bluuebunny/crossref_metadata_2025 huggingface dataset:
The action of palytoxin on the isolated detrusor muscle of the rat
Authors: Posangi J. , Zar M.A. , Harris J.B.
Published: July 2012

The effects of a coelenterate toxin, palytoxin (PTX) have been studied in the isolated detrusor muscle of the rat.

PTX (1–100 nm) initiated concentration‐dependent contractions of the detrusor; the contraction led to an irreversible tachyphylaxis. Muscle desensitized to PTX continued to respond to acetylcholine (ACh) and excess K+ but the contractions were reduced compared to pre‐PTX contractions.

Contractions evoked by PTX were not affected by the presence of atropine (10 μm), indomethacin (10 μm) or tetrodotoxin (0.5 μm) but were greatly reduced by nifedipine (3 μm) and by the absence of K+. PTX could not evoke contractions in the absence of Ca2+ or in tissues depolarized by exposure to excess K+.

PTX abolished the neurogenic contractile responses to electrical field stimulation (EFS).

Combined treatment with atropine (10 μm) plus nifedipine (3 μm) abolished contractile responses to EFS and greatly reduced the contractile response to PTX.

The contractile response to PTX (100 nm) was reduced following exposure of the muscle to α,β‐methylene ATP.

Exposure to PTX (100 nm) for 1–3 h reduced both the ACh content of the detrusor (by more than 80%), and the immunoreactivity of neuropeptide Y‐containing nerve fibres compared to control.

It is concluded that the primary effect of PTX is to promote the release of endogenous motor transmitters, leading to their eventual depletion.
The effects of combined angiotensin converting enzyme inhibition and β‐adrenoceptor blockade on plasma renin activity in anaesthetized dogs
Authors: Cambridge D. , Whiting M.V. , Butterfield L.J. , Allan G.
Published: July 2012

The effects of β‐adrenoceptor blockade on the changes in plasma renin activity (PRA) following angiotensin enzyme (ACE) inhibition were investigated in pentobarbitone‐chloralose anaesthetized dogs.

ACE‐inhibition, with enalapril (2 mg kg−1), caused a significant reduction in systemic arterial blood pressure (BP) with little or no effect on cardiac function, and a significant elevation of plasma renin activity (PRA). By contrast β‐adrenoceptor blockade with atenolol (1 mg kg−1), caused a similar reduction in BP but in addition, significantly reduced cardiac function and PRA.

A combination of enalapril with atenolol, caused a significant reduction in BP, cardiac function and PRA, hence there was no elevation of PRA, as was seen following ACE‐inhibition with enalapril alone.

The observations with β‐adrenoceptor blockade alone, show that there is an important homeostatic role for the renal sympathetic innervation, mediated by β‐adrenoceptors, in controlling basal renin levels. Furthermore, the renal sympathetic innervation appears to be an important contributor to the renin release caused by an ACE‐inhibitor as the additional presence of a β‐adrenoceptor blocking agent will prevent this release.

BW B385C (2 mg kg−1), which combines both ACE‐inhibition and β‐adrenoceptor blocking properties, also produced reductions in BP and cardiac function similar to those seen with the enalapril/atenolol combination. In addition, for an equivalent degree of ACE‐inhibition by BW 385C, to that seen with enalapril alone, the elevation of PRA was attenuated.

A combination of ACE‐inhibition and β‐adrenoceptor blocking activity in a single entity, such as BW B385C, therefore also produces a reduced renin release when compared with an ACE‐inhibitor, such as enalapril. This provides further confirmation of the importance of the renal sympathetic innervation in the renin response to ACE‐inhibition, and supports the concept of combining ACE‐inhibition with β‐adrenoceptor blockade.
Evidence for a glutamate receptor of the AMPA subtype which mediates insulin release from rat perfused pancreas
Authors: Bertrand G. , Gross R. , Puech R. , Loubatières‐Mariani M.M. , Bockaert J.
Published: July 2012

The effect of l‐glutamate has been studied on insulin secretion by the isolated perfused pancreas of the rat. The glutamate receptor subtype involved has been characterized.

In the presence of a slightly stimulating glucose concentration (8.3 mm), l‐glutamate (5 × 10−5−4 × 10−3 m) induced an immediate, transient and concentration‐dependent insulin response. On the other hand, in the presence of a non stimulating glucose concentration (2.8 mm), l‐glutamate (10−3 m) did not modify the basal insulin secretion.

The three non‐NMDA receptor agonists, kainate (10−4−10−3 m), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA, 5 × 10−5−10−4 m) and quisqualate (5 × 10−6−5 × 10−5 m) all provoked a transient and concentration‐dependent insulin response from pancreas perfused with 8.3 mm glucose. Compared with glutamate, kainate exhibited a similar efficacy, whereas AMPA and quisqualate elicited only a 3 fold lower maximal insulin response. In contrast, NMDA (10−4−10−3 m) was ineffective.

An antagonist of non‐NMDA receptors, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; 5 × 10−5 m) totally prevented the stimulatory effect of l‐glutamate (4 × 10−4 m) and kainate (2 × 10−4 m). In contrast, the NMDA receptor antagonist, (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclohepten‐5,10‐imine ((+) MK801) was without effect.

The insulin secretory effect of glutamate (4 × 10−4 m) was not affected by atropine (3 × 10−7 m) or tetrodotoxin (3 × 10−6 m).

Quisqualate at a high maximally effective concentration (4 × 10−4 m) inhibited glutamate (10−3 m) or kainate (4 × 10−4 m)‐induced insulin release.

This study shows that l‐glutamate stimulates insulin secretion in rat pancreas, by acting on an excitatory amino acid receptor of the AMPA subtype.
Purinoceptors mediating relaxation and spasm in the rat gastric fundus
Authors: Matharu Manjit S. , Hollingsworth Michael
Published: July 2012

The relaxant and spasmogenic effects of purines and analogues were studied in longitudinal strips of rat gastric fundus to characterize the purinoceptors involved. Classification was studied by use of agonist potency orders and of antagonists in circumstances where the influence of confounding factors was reduced. In general tone was raised by carbachol (0.1 μm).

