bluuebunny/crossref_metadata_2025 huggingface dataset:
Regional haemodynamic effects of angiotensin II (3–8) in conscious rats
Authors: Gardiner S.M. , Kemp P.A. , March J.E. , Bennett T.
Published: July 2012

It has been reported that angiotensin II (AII) (3–8) causes endothelium‐dependent renal cortical vasodilatation, in anaesthetized rats, through interaction with a novel receptor that shows no affinity for the AT1‐receptor antagonist, losartan. Therefore in order to get a fuller profile of the regional haemodynamic effects of AII (3–8) in conscious rats we assessed its renal, mesenteric and hindquarters vascular effects, and compared them to the responses elicited by AII and AIII.

AII and AIII (1.25, 12.5 and 125 pmol kg−1) caused dose‐dependent pressor and renal and mesenteric vasoconstrictor effects. At doses up to 125 pmol kg−1, AII (3–8) was without any cardiovascular effects, but with doses of 1.25 and 12.5 nmol kg−1 there were dose‐dependent increases in mean arterial blood pressure and reductions in renal and mesenteric flows and vascular conductances. The responses to AII (3–8) (12.5 nmol kg−1) were abolished by losartan (20 μmol kg−1).

Since it has been found that pretreatment with l‐arginine can reveal a vasodilator effect of AII (3–8) on rabbit pial arterioles, we assessed responses to AII (3–8) (12.5 nmol kg−1) before and 5 min after onset of a primed infusion of l‐arginine (1.4 mmol kg−1 bolus, 1.4 mmol kg−1 h−1 infusion). Responses to AII (3–8) were unchanged by l‐arginine.

The results are consistent with AII (3–8) being a less effective agonist than AII (or AIII) at the AT1‐receptor, but provide no evidence for AII (3–8) interacting with a novel receptor that shows no affinity for losartan.
Effects of the central analgesic tramadol and its main metabolite, O‐desmethyltramadol, on rat locus coeruleus neurones
Authors: Sevcik Jan , Nieber Karen , Driessen Bernd , Illes Peter
Published: July 2012

Tramadol is a centrally acting analgesic with low opioid receptor affinity and, therefore, presumably additional mechanisms of analgesic action. Tramadol and its main metabolite O‐desmethyltramadol were tested on rat central noradrenergic neurones of the nucleus locus coeruleus (LC), which are involved in the modulation of nociceptive afferent stimuli.

In pontine slices of the rat brain the spontaneous discharge of action potentials of LC cells was recorded extracellularly. (−)‐Tramadol (0.1–100μm), (+)‐tramadol (0.1–100 μm), (−)‐O‐desmethyltramadol (0.1–100 μm) and (+)‐O‐desmetnyltramadol (0.01–1 μm) inhibited the firing rate in a concentration‐dependent manner. (+)‐O‐desmetnyltramadol had the highest potency, while all other agonists were active at a similar range of concentrations.

(−)‐Tramadol (10, 100 μm) was less inhibitory in brain slices of rats pretreated with reserpine (5 mg kg−1, 5 h before decapitation) than in controls.

The effect of (−)‐tramadol (10 μm) was abolished in the presence of the α2‐adrenoceptor antagonist, rauwolscine (1 μm), whilst that of (+)‐O‐desmetnyltramadol (0.3 μm) virtually disappeared in the presence of the opioid antagonist, naloxone (0.1 μm). (+)‐Tramadol (30 μm) and (−)‐O‐desmethyltramadol (10 μm) became inactive only in the combined presence of naloxone (0.1 μm) and rauwolscine (1 μm).

In another series of experiments, the membrane potential of LC neurones was determined with intracellular microelectrodes. (−)‐Tramadol (100 μm) inhibited the spontaneous firing and hyperpolarized the cells; this effect was abolished by rauwolscine (1 μm). (+)‐O‐desmethyltramadol (10 μm) had a similar but somewhat larger effect on the membrane potential than (−)‐tramadol. The (+)‐O‐desmethyltramadol‐ (10 μm) induced hyperpolarization was abolished by naloxone (0.1 μm).

The hyperpolarizing effect of noradrenaline (30 μm) was potentiated in the presence of (−)‐tramadol (100 μm), but not in the presence of (+)‐O‐desmethyltramadol (10 μm). There was no potentiation of the noradrenaline (30 μm) effect, when the cells were hyperpolarized by current injection to an extent similar to that produced by (−)‐tramadol (100 μm).

Both noradrenaline (100 μm) and (−)‐tramadol (100 μm) decreased the input resistance.

The results confirm that the analgesic action of tramadol involves both opioid and non‐opioid components. It appears that (−)‐tramadol inhibits the uptake of noradrenaline and via a subsequent increase in the concentration of endogenous noradrenaline indirectly stimulates α2‐adrenoceptors. (+)‐O‐desmethyltramadol seems to stimulate directly opioid μ‐receptors. The effects of (+)‐tramadol and (−)‐O‐desmetnyltramadol consist of combined μ‐opioid and α2‐adrenergic components.
Role of tumour necrosis factor in the induction of nitric oxide synthase in a rat model of endotoxin shock
Authors: Thiemermann Christoph , Wu Chin‐Chen , Szabó Csaba , Perretti Mauro , Vane John R.
Published: July 2012

This study investigates the role of tumour necrosis factor (TNF) in the induction of nitric oxide synthase (NOS) by bacterial endotoxin (lipopolysaccharide; LPS) in a rat model of endotoxin shock.

In anaesthetized rats, pretreatment with a monoclonal antibody for TNF (TNFab; 20 mg kg−1, s.c., at 16 h prior to LPS) ameliorated the fall in mean arterial blood pressure (MAP) in response to LPS (2 mg kg−1, i.v.). For instance, endotoxaemia for 180 min resulted in a fall in MAP from 114 ± 6 (control) to 84 ± 5 mmHg (P < 0.01; n = 7). In contrast, animals pretreated with TNFab prior to LPS injection maintained significantly higher MAP when compared to LPS‐control (MAP at 180 min; 118 ± 3 mmHg; P < 0.01, n = 5).

