred , Lippe Irmgard Th. , Setnikar Ivo
Published: July 2012

The potency and selectivity of d,l‐4‐(3,4‐dichloro‐benzoyl‐amino)‐5‐(dipentyl‐amino)‐5‐oxo‐pentanoic acid (CR 1409) as a cholecystokinin (CCK) antagonist was investigated on motor responses of the longitudinal and circular muscles of the guinea‐pig isolated ileum. CR 1409 was further used to examine whether nerve‐mediated motor responses to electrical field stimulation or distension of the gut wall may involve the release of CCK‐like peptides

CR 1409 (0.06‐2.1 μm) antagonized longitudinal muscle responses to ceruletide (caerulein, a CCK‐related decapeptide) in a concentration dependent and competitive manner (pA2 7.77); responses to CCK‐octapeptide (CCK‐8) were antagonized with a similar potency. Contractions of the circular muscle evoked by ceruletide were also blocked by CR 1409 (0.2‐0.4 μm).

Longitudinal muscle contractions in response to dimethylphenylpiperazinium, bethanechol, histamine, substance P, or 5‐hydroxytryptamine (5‐HT), and circular muscle contractions evoked by acetylcholine, 5‐HT, substance P, or substance K were not altered by CR 1409 (0.4 μm). Longitudinal muscle contractions induced by electrical field stimulation (with pulses delivered at 0.05 and 1 Hz in the absence, and at 5 Hz in the presence of atropine) were not or only slightly reduced by CR 1409 (0.4 μm). Longitudinal contractions due to activation of extrinsic nerves by capsaicin remained unaltered in the presence of CR 1409 (0.4 μm).

Reflex contractions of the circular muscle, induced by balloon distension and recorded orally to the site of distension, and peristaltic activity elicited by intraluminal infusion of Tyrode solution remained unaffected by CR 1409 (0.4 μm).

These findings indicate that CR 1409 is a potent and selective antagonist of CCK‐like peptides in the guinea‐pig ileum. The results do not provide any evidence that CCK‐like peptides, released from extrinsic or intrinsic neurones, are involved in nerve‐mediated contractions of intestinal muscle and in the peristaltic reflex.
Bicarbonate‐dependence of responses to ethylenediamine in the guinea‐pig isolated ileum: involvement of ethylenediamine‐monocarbamate
Authors: Kerr David I.B. , Ong Jennifer
Published: July 2012

γ‐Aminobutyric‐acid (GABA)‐mimetic responses were induced by ethylenediamine (EDA) in the isolated ileum of the guinea‐pig maintained in bicarbonate buffered Krebs‐Henseleit (KBC) solution, pH 7.4, 37°C, the responses consisting of a contraction followed by a relaxation. There were no such responses to EDA in bicarbonate‐free phosphate buffered (KPO) or HEPES buffered (KHO) Krebs solution, gassed with 100% O2, pH 7.4, 37°C, yet the ileum responded to GABA in bicarbonate‐free Krebs solution.

Similar GABA‐mimetic responses were induced by EDA in the isolated ileum maintained in bicarbonate‐free KPO or KHO modified Krebs solution, gassed with O2, if HCO3− (5 mm) was first added immediately before the test dose of EDA (0.1–1 mm), the threshold [HCO3−] being 2 mm for EDA‐induced responses in these preparations. However, ileal GABA‐mimetic responses were induced in bicarbonate‐free KPO or KHO solutions by EDA that had been pretreated with carbon dioxide, where the final [HCO3−] in the bath did not exceed 25 μm.

Ethylenediamine monocarbamate (synthetic EDAC) released [3H]‐GABA from preloaded segments of ileum maintained in bicarbonate‐free KPO or KHO solution containing amino‐oxyacetic acid and β‐alanine, the release being sensitive to 3‐mercaptopropionic acid which prevents GABA release. EDA itself did not evoke any such release in the absence of bicarbonate, but released [3H]‐GABA from segments maintained in KBC solution.

GABA‐mimetic responses were induced by EDAC in the isolated ileum maintained in bicarbonate‐free KPO solution, as was a δ‐aminovalerate‐sensitive depression of ileal twitch responses elicited by transmural stimulation, all of which were also sensitive to 3‐mercaptopropionic acid.

It is concluded that GABA‐mimetic responses to EDA in the isolated ileum of the guinea‐pig, maintained in normal Krebs bicarbonate medium, result from the release of endogenous GABA by ethylenediamine monocarbamate formed through the rapid reaction of EDA with the carbon dioxide of bicarbonate buffered Krebs solution. Furthermore, in the ileum, HCO3− ions per se are not necessary for this GABA‐releasing property of EDA if the latter is first converted to the monocarbamate, since synthetic ethylenediamine monocarbamate elicits ileal GABA‐mimetic responses in the total absence of bicarbonate.
Antagonism of vasoconstriction induced by platelet‐activating factor in guinea‐pig perfused hearts by selective platelet‐activating factor receptor antagonists
Authors: Piper Priscilla J. , Stewart A.G.
Published: July 2012

Platelet‐activating factor (Paf) is a potent coronary vasoconstrictor in rat, guinea‐pig, dog and pig. The present study investigated the mechanism and duration of action of Paf in guinea‐pig isolated, Krebs‐perfused hearts.

Dose‐related and sustained decreases in cardiac contractility and increases in coronary perfusion pressure were elicited by bolus doses of Paf (0.3–100 pmol).

Platelet‐activating factor (30 pmol) induced increases in the production of immunoreactive thromboxane B2 (TXB2), leukotriene B4 (LTB4) and LTC4, but not 6‐keto‐prostaglandin F1α (6‐keto‐PGF1α). In addition, the release of leukotriene‐like material following Paf was observed using on‐line superfusion bioassay.

The coronary vasoconstrictor actions of Paf were partially antagonized by the leukotriene receptor antagonist, FPL 55712 (1.9 μm), or by indomethacin (2.8 μm). The combined use of these compounds did not result in further significant inhibition.