Adenosine produced relaxation and was potentiated by nitrobenzylthioinosine (NBTI, 0.3 and 30 μm), an adenosine‐uptake inhibitor. 8‐Sulphophenyl‐theophylline (8‐SPT, 30 μm), a selective P1‐purinoceptor antagonist, antagonized adenosine and 5′‐N‐ethylcarboxamidoadenosine (NECA), a selective agonist at P1‐purinoceptors.

At resting tone, adenosine 5′‐triphosphate (ATP) induced a small, phasic relaxation followed by a maintained spasm. When tone was raised by carbachol, ATP induced a larger relaxation followed by a smaller spasm. NBTI did not potentiate ATP, nor did 8‐SPT antagonize ATP, suggesting that ATP does not act directly or indirectly at P1‐purinoceptors.

With raised tone, and in the presence of indomethacin (10 μm) and 8‐SPT (30 μm), 2‐methylthio ATP (2‐MeSATP) and ATP produced relaxations followed by spasms while α,β‐methylene ATP (α,β‐MeATP) induced only relaxation; all responses were concentration‐dependent. The compounds had similar slopes and maxima for relaxation and spasm. The rank orders of potency were 2‐MeSATP ≫ α,β‐MeATP > ATP for relaxation and 2‐MeSATP ≫ ATP for spasm.

With raised tone, and in the presence of indomethacin and 8‐SPT, desensitization to α,β‐MeATP (100 μm) completely and only slightly suppressed responses to ATP and 2‐MeSATP, respectively, as relaxants but had no effect on relaxant responses to adenosine. The magnitude of the spasms to ATP and 2‐MeSATP was considerably increased by desensitization with α,β‐MeATP but the spasm to KCl was not affected.

With raised tone, and in the presence of indomethacin and 8‐SPT, reactive blue 2 (10 μm) non‐selectively antagonized ATP, 2‐MeATP, α,β‐MeATP, adenosine and isoprenaline as relaxants. Reactive blue 2 prevented the spasms to ATP and 2‐MeSATP but not spasm to KCl.

With raised tone, and in the presence of indomethacin, suramin (100 μm) antagonized ATP, but not adenosine, as relaxants and antagonized ATP, but not KCl, as spasmogens.

It is proposed that adenosine is susceptible to nucleoside‐specific uptake and acts predominantly via a P1‐purinoceptor and also by a non‐P1‐purinoceptor mechanism. ATP‐ and α,β‐MeATP‐induced relaxations probably occur via a P2X‐purinoceptor. The anomalous nature of the 2‐MeSATP‐induced relaxation suggests it acts both via a P2X‐purinoceptor and an additional mechanism. A P2Y‐purinoceptor is most likely to be involved in the spasms to ATP and 2‐MeSATP. Therefore, the functional nature of the responses mediated by P2X‐ and P2Y‐purinoceptors, relaxation and spasm respectively, are opposite to those seen in most smooth muscles.
Effects of a potassium channel opener (SDZ PCO 400) on guinea‐pig and human pulmonary airways
Authors: Chapman I.D. , Kristersson A. , Mathelin G. , Schaeublin E. , Mazzoni L. , Boubekeur K. , Murphy N. , Morley J.
Published: July 2012

SDZ PCO 400 evoked dose‐related relaxation of isolated airway smooth muscle. For human bronchus precontracted by endogenous tone or addition of carbachol (10−5 m), IC50 values were 1.74 μm and 1.82 μm respectively. With guinea‐pig trachea contracted by endogenous tone, a comparable IC50 (1.79 μm) was observed, but no IC50 (< 100 μm) could be determined following contraction by carbachol (10−6 m).

Airway obstruction induced by intravenous bombesin in the anaesthetized ventilated guinea‐pig was diminished by intravenous injection of SDZ PCO 400 (ID50 54 μg kg−1) or by introduction into the duodenum (ID50 1.0 mg kg−1). Inhalation of nebulized SDZ PCO 400 (0.1 mg kg−1) diminished airway obstruction due to intravenous injection of histamine (3.2–5.6 μg kg−1) for up to 20 min.

Increased bronchoconstrictor responses to bombesin (180–240 ng kg−1) following intravenous infusion of platelet activating factor (PAF) or (±)‐isoprenaline, or to histamine (1.0–3.2 μg kg−1) following intravenous injections of immune complexes, were suppressed following concomitant intravenous infusion of SDZ PCO 400 (ID50 0.3 mg kg−1 h−1, 1.0 mg kg−1 h−1 and 0.1 mg kg−1 h−1 respectively).

Intravenous injection of SDZ PCO 400 (0.1 mg kg−1) effected transient (< 10 min) inhibition of histamine‐induced bronchospasm, yet diminished, for prolonged periods [up to 40 min] the enhanced bronchoconstrictor responses to histamine that followed intravenous injections of immune complexes. The capacity of SDZ PCO 400 to resolve such established airway hyperreactivity was prevented by prior intraduodenal instillation of a potassium channel antagonist, glibenclamide (30 mg kg−1).

In sensitized guinea‐pigs, SDZ PCO 400 inhaled as a dry powder (5.7 mg kg−1) suppressed development of allergic airway hyperreactivity to histamine (1.8–3.2 μg kg−1, i.v.), but failed to diminish accumulation of eosinophils or other inflammatory cells within the airway lumen 24 h after inhalation of ovalbumin.

Preincubation (30 min) of isolated sensitized trachea of guinea‐pig with SDZ PCO 400 (10−5−10−4 m) did not influence contractile responses to ovalbumin. However in anaesthetized sensitized guinea‐pigs, insufflation of SDZ PCO 400 (1.25 mg) as a powder substantially diminished airway obstruction that followed inhalation of ovalbumin. This effect was prevented by prior vagal section.

It is concluded that SDZ PCO 400 reduces airway obstruction not only through direct actions on airway smooth muscle but also by impairing the expression of airway hyperreactivity, without directly influencing inflammatory events in the airways.
The role of induction of nitric oxide synthesis in the altered responses of jugular veins from endotoxaemic rabbits
Authors: Vallance Patrick , Palmer Richard M.J. , Moncada Salvador
Published: July 2012

Endotoxaemia is characterized by hypotension, peripheral vasodilatation and a reduced response to vasoconstrictors. Clinical studies have indicated that venodilatation contributes to the haemodynamic changes, although there is no direct evidence for abnormal venous reactivity. In the present study, the role of nitric oxide (NO) in modifying the responses of rabbit isolated jugular veins was examined in vitro, 4 h after intravenous injection of endotoxin.