Three hours of endotoxaemia was also associated with a significant reduction of the contractile effects of noradrenaline (NA) (10−1–10−6 m) on the thoracic aorta ex vivo. This hyporeactivity to NA was partially restored by in vitro treatment of the vessels with NG‐nitro‐l‐arginine methyl ester (l‐NAME, 20 min, 3 × 10−4 m). Pretreatment of rats with TNFab (20 mg kg−1; at 16 h prior to LPS) significantly (P < 0.05) attenuated the LPS‐induced hyporeactivity of rat aortic rings ex vivo. l‐NAME did not enhance the contractions of aortic rings obtained from TNFab pretreated LPS‐rats.

At 180 min after LPS there was a significant elevation of the induced NOS activity in the lung (5.14 ± 0.57 pmol citrulline mg−1 min−1, n = 8). TNFab pretreatment significantly attenuated this induction of NOS in response to LPS by 37 ± 6% (n = 5; P < 0.05).

We conclude that the formation of endogenous TNF contributes to the induction of the calcium‐independent isoform of NOS in response to LPS in vivo. Thus, the beneficial effects of agents which inhibit either the release or the action of TNF in circulatory shock may be, in part, due to inhibition of NOS induction.
Use‐dependent block of Na+ currents by mexiletine at the single channel level in guinea‐pig ventricular myocytes
Authors: Sunami Akihiko , Fan Zheng , Sawanobori Tohru , Hiraoka Masayasu
Published: July 2012

The mechanism of use‐dependent block of Na+ current by mexiletine was studied at the single channel level in guinea‐pig ventricular myocytes by the patch‐clamp techniques. All experiments were performed using stimulation protocols to enable us to analyze the strict dependence of changes in channel properties on channel use.

In cell‐attached patches, bath or pipette application of mexiletine (40 μm) produced a use‐dependent reduction of the peak average current without changes in single channel conductance. Null sweeps were increased and the number of openings per sweep decreased with successive pulses, whereas no significant change in the mean open time was detected during the train.

Block by mexiletine became greater when pulse duration was extended beyond the period in which channels were open, suggesting that block progressed without channel opening.

At near threshold potentials, mexiletine decreased the later occurrence of first openings. Additionally, late openings were reduced in a use‐dependent way.

We conclude that mexiltine binds to the inactivated closed states of the Na+ channel and then causes a failure of late openings as well as early, which results in null sweeps on subsequent depolarization.
Characterization of the novel nitric oxide synthase inhibitor 7‐nitro indazole and related indazoles: antinociceptive and cardiovascular effects
Authors: Moore P.K. , Wallace P. , Gaffen Z. , Hart S.L. , Babbedge R.C.
Published: July 2012

7‐Nitro indazole (7‐NI, 10–50 mg kg−1), 6‐nitro indazole and indazole (25–100 mg kg−1) administered i.p. in the mouse produce dose‐related antinociception in the late phase of the formalin‐induced hindpaw licking and acetic acid‐induced abdominal constriction assays. The ED50 values (mg kg−1) were as follows: 7‐NI (27.5 and 22.5), 6‐nitro indazole (62.5 and 44.0) and indazole (41.0 and 48.5) in the two assays respectively. 3‐Indazolinone, 6 amino indazole and 6‐sulphanilimido indazole (all 50 mg kg−1) were without effect. With the exception of 5‐nitro indazole (50 mg kg−1) which produced sedation, none of the other indazole derivates examined caused overt behavioural changes.

The antinociceptive effect of 7‐NI (25 mg kg−1, i.p.) in the late phase of the formalin‐induced hindpaw licking assay was partially (46.7 ± 16.2%, n = 18) reversed by pretreatment with l‐ but not d‐arginine (both 50 mg kg−1, i.p.).

The time course of 7‐NI induced antinociception in the mouse was correlated with inhibition of brain (cerebellum) nitric oxide synthase (NOS) activity. Maximum antinociceptive activity and NOS inhibition were detected 18–30 min following i.p. administration. In contrast, no antinociceptive effect or inhibition of cerebellar NOS was detected 75 min post‐injection.

7‐NI, 6‐nitro indazole, indazole, 3‐indazolinone and 6‐amino indazole (all 50 mg kg−1) failed to influence mean arterial pressure (MAP) over the 45 min after i.p. administration in the anaesthetized mouse. Similarly, 7‐NI (25 mg kg−1) administered i.v. in the anaesthetized rat did not increase MAP or influence the vasodepressor effect of i.v. injected acetylcholine (ACh) over the same period.

7‐NI (100 μm) did not influence the vasorelaxant effect of ACh (IC50, 0.2 ± 0.04 μm, cf. 0.16 ± 0.06 μm, n = 6) in phenylephrine‐precontracted rabbit aortic rings.

These data provide further evidence that antinociception following administration of 7‐NI in the mouse results from inhibition of central NOS activity and is not associated with inhibition of in vivo vascular endothelial cells NOS. Accordingly, 7‐NI (or a derivative thereof) may provide an alternative approach to the development of novel antinociceptive drugs.
Dissociation of the anti‐ischaemic effects of cloricromene from its anti‐platelet activity
Authors: Lidbury Paul S. , Cirillo Rocco , Vane John R.
Published: July 2012

Cloricromene is a non‐anticoagulant coumarin derivative with anti‐platelet and anti‐leukocyte properties, which has beneficial effects in various models of ischaemia and shock.

We have assessed the effects of cloricromene on (a) ex vivo platelet aggregation, and (b) infarct size using a model of myocardial ischaemia in the anaesthetized rabbit.

Cloricromene (1–1000 μg kg−1 min−1 for 15 min) induced a dose‐dependent inhibition of ex vivo platelet aggregation, causing only a minimal increase in heart rate and no change in mean arterial blood pressure. The inhibitory activity was considerably stronger when platelet aggregation was induced by collagen than by ADP.

Cloricromene inhibited ex vivo platelet aggregation in rabbits pretreated with indomethacin (5 mg kg−1) and this inhibition persisted for 30–60 min.

The model of myocardial ischaemia involved 1 h occlusion of the first antero‐lateral branch of the left coronary artery followed by 2 h of reperfusion. Infusion of cloricromene (30 or 300 μg kg−1 min−1), ibuprofen (80 μg kg−1 min−1) or vehicle began 15 min prior to occlusion, and continued throughout the experiment.