The Paf receptor antagonists, BN 52021 (30 μm) and L 652, 731 (10 μm), antagonized both the increase in coronary perfusion pressure and the decrease in cardiac contractility induced by Paf (10–100 pmol) in a surmountable and relatively selective manner.

The effects of a bolus dose of 100 pmol Paf were sustained in excess of 18 min. Exogenous Paf underwent little metabolism on passing through the coronary circulation with only 2% being converted to lyso‐Paf and approximately 4% being retained by the heart after 18 min of perfusion.

These results suggest that the coronary vasoconstrictor actions of Paf are partially dependent on the release of vasoactive arachidonic acid metabolites. The extraordinary potency and the long‐lasting action of Paf indicate a potential role for this pro‐inflammatory mediator in disorders of the coronary circulation.
Endothelium‐dependent relaxation in coronary arteries requires magnesium ions
Authors: Altura Bella T. , Altura Burton M.
Published: July 2012

A great deal of interest has recently focused upon the mechanism(s) associated with the generation and action of endothelium‐derived relaxant factors (EDRFs) in blood vessels. Since we have shown that extracellular magnesium ions ([Mg2+]o) are important in control of coronary vascular tone and reactivity, we wondered whether these divalent cations play any role in the generation or action of EDRF in coronary arterial smooth muscle. Using isolated canine coronary arterial rings, we have now found that removal of [Mg2+]o inhibits the ability of these vascular preparations to relax when challenged with acetylcholine; in the absence of [Mg2+]o, the relaxation concentration‐response curves for acetylcholine are shifted markedly to higher concentrations with small maxima. It, thus, appears that [Mg2+]o is an important co‐factor for acetylcholine‐induced endothelium‐dependent relaxation in canine coronary arteries. These findings support our previous hypothesis that dietary deficiency of Mg may be an important factor in aetiology of coronary vasopasm.
Inhibition of Uptake1 by dopexamine hydrochloride in vitro)
Authors: Mitchell Paul D. , Smith George W. , Wells Edward , West Philip A.
Published: July 2012

Dopexamine hydrochloride, a compound under evaluation for the acute treatment of heart failure, was examined in vitro for its ability to prevent neuronal uptake of noradrenaline.

Despite possessing only weak β1‐adrenoceptor agonist activity in paced guinea‐pig left atria, dopexamine hydrochloride was only 23 times less potent than isoprenaline in augmenting responses of field‐stimulated atrial preparations.

This potent effect was not observed in field‐stimulated atria depleted of noradrenaline by reserpine and in the presence of cocaine was greatly reduced (1 μm) or abolished (50 μm).

Dopexamine hydrochloride (3 μm) potentiated the inotropic effect of exogenous noradrenaline in paced atria, thereby resembling cocaine (10 μm) and dopamine (30 μm), both of which are known inhibitors of Uptake1.

The sodium‐dependent uptake of [3H]‐noradrenaline into rabbit brain synaptosomes was prevented by dopexamine hydrochloride (IC50 26 nm) and cocaine (IC50 108 nm), as well as by two other catecholamines used in the treatment of heart failure, dopamine (IC50 270 nm) and dobutamine (IC50 380 nm).

The cardiac stimulant effect of dopexamine hydrochloride reported in dogs and in patients with heart failure, may therefore be due in part to potentiation of endogenous catecholamines.
External ATP mimics carbachol in initiating calcium mobilization from pancreatic β‐cells conditioned by previous exposure to glucose
Authors: Gylfe Erik , Hellman Bo
Published: July 2012

Exposure to ATP (2–200 μm) resulted in a prominent peak of 45Ca efflux, when β‐cell‐rich pancreatic islets from ob/ob‐mice were perifused with a Ca2+‐deficient medium. ADP and the stable α/β‐methylene analogues of ATP and ADP also had stimulatory effects.

The nucleotide initiation of 45Ca efflux mimicked that obtained with carbachol both in requiring previous exposure to glucose and in being more pronounced after replacing extracellular Na+ by K+.

It was possible to induce repeated peaks of stimulated 45Ca efflux, when the exposure to ATP was interrupted with intervals of perifusion with glucose‐containing media.

The observations are consistent with the existence of P2‐purinoceptors in islets, suggesting that these receptors mediate a similar mobilization of calcium as noted when activating polyphosphoinositide breakdown with carbachol. In view of the high contents of ATP and ADP in the β‐cell secretory granules, activation of P2‐purinoceptors should be considered as a possible mechanism for amplification of the initial insulin secretory response.
Effect of bradykinin antagonists on bradykinin‐induced plasma extravasation, venoconstriction, prostaglandin E2 release, nociceptor stimulation and contraction of the iris sphincter muscle in the rabbit
Authors: Griesbacher Thomas , Lembeck Fred
Published: July 2012

The inhibition of the bradykinin‐induced plasma extravasation by six bradykinin (Bk) antagonists was tested on rabbit skin. All of them showed inhibitory effects without an agonistic action in the doses used. B4310 (Lys‐Lys‐3‐Hyp‐5,8‐Thi‐7‐DPhe‐Bk) was the most active antagonist and was therefore used in the subsequent experiments.

B4310 (5–500 nm) antagonized the bradykinin‐induced reduction of the venous outflow from the rabbit isolated ear in a dose‐dependent manner without affecting the arterial vasoconstriction induced by angiotensin II.

The bradykinin‐induced release of prostaglandin E2 (PGE2) from the perfused rabbit ear was reduced by 63% when B4310 (800 nm) was infused before, during and after the bradykinin injection.

Bradykinin was injected into the ear artery of anaesthetized rabbits and the reflex hypotensive response was used as indicator of the nociception. The response was antagonized by a local infusion of B4310 (50 and 500 nm). The antagonism was dose‐dependent and reversible. The parallel shift of the dose‐response curve to bradykinin suggests a competitive inhibition. However, B4310 did not antagonize acetylcholine‐induced nociceptor stimulation.