Treatment with endotoxin reduced the contractile response to the thromboxane‐mimetic, 9,11‐dideoxy‐11α, 9α‐epoxymethano‐prostaglandin F2α (U‐46619). This affect was endothelium‐independent. The response was partially restored by the NO synthase inhibitor, NG‐monomethyl‐l‐arginine (l‐NMMA 300 μm).

Jugular veins from control animals did not contract to l‐NMMA whereas those from endotoxin‐treated animals showed concentration‐dependent contractions to l‐NMMA. The contractions produced by l‐NMMA were reversed by l‐arginine but not by d‐arginine. Treatment of the animals with dexamethasone (4 mg kg−1) 1 h prior to administration of endotoxin significantly attenuated the response to l‐NMMA.

The response to sodium nitroprusside did not differ significantly between veins from control and endotoxin‐treated animals. Endothelial denudation did not alter the sensitivity of the veins to sodium nitroprusside. Acetylcholine produced endothelium‐dependent relaxations which were similar in veins from control and endotoxin‐treated animals.

The results of this study demonstrate that intravenous administration of endotoxin induces hyporesponsiveness to U‐46619 in jugular veins. This effect is mediated, at least in part, by the induction of NO synthesis in smooth muscle. The induction is prevented by prior treatment with dexamethasone.
Human brain contains a metalloprotease that converts big endothelin‐1 to endothelin‐1 and is inhibited by phosphoramidon and EDTA
Authors: Warner Timothy D. , Schmidt Harald H.H.W. , Kuk Jane , Mitchell Jane A. , Murad Ferid
Published: July 2012

Incubation of big endothelin‐1 (bET‐1) with protein derived from the detergent‐extracted 100,000 g pellet prepared from human brain tissue resulted in the formation of endothelin‐1 (ET‐1) at a rate of 90 fmol mg−1 protein min−1. This formation was inhibited in a concentration‐dependent manner by either phosphoramidon or EDTA, with half‐maximal inhibitory concentrations of 2 and 20 μm, respectively. No conversion of big endothelin‐3 (bET‐3) to endothelin‐3 (ET‐3) was detected under the same conditions. These results show the presence in the human brain of a metalloprotease‐like enzymatic activity which selectively converts bET‐1 and ET‐1. Together with earlier reports of mRNA for ET‐1 this suggests the presence of the entire synthetic pathway for ET‐1 in human brain.
Pharmacological evidence for distinct endothelin receptors in guinea‐pig bronchus and aorta
Authors: Hay D.W.P.
Published: July 2012

The ETA receptor antagonist, BQ‐123 (1 μm) potently antagonized endothelin‐1 (ET‐1) concentration‐response curves in guinea‐pig aorta (pKB = 7.1). However, 10 μm BQ‐123 was without effect on ET‐1‐induced contractions in guinea‐pig bronchus. The ETB‐selective agonist, sarafotoxin S6c did not contract the aorta but was a potent and effective contractile agonist in the bronchus. BQ‐123 (10 μm) was without effect on sarafotoxin S6c‐induced contractions in the bronchus. These data provide evidence for distinct endothelin receptors in guinea‐pig aorta and bronchus, which appear to be predominantly of the ETA and non‐ETA, perhaps ETB, subtypes, respectively.
Dose‐dependent effects of angiotensin converting enzyme (ACE) inhibitors on glomerular prostanoid production by normotensive rats
Authors: Harding P. , Stonier C. , Aber G.M.
Published: July 2012

This study was designed to investigate whether the angiotensin converting enzyme (ACE) inhibitors, captopril, enalapril and fosinopril have a dose‐dependent effect on the production of prostaglandin E2 (PGE2), prostaglandin I2 (prostacyclin, PGI2) and thromboxane A2 (TxA2) by glomeruli isolated from normotensive Wistar‐Kyoto rats.

Measurements of glomerular prostanoid production were made under basal conditions and in the presence of excess exogenous arachidonic acid.

All three ACE inhibitors demonstrated dose‐dependent effects upon glomerular prostanoid production which varied with the individual ACE inhibitor.

Enalapril induced a dose‐dependent increase in the ratio of (PGE2 + PGI2)/TxA2, from 2.17 ± 0.20 to 5.35 ± 0.84 and to 10.0 ± 1.16 with the low and high doses of enalapril respectively. In contrast, the high dose of captopril tended to reduce the ratio when compared to the low dose.

The results obtained in this study suggest that although all three ACE inhibitors appear to induce prostacyclin synthetase and/or modulate phospholipase A2 (PLA2) activity, these effects differ with the ACE inhibitor studied and the dose employed.

This study has demonstrated dose‐dependent effects of three ACE inhibitors on glomerular prostanoid production which may be significant in modulating glomerular haemodynamics and growth characteristics of glomerular cells.
Time‐dependent blockade of neurogenic plasma extravasation in dura mater by 5‐HT1B/D agonists and endopeptidase 24.11
Authors: Huang Zhihong , Byun Barkjang , Matsubara Toshio , Moskowitz Michael A.
Published: July 2012

The delayed effects of stimulating the trigeminal ganglion unilaterally in rats and guinea‐pigs were assessed by measuring the leakage of radiolabelled albumin from blood into the dura mater at intervals for up to 120 min after a 5 min stimulation period (5 Hz, 0.6 mA, 5 ms).

[125I]‐albumin (50 μCi kg−1) was injected i.v. as a tracer 0, 20, 50, 80 or 110 min after stimulation and the animals were killed 10 min later. Extravasation of plasma protein developed for up to 90 min poststimulation.

To examine the mechanism underlying delayed plasma protein extravasation, CP‐93,129 (5‐HT1B receptor agonist, 460 nmol kg−1), sumatriptan (5‐HT1B/D receptor agonist, 24 nmol kg−1), or neutral endopeptidase 24.11 (1 nmol kg−1) were administered 45 or 75 min after trigeminal stimulation and 5 min before radiolabelled albumin. The extravasation response was reduced at 45 min. CP‐23,129 also blocked extravasation when injected 25 min after capsaicin administration (1 μmol kg−1).