While area at risk was similar for all groups studied, cloricromene (30 or 300 μg kg−1 min−1) or ibuprofen caused a reduction in infarct size, and decreased myeloperoxidase activity in the tissue of the infarcted myocardium.

Cloricromene at 300 μg kg−1 min−1 also reduced the occlusion‐induced elevation of the ST‐segment of the rabbit electrocardiogram, and inhibited platelet aggregation ex vivo. Ibuprofen or cloricromene at 30 μg kg−1 min−1 had no effect on either the ST‐elevation or platelet reactivity.

Thus, cloricromene exhibits a cardioprotective activity via an inhibition of leukocyte infiltration, in the presence (300 μg kg−1 min−1) or absence (30 μg kg−1 min−1) of inhibition of platelet activity ex vivo. The anti‐aggregatory activity of cloricromene acts via a mechanism that is either different from, or in addition to, inhibition of cyclo‐oxygenase, and is of long duration.
A facilitatory effect of anti‐angiotensin drugs on vagal bradycardia in the pithed rat and guinea‐pig
Authors: Rechtman M. , Majewski H.
Published: July 2012

In pithed rats, preganglionic vagal nerve stimulation (at 5 Hz) elicited a bradycardia. This bradycardia was potentiated by the angiotensin converting enzyme inhibitor, captopril (1 mg kg−1, i.v.) by about 40%. Subsequent angiotensin II infusion (0.03 μg kg−1 min−1) reversed this effect. A similar facilitatory effect was also seen with the angiotensin receptor antagonist, losartan (10 mg kg−1, i.v.). These results suggest a tonic inhibitory effect of endogenous angiotensin II on vagal transmission.

The effect of captopril in potentiating vagal bradycardia appears to be at the level of vagal neurones, since the bradycardia elicited by the muscarinic agonist, methacholine was unaffected.

After the pithed rats were nephrectomized, captopril had no effect on vagally‐induced bradycardia, suggesting that the formation of the endogenous angiotensin II responsible for the effect was dependent on renin release from the kidney.

When the sympathetic nerves of the pithed rat were electrically stimulated there was a tachycardia, and this was unaffected by captopril. However, when the sympathetic and vagus nerves were activated concurrently, the resulting tachycardia was inhibited by captopril.

In pithed guinea‐pigs, captopril also potentiated the bradycardia caused by vagal nerve stimulation. This appears to be a tissue‐selective effect since the bronchoconstriction due to the vagal stimulation was not affected by captopril.

These results suggest that endogenous angiotensin II can have a tonic inhibitory effect on cardiac vagal transmission. Disruption of this mechanism by anti‐angiotensin drugs may attenuate the reflex tachycardia associated with the fall in blood pressure in anti‐hypertensive therapy.
Comparison of contractile responses to 5‐hydroxytryptamine and sumatriptan in human isolated coronary artery: synergy with the thromboxane A2‐receptor agonist, U46619
Authors: Cocks T.M. , Kemp B.K. , Pruneau D. , Angus J.A.
Published: July 2012

The interaction between the thromboxane A2 receptor agonist, U46619 and two 5‐hydroxytryptamine (5‐HT) receptor agonists, the non‐selective, naturally occurring agonist, 5‐HT and the selective 5‐HT1‐like agonist, sumatriptan were studied in human epicardial coronary arteries in vitro.

Coronary artery rings (2–4 mm in diameter) were prepared from epicardial arteries from explant hearts of patients undergoing heart transplant (cardiomyopathy, n = 13; ischaemic heart disease, n = 10) and unused donor hearts (n = 5). Each ring of artery was set at optimal resting conditions to record changes in isometric force.

The majority of artery rings developed phasic, rhythmic contractions either spontaneously or in response to all vasoconstrictor agonists tested. Both the spontaneous and agonist‐induced phasic contractions were abolished by nifedipine (0.1 μm).

Concentration‐contraction curves to 5‐HT‐receptor agonists and noradrenaline (NA), were first constructed in artery rings that did not develop phasic activity. 5‐HT and ergometrine were the most potent agonists with EC50 values of 6.8 ± 0.2 and 7.7 ± 0.2 (−log m) respectively. Potencies (EC50's) to sumatriptan, methysergide and noradrenaline could not be determined due to their poor ability to contract the coronary artery. Maximum contractions (Emax; normalized as a percentage of the contraction to a maximum‐depolarizing concentration of K+ in physiological salt solution (KPSS)) for 5‐HT, ergometrine, sumatriptan, methysergide and noradrenaline were 40 ± 10, 9 ± 3, < 5, < 5 and < 5% respectively.

In arteries without phasic activity, U46619 (1 nm) caused an increase in force of 3.8 ± 1% KPSS. With U46619 present, the Emax values for 5‐HT, ergometrine, sumatriptan and methysergide were all markedly increased. For 5‐HT and sumatriptan, Emax values were 92 ± 4% and 49 ± 14% KPSS respectively. The presence of U46619 did not significantly change the sensitivity (EC50) to 5‐HT.

In a separate series of arteries, nifedipine (0.1 μm) was used to block phasic, contractile activity. The synergy observed between U46619 and 5‐HT or sumatriptan still occurred although the Emax values for each agonist were depressed but the EC50 values were again unaffected.

In conclusion, these in vitro studies indicate that the normally poor contractions to sumatriptan, in human coronary arteries are significantly enhanced when active force is induced with a thromboxane A2‐receptor agonist, U46619. The enhanced response is not specific for either sumatriptan or 5‐HT1‐like receptors since contractions to 5‐HT, ergometrine and methysergide were also potentiated by U46619.
Bradykinin‐induced release of PGI2 from aortic endothelial cell lines: responses mediated selectively by Ca2+ ions or a staurosporine‐sensitive kinase
Authors: Parsaee Heydar , McEwan Jean R. , MacDermot John
Published: July 2012

Bradykinin (100 nm) triggers release of nitric oxide and prostacyclin from both AG07680A and AG04762 bovine cultured aortic endothelial cells. The exposure of these cells to bradykinin is in each case associated with a striking rise in intracellular calcium ion concentration.

Exposure of AG07680A cells to 250 nm ionomycin was followed also by a significant release of prostacyclin, whereas 250 nm ionomycin had no capacity to stimulate release of prostacyclin from AG04762 cells.