B4310 inhibited bradykinin‐induced stimulation of the trigeminal nerve which results in a substance P‐mediated contraction of the iris sphincter muscle. A pA2 of 7.59 was calculated. B4310 did not inhibit capsaicin‐induced contractions.

It is concluded that B4310 inhibits specifically five different actions of bradykinin which are related to its possible pathophysiological role.
Membrane mechanism associated with muscarinic receptor activation in single cells freshly dispersed from the rat anococcygeus muscle
Authors: Byrne N.G. , Large W.A.
Published: July 2012

The mechanism of action of carbachol was studied on freshly dispersed cells of the rat anococcygeus using microelectrodes and patch pipettes.

Micro‐ionophoretic application of carbachol evoked reproducible depolarizations which were reduced or blocked by atropine (10−7‐10−6 m). The time courses of the responses to noradrenaline and carbachol were similar.

The reversal potential of the carbachol‐induced response was −3.8 mV and similar to the value (‐6.2 mV) found for noradrenaline.

During the response to carbachol the membrane conductance was increased. At depolarized membrane potentials carbachol evoked biphasic membrane responses suggesting an increase in two separate ionic conductances.

With patch pipettes in the whole‐cell configuration under voltage‐clamp, carbachol produced an inward current at a holding potential of −50 mV. The inward current was associated with an increase in membrane conductance with an equilibrium potential of about 0 mV.

It is suggested that muscarinic receptors and adrenoceptors in the rat anococcygeus may activate similar membrane conductances. The most prominent mechanism is an increase in chloride ion conductance.
Platelet‐leukocyte interaction: activation of rabbit platelets by FMLP‐stimulated neutrophils
Authors: Coëffier Eliane , Joseph Danielle , Prévost Marie‐Christine , Vargaftig B. Boris
Published: July 2012

The effect of the chemotactic peptide, N‐fonnyl‐l‐methionyl‐l‐leucyl‐l‐phenylalanine (FMLP) was studied on cells in whole rabbit blood or on a mixture of purified rabbit platelets and neutrophils.

In blood, FMLP triggered cell aggregation (measured by electrical impedance) which was dependent upon the concentration of FMLP (9.9 ± 0.7 and 5.2 ± 1.2 ohms at 1 and 0.01 μm FMLP respectively). This aggregation was accompanied by a strong decrease in platelet counts (54.6 ± 6.0 and 45.6 ± 3.8% for 1 and 0.01 μm FMLP respectively) and by a smaller decrease in neutrophil counts (25.0 ± 1.9 and 12.9 ± 1.7% at 1 and 0.01 μm FMLP respectively).

When purified platelets and neutrophils were co‐incubated, the addition of 0.1 μm induced a marked aggregation (50.0 ±1.6 vs. 19.5 ±1.6% of light transmission, n = 8, P < 0.001), ATP secretion (8.4 ± 1.0 vs. 0.1 ± 0.1 nmol ml−1, n = 6, P < 0.001) and a decrease in platelet counts. FMLP induced aggregation of purified neutrophils and release of lysozyme but lacked direct platelet‐stimulating effects. The release of lactate dehydrogenase, a cytoplasmic marker and lysozyme were unchanged under the interaction conditions.

Platelet activation was reduced by about 30% with 100 μm aspirin or indomethacin and by about 70% with 100 μm BW 755C. Two Paf‐acether antagonists, BN 52021 (100 μm) and WEB 2086 (1 μm) suppressed platelet activation by 70–80%.

The supernatant of FMLP‐stimulated neutrophils induced platelet activation only when bovine serum albumin was present. Rabbit neutrophils stimulated in the presence of serum albumin by 1 μm FMLP formed 2 nm Paf‐acether of which half was released to the extracellular medium.

Our results indicate that the stimulation of neutrophils by FMLP induces platelet activation in whole blood and on isolated cells and that both arachidonic acid‐metabolites and Paf‐acether participate in platelet activation.
Effects of ouabain on isolated cerebral and femoral arteries of the cat: a functional and biochemical study
Authors: Marín Jesús , Sánchez‐Ferrer Carlos F. , Salaices Mercedes
Published: July 2012

This study analyzes the mechanisms involved in the responses to ouabain in cat cerebral and femoral arteries and characterizes the electrogenic Na+ pump present in these vessels. The latter was accomplished by measurement of [3H]‐ouabain binding to arterial membrane fractions, K+‐elicited relaxation and ouabain‐sensitive 86Rb+ uptake.

Ouabain induced transient contraction in cylindrical segments of cerebral arteries. This contraction was reduced by verapamil (3 × 10−6 m) and Ca2+‐removal from the medium but was not modified by phentolamine (3 × 10−6 m) or pretreatment with reserpine. However, the contraction elicited by ouabain in femoral artery segments lasted longer, and was reduced by Ca2+‐omission, phentolamine or reserpine, but remained unaffected by verapamil.

The immersion of the arteries in low‐Na+ (25 mm) medium abolished the contraction caused by ouabain.

The exposure of the arteries to a K+‐free medium induced a small transient increase in tension, and the subsequent application of K+ (7.5 mm) elicited a marked relaxation. This effect was greater in cerebral than in peripheral arteries, and was suppressed by ouabain (10−4 m).

Scatchard analysis of the [3H]‐ouabain binding to arterial membrane fractions suggested a single class of binding sites. The KD values for both kinds of arteries were of similar order, while the Bmax value was greater in cerebral than in femoral arteries.

Total and ouabain‐sensitive 86Rb+ uptakes were greater in cerebral than in femoral vessels.

