bluuebunny/crossref_metadata_2025 huggingface dataset:
The α‐ and β‐adrenoceptor blocking activities of labetalol and its RR‐SR (50:50) stereoisomers
Authors: Riva E. , Mennini T. , Latini R.
Published: July 2012

We compared the α1, α2‐ and β1‐adrenoceptor blocking potencies of labetalol with those of its two stereoisomers (RR and SR) in pithed rats and in homogenized rat cerebral cortex and heart.

In pithed rats, labetalol and the RR‐SR combination were given orally either at doses of 25 and 50 mg kg−1 body wt. or intravenously at doses of 1 and 5 mg kg−1 body wt. Prazosin 4 and 20 μg kg−1 body wt. and propranolol 1 and 5 mg kg−1 body wt., were given intravenously for comparison studies of potency at α1‐ and β1‐adrenoceptors, respectively. Effects were studied before and after i.v. administration of either phenylephrine (at doses which increased the mean arterial pressure by approximately 80 mmHg) or isoprenaline (at doses that increased heart rate by approximately 100 beats min−1).

In pithed rats, labetalol and the RR‐SR combination antagonized, in a dose‐dependent manner, the pressor effect of phenylephrine (P < 0.05) and the chronotropic effect of isoprenaline (P < 0.05). Following both oral and intravenous dosing, the RR‐SR combination was twice potent as labetalol in terms of α1‐and β1‐adrenoceptor antagonism at equivalent doses.

Labetalol and the enantiomers lacked affinity at α2‐adrenoceptors while at α1‐adrenoceptors the order of potency was prazosin ≫ RR‐SR > labetalol. At β1‐adrenoceptors, the affinity of the compound RR‐SR was about 3 times that of labetalol.

As labetalol is a mixture of active (RR and SR) and inactive (SS and SR) enantiomers (in terms of α‐ and β‐receptor actions), the combination of RR and SR may be a valuable substitute for labetalol in the treatment of systemic hypertension. Although the potential for non‐specific side effects (common to all four enantiomers) could be expected to be diminished, recent reports by postmarketing surveillance indicate that the RR isomer (dilevalol) can induce liver toxicity. Interestingly, labetalol is devoid of this effect; whether the combination of RR and SR enantiomers could be of clinical importance warrants further investigation.
An analysis of the nitrate‐like and K channel opening actions of KRN2391 in canine coronary arterial smooth muscle
Authors: Okada Yuji , Yanagisawa Teruyuki , Taira Norio
Published: July 2012

To clarify the mechanism of action of KRN2391, a new vasodilator containing a nitroxy group, its effects on intracellular Ca2+ concentration ([Ca2+]i) and force of contraction in canine coronary artery were compared with those of two derivatives lacking the nitro group.

KRN2391, its hydroxy and acetoxy derivative (Compound 2 and Compound 3, respectively) partially reduced [Ca2+]i in 5 or 30 mm KCl physiological salt solution (PSS), effects which were antagonized by glibenclamide. No KRN2391‐induced change in [Ca2+]i was observed in 90 mm KCl‐PSS.

The order of potency in reducing [Ca2+]i and inhibiting the contracture in 30 mm KCl‐PSS was: KRN2391 > Compound 3 > Compound 2.

In 30 mm KCl‐PSS, KRN2391 shifted the [Ca2+]i‐force relationship so that a greater increase in [Ca2+]i was needed to produce force. Compounds 2 and 3 were ineffective. The [Ca2+]i‐force curve obtained in 90 mm KCl‐PSS was shifted to the right by KRN2391 (10−4 m).

The ability of KRN2391 to reduce the force of contraction in both 30 mm and 90 mm KCl‐PSS was inhibited by 10−5 m methylene blue.

KRN2391 inhibited U46619‐induced contractions; this effect was associated with a reduction of [Ca2+]i, which decreased below the basal level.