There was a similar concentration‐dependent increase in intracellular calcium ion concentration on exposure of AG07680A and AG04762 cells to ionomycin.

Exposure of AG04762 cells for 10 min to staurosporine produced a concentration‐dependent inhibition (IC50 = 107 ± 14 nm) in bradykinin‐stimulated prostacyclin release. There was no similar inhibitory effect of staurosporine in AG07680A cells.

Bradykinin (10 nm) triggered release of nitric oxide from both AG07680A and AG04762 cells, and the effect was not inhibited by 500 nm staurosporine. There was a similar ionomycin‐dependent release of nitric oxide from both cell types.

These results identify a common pathway for bradykinin‐dependent nitric oxide release from both AG07680A and AG04762 cells, involving increases in intracellular calcium ion concentration. In contrast, the bradykinin‐dependent release of prostacyclin may involve one of two pathways (involving an increase in intracellular calcium or activation of a staurosporine‐sensitive kinase), and the two pathways are selectively exploited in AG07680A and AG04762 cells, respectively.
Specific inhibition of leukotriene B4 (LTB4)‐induced neutrophil emigration by 20‐hydroxy LTB4: implications for the regulation of inflammatory responses
Authors: Pettipher E.R. , Salter E.D. , Breslow R. , Raycroft L. , Showell H.J.
Published: July 2012

The interaction between leukotriene B4 (LTB4) and its metabolite, 20‐hydroxy LTB4 in the control of neutrophil emigration was examined in guinea‐pig skin.

Leukotriene B4 (10–300 ng) elicited a dose‐dependent increase in neutrophil infiltration (as measured by myeloperoxidase activity) 4 h after injection into guinea‐pig skin. In contrast, 20‐hydroxy LTB4 (30–1000 ng) displayed only weak inflammatory activity in this assay.

Although 20‐hydroxy LTB4 had low agonist activity, this metabolite caused a potent dose‐dependent inhibition of responses to LTB4 (100 ng), when administered systemically (ED50= 1.3 μg kg−1, s.c.) without significantly affecting neutrophil infiltration in response to C5a (2 μg). Systemic administration of 20‐carboxy LTB4 (10 μg) did not affect neutrophil accumulation in response to LTB4 or C5a. In addition, neither 15(S)‐hydroxy 5(S)‐HPETE(10 μg) nor lipoxin A4 (10 μg) inhibited responses to LTB4.

Addition of 20‐hydroxy LTB4 (10−11–10−8 m) to human blood prior to isolation of the neutrophils led to concentration‐dependent decrease in the number of LTB4 receptors and decreased chemotactic responsiveness to LTB4 without affecting responses to C5a. Incubation of blood with 20‐carboxy LTB4 (10−8 m) did not reduce LTB4 receptor number of chemotactic responsivness to LTB4.

These data indicate that although 20‐hydroxy LTB4 is a weak agonist at LTB4 receptors, it can desensitize neutrophils to the effects of LTB4 via down‐regulation of the high affinity receptor and thus provides evidence for a mechanism whereby inflammatory responses may be regulated.
Cerebral blood flow and cerebrovascular reactivity after inhibition of nitric oxide synthesis in conscious goats
Authors: Fernández N. , García J.L. , García‐Villalón A.L. , Monge L. , Gómez B. , Diéguez G.
Published: July 2012

The role of nitric oxide in the cerebral circulation under basal conditions and after vasodilator stimulation was studied in instrumented, conscious goats, by examining the action of inhibiting endogenous nitric oxide production with NG‐nitro‐l‐arginine methyl ester (l‐NAME).

In 6 unanaesthetized goats, blood flow to one brain hemisphere (electromagnetically measured), systemic arterial blood pressure and heart rate were continuously recorded. l‐NAME (35 mg kg−1 by i.v. bolus) decreased resting cerebral blood flow by 43 ± 3%, increased mean arterial pressure by 21 ± 2%, and decreased heart rate by 41 ± 2%; cerebrovascular resistance increased by 114 ± 13% (P < 0.01); the immediate addition of i.v. infusion of l‐NAME (0.15–0.20 mg kg−1 during 60–80 min) did not significantly modify these effects. Cerebral blood flow recovered at 72 h, arterial pressure and cerebrovascular resistance at 48 h, and heart rate at 6 days after l‐NAME treatment.

A second treatment with l‐NAME scheduled as above reproduced the immediate haemodynamic effects of the first treatment, which (except bradycardia) reversed with l‐arginine (200–300 mg kg−1 by i.v. bolus).

Acetylcholine (0.01–0.3 μg), sodium nitroprusside (3–100 μg) and diazoxide (0.3–9 mg), injected into the cerebral circulation of 5 conscious goats, produced dose‐dependent increases in cerebral blood flow, and decreases in cerebrovascular resistance; sodium nitroprusside (30 and 100 μg) also caused hypotension and tachycardia.

The reduction in cerebrovascular resistance from resting levels (in absolute values) to lower doses, but not to the highest dose, of acetylcholine was diminished, to sodium nitroprusside was increased, and to diazoxide was unaffected after l‐NAME, compared to control conditions. The effects on cerebrovascular resistance to acetycholine normalized within 24 h and to sodium nitroprusside within 48 h after l‐NAME treatment.

This study provides information about the evolution of the changes in cerebral blood flow and cerebrovascular reactivity after inhibition of endogenous nitric oxide in conscious animals. The results suggest: (a) endogenous nitric oxide is involved in regulation of the cerebral circulation by producing a resting vasodilator tone, (b) the cerebral vasodilatation to acetylcholine is mediated, at least in part, by nitric oxide release, and (c) inhibition of nitric oxide production induces supersensitivity of cerebral vasculature to nitrovasodilators.
Suppression of inflammatory responses to 12‐O‐tetradecanoylphorbol‐13‐acetate and carrageenin by YM‐26734, a selective inhibitor of extracellular group II phospholipase A2
Authors: Miyake Akira , Yamamoto Hirokazu , Kubota Emi , Hamaguchi Katsuhiko , Kouda Akio , Honda Kazuo , Kawashima Hiroyuki
Published: July 2012

YM‐26734 [4‐(3,5‐didodecanoyl‐2,4,6‐trihydroxyphenyl)‐7‐hydroxy‐2‐(4‐hydroxyphenyl)chroman] dose‐dependently inhibited the activities of extracellular phospholipase A2 (PLA2): rabbit platelet‐derived group II and porcine pancreas‐derived group I PLA2, with IC50 values of 0.085 (0.056–0.129, n = 5) and 6.8 (5.0–9.6, n = 5) μm, respectively.