These results indicate that: (1) ouabain‐induced contraction of cerebral arteries is due to a direct effect on vascular smooth muscle cells, while in femoral arteries it is due to noradrenaline release from adrenergic nerve terminals; and (2) the electrogenic Na+ pump activity is greater in cerebral than in peripheral arteries.
Actions of vanadate on vascular tension and sodium pump activity in cat isolated cerebral and femoral arteries
Authors: Sánchez‐Ferrer Carlos F. , Marín Jesús , Lluch Magdalena , Valverde Angel , Salaices Mercedes
Published: July 2012

The mechanisms involved in the responses induced by sodium vanadate (Va3 VO4) on cat cerebral and femoral arteries were studied. The possibility that these responses were due to Na+, K+‐ATPase inhibition was investigated by measuring the effect of vanadate on [3H]‐ouabain binding to arterial membrane fractions, K+‐induced vasodilatation and ouabain‐sensitive 86Rb+ uptake.

The vanadium compounds (Na3VO4, VOSO4, VCl3 and O5V3) induced similar, concentration‐dependent contractions in each kind of artery, the cerebral vessels being the most sensitive to these compounds.

Exposure of the arteries to a low‐Na+ (25 mm) solution suppressed the contraction caused by vanadate in femoral but not in cerebral arteries.

Vanadate‐induced contractions were reduced in Ca2+‐free medium but remained unaffected by 3 × 10−6 m phentolamine, reserpine pretreatment or 3 × 10−6 m verapamil in both kinds of artery.

The addition of 7.5 mm K+ to the arteries immersed in a K+‐free solution induced vasodilatation, which was not modified by 10−3 m vanadate.

The consecutive administration of ouabain (10−4 m) and vanadate (10−3 m) (or vice versa), or the simultaneous administration of both agents (10−8 to 10−3 m) appeared to produce an additive contraction in both types of artery.

Vanadate (10−7 to 10−3 m) did not displace the [3H]‐ouabain binding to arterial membrane fractions of these arteries, whereas 10−4 m ouabain did.

In both kinds of artery, total 86Rb+ uptake was reduced by ouabain (10−8 to 10−3 m), in a concentration‐dependent manner, whereas it was not modified by vanadate (10−8‐10−3 m).

These results suggest that vanadate induces contraction in both types of artery by a mechanism unrelated to Na+, K+‐ATPase inhibition. Such a mechanism is likely to be related to inhibition of the Ca2+‐ATPase of the cell membrane and/or the sarcoplasmic reticulum.
The NK‐3 tachykinin receptor agonist senktide elicits 5‐HT‐mediated behaviour following central or peripheral administration in mice and rats
Authors: Stoessl A.J. , Dourish983 C.T. , Iversen S.D.
Published: July 2012

The behavioural effects of the selective NK‐3 tachykinin receptor agonist senktide were studied following intracisternal and subcutaneous administration in rodents. Behavioural manifestations of 5‐hydroxytryptaminergic stimulation, including head twitches (mice), wet dog shakes (rats), forepaw treading, flat body posture, hind‐limb splaying and Straub tail, were seen following the intracisternal (0.01–1.2 nmol) or subcutaneous (0.1–2.4 μmol kg−1) administration of senktide in both species. We conclude that stimulation of NK‐3 receptors stimulates 5‐hydroxytryptaminergic pathways in rodent brain, and that senktide may cross the blood‐brain barrier in biologically significant amounts.
Simultaneous release by bradykinin of substance P‐and calcitonin gene‐related peptide immunoreactivities from capsaicin‐sensitive structures in guinea‐pig heart
Authors: Geppetti Pierangelo , Maggi Carlo Alberto , Perretti Francesca , Frilli Stefania , Manzini Stefano
Published: July 2012

Both bradykinin and capsaicin infusion evoked a marked increase in the outflow of substance P‐ (SP‐LI) and calcitonin gene‐related peptide‐like immunoreactivity (CGRP‐LI) from guinea‐pig isolated, perfused heart. After acute exposure to capsaicin in vitro, or in hearts taken from animals pretreated in vivo with capsaicin, bradykinin failed to induce any release. The positive chronotropic effect of bradykinin was reduced after acute capsaicin administration. The effect of bradykinin in the guinea‐pig heart could be mediated, at least partly, by release of neuropeptides from peripheral endings of capsaicin‐sensitive sensory neurones.
Comparison of mucus flow rate, radiolabelled glycoprotein output and smooth muscle contraction in the ferret trachea in vitro
Authors: Kyle Helen , Widdicombe J.G. , Wilffert B.
Published: July 2012

The concentration‐response curves for rate of mucus output, labelled‐glycoprotein output and smooth muscle contraction in response to methacholine, phenylephrine and salbutamol were determined in the ferret trachea in vitro.

The potencies of methacholine and phenylephrine are both in order: smooth muscle contraction, glycoprotein output, rate of mucus output.

At lower concentrations methacholine is more potent than is phenylephrine on smooth muscle contraction, glycoprotein output and rate of mucus output.

Concentration‐response curves for salbutamol show very little change in rate of mucus output but a large increase in glycoprotein output.

It is concluded that the glycoprotein output induced by salbutamol may come from a source different from those induced by methacholine and phenylephrine.
Role of α1‐ and α2‐adrenoceptors in catecholamine‐induced hyperglycaemia, lipolysis and insulin secretion in conscious fasted rabbits
Authors: Moratinos J. , Carpene C. , de Pablos I. , Reverte M.
Published: July 2012

In conscious fasted rabbits an intravenous infusion of clonidine (2 μg kg−1 min−1) induced hyperglycaemia. The increase in blood glucose was accompanied by an inhibition of insulin secretion and basal lipolysis.

Yohimbine infused at a rate of 20 μg kg−1 min−1 suppressed clonidine‐induced hyperglycaemia and blocked the inhibitory effect on insulin secretion mediated by the α2‐adrenoceptor agonist.

The intravenous infusion of amidephrine (10 μg kg−1 min−1) induced an increase in insulin secretion in the absence of patent hyperglycaemia. Prazosin, 0.3 mg kg−1 s.c. selectively antagonized the effect of amidephrine on insulin secretion.

Isoprenaline infusion (4.4 μg kg−1 min−1) evoked a significant increase in blood glycerol and immunoreactive insulin plasma levels. Both responses were clearly attenuated when α2‐adrenoceptors were simultaneously stimulated by selective (clonidine) and less selective (phenylephrine, 20 μg kg−1 min−1) agonists.