Thus, KRN2391 is a potent vasodilator in canine coronary artery. It possesses nitrate‐like and potassium channel opening actions and can be designated as a nitrate‐potassium channel opener (N‐K) hybrid. The denitrate derivatives of KRN2391 are specific K channel openers. The nitroxy moiety in KRN2391 is important for not only its action as a nitrate but also its potency as a K channel opener.
The mechanism of LTE4‐induced histamine hyperresponsiveness in guinea‐pig tracheal and human bronchial smooth muscle, in vitro
Authors: Jacques Crawford A.J. , Spur Bernd W. , Johnson Malcolm , Lee Tak H.
Published: July 2012

Preincubation of guinea‐pig tracheal smooth muscle with leukotriene E4 (LTE4) in vitro increased its subsequent responsiveness to histamine.

LTE4 pretreatment of guinea‐pig tracheal strips did not affect the subsequent responsiveness to either the contractile agents, carbachol and KCl, or to the relaxant β‐adrenoceptor agonist, isoprenaline.

LTE4‐induced airway histamine hyperresponsiveness was blocked by indomethacin (5 μm), GR32191 (3 μm), atropine (1 μm) and tetrodotoxin (1 μm).

U46619, a stable thromboxane A2‐analogue, at a non‐contractile concentration of 4 nm, increased tracheal smooth muscle sensitivity to histamine.

Both LTE4 and U46619 pretreatment increased the contractile response of tracheal smooth muscle to electrical field stimulation.

Preincubation of human bronchial spirals with LTE4 in vitro increased its subsequent responsiveness to histamine.

LTE4‐induced histamine hyperresponsiveness of human bronchus was inhibited by GR32191 (3 μm) and atropine (1 μm).

It is proposed that LTE4 induces guinea‐pig airway smooth muscle hyperresponsiveness to histamine via a facilitation of cholinergic neurotransmission, which is dependent upon the secondary generation of prostanoid mediator(s) acting on TP‐receptors situated on cholinergic nerve terminals. In addition, it is suggested that LTE4 may induce histamine hyperresponsiveness of human bronchus in vitro by a similar mechanism as to that seen in guinea‐pig central airway smooth muscle.
An analysis of the mechanism of the inotropic action of some milrinone analogues in guinea‐pig isolated atria
Authors: Dorigo P. , Gaion R.M. , Belluco P. , Mosti L. , Borea P.A. , Maragno I.
Published: July 2012

It has been reported previously that the milrinone analogues, ethyl 5‐cyano‐1,6‐dihydro‐2‐methyl‐6‐oxo‐3 pyridine carboxylate (I) and ethyl 5‐cyano‐1,6‐dihydro‐2‐ethyl‐6‐oxo‐3 pyridine carboxilate (II) exert a positive inotropic effect (EC50 = 15.6 ± 0.2 μm and 40.3 ± 0.1 μm) both on spontaneously beating and on electrically driven atria from reserpine‐treated guinea‐pigs. In the present study the mechanism of the inotropic action of these two agents was investigated.

In electrically driven left atrium from resperpine‐treated guinea‐pigs the EC50 values for inotropic activity for compounds (I) and (II) corresponded to that of milrinone (EC50 = 25 ± 0.1 μm) but compound (I) induced a greater maximum effect. This corresponded to a percentage increase in developed tension over control of 63 ± 0.3 whereas the maximum inotropic effect of milrinone was 48 ± 0.3 and that of compound (II) was 47 ± 0.2.

The inotropic activity of compounds (I) and (II) (10–100 μm) was resistant to propranolol (0.1 μm), thus excluding the involvement of β‐adrenoceptors.

Since the inotropism induced by compounds (I) and (II) was not reduced by carbachol (1 nm‐0.5 μm), an action involving changes in adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) can be excluded.

The inotropic action of compounds (I) and (II) was blocked selectively by 8‐phenyltheophyline (10 μm) or adenosine deaminase (2 u ml−1).

Both (I) and (II) inhibited, in an apparently competitive manner, the negative inotropic effect induced by N6‐(l‐phenylisopropyl) adenosine (l‐PIA), a stable adenosine agonist. The pA2 values for (I) and (II) were 4.79 and 4.36, respectively.