If the tracer was injected 5 min prior to electrical trigeminal stimulation, endopeptidase 24.11 (1 nmol kg−1) given 10 min before stimulation blocked the leakage (as reported previously for CP‐93,129 or sumatriptan). All three compounds blocked the leakage when administered 30 min (but not 60 min) poststimulation in this paradigm.

The data support the previously made contention that neuropeptide release from sensory fibres mediates the plasma extravasation response following trigeminal ganglion stimulation, and that release and plasma leakage continue many minutes beyond the stimulation period. Hence, drugs that inhibit neuropeptide release (CP‐93,129, sumatriptan), or enhance breakdown of neuropeptide mediators (endopeptidase 24.11) block the delayed extravasation response. Extravasation developing later than 45 min poststimulation was not neurogenically mediated.
Potentiation of aggregation and inhibition of adenylate cyclase in human platelets by prostaglandin E analogues
Authors: Matthews Jane S. , Jones Robert L.
Published: July 2012

The 16‐phenoxy prostaglandin E analogue sulprostone consistently potentiates primary aggregation waves induced by adenosine 5′‐diphosphate (ADP), PAF and 11,9‐epoxymethano PGH2 (U‐46619) in platelet‐rich plasma from human donors. The effect is not blocked by the TP‐receptor antagonists, EP 092 and GR 32191. The high potency of sulprostone (threshold concentration = 4–10 nm) and the weak block of sulprostone potentiation by the EP1‐receptor antagonist, AH 6809 (pA2 = 4.3) suggest the involvement of EP3‐receptors as opposed to EP1‐ or EP2‐subtypes.

Eight prostaglandin E (PGE) analogues were compared against sulprostone for their effects on PAF‐induced aggregation in human platelet‐rich plasma (PRP) in the presence of GR 32191 and the DP‐receptor antagonist, BW A868C. PGE2 and 11‐deoxy PGE2‐1‐alcohol showed evidence of both potentiating and inhibitory actions and butaprost showed only inhibitory activity at high concentrations. The remaining analogues always elicited potentiation, with the following potency ranking: sulprostone = 16,16‐dimethyl PGE2 > MB 28767 > misoprostol >GR 63779X = 17‐phenyl‐ω‐trinor PGE2. The results again indicate that EP3‐ rather than EP1‐ or EP2‐receptors are involved. However, relative potentiating potency could be affected by differences in plasma protein binding and the very high sensitivity of the human platelet to prostacyclin (IP)‐receptor‐mediated inhibition (IC50 for the specific IP‐receptor agonist cicaprost = 0.8 nm).

On human washed platelet suspensions the PGE analogues, with the exception of butaprost, inhibited the rise in adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) induced by cicaprost (8 nm). PGE2 produced a monophasic inhibition curve (IC50 = 5.4 nm, 92% inhibition at 600 nm). The potency ranking was 16,16‐dimethyl PGE2 > sulprostone > MB 28767 = PGE2 > misoprostol > GR 63778X > 17‐phenyl‐ω‐trinor PGE2> 11‐deoxy PGE2‐1‐alcohol. AH 6809 inhibited the effect of sulprostone and 17‐phenyl‐ω‐trinor PGE2 with pA2 values of 5.75 and 5.32 respectively; these values are at least one log unit lower than those found for EP1‐receptor block in smooth muscle.

There is a statistically significant correlation between IC50 values for the PGE analogues on the human platelet cyclic AMP assay and the guinea‐pig vas deferens (standard EP3 preparation): slope = 1.00, r = 0.80, P < 0.05. However the correlation is far from ideal and GR 63779X in particular has a lower potency in the cyclic AMP assay. At this time we suggest that it is prudent to describe the human platelet receptor as ‘EP3‐like’.

We believe that our results provide further evidence for linking PGE‐induced potentiation of aggregation to inhibition of adenylate cyclase. Sulprostone is a suitable agonist for further study of this system and in particular the nature of the G‐protein linkage(s) involved. In addition the necessity to consider potentiation of platelet aggregation in relation to the clinical use of PGE analogues in man is emphasised.
Interaction of selective compounds with muscarinic receptors at dispersed intestinal smooth muscle cells
Authors: Barocelli E. , Chiavarini M. , Ballabeni V. , Bordi F. , Impicciatore M.
Published: July 2012

The characterization of muscarinic receptors on single cells of the guinea‐pig ileum longitudinal smooth muscle, devoid of neuronal elements, was functionally studied by estimating the affinities of muscarinic antagonists on acetylcholine‐induced contractions.

Atropine (5 × 10−11 to 5 × 10−6 m), 4‐diphenylacetoxy‐N‐methyl‐piperidine methiodide (4‐DAMP, 5 × 10−8 to 5 × 10−6 m), cyclohexyl(4‐fluoro‐phenyl) (3‐piperidinopropyl) silanol (pFHHSiD, 5 × 10−7 to 5 × 10−5 m) as well as pirenzepine (5 × 10−7 to 5 × 10−5 m) competitively antagonized the acetylcholine‐dependent contractions with different affinities (atropine > 4‐DAMP > pFHHSiD > pirenzepine).

Methoctramine (5 × 10−7 to 5 × 10−5 m), and AF‐DX 116 (5 × 10−6 and 5 × 10−5 m) also showed antagonist properties but these deviated from simple competition. These compounds, which discriminate between M2 and M3 receptors, showed a potency lower than that of pirenzepine, the rank order of potencies being pirenzepine > methoctramine > AF‐DX 116. When concentrations of AF‐DX 116, methoctramine and pirenzepine were increased an unspecific contractile effect occurred.

McN‐A‐343, a partial agonist on intact guinea‐pig longitudinal smooth muscle strips, on this preparation induced a weak contraction (about 7% in comparison to control) that was not reversed by antimuscarinic agents.

These data indicate that M3 rather than M2 receptor sites are present on this tissue.
A comparison of the inhibitory effects of sodium nitroprusside, pinacidil and nifedipine on pressor response to NG‐nitro‐l‐arginine
Authors: Wang Yong‐Xiang , Zhou Ting , Pang Catherine C.Y.
Published: July 2012

The inhibitory effects of sodium nitroprusside (SNP), a nitric oxide (NO) donor, on mean arterial pressure (MAP) responses to NG‐nitro‐l‐arginine (l‐NNA) (NO synthase inhibitor), angiotensin II (AII) and noradrenaline (NA) were compared with those of pinacidil (KATP channel opener) and nifedipine (L‐type calcium antagonist) in conscious, unrestrained rats.