Amidephrine infusion did not induce appreciable changes in blood glycerol nor did it modify, isoprenaline‐induced lipolytic response.

Simultaneous infusion of isoprenaline and amidephrine induced a remarkable increase in insulin secretion.

It is concluded that in normal fasted rabbits stimulation of α2‐adrenoceptors depresses basal and β‐adrenoceptor mediated lipolysis and insulin secretion. On the other hand, selective stimulation of α1‐adrenoceptors does not affect lipolysis but induces insulin release. Simultaneous stimulation of α1‐ and β‐adrenoceptors potentiates the insulin secretory response.
Impairment of endothelium‐dependent relaxation: an early marker for atherosclerosis in the rabbit
Authors: Jayakody Laal , Kappagoda Tissa , Senaratne Manohara P.J. , Thomson Alan B.R.
Published: July 2012

Cholesterol feeding of rabbits impairs the endothelium‐dependent relaxation (EDR) evoked by acetylcholine (ACh) in the aorta. The experiments described in this paper were undertaken to examine the influence of age upon this phenomenon.

Rabbits aged 8 weeks and 46 weeks were fed a diet containing 2% cholesterol and other lipids for 4 weeks. Age‐matched control animals were fed a standard rabbit diet. The concentrations of cholesterol and triglycerides in plasma were measured and the extent of atherosclerosis was estimated by staining the aortae with Sudan Red. Light and electron microscopy were undertaken also.

Rings of aorta were prepared for recording isometric tension. They were contracted with noradrenaline (NA) and EDR elicited by adding ACh.

The young rabbits showed weight gain, hypercholesterolaemia, prominent Sudan Red staining, together with scanning and transmission electron microscopic (SEM and TEM) features of cholesterol‐induced atherosclerosis. The older animals showed significant weight loss and hypercholesterolaemia. The aortae of these animals showed no significant sudanophilia or light microscopic features of atherosclerosis. The SEM appearances were similar to the young animals fed cholesterol.

EDR to ACh was significantly impaired in both groups of cholesterol‐fed rabbits. The maximal relaxations to ACh in young control and cholesterol‐fed rabbits were 46.4 ± 2.9% and 24.0 ± 4.3% (mean ± s.e. mean, n = 8, P < 0.05) of the contractile response to NA (1 μmol 1‐1). The corresponding results in the age control and cholesterol‐fed rabbits were 31.8 ± 3.9% and 9.1 ± 1.5% (n = 9, P < 0.05).

The young rabbits were far more susceptible to cholesterol‐induced atherosclerosis than older animals and these changes were accompanied by loss of EDR. In the older animals the loss of the latter property was not accompanied by a significant degree of atherosclerosis although hypercholesterolaemia was present.
PA2 values for antagonists of platelet activating factor on aggregation of rabbit platelets
Authors: O'Donnell Stella R. , Barnett Christopher J.K.
Published: July 2012

The relative potencies, and equilibrium dissociation constants, for nine antagonists of platelet activating factor (Paf) have been determined on rabbit platelets (in diluted platelet‐rich plasma (PRP)) in experiments in which the aggregatory response to Paf was measured.

Log concentration‐response (% maximum) curves to Paf were obtained in the absence (controls) and presence of different concentrations of each Paf antagonist drug. The antagonists shifted the Paf curves to a higher concentration range and the slopes of the Schild plots, constructed from these data, suggested that the drugs were competitive antagonists of Paf. The slopes of the Schild plots for CV‐3988 and SRI 63–119 were > 1.

The pA2 values (pKB values in parentheses) were: WEB 2086 7.31 (7.63); SRI 63–119 6.95; L‐652,731 6.71 (6.73); BN 52021 6.38 (6.47); SRI 63–072 6.36 (6.43); CV‐3988 5.87; 48740 RP 4.97 (5.07); ketotifen 4.94 (4.95); thiazinamium 4.73 (4.76).

This study provides, for the first time, some functional response data for Paf antagonists (pKB values) which are in an appropriate form for use in classifying putative Paf receptors. The study also provides the comparative potencies of these Paf antagonists in inhibiting Paf‐induced platelet aggregation. WEB 2086 was the most potent of the drugs examined.
Vagal mechanisms and the effect of indomethacin on bronchoconstrictor stimuli in the guinea‐pig
Authors: Mitchell H.W. , Adcock J.
Published: July 2012

In urethane‐anaesthetized guinea‐pigs, under spontaneous respiration, indomethacin (1 mg kg−1 i.v., 10–45 min) approximately doubled the bronchoconstrictor effect (increase in airways resistance, Raw) of equieffective doses of histamine and 5‐hydroxytryptamine (5‐HT), but not that of acetylcholine or leukotriene D4 (LTD4).

In mechanically ventilated guinea‐pigs indomethacin increased Raw responses to histamine as well as increasing the fall in dynamic compliance (Cdyn) evoked by this agent.

Cooling the cervical vagi, to temperatures shown to block efferent and probably afferent pathways (∼9°C), abolished the effect of indomethacin on airways responses. Inhibition of indomethacin‐induced hyperreactivity was also observed after vagal section.

Electrical stimulation of the peripheral vagus (1–20 Hz, 0.75–5 ms pulses) increased Raw and decreased Cdyn but these responses were not markedly altered by indomethacin.

It was concluded that the indomethacin‐induced hyperreactivity of tracheal smooth muscle, which was demonstrated in vitro, may not account for the airways hyperreactivity observed in the present in vivo experiments. The hyperreactivity to histamine induced by indomethacin in vivo depends on the functional integrity of vagal reflex pathways.
Selective inhibition of arachidonate 5‐lipoxygenase by novel acetohydroxamic acids: biochemical assessment in vitro and ex vivo
Authors: Tateson J.E. , Randall R.W. , Reynolds C.H. , Jackson W.P. , Bhattacherjee P. , Salmon J.A. , Garland L.G.
Published: July 2012

The chemically novel acetohydroxamic acids, BW A4C, BW A137C and BW A797C, are potent inhibitors of the synthesis of leukotriene B4 (LTB4) from arachidonic acid by human leucocyte homogenates: the concentrations required for 50% inhibition (IC50) were 0.1 μm, 0.8 μm and 0.5μm respectively. Inhibition was less at higher concentrations of arachidonic add.