In contrast, YM‐26734 did not reduce the activity of intracellular PLA2 prepared from mouse macrophages, which preferentially hydrolyzed arachidonoyl phospholipids at concentrations up to 50 μm. YM‐26734 also showed no effect against either sheep seminal vesicle cyclo‐oxygenase or rat leukocyte 5‐lipoxygenase.

Lineweaver‐Burk analysis showed that YM‐26567‐1 behaved as a competitive inhibitor of group II PLA2 derived from rabbit platelets, with a Ki value of 48 nm.

In mice, YM‐26734 inhibited 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA, 1 μg/ear)‐induced ear oedema in a dose‐dependent manner, with ED50 values of 45 (30–67) μg/ear (n = 5) and 11 (4–32) mg kg−1, i.v. (n = 5), but did not decrease arachidonic acid (4 mg/ear)‐induced ear oedema at 1 mg/ear and 30 mg kg−1, i.v.

In rats, the accumulation of exudate fluids and leukocytes in the pleural cavity in response to carrageenin injection (2 mg) was significantly less in a group treated with YM‐26734 (20 mg kg−1, i.v.) than in the control group (0.43 ± 0.02 vs 0.59 ± 0.03 g per cavity and 3.8 ± 0.2 vs 4.9 ± 0.3 × 107 cells per cavity, respectively; n = 5).

These results suggest that YM‐26734 is a potent and competitive inhibitor of extracellular PLA2 with selectivity for group II PLA2, and that the inhibition of group II enzymes activity may cause the suppression of inflammatory responses to TPA and carrageenin.
Vascular actions of purines in the foetal circulation of the human placenta
Authors: Read M.A. , Boura A.L.A. , Walters W.A.W.
Published: July 2012

The vasoactive effects of adenosine triphosphate (ATP), adenosine and other purines in the foetal circulation of the human placenta were examined. Single lobules of the placenta were bilaterally perfused in vitro with Krebs buffer (maternal and foetal sides 5 ml min−1 each, 95% O2:5% CO2, 37°C). Changes in foetal vascular tone were assessed by recording perfusion pressure during constant infusion of each purine. To allow recording of the vasodilator effects, submaximal vasoconstriction was induced by concomitant infusion of prostaglandin F2α (0.7–2.0 μmol 1−1).

ATP (1.0–100 μmol 1−1) usually caused concentration‐dependent reductions in perfusion pressure. However, biphasic with initial transient increases, or only increases in pressure were sometimes observed. Falls in pressure caused by ATP were significantly reduced by addition to the perfusate of NG‐nitro‐l‐arginine (l‐NOARG) (100 μmol 1−1) but not NG‐nitro‐d‐arginine (d‐NOARG) (100 μmol 1−1). They were not influenced by addition of indomethacin (10 μmol 1−1) or l‐arginine (100 μmol 1−1).

Adenosine (0.01–1.0 mmol 1−1) consistently caused concentration‐dependent reductions in perfusion pressure, this effect not being influenced by indomethacin. l‐NOARG, but not d‐NOARG, reduced the potency of adenosine approximately three fold. l‐Arginine, but not d‐arginine enhanced its potency by a similar amount.

2‐Methylthio‐ATP, a selective P2y agonist was approximately 50 times more potent than ATP as a vasodilator agent, always causing decreases in perfusion pressure.

β‐γ‐Methylene ATP, a selective P2x agonist, was approximately 100 times more potent than ATP as a vasoconstrictor, but only caused transient increases in perfusion pressure.

The rank order of vasodilator potencies of a selection of adenosine receptor agonists was, 2‐chloroadenosine >> 5‐(N‐cyclopropyl)‐carboxamidoadenosine, >5‐N‐ethylcarboxamidoadenosine, >2‐chloro‐N6‐cyclopentyladenosine, >CGS‐21680 > N6‐cyclohexyladenosine = adenosine. Vasodilatation due to adenosine was inhibited by the P1‐A2 receptor antagonist 3,7‐dimethyl‐1‐propargylxanthine (DMPX).

These results suggest that ATP may cause an endothelium‐dependent vasodilatation in the foetal vessels of the human placenta via activation of a P2y receptor linked to the formation of nitric oxide (NO). Vasodilatation caused by ATP may mask an accompanying vasoconstrictor effect mediated, via a P2x receptor, in the villous vascular smooth muscle. Adenosine acting on P1‐A2 receptors, which are also present in the foetal vasculature, may require synergistic interaction with NO to achieve a maximal vasodilator response.
Human liver microsomal metabolism of the enantiomers of warfarin and acenocoumarol: P450 isozyme diversity determines the differences in their pharmacokinetics
Authors: Hermans J.J.R. , Thijssen H.H.W.
Published: July 2012

To explain the large differences in (the stereoselectivity of) the clearances of the enantiomers of warfarin and acenocoumarol (4′‐nitrowarfarin) their human liver microsomal metabolism has been studied and enzyme kinetic parameters determined. The effects of cimetidine, propafenone, sulphaphenazole, and omeprazole on their metabolism has been investigated.

The 4‐hydroxycoumarins follow similar metabolic routes and are mainly hydroxylated at the 6‐ and 7‐position (accounting for 63 to 99% of the metabolic clearances).

Due to the lower Km values of R‐ and S‐acenocoumarol and higher Vmax values of S‐acenocoumarol, the overall metabolic clearances of R/S acenocoumarol exceed those of R/S warfarin 6 and 66 times respectively.

The metabolism of both compounds is stereoselective for the S‐enantiomers, which is 10 times more pronounced in the case of acenocoumarol.

Except for the 7‐hydroxylation of the R‐enantiomers (r = 0.90; P < 0.025), the 6‐ and 7‐hydroxylation rates of R/S warfarin do not correlate with those of R/S acenocoumarol.