In rat brain compounds (I) and (II) inhibited the specific binding of N6‐cyclohexyl[3H]‐adenosine‐([3H]‐CHA) with an IC50 of 0.18 ± 0.01 mm and 0.25 ± 0.02 mm, respectively, which were similar to their IC50 values for blocking the PIA‐induced negative inotropic effect and which are also in the range of concentrations that are effective in inducing positive inotropism in guinea‐pig atria.

The results from the present study suggest that antagonism of endogenous purines causes positive inotropism without affecting intracellular cyclic AMP levels.
Analysis of the 5‐HT receptors mediating contractions in the rabbit isolated renal artery
Authors: Tadipatri Sreekanth , van Heuven‐Nolsen Dicky , Feniuk Wasyl , Saxena Pramod R.
Published: July 2012

Using a number of agonist and antagonist compounds, we have attempted to characterize the responses and receptors involved in the effects of 5‐hydroxytryptamine (5‐HT) in the rabbit isolated renal artery.

In vessel segments precontracted with the thromboxane‐mimetic agent, U46619 (100 nm), neither 5‐HT (10−8 to 10−4 m) nor 5‐carboxamidotryptamine (5‐CT; 10−8 to 3 × 10−4 m) caused relaxations like those observed with methacholine. Both 5‐HT and 5‐CT further increased the tone of the vessels, with pD2 values of 7.1 and 7.9, respectively.

In the absence of U46619, both 5‐HT (10−7 to 3 × 10−3 m) and 5‐CT (10−7 to 10−3 m) contracted the rabbit renal artery, but with reduced potencies. The contractions to 5‐HT were reproducible and the rank order of potency (pD2) of the agonists was: α‐methyl‐5‐HT (5.7), sumatriptan (5.3), 5‐HT (5.1), 8‐hydroxy‐2(di‐n‐propylamino)tetralin (5.0), 5‐CT (4.7) and 5‐methoxytryptamine (4.3). 1‐(2,5‐Dimethoxy‐4‐iodophenyl)‐2‐aminopropane, flesinoxan and RU 24969 elicited either only small contractions or none at all.

The contractile effect of 5‐HT was unaffected by MDL 72222 (10−6 m) and metergoline (10−8 and 10−7 m), was weakly antagonized by ketanserin and phentolamine (pKB: 6.6 and 6.8, respectively), but was effectively antagonized by methiothepin (pKB: 8.6). Responses to 5‐CT and sumatriptan were affected by ketanserin, phentolamine and methiothepin similarly to 5‐HT‐induced responses.

Ketanserin was ineffective against noradrenaline‐induced contractions, which were antagonized by phentolamine with a pKB of 7.3. The pKB values of phentolamine against 5‐HT, 5‐CT or sumatriptan were about half a log unit lower than against noradrenaline.

In vascular preparations treated with cocaine (3 × 10−5 m), the potency (pKB) of phentolamine as an antagonist of the responses to noradrenaline (7.6) and 5‐HT (6.7) did not differ significantly from the values in untreated preparations. However, the difference between the pKB values of phentolamine against the two agonists was now about one log unit.

Pretreatment of the vascular strips with 6‐hydroxydopamine (1.5 × 10−3 m) did not significantly affect responses to 5‐HT or 5‐CT, but almost eliminated those to tyramine. Cocaine (3 × 10−5 m) slightly potentiated noradrenaline‐induced contractions, but did not significantly affect those induced by 5‐HT.

These data suggest that: (i) 5‐HT receptors mediating vasodilatation are not present in the rabbit renal artery smooth muscle or endothelium; (ii) the contractile effect of 5‐HT does not involve the release of noradrenaline from sympathetic nerve stores; (iii) the 5‐HT receptor in the rabbit renal artery is not of the 5‐HT2, 5‐HT3 or 5‐HT4 type. The pharmacological properties of this receptor most closely resemble those described for the heterogeneous 5‐HT1‐like category.
Attenuated responses to endothelin‐1, KCl and CaCl2, but not noradrenaline, of aortae from rats with streptozotocin‐induced diabetes mellitus
Authors: Fulton DJ.R. , Hodgson W.C. , Sikorski B.W. , King R.G.
Published: July 2012

This study investigated the responsiveness to vasoconstrictor agents (including endothelin‐1, ET‐1) of aortic rings from rats with two‐week streptozotocin (STZ, 60 mg kg−1, i.v.)‐induced diabetes and vehicle‐treated control rats. The basal tension was 10 g, which was estimated to be more physiological than the tension of 1–2 g that has been previously used for most studies of aortic rings from diabetic rats.