These compounds also inhibited the synthesis of [14C]‐5‐HETE from [14C]‐arachidonic acid and the calcium‐dependent synthesis of LTB4 from 5‐HPETE. This, therefore, suggests that they inhibit 5‐lipoxygenase and LTA4 synthase.

Concentrations of acetohydroxamic acids required to inhibit metabolism of arachidonic acid by cyclo‐oxygenase, 12‐lipoxygenase and 15‐lipoxygenase were 10 to 100 times higher than those required to inhibit 5‐lipoxygenase.

The compounds were potent inhibitors of LTB4 synthesis induced by the ionophore, A23187, in human intact leucocytes. This inhibition was reversed by washing the cells. They were also potent, selective inhibitors of LTB4 synthesis induced by A23187 in whole rat blood: binding to rat plasma proteins did not greatly reduce the effectiveness of the compounds.

The effects of the acetohydroxamic acids, administered either intravenously or orally to rats, on the synthesis of LTB4, and thromboxane B2 (TXB2) in A23187‐stimulated blood ex vivo was studied. The three compounds caused dose‐dependent inhibition of the synthesis of LTB4 but not TXB2. Inhibition of LTB4 synthesis persisted for up to 6 h after a single oral dose of 50 mg kg−1.

The plasma concentrations of unchanged compound determined by h.p.l.c. correlated with the inhibition of LTB4 synthesis ex vivo.
Selective inhibition of arachidonate 5‐lipoxygenase by novel acetohydroxamic acids: effects on acute inflammatory responses
Authors: Higgs G.A. , Follenfant R.L. , Garland L.G.
Published: July 2012

Two selective inhibitors of arachidonate 5‐lipoxygenase, BW A4C and BW A797C, have been studied for their effects on acute inflammatory responses following oral administration to rats and mice.

The concentrations of the lipoxygenase product leukotriene B4 (LTB4) in 6h inflammatory exudates, induced in rats by the subcutaneous implantation of carrageenin‐soaked polyester sponges, were reduced dose‐dependently by BW A4C (ED50 = 2.6 mg kg−1) or BW A797C (ED50 = 14.3 mg kg−1).

BW A4C and BW A797C had little or no effect on prostaglandin E2 (PGE2) concentrations in inflammatory exudates (ED50S > 100 mg kg−1).

Doses of up to 200 mg kg−1 of either BW A4C or BW A797C had no effect on carrageenin‐induced oedema in rat paws.

BW A4C and BW A797C had little or no effect on carrageenin‐induced hyperalgesia in rats or phenyl‐benzoquinone‐induced writhing in mice.

Yeast‐induced pyrexia in rats was reduced by both BW A4C (ED50 = 32 mg kg−1) and BW A797C (ED50 = 23 mg kg−1).

The accumulation of leucocytes in sponge exudates was reduced dose‐dependently by BW A4C (ED50 = 54 mg kg−1) and BW A797C (ED50 = 16.7 mg kg−1).

The selective lipoxygenase inhibitors BW A4C and BW A797C do not suppress inflammatory oedema or pain although they are anti‐pyretic and they do inhibit leucocyte migration. There is not, however, a close agreement between these in vivo activities and their potencies as lipoxygenase inhibitors.
Pharmacological characterization of muscarinic receptors involved in McN‐A‐343‐induced effects on intestinal motility and heart rate in conscious dogs
Authors: Schiavone A. , Sagrada A. , Micheletti R. , Giachetti A.
Published: July 2012

Intravenous injection of the muscarinic agonist, McN‐A‐343, in conscious dogs equipped with an ileal Thiry fistula produced a dose‐related inhibition of intestinal phasic contractile activity, and an increase in heart rate.

The inhibitory action of McN‐A‐343 on motility was antagonized with different potencies by antimuscarinic drugs. The non‐selective drug, N‐methylatropine, blocked the McN‐A‐343 effect as well as the reflex phasic activity. The M1‐selective compound, pirenzepine (1–30 μg kg−1), was a potent antagonist of the McN‐A‐343 effect, whereas the cardioselective M2‐antagonist, AF‐DX 116, and the smooth muscle selective compound, 4‐diphenylacetoxy‐N‐methyl piperidine (4‐DAMP), were completely ineffective at the doses tested.

The McN‐A‐343‐induced inhibition of intestinal motility was blocked by locally applied lignocaine, suggesting the involvement of a neural inhibitory pathway. The resistance to hexamethonium and (α1‐, α2‐ β−) adrenoceptor blocking drugs excluded transmission through a nicotinic synapse or release of catecholamines.

McN‐A‐343‐induced tachycardia was also the result of muscarinic receptor activation. It was very sensitive to antagonism by 4‐DAMP, while being completely unaffected by AF‐DX 116. Pirenzepine displayed an intermediate profile, reducing tachycardia at doses fully active in reversing the agonist‐mediated effect on intestinal motility. Propranolol partially reduced McN‐A‐343 tachycardia, suggesting catecholamine release.

The two McN‐A‐343 effects investigated in the present study appear to be mediated by different muscarinic receptor subtypes. While the inhibitory action on intestinal motility results from stimulation of M1‐muscarinic receptors, the tachycardia is mediated by receptors blocked selectively by 4‐DAMP.
Effect of atenolol and pindolol on the phorbol ester‐induced coronary vasoconstriction in the isolated perfused heart of the rat
Authors: Ruskoaho Heikki
Published: July 2012

The effects of atenolol (β1‐adrenoceptor antagonist without partial agonistic activity) and pindolol (β1 and β2‐antagonist with partial agonistic activity) were studied on basal coronary vascular tone and on the phorbol ester‐induced coronary vasoconstriction in the rat perfused heart.