Sulphaphenazole competitively inhibits the 7‐ and in some samples partly (up to 50%) the 6‐hydroxylation of S‐warfarin as well as the 7‐hydroxylation of R‐ and S‐acenocoumarol and the 6‐hydroxylation of S‐acenocoumarol (Kis ranging from 0.5– 1.3 μm).

Omeprazole partly (40–80%) inhibits the 6‐ and 7‐hydroxylation of R‐warfarin (Ki = 99 and 117 μm) and of R‐ (Ki = 219 and 7.2 μm) and S‐acenocoumarol (Ki = 6.1 and 7.7 μm) but not S‐warfarin in a competitive manner.

Differences in the partial (up to 40%) inhibition of the metabolism of the enantiomers of the 4‐hydroxycoumarins were also observed for the relatively weak inhibitors, propafenone and cimetidine.

The results suggest that the coumarin ring hydroxylations of both compounds are catalysed by different combinations of P450 isozymes. The 7‐hydroxylation of R/S acenocoumarol and the 6‐hydroxylation of S‐acenocoumarol are at least partly conducted by (a) P450 isozyme(s) of the 2C subfamily different from P450 2C9 (the main S‐warfarin 7‐ and 6‐hydroxylase).
Induction of a glibenclamide‐sensitive K‐current by modification of a delayed rectifier channel in rat portal vein and insulinoma cells
Authors: Edwards G. , Weston A.H.
Published: July 2012

In insulinoma cells (RINm5F), the glibenclamide‐sensitive K‐current (IK(ATP)) which developed spontaneously or after exposure to levcromakalim or to butanedione monoxime was always accompanied by a reduction in the delayed rectifier current (IK(V)). At potentials over which IK(V) was fully activated, the total outward current remained constant. In rat portal vein, the delayed rectifier channel inhibitor, margatoxin, reduced the combined induction of IK(ATP) and inhibition of IK(V) by levcromakalim. These data suggest that the ATP‐sensitive K‐channel, K(ATP), is a voltage‐insensitive state of the delayed rectifier, KV.
Action of purine and pyrimidine nucleotides on the rat superior cervical ganglion
Authors: Connolly G.P. , Harrison P.J. , Stone T.W.
Published: July 2012

Using a grease‐gap technique, we have investigated the effects of purine and pyrimidine nucleotides on the d.c. potential of the rat isolated superior cervical ganglion (SCG).

Of the purines tested, adenosine, adenosine 5′‐triphosphate (ATP), β,γ‐methylene‐adenosine 5′‐triphosphate (β,γ‐MeATP) at up to 300 μm produced concentration‐dependent hyperpolarizations, whereas 2‐methyl‐thio‐ATP (2‐Me.S.ATP) and α,β‐methylene‐ATP (α,β‐MeATP) depolarized ganglia. Of the pyrimidines tested, uridine 5′‐triphosphate (UTP) produced concentration‐dependent depolarizations and cytosine 5′‐triphosphate (CTP) at 1000 μm produced considerably smaller but significant depolarizations. In contrast uridine 5′‐monophosphate (UMP) at 1000 μm hyperpolarized ganglia. The relative order of potency of purines and pyrimidines to depolarize ganglia was:‐ UTP > α,β‐MeATP >> CTP > 2‐Me.S.ATP and to hyperpolarize ganglia was:‐ adenosine = β,γ‐MeATP > ATP > UMP.

The ability of purines and pyrimidines to alter the depolarizing response caused by muscarine and of purines to alter depolarization induced by γ‐aminobutyric acid (GABA) was determined. The relative order of potency of nucleotides in depressing submaximal depolarization caused by muscarine (100 nm) was: adenosine = ATP > β,γ‐MeATP whereas 2‐Me.S.ATP, α,β‐MeATP and UTP did not significantly alter depolarization caused by muscarine. At 100 μm β,γ‐MeATP and adenosine but not ATP potentiated GABA‐induced depolarizations.

Hyperpolarizations caused by adenosine, ATP, β,γ‐MeATP and UMP and depolarizations caused by α,β‐MeATP were enhanced in medium containing reduced concentrations of calcium (0.1 mm) and potassium (2 mm). In this medium 8‐phenyltheophylline abolished hyperpolarizations caused by adenosine and reversed hyperpolarizations caused by ATP into depolarizations. Suramin (300 μm), a P2‐purinoceptor antagonist, significantly reduced the depolarizing response caused by α,β‐MeATP and significantly increased hyperpolarizations caused by ATP and β,γ‐MeATP. Suramin (300 μm) did not significantly alter depolarizations caused by 1,1‐dimethyl‐4‐phenylpiperazinium (10 μm), potassium (3 mm) or muscarine (100 nm) and significantly potentiated depolarizations caused by UTP (100 μm).

It is concluded that the rat SCG contains P1‐purinoceptors that hyperpolarize the ganglion and diminish sensitivity to muscarine, and P2X‐purinoceptors that depolarize the SCG. There is also some evidence to suggest the presence of receptors for UTP, i.e., pyrimidinoceptors, which depolarize SCG neurones.
Modulation by nitric oxide of platelet‐activating factor‐induced albumin extravasation in the conscious rat
Authors: Filep János G. , Földes‐Filep Éva
Published: July 2012

The objective of this study was to assess whether or not endogenous nitric oxide (NO) could mediate the hypotensive response to platelet‐activating factor (PAF) and modulate PAF‐induced microvascular albumin leakage in the conscious rat.

PAF (0.19 and 1.9 nmol kg−1, i.v.) evoked dose‐dependent hypotension and significantly enhanced albumin extravasation in the large airways, pancreas, stomach and duodenum 15 min after its administration. Inhibition of NO synthesis by NG‐nitro‐l‐arginine methyl ester (l‐NAME, 0.125–2 mg kg−1, i.v.) produced marked dose‐dependent increases in albumin accumulation (up to 290%) in large airways, liver, spleen, pancreas, kidney, stomach and duodenum as measured by the extravasation of Evans blue dye. l‐NAME (2 mg kg−1) treatment markedly potentiated PAF (1.9 nmol kg−1)‐induced albumin extravasation in these tissues, whereas it did not modify the hypotensive response to PAF.