Intravenous bolus injections of l‐NNA (1–64 mg kg−1), AII (0.02–1.28 μg kg−1) and NA (0.25–16 μg kg−1) dose‐dependently increased MAP to similar maxima. Intravenous infusions of SNP (1, 4 and 16 μg kg−1 min−1) dose‐dependently increased ED50s of l‐NNA, AII and NA. However, the maximum response evoked by l‐NNA, but not by AII nor NA, was dose‐dependently reduced by SNP. Moreover, the inhibitory effect of SNP on the pressor response to l‐NNA ceased when the infusion of SNP was terminated.

Pinacidil (80 μg kg−1 min−1 for 30 min followed by 5 μg kg−1 min−1) increased ED50s of l‐NNA, AII and NA but did not decrease the maximum responses to any of these agents.

Nifedipine (1 mg kg−1 min−1) non‐selectively reduced maximum responses to l‐NNA, AII and NA to similar levels and increased ED50s of AII and NA but not l‐NNA.

The results show that SNP causes a selective, non‐competitive and reversible inhibition of the pressor response to l‐NNA. This inhibition by SNP is unlikely to be related to hypotension, the opening of ATP‐sensitive potassium channels or blockade of L‐type calcium channels.
Endothelin‐1 does not mediate hypoxic vasoconstriction in canine isolated blood vessels: effect of BQ‐123
Authors: Douglas Stephen A. , Vickery‐Clark Lynne M. , Ohlstein Eliot H.
Published: July 2012

The role of endothelin‐1 in mediating the phenomenon of hypoxic vasoconstriction was examined in canine, isolated pulmonary, circumflex coronary and femoral arterial rings.

In tissues with an intact endothelium, the exogenous application of endothelin‐1 (0.1–300 nm) caused concentration‐dependent increases in canine, isolated pulmonary artery tone. Endothelin‐3 (1–300 nm) was approximately 30 fold less potent than endothelin‐1 as a vasoconstrictor in this tissue. In contrast, the selective ETB‐receptor agonist, sarafotoxin S6c (0.01–1 μm), failed to elicit vasoconstriction in this tissue. Thus, endothelin isopeptide‐induced vasoconstriction of the canine isolated pulmonary artery is mediated exclusively by the ETA‐receptor subtype.

The concentration‐dependent increases in isometric tension induced by endothelin‐1 (0.1–300 nm) were antagonized by the ETA‐selective antagonist, BQ‐123 (10 μm); this concentration of antagonist caused a shift to the right in the concentration‐response curve for endothelin‐1 of approximately two orders of magnitude. This concentration of BQ‐123 did not unmask any ETB‐receptor‐mediated vasoconstriction since sarafotoxin S6c (0.01–1 μm) still failed to elicit contraction in the presence of this concentration of BQ‐123.

The hypoxia‐induced vasoconstriction of canine, isolated pulmonary, circumflex coronary and femoral arterial rings was unaffected by pretreatment with the endothelin receptor antagonist, BQ‐123 (10 μm), a concentration shown previously to antagonize the contractile actions of exogenously applied endothelin‐1 in the isolated pulmonary artery.

These results are the first to provide direct evidence showing that the endothelium‐dependent vasoconstriction observed during acute periods of hypoxia in vitro is not mediated by an endothelin‐related isopeptide.
Two distinct cytosolic calcium responses to extracellular ATP in rat parotid acinar cells
Authors: McMillian Michael K. , Soltoff Stephen P. , Cantley Lewis C. , Rudel RuthAnn , Talamo Barbara R.
Published: July 2012

Increasing concentrations of ATP (0.5 μm‐300 μm) produced a biphasic increase in intracellular calcium concentration [Ca]i in rat parotid acinar cells, reflecting two distinct Cai responses to extracellular ATP.

In the absence of Mg2+ (with 3 mm CaCl2 in the buffer solution), the more sensitive response was maximal at 3–5 μm and was not further increased by 30 μm ATP. This response to ATP was not well maintained and was blocked by ADP (0.5 mm). A second, much larger increase in Cai was observed on addition of 300 μm ATP. This larger effect, which we have described previously, appears to be mediated by ATP4–, and was selectively reversed by 4,4′‐di‐isothiocyanato‐dihydrostilbene‐2,2′‐disulphonate as well as by high concentrations of α,β‐methylene ATP.

Among ATP analogues, only the putative P2Z agonist, 3′‐0‐(4‐benzoyl)benzoyl‐ATP distinguished between the two responses. This analogue was at least 10 fold more potent than ATP in stimulating the ATP4–‐response, but did not evoke the more sensitive response. The agonist potency series for both responses to ATP was identical for other analogues examined (ATP>ATP‐γS = 2‐methylthio ATP (a P2y‐selective agonist) 72>ADP, ITP and α,β‐methylene ATP (a P2X‐selective agonist)).

Although the effect of ATP4– could best be characterized as a P2Z‐type purinoceptor response, this effect was strongly and selectively blocked by reactive blue 2, a putative P2y‐purinoceptor antagonist. Reactive blue 2 may bind to and block P2Z purinoceptors since [γ32P]‐ATP binding to parotid cells was inhibited by this compound.

In contrast to the response to ATP4–, the more sensitive response to ATP was potentiated by reactive blue 2 and was less affected by increases in external Mg2+ and Ca2+.

Parasympathetic denervation selectively increased the more sensitive response, suggesting that it may be physiologically regulated.
Cyclic AMP and Ca2+ interactions affecting epithelial chloride secretion in human cultured colonic epithelia
Authors: MacVinish L.J. , Pickles R.J. , Cuthbert A.W.
Published: July 2012

Chloride secretion in three types of cultured epithelial monolayers derived from a single human colonic adenocarcinoma was measured in terms of short circuit current. The three cell types were designated HCA‐7, Colony 3 and Colony 29.

Responses of HCA‐7 monolayers to basolaterally applied lysylbradykinin (LBK) (10–1000 nm) or carbachol (1–100 μm) were potentiated by pre‐exposure to forskolin (10 μm) for 5 min. Forskolin itself increased short circuit current (SCC), so that the total response to forskolin and LBK or carbachol were non‐additive.