The addition of the phorbol ester 12‐0‐tetradecanoyl‐phorbol‐13‐acetate (TPA; 1.8 × 10−8‐1.6 × 10−7 m) into the perfusion fluid during perfusion of rat heart at constant flow caused a dose‐dependent, sustained increase in perfusion pressure. The vasoconstrictor response in hearts of reserpine‐treated rats to infusion of TPA was similar to that of non‐reserpine treated hearts.

Infusion of a calcium channel agonist Bay K 8644 at a concentration of 4 × 10−7m enhanced, whereas isoprenaline (1 × 10−5m), dibuturyl‐cyclic AMP (1.6 × 10−4m) and forskolin (1 × 10−6m), which elevate intracellular concentrations of cyclic AMP, all inhibited the coronary vasoconstriction induced by TPA.

Pindolol, in doses which produced comparable inhibition of isoprenaline‐induced tachycardia, dose‐dependently attenuated the phorbol ester‐induced increase in perfusion pressure, whereas atenolol had no effect. The inhibitory action of pindolol (2 × 10−5m) on TPA‐induced vasoconstriction was blocked by addition of 2.2 × 10−5 propranolol into the perfusion fluid. When infused alone, atenolol (2 × 10−4 m) significantly increased coronary vascular tone, but pindolol had no effect.

The present results indicate that pindolol has coronary vasodilator properties due to stimulation of vascular β‐adrenoceptors. If stenosis dilatation of coronary artery spasm is an important component of the anti‐anginal effect of β‐blocking drugs, the possession of partial agonistic property by a β‐blocking drug may be of importance in maintaining coronary flow.
Effect of adenosine on the formation of prostacyclin in the rabbit isolated heart
Authors: Karwatowska‐Prokopczuk Ewa , Ciabattoni Giovanni , Wennmalm Åke
Published: July 2012

The effect of adenosine on cardiac biosynthesis of prostacyclin (PGI2) was investigated. Rabbit hearts were perfused according to Langendorff at controlled pressure (with or without theophylline), or at controlled flow. The content of 6‐keto‐prostaglandinlflt (6‐keto‐PGF1α, metabolite of PGI2) in the coronary effluent under basal conditions and during infusion of adenosine was determined using a highly specific radioimmunoassay.

In other experiments, rings of rabbit aorta were incubated with or without adenosine and the production of 6‐keto‐PGF1α was analysed as above.

Administration of adenosine (10 μm) to hearts perfused at controlled pressure increased the coronary flow by up to 38%. The peak concentration of 6‐keto‐PGF1α in the effluent exceeded the control by 177% (P < 0.01), and the total efflux of 6‐keto‐PGF1α exceeded the control by 179% (P < 0.001). Theophylline (50 μm) reduced these effects of adenosine by 23%, 43% and 51%, respectively, without influencing the uptake of adenosine into the heart.

When adenosine (1–10 μm) was administered to hearts perfused at controlled flow, a dose‐dependent decrease in the perfusion pressure, by 27% and 44% respectively, was observed. In parallel, the resulting increase in 6‐keto‐PGF1α efflux was considerably lower (49% (P < 0.05) and 43% (NS), respectively). A similar decrease in perfusion pressure induced in the absence of adenosine decreased the efflux of 6‐keto‐PGF1α, by 15% (P < 0.01) and 32% (P < 0.001), respectively.

Addition of adenosine (1–10 μm) to incubates of rabbit aortic rings did not significantly affect the concentration of 6‐keto‐PGF1α in the incubation medium in comparison with control.

We conclude that adenosine stimulates rabbit heart PGI2 formation, mainly by an action related to the vasodilator effect of the nucleoside.
Adenosine 3′,5′‐cyclic monophosphate‐mediated enhancement of calcium‐evoked prolactin release from electrically permeabilised 7315c tumour cells
Authors: Guild Simon , Frey Elisabeth A. , Pocotte Susan L. , Kebabian John W.
Published: July 2012

The 7315c tumour cell was used as a model system for the investigation of adenosine 3′,5′‐cyclic monophosphate (cyclic AMP)‐mediated enhancement of calcium‐evoked prolactin release.

7315c cells were permeabilised by subjecting the cells to intense electric fields. Studies investigating the penetration of the dye ethidium bromide indicated that the cells were completely permeabilised after 2 discharges of 2000 volts and that the pores remained open for at least 30 min before beginning to reseal. These permeabilisation parameters were consistent with those which gave maximal calcium‐stimulated prolactin release.

In the absence of calcium and in the presence of EGTA (1 mm), permeabilised 7315c cells secreted prolactin at a rate of 0.23 ng min−1 per 106 cells. When EGTA was replaced by 1.5 mM calcium, permeabilised cells secreted prolactin at a rate of 2.20 ± 0.30 ng min−1 per 106 cells in the first 5 min of exposure. Maximal calcium‐dependent prolactin secretion from permeabilised cells occurred at 37°C.

The amount of prolactin secreted, in a 5 min incubation at 37°C, from permeabilised cells depended upon the free calcium concentration in the permeabilisation medium. Calcium stimulated prolactin release from permeabilised cells in the concentration range 0.1–10 μm (half maximal = 5.8 μm). When permeabilised cells were exposed to cyclic AMP (100 μm) for 5 min prior to and during a 5 min challenge with various concentrations of calcium, the amount of prolactin secreted at each effective concentration of calcium was increased. However, cyclic AMP did not alter the potency of calcium as a stimulant of prolactin secretion.

The results suggest that cyclic AMP potentiates calcium‐evoked secretion from 7315c cells, not by increasing the entry of calcium into the cytosol, but at a step in the secretory process, distal to calcium entry, which modulates the ability of an increase in cytosolic calcium concentration to stimulate prolactin release.
Age and the antihypertensive effect of aspirin in rats
Authors: Tuttle Richard S. , Yager Janice , Northrup Nicole
Published: July 2012

We previously showed that chronic exposure to aspirin (100 mg kg−1 daily, by mouth) is effective in preventing the onset of hypertension in young (28–84 day old) spontaneously hypertensive rats (SHRs). This is contrary to what others have reported using older SHRs.