Maintenance of mean arterial blood pressure at the level observed following 2 mg kg−1 l‐NAME by infusion of noradrenaline (620–790 ng kg−1 min−1) neither affected significantly albumin extravasation nor potentiated the permeability effect of PAF in the vascular beds studied with the exception of large airways, where noradrenaline mimicked the effects of l‐NAME.

These results indicate that inhibition of endogenous NO formation leads to an increase in albumin extravasation and to potentiation of the vascular permeability effect of PAF, whereas the hypotensive action of PAF seems to be independent of NO formation in the conscious rat. These data suggest an important role for NO in the regulation of albumin extravasation.
[Ca2+]i‐sensitive, IP3‐independent Ca2+ influx in smooth muscle of rat vas deferens revealed by procaine
Authors: Khoyi Mohammad A. , Dalziel Hugh H. , Zhang Lubo , Bjur Richard A. , Gerthoffer William T. , Buxton Iain L.O. , Westfall David P.
Published: July 2012

The actions of procaine (10 mm) on noradrenaline‐induced effects on 45Ca‐influx, 45Ca‐efflux, 45Ca‐content, total inositol phosphates, inositol‐1,4,5‐trisphosphate, and contractile status of the rat vas deferens were examined.

Noradrenaline alone had no effect on 45Ca‐influx or 45Ca‐content, but released Ca2+ from intracellular stores as indicated by an increased 45Ca‐efflux and increased total inositol phosphates, specifically inositol‐1,4,5‐trisphosphate, leading to contraction of the rat vas deferens.

Noradrenaline, in the presence of 10 mm procaine, increased 45Ca‐influx and 45Ca‐content. Procaine blocked the noradrenaline‐induced 45Ca‐efflux, the increase in total inositol phosphates, the increase in inositol‐1,4,5‐trisphosphate, and contraction.

The noradrenaline‐induced increase in 45Ca influx which was observed in the presence of procaine was abolished by phentolamine and nifedipine but was not altered significantly by propranolol suggesting that, in the presence of procaine, noradrenaline activates dihydropyridine‐sensitive calcium channels through α‐adrenoceptors.

These findings indicate that, in the rat vas deferens, noradrenaline induces contraction by releasing intracellularly stored Ca2+. The effects of procaine appear to be due to its ability to block the release of Ca2+ from intracellular stores. Furthermore, the simultaneous increase in 45Ca influx and inhibition of inositol‐1,4,5‐trisphosphate formation in tissues treated with procaine plus noradrenaline indicates that Ca2+ influx is independent of inositol‐1,4,5‐trisphosphate formation.
Effects of sumatriptan on the cerebral intraparenchymal microcirculation in the cat
Authors: Kobari Masahiro , Fukuuchi Yasuo , Tomita Minora , Tanahashi Norio , Konno Shizuko , Takeda Hidetaka
Published: July 2012

Sumatriptan, a 5‐hydroxytryptamine (5‐HT)1‐like receptor agonist, is effective against the headache of migraine. The effects of sumatriptan injected via the carotid artery on the cerebral microcirculation were studied in 10 anaesthetized cats.

The local cerebral blood volume (CBV), mean transit time of blood (MTT) and cerebral blood flow (CBF) in the parieto‐temporal cortex were measured by a photoelectric method. CBV represents the cumulative dimensions of the cerebral microvessels.

Sumatriptan at 5 and 50 μg kg−1 had no significant effects on the CBV, MTT, CBF, and mean arterial blood pressure (MABP); 500 μg kg−1 of sumatriptan reduced the CBV, prolonged the MTT, and decreased the CBF (approximately −20%) without affecting the MABP. Sumatriptan, 5 mg kg−1, elicited transient reductions in CBV and CBF, which were attributable to the rapid and marked falls of MABP seen with this dose.

Thus, while a high dose of sumatriptan (500 μg kg−1) exhibits direct vasoconstrictor actions on the cerebral vessels, low doses of sumatriptan, within the therapeutic range, elicit no vasoconstriction. The data do not support a vasoconstrictor action of sumatriptan playing a primary role in reversing the headache of migraine.
Regional and cardiac haemodynamic effects of NG, NG,dimethyl‐l‐arginne and their reversibility by vasodilators in conscious rats
Authors: Gardiner S.M. , Kemp P.A. , Bennett T. , Palmer R.M.J. , Moncada S.
Published: July 2012

A series of experiments was carried out on 3 separate groups of male Long Evans rats, chronically instrumented for the measurement of regional haemodynamics, to compare the effects of NG,NG, dimethyl‐l‐arginine (ADMA) and NG‐monomethyl‐l‐arginine (l‐NMMA), and their reversibility by the nitric oxide donors, S‐nitroso‐N‐acetyl‐penicillamine (SNAP), S‐nitroso‐glutathione (SNOG), sodium nitroprusside (SNP), and the vasodilator, hydralazine.

As previously reported for l‐NMMA, ADMA (1–100 mg kg−1) caused dose‐dependent pressor and bradycardic effects, accompanied by renal, mesenteric and hindquarters vasoconstrictions. The magnitude and duration of these effects were similar for ADMA and l‐NMMA, consistent with their being equipotent inhibitors of nitric oxide synthase.

Infusion of SNAP or SNOG (300 μg kg−1 h−i) after injection of ADMA or l‐NMMA (100 mg kg−1) reversed the pressor but did not abolish the vasoconstrictor, effects of ADMA or l‐NMMA. However, a higher dose of SNAP (3 mg kg−1 h−1) caused complete reversal of the pressor and mesenteric haemodynamic effects of ADMA (100 mg kg−1), although its renal and hindquarters vasoconstrictor effects were not abolished.

Infusion of SNP (300 μg kg−1 h−1) after administration of l‐NMMA (100 mg kg−1), caused complete reversal of its pressor and mesenteric and hindquarters haemodynamic effects, and reduced substantially its renal vasoconstrictor action; hydralazine (7.5 mg kg−1 h−1) was almost as effective as SNP in reversing all these variables.

In animals chronically instrumented for the measurement of cardiac haemodynamics, ADMA (100 mg kg−1) caused a pressor effect accompanied by a rise in central venous pressure, and reductions in heart rate, cardiac index, stroke index, peak aortic flow, maximum rate of rise of aortic flow and total peripheral conductance. The reversal of the pressor effect of ADMA by SNAP (300 μg kg−1 h−1) was accompanied by a reduction of central venous pressure below resting levels and a further diminution of stroke index; all other variables showed an increase, but they still remained below resting levels (with the exception of heart rate).