Colony 3 cells did not respond to LBK on either face but did to carbachol on the basolateral side, while Colony 29 epithelia responded to LBK on both sides and to carbachol and histamine basolaterally. Unlike HCA‐7 epithelia, responses in Colony 3 and Colony 29 epithelia were not potentiated by forskolin, but were attenuated by piroxicam.

In the presence of piroxicam, both forskolin and prostaglandin E2 were able to potentiate the action of both LBK and carbachol in Colony 29 epithelia.

LBK receptor activation in Colony 29 epithelia is transduced into an increase in intracellular Ca2+ and cyclic AMP, while in HCA‐7 epithelia there is only an increase in intracellular Ca2+ (Cai). These conclusions are considered to apply to both apical and basolateral kinin receptors.

It is shown that forskolin has no effect on the elevation of Ca2+ by LBK in either HCA‐7 or Colony 29 cells.

It is concluded that potentiation of agonist responses occurs when cyclic AMP is raised at the time that intracellular Ca2+ increases. No potentiation of LBK or carbachol by forskolin occurs in Colony 29 monolayers as these agonists increase cyclic AMP via eicosanoid production.
Electropharmacological effects of berberine on canine cardiac Purkinje fibres and ventricular muscle and atrial muscle of the rabbit
Authors: Neto Francisco Riccioppo
Published: July 2012

Conventional microelectrode techniques were used for intracellular recordings of the transmembrane electrical potentials, the effects of berberine were studied on canine cardiac Purkinje and ventricular muscle fibres and on rabbit atrial fibres.

Berberine (3–30 μm) increased in a concentration‐dependent manner, the action potential duration (APD) in canine Purkinje and ventricular muscle without affecting other parameters of the action potential.

The berberine‐induced enlargement of the APD showed reverse use‐dependence, so that the effect was greater at lower rates of stimulation.

Preparations perfused with berberine (30 μm) and driven at rates below 0.5 Hz exhibited early after depolarizations which persisted 3–4 h after washing.

The early afterdepolarizations were reversibly abolished by perfusion with lignocaine (3 μm) or by the increase in the rate of stimulation.

The effective refractory period (ERP) of Purkinje fibres was greatly increased by berberine (30 μm); however, the ratio ERP/APD was not significantly affected.

Berberine (10–100 μm) decreased in a concentration‐dependent manner the spontaneous frequency of rabbit sinoatrial cells. The decrease in frequency was accompanied by a depression of the phase 4 depolarization, without significant changes in other parameters of the nodal action potential.

Atropine (2.5 μm) did not affect the bradycardic effect of berberine. On the other hand, berberine (30 μm) did not alter the chronotropic effect of isoprenaline.

Berberine (30 μm) also increased the duration of slow responses in K‐depolarized rabbit atrial muscle fibres, other parameters being unaffected.

It is suggested that berberine exerts Class III antiarrhythimic and proarrhythmic actions in cardiac muscle of the dog in vitro.
Investigations into the mechanism of vasoconstrictor action of the topical steroid betamethasone‐17‐valerate in the rat
Authors: Ahluwalia A. , Flower R.J.
Published: July 2012

The effect of topical betamethasone upon skin blood flow was investigated in the rat. Two types of vasodilator stimuli were used; local heating to the surface of the skin and intradermal application of inflammatory agents. Blood flow was measured by laser doppler velocimetry.

Topical betamethasone‐17‐valerate (1 g with an 18 h pretreatment) significantly inhibited the heat‐induced vasodilatation in the rat skin, as also did systemically administered betamethasone (1 mg kg−1, 3 h pretreatment).

Angiotensin converting enzyme (ACE) inhibitors (captopril, 5 mg kg−1 and enalapril, 1 mg kg−1, 30 min pretreatments) were the only drugs out of several different types of systemically administered inhibitors and antagonists that were tested which also inhibited the heat‐induced vasodilatation. Aprotinin (100,000 KIU kg−1, 5 min pretreatment) a serine protease inhibitor, significantly potentiated the heat‐induced response.

Bradykinin (50 nmol per site), des‐Arg9‐bradykinin (5 nmol per site), substance P (0.1 nmol per site) and capsaicin (1 μmol per site) induced an increase in skin blood flow.

Topical betamethasone treatment resulted in a significant inhibition of the vasodilator response to des‐Arg9‐bradykinin, whereas captopril treatment inhibited the responses to substance P, capsaicin, bradykinin and des‐Arg9‐bradykinin.

Intradermal application of captopril (10–100 μg) also caused a dose‐dependent inhibition of the heat‐induced vasodilatation.

These results suggest that topical betamethasone may be acting in a manner similar to that of the ACE inhibitors to produce an inhibition of the flow responses in the skin and that this effect may be brought about by interfering with the action of vasodilator peptide(s) or protein(s).
Incomplete inhibition of the pressor effects of endothelin‐1 and related peptides in the anaesthetized rat with BQ‐123 provides evidence for more than one vasoconstrictor receptor
Authors: McMurdo Lorraine , Corder Roger , Thiemermann Christoph , Vane John R.
Published: July 2012

The effects of the ETA receptor antagonist, BQ‐123 on blood pressure changes induced by various members of the endothelin (ET)/sarafotoxin (SX) peptide superfamily were investigated in the anaesthetized rat.

ET‐1 (1 nmol kg−1, i.v. bolus) induced a sustained increase in mean arterial pressure (MAP, maximum increase 44 ± 3 mmHg). Intravenous injection of BQ‐123 at 0.2, 1.0 or 5.0 mg kg−1 5 min before ET‐1 inhibited the pressor response by 18, 50 and 61%, respectively. The ET‐1 pressor response was inhibited by 75% when the peptide was given 60 min after the start of a 120 min i.v. infusion of BQ‐123 (0.2 mg kg−1 min−1).

In addition to ET‐1, BQ‐123 (1 mg kg−1, i.v. bolus) attenuated the pressor responses to big ET‐1 (1 nmol kg−1, i.v., bolus, maximum increase in MAP: 68 ± 7 mmHg), ET‐3 (3 nmol kg−1, i.v., bolus, maximum response: 30 ± 3 mmHg), SX6b (1 nmol kg−1, i.v., bolus, maximum response: 41 ± 5 mmHg) and SX6c (1 nmol kg−1, i.v., bolus, maximum response: 24 ± 4 mmHg) by 65, 60, 88 and 50%, respectively.