Renal prostaglandin F2α was also reduced in young SHRs and Wistar‐Okamoto strain rats (WKYs) exposed to aspirin.

In the present study we extended the period of aspirin treatment in young rats to beyond 84 days of age. We found that aspirin lost its antihypertensive effect in SHR and WKY rats at 110 ± 7 days of age regardless of whether the exposure to aspirin had begun at age 28, 49 or 87 days.

We conclude that the loss of antihypertensive effect of aspirin in the SHR and in older WKY rats, is determined by some factor(s) probably not related to prostaglandin F2α, which reaches full expression in the 110 ± 7 day old rat, or is fully dissipated at this age.

The anti‐PGF2α activity of aspirin in the SHR and WKY rat was short‐lived and apparently unrelated in time to the antihypertensive effect of aspirin.
The release of prostaglandin D2 from human skin in vivo and in vitro during immediate allergic reactions
Authors: Barr R.M. , Koro O. , Francis D.M. , Black A. Kobza , Numata T. , Greaves M.W.
Published: July 2012

The release of prostaglandin D2 (PGD2) during immediate allergic reactions in human skin was investigated in vivo and in vitro.

Skin exudates were collected from abraded sites on the thigh of atopic subjects sensitive to D. pteronyssinus antigen and from non‐atopic control subjects. Challenge with antigen caused the release of PGD2 and histamine, but not PGE2, from the skin of the atopic subjects. The molar ratio of histamine to PGD2 was about 140:1. Control subjects were unresponsive.

PGD2 was released from passively sensitized human skin challenged with antigen in vitro. The time course was similar in vitro and in vivo. The ratio of histamine to PGD2 in vitro was 78:1.

The identities of the prostaglandins were confirmed by high performance liquid chromatography and radioimmunoassay to PGD2 and PGE2.

PGD2 is the major arachidonic acid cyclo‐oxygenase product synthesized by human mast cells. It is pro‐inflammatory in human skin but its functions as a mediator in immediate hypersensitivity reactions in human skin are not clear. The results of this study suggest that, relative to histamine, PGD2 contributes little to the oedema and erythema of immediate reactions in human skin.
[3H]‐(+)‐N‐methyl‐4‐methyldiphenhydramine, a quaternary radioligand for the histamine H1‐receptor
Authors: Treherne J.M. , Young J.M.
Published: July 2012

A series of derivatives of 4‐methyldiphenhydramine have been examined as potential quaternary radioligands for the histamine H1‐receptor.

[3H]‐(+)‐N‐methyl‐4‐methyldiphenhydramine ([3H]‐QMDP), 83 Ci mmol−1, was synthesized by methylation of the tertiary analogue and purified by high‐voltage electrophoresis.

[3H]‐QMDP bound to H1‐receptors in a washed homogenate from guinea‐pig cerebellum with an affinity constant, Ka, of 1.14 ± 0.03 × 109 M−1. The proportion of non‐specific binding of 0.3–0.6 nM [3H]‐QMDP, defined by 0.4 μm mepyramine, was usually in the range 15–45%, depending on the method of measurement of binding. The affinity of [3H]‐QMDP was similar in guinea‐pig cerebellum, cerebral cortex and hippocampus, but was lower, 1.4 × 108 M−1, in rat cerebral cortex.

Evidence was obtained for the presence of a secondary, non‐muscarinic, binding site for [3H]‐QMDP in guinea‐pig cerebellum, approximate Ka 1.5 × 107M−1, accounting for circa 4% of the total binding of 1 nM [3H]‐QMDP.

There was a very good correlation between the affinities of 15 compounds for the H1‐receptor determined from inhibition of [3H]‐QMDP binding and from inhibition of [3H]‐mepyramine binding.

The potential utility of [3H]‐QMDP for studies of H1‐receptors in the plasma membrane of cells in culture is discussed.
Potassium channel blocking actions of β‐bungarotoxin and related toxins on mouse and frog motor nerve terminals
Authors: Rowan E.G. , Harvey A.L.
Published: July 2012

β‐Bungarotoxin and other snake toxins with phospholipase activity augment acetylcholine release evoked from mouse motor nerve terminals before they produce blockade. This action of the toxins is independent of their phospholipase A2 activity, but the underlying mechanism for the facilitation of release is unclear. To determine whether the toxins affect ionic currents at motor nerve terminals, extracellular recordings were made from perineural sheaths of motor nerves innervating mouse triangularis sterni muscles.

Perineural waveforms had a characteristic shape, with two major negative deflections, the first being associated with nodal Na+ currents and the second with terminal K+ currents. Block of the K+ currents revealed a Ca2+‐dependent component.

During the facilitatory phase of its action, β‐bungarotoxin (150 nm) reduced the second negative component of the perineural waveform by 30–50%.

The reduction could be a consequence of a decreased K+ ion contribution or of an increase in the current carried by Ca2+. As β‐bungarotoxin had similar effects in solutions which contained no added Ca2+, it is unlikely to be acting on the Ca2+ current. Also, it is unlikely to be blocking the Ca2+‐activated K+ current, which is suppressed in zero Ca2+ conditions.

Other prejunctionally active snake toxins (taipoxin, notexin and crotoxin) had similar effects to those of β‐bungarotoxin, but a similar basic phospholipase of low toxicity from cobra venom had no effect.

Thus, β‐bungarotoxin and related toxins block a fraction of the K+ current in the motor nerve terminals of mouse preparations. Such an effect could explain the facilitation of acetylcholine release caused by these toxins before the onset of presynaptic blockade.

In frog cutaneous pectoris preparations, β‐bungarotoxin reduced endplate potential amplitude but had little effect on perineural waveforms. Therefore, the consequences of toxin binding must be different in frog terminals.