Thus, following inhibition of NO synthesis, pharmacological intervention with NO donors, or other vasodilators, may cause normalisation of the mean arterial pressure without necessarily returning all associated cardiovascular variables to normal.
Modulation of acetylcholine‐induced contractions of the rat anococcygeus muscle by activation of nitrergic nerves
Authors: Rand M.J. , Li C.G.
Published: July 2012

Acetylcholine‐induced contractions of the rat isolated anococcygeus muscle were blocked by atropine (0.1 μm), slightly enhanced by hexamethonium (0.1 mm) and tetrodotoxin (1 μm), but little affected by prazosin (0.1 μm).

In the presence of the α2‐adrenoceptor agonist, UK14304, which raised the tone of the muscle, acetylcholine had a biphasic effect consisting of an initial relaxation followed by a contraction.

Atropine (0.1 μm) enhanced the relaxant component and abolished the contractile component of the response, whereas tetrodotoxin, ω‐conotoxin GVIA or hexamethonium abolished or greatly reduced the relaxant component.

The nitric oxide synthesis inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME, 100 μm) increased acetylcholine‐induced contractions in the absence of UK14304 and markedly reduced the relaxant component to acetylcholine in the presence of UK14304. The effects of l‐NAME were annulled by l‐arginine (300 μm).

The results suggest that acetylcholine acts concurrently on muscarinic receptors of the smooth muscle to cause contraction and nicotinic receptors of nitrergic nerves to cause relaxation. The observed response is the resultant of these two opposing effects and depends also on the prevailing tone.
Cross‐tolerance between delta‐9‐tetrahydrocannabinol and the cannabimimetic agents, CP 55,940, WIN 55,212‐2 and anandamide
Authors: Pertwee R.G. , Stevenson L.A. , Griffin G.
Published: July 2012

Mice pretreated intraperitoneally for 2 days with delta‐9‐tetrahydrocannabinol (delta‐9‐THC) at a dose of 20 mg kg−1 day−1 and then challenged intravenously with this drug, 24 h after the second pretreatment, showed a 6 fold tolerance to the hypothermic effect of delta‐9‐THC. This pretreatment also induced tolerance to the hypothermic effects of the cannabimimetic agents, CP 55,940 (4.6 fold) and WIN 55,212‐2 (4.9 fold), but not to the hypothermic effect of the putative endogenous cannabinoid, anandamide.

Vasa deferentia removed from mice pretreated intraperitoneally with delta‐9‐THC twice at a dose of 20 mg kg−1 day−1 were less sensitive to its inhibitory effect on electrically‐evoked contractions than vasa deferentia obtained from control animals. The cannabinoid pretreatment induced a 30 fold parallel rightward shift in the lower part of the concentration‐response curve of delta‐9‐THC and a marked reduction in the maximal inhibitory effect of the drug. It also induced tolerance to the inhibitory effects on the twitch response of CP 55,940 (8.7 fold), WIN 55,212‐2 (9.6 fold) and anandamide (12.3 fold).

The results confirm that cannabinoid tolerance can be rapid in onset and support the hypothesis that it is mainly pharmacodynamic in nature. The finding that in vivo pretreatment with delta‐9‐THC can produce tolerance not only to its own inhibitory effect on the vas deferens but also to that of three other cannabimimetic agents, suggests that this tissue would be suitable as an experimental model for investigating the mechanisms responsible for cannabinoid tolerance.

Further experiments are required to establish why tolerance to anandamide‐induced hypothermia was not produced by a pretreatment with delta‐9‐THC that did induce tolerance to the hypothermic effects of delta‐9‐THC, CP 55,940 and WIN 55,212‐2 and to the inhibitory effects of delta‐9‐THC, CP 55,940, WIN 55,212‐2 and anandamide on the twitch response of the vas deferens.
Effect of the platelet‐activating factor antagonist, TCV‐309, and the cyclo‐oxygenase inhibitor, ibuprofen, on the haemodynamic changes in canine experimental endotoxic shock
Authors: Yamanaka Shinya , Iwao Hiroshi , Yukimura Tokihito , Kim Shokei , Miura Katsuyuki
Published: July 2012

The present study was conducted in order to examine the effects of the platelet‐activating factor (PAF) antagonist, TCV‐309, and the cyclo‐oxygenase inhibitor, ibuprofen, on the acute haemodynamic responses to endotoxin in anaesthetized dogs.

Endotoxin (2 mg kg−1, i.v.) induced a severe hypotension by decreasing both total peripheral resistance (TPR) and cardiac output. Endotoxin also decreased central venous pressure and increased effective vascular compliance (EVC), indicating a blood pooling in the capacitance vessels.

The endotoxin‐induced hypotension but not the fall in cardiac output, was markedly attenuated by ibuprofen. Ibuprofen abolished the decrease in TPR and even caused a systemic vasoconstriction. Ibuprofen abolished the increase in EVC.

The hypotension caused by endotoxin was attenuated by TCV‐309 to a lesser extent than ibuprofen. However, the reduction in cardiac output produced by endotoxin was markedly attenuated by the PAF antagonist. TCV‐309 also abolished the increase in EVC. In contrast to ibuprofen, TCV‐309 did not affect the decrease in TPR caused by endotoxin.

Combined treatment with ibuprofen and TCV‐309 markedly attenuated the endotoxin‐induced hypotension, but not the fall in cardiac output. Nevertheless, when compared with animals treated with ibuprofen alone, treatment with ibuprofen and TCV‐309 partly attenuated the endotoxin‐induced reduction in cardiac output and systemic vasoconstriction.

These data indicate that dilatation of both resistance vessels and capacitance vessels contributes to the endotoxin‐induced hypotension. It is suggested that (i) both prostanoids and PAF are involved in dilatation of capacitance vessels, (ii) prostanoids, but not PAF cause dilatation of resistance vessels and (iii) PAF may partly contribute to prostanoid‐independent reduction in cardiac output in acute canine experimental endotoxin shock.