With the exception of big ET‐1, all the peptides used in this study induced an initial transient depressor response (–32 ±3 mmHg, n = 18). Although BQ‐123 (1 mg kg−1, i.v., bolus) did not affect the absolute magnitude of the fall in MAP, the ETA receptor antagonist significantly prolonged the depressor responses induced by ET‐3 and SX6b.

Thus, BQ‐123 attenuates the pressor, but not the depressor effects of ET‐1, big ET‐1, ET‐3, SX6b and SX6c. Complete inhibition of the pressor responses could not be achieved, suggesting that a component of the pressor response is not mediated via the ETA receptor.
Anti‐inflammatory actions of an N‐terminal peptide from human lipocortin 1
Authors: Cirino G. , Cicala C. , Sorrentino L. , Ciliberto G. , Arpaia G. , Perretti M. , Flower R.J.
Published: July 2012

An acetylated polypeptide corresponding to residues 2–26 of human lipocortin 1 was synthesized and the anti‐inflammatory activity assessed in three models of acute inflammation in rat and mouse. In the carrageenin rat paw oedema test, the peptide produced a maximal inhibition of approximately 41% at the 3 h time point with a 10 μg dose. When rat paw oedema was induced by the injection of venom phospholipase A2, the peptide produced a significant inhibition (31%) at the top dose of 20 μg per paw. In the mouse air‐pouch model, systemic treatment with the peptide produced a dramatic reduction in cytokine‐induced leukocyte migration with an ID50 of approximately 40 μg per mouse. The N‐terminal peptide 2–26 shares the actions of lipocortin 1 in these acute models of inflammation.
[Leu8]des‐Arg9‐bradykinin inhibits the angiogenic effect of bradykinin and interleukin‐1 in rats
Authors: Hu De‐En , Fan Tai‐Ping D.
Published: July 2012

Subcutaneous implantation of sterile polyether sponges in rats elicited a reproducible neovascular response over 14 days, as determined by measurements of relative sponge blood flow by a 133Xe clearance technique. The angiogenic response was verified by quantitation of haemoglobin contents and histological evaluation of vascularized sponges.

Daily administration of 1 nmol of bradykinin (BK) into the implants significantly enhanced the basal sponge‐induced neovascularization, leading to higher 133Xe clearance values, increased haemoglobin contents, cellularity and vascularity.

When given alone, lower doses of BK (10 pmol) or recombinant human interleukin‐1 α (IL‐1α, 0.3 pmol) produced no apparent effects on the basal sponge‐induced angiogenesis. However, co‐administration of these two peptides produced an angiogenic response similar to that elicited by 1 nmol of BK.

The BK/IL‐1α‐induced neovascularization was abolished by the bradykinin B1 receptor antagonist, [Leu8]des‐Arg9‐BK (1 nmol day−1), but not by the B2 receptor antagonist Ac‐d‐Arg‐[Hyp3,d‐Phe7,Leu8]‐BK (1 nmol day−1).

Thus, if such interaction between BK and IL‐1α contributes to the excessive neovascularization in chronic inflammatory diseases, the blockade of B1 receptors may provide an effective treatment.
Role of cyclic AMP in promoting the thromboresistance of human endothelial cells by enhancing thrombomodulin and decreasing tissue factor activities
Authors: Archipoff Gisèle , Beretz Alain , Bartha Katalin , Brisson Christine , de la Salle Corinne , Froget‐Léon Catherine , Klein‐Soyer Claudine , Cazenave Jean‐Pierre
Published: July 2012

The effects of forskolin, prostaglandin E1 (PGE1), dibutyryl cyclic AMP (db cyclic AMP), dibutyryl cyclic GMP (db cyclic GMP) and 3‐isobutyl‐1‐methyl‐xanthine (IBMX) were investigated on the expression of tissue factor and thrombomodulin activities on the surface of human saphenous vein endothelial cells (HSVEC) in culture.

Forskolin (10−6 to 10−4 m), PGE1 (10−7 to 10−5 m) and db cyclic AMP (10−4 to 10−3 m) caused a concentration‐dependent decrease of cytokine‐induced tissue factor activity.

Similar concentrations of forskolin, PGE1 and db cyclic AMP enhanced significantly constitutive thrombomodulin activity and reversed the decrease of this activity caused by interleukin‐1 (IL‐1).

IBMX (10−4 m) decreased tissue factor activity and enhanced the effect of forskolin on tissue factor and thrombomodulin activities.

Forskolin (10−4 m) decreased the IL‐1‐induced tissue factor mRNA and increased the thrombomodulin mRNA level. IL‐1 did not change the thrombomodulin mRNA level after 2 h of incubation with HSVEC in culture.

Dibutyryl cyclic GMP (10−4 m to 10−3 m) did not influence tissue factor or thrombomodulin activity.

Our data suggest that elevation of intracellular cyclic AMP levels may participate in the regulation of tissue factor and thrombomodulin expression, thus contributing to promote or restore antithrombotic properties of the endothelium.
Investigation of the subtypes of α1‐adrenoceptor mediating contractions of rat aorta, vas deferens and spleen
Authors: Aboud R. , Shafii M. , Docherty J.R.
Published: July 2012

The subtypes of α1‐adrenoceptor mediating contractions to exogenous noradrenaline (NA) or phenylephrine in rat vas deferens, spleen and aorta, and mediating contractions to endogenous NA in rat vas deferens have been examined.

In rat vas deferens, the competitive antagonists prazosin, WB 4101, benoxathian and 5‐methyl‐urapidil inhibited contractions to NA with pA2 values of 9.26, 9.54, 9.02 and 8.43, respectively. The irreversible antagonist chloroethylclonidine (CEC) (100 μm) failed to affect contractions to NA.

In rat vas deferens in the presence of nifedipine (10 μm), contractions to NA were significantly attenuated and under these conditions, CEC (100 μm) significantly reduced the maximum response to NA.

In rat spleen, the competitive antagonists prazosin, WB 4101 and benoxathian inhibited contractions to phenylephrine with pA2 values of 9.56, 8.85 and 7.60, respectively, and 5‐methyl‐urapidil had a KB of 6.62. CEC (100 μm) significantly reduced the maximum contraction to phenylephrine.

In rat aorta, the competitive antagonists, prazosin, WB 4101, benoxathian and 5‐methyl‐urapidil inhibited contractions to NA with pA2 values of 9.45, 9.21, 8.55 and 8.12, respectively. CEC (100 μm) produced an approximately parallel shift in the potency of NA, without significantly reducing the maximum response.

In epididymal portions of rat vas deferens in the presence of nifedipine (10 μm), the isometric contraction to a single electrical pulse was significantly reduced by CEC (100 μm), and by the competitive antagonists prazosin, WB 4101, benoxathian and 5‐methyl‐urapidil at concentrations of 1 nm.

In prostatic portions of rat vas deferens, the α1‐adrenoceptor agonist, amidephrine, produced concentration‐dependent increases in the isometric contraction to a single electrical stimulus and the maximum increase in the evoked response produced by amidephrine was unaffected by CEC (100 μm).

Contractions of rat vas deferens produced by NA (and amidephrine) are mediated predominantly by α1A‐adrenoceptors as shown by the high potency of α1A‐adrenoceptor selective antagonists and the lack of effect of CEC. A small CEC‐sensitive response, particularly in epididymal portions, was revealed in the presence of nifedipine. Contractions of rat spleen are mediated by α1B‐adrenoceptors since α1A‐selective antagonists showed low potency and CEC significantly reduced the maximum contraction to phenylephrine. Contractions of rat aorta to NA are mediated by non‐α1A, non‐α1B‐adrenoceptors, due to the high potency of the α1A‐selective antagonists and sensitivity to CEC.

The noradrenergic contraction of epididymal portions of rat vas deferens in the presence of nifedipine is CEC‐sensitive, but the α1A‐selective antagonists showed high potency, suggesting that this response is mediated by non‐α1A, non‐α1B‐adrenoceptors.

In conclusion, at least three subtypes of functional α1‐adrenoceptors have been demonstrated in these studies.
Effects of pyrogenic immunomodulators on the release of corticotrophin‐releasing factor‐41 and prostaglandin E2 from the intact rat hypothalamus in vitro
Authors: Milton N.G.N. , Self C.H. , Hillhouse E.W.
Published: July 2012

The actions of the following pyrogens: lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (Poly‐I:C), human interleukin (IL)‐1α and IL‐1β, human IL‐6 and rat interferon (INF) on corticotrophin‐releasing factor‐41 (CRF‐41) and prostanglandin E2 (PGE2) release from the intact rat hypothalamus in vitro have been studied.

Rat hypothalami were incubated in vitro in an artificial cerebrospinal fluid. Immunoreactive (ir)‐CFR‐41 and PGE2 released into the medium were measured by two‐site enzyme amplified immunometric assay (EAIA) and radioimmunoassay (RIA) respectively.

Human IL‐6 (1 to 10,000 iu ml−1) caused a dose‐dependent release of irCRF‐41, rising to a maximal 3–4 fold increase over basal at the highest dose tested. Human IL‐1α (1 to 1000 iu ml−1), human IL‐1β (1 to 1000 iu ml−1), poly‐I:C (10 pg ml−1 to 100 μg ml−1) and rat INF (1 to 10,000 IRu ml−1) all failed to alter irCRF‐41 release.

LPS (1 mg ml−1) caused a 35% decrease in irCRF‐41 release; however, over the dose‐range of 0.1 μg ml−1 to 100 μg ml−1, LPS failed to alter irCRF‐41 release. The decreased irCRF‐41 release in response to LPS (1 mg ml−1) was accompanied by a decrease in the subsequent 56 mm KCl stimulation of irCRF‐41.

Human IL‐1α and IL‐1β (1000 iu ml−1) were able to stimulate the release of irPGE2 from intact hypothalami, causing a 2 fold increase over basal release. Poly‐I:C (100 μg ml−1), LPS (0.1 μg ml−1 to 1 mg ml−1), rat INF (10,000 IRu ml−1) and human IL‐6 (1 to 10,000 iu ml−1) all failed to alter irPGE2 release.

In conclusion, these results suggest that the in vitro release of CRF‐41 and PGE2, in response to pyrogens, are mediated via different cytokines. In view of this it is possible that different cytokines may mediate the temperature, prostaglandin and hypothalamo‐pituitary‐adrenocortical axis activation seen during pyrogenic stimulation in vivo.
Effects of pH on the actions of dizocilpine at the N‐methyl‐D‐aspartate receptor complex
Authors: Rajdev Sunita , Reynolds Ian J.
Published: July 2012

The effects of varying pH from 6.5 to 7.4 and 8.0 on the actions of dizocilpine (MK801) on the N‐methyl‐d‐aspartate (NMDA) receptor were investigated by use of a [3H]‐dizocilpine binding assay and NMDA‐induced intracellular free Ca2+ ([Ca2+]i) increases in cultured forebrain neurones.

Increasing pH from 6.5 to 8.0 significantly increased the rate of association and dissociation of [3H]‐dizocilpine. The association process was better described by two rate constants under each condition, while only dissociation of [3H]‐dizocilpine at pH 8.0 required two rate constants adequately to describe the curve. Equilibrium affinity of [3H]‐dizocilpine was not altered by changing pH from 6.5 to 8.0.

NMDA and glycine together increased [Ca2+]i measured by fura‐2 microspectrofluorimetry in single cultured neurones from rat forebrain. Compared to control response measured at pH 7.4, the combined effects of NMDA and glycine were reduced to 38.9% of control values by lowering pH to 6.5 and increased to 148.9% by raising pH to 8.0.

Dizocilpine (200 nm) effectively reversed increases in [Ca2+]i produced by NMDA together with glycine. The rate of reversal produced by this concentration of dizocilpine was considerably slower than that required for cells to recover to baseline following agonist removal. The rate at which dizocilpine reversed NMDA‐ and glycine‐induced [Ca2+]i increases was not altered by raising pH from 6.5 to 8.0.

These data support the hypothesis that the rates associated with [3H]‐dizocilpine binding are controlled by the level of activation of the receptor. In addition, these data confirm previous findings that NMDA responses are sensitive to small changes in pH. However, the lack of sensitivity to pH changes of dizocilpine inhibition of NMDA responses show that other factors are also important in controlling the action of channel‐blocking NMDA receptor antagonists.