Maximum responses to ET‐1 (0.13–18 nm), KCl (2–20 mm) or CaCl2 (10 μm–10 mm) were reduced in aortae from STZ‐treated rats compared to those from control rats. Such reductions were still evident after removal of the endothelium.

Responses to noradrenaline (NA, 0.1 nm‐26 μm) of aortae from STZ‐treated rats were not significantly different from responses of aortae of control rats.

Removal of endothelium resulted in a significant reduction in the EC50 values for NA of rings from both STZ‐treated rats (6.90 ± 0.13 and 8.17 ± 0.35 (–log m) with and without endothelium, respectively, n = 5) and control rats (6.90 ± 0.15 and 8.37 ± 0.44 (–log m) with and without endothelium, respectively, n = 5).

In calcium‐free medium (with 1 mm EGTA), responses to NA and ET‐1 were reduced compared with those in normal Krebs solution and maximum responses were less in rings from STZ‐treated compared with control rats.

Indomethacin (5 μm) did not prevent the reduced maximum responsiveness to ET‐1 in rings from STZ‐treated rats compared with those from controls.

This study indicates that changes in vascular responsiveness to ET‐1, KCl and CaCl2 (but not NA) occur in aortae of two‐week STZ‐treated rats. The endothelium does not appear to play a major role in mediating changes in responsiveness to ET‐1.
Potentiation by endothelin‐1 of 5‐hydroxytryptamine‐induced contraction in coronary artery of the pig
Authors: Nakayama Koichi , Ishigai Yutaka , Uchida Hirohisa , Tanaka Yoshio
Published: July 2012

In order to elucidate the physiological and potential pathological roles of endothelin‐1 (ET‐1) in coronary artery contraction and relaxation, we undertook the present study to examine the action of ET‐1 itself, and the combined effects of ET‐1 with vasoconstrictor agonists such as acetylcholine (ACh), histamine, and 5‐hydroxytryptamine (5‐HT), all of which have been implicated in the genesis of coronary spasm.

Isometric tension and cytosolic Ca2+ concentration ([Ca2+]i) in a ring segment of porcine coronary artery loaded with fura‐2 were measured simultaneously.

ET‐1 contracted the artery in a concentration‐dependent manner; and nisoldipine, a Ca2+ channel blocking drug of the 1,4‐dihydropyridine type, antagonized the ET‐1 action non‐competitively. A radioreceptor binding assay also indicated the mutually exclusive binding of ET‐1 and (+)‐[3H]‐PN200–110, a Ca2+ channel ligand, to the membrane fraction of porcine coronary artery.

ET‐1 (10–100 pm) increased tension and [Ca2+]i in a parallel manner, while at higher concentrations (1–10 nm) it produced further contraction with a small increase in [Ca2+]i.

ET‐1 (30–100 pm) selectively potentiated the 5‐HT‐induced contraction 1.5 to 2 times over the control without causing a significant increase in [Ca2+]i, which seems to be qualitatively similar to a tumour promoting phorbol ester, 12‐deoxyphorbol 13‐isobutylate (DPB). Bay K 8644 (10 nm), on the other hand, potentiated the contraction in response to practically all agonists used and affected a concomitant increase in [Ca2+]i.

A Ca2+ channel blocking drug such as diltiazem abolished the increase in [Ca2+]i and partially attenuated the mechanical potentiation produced by a small amount of ET‐1 in combination with 5‐HT.

The results suggest that ET‐1 and 5‐HT interact functionally at the cellular or subcellular level and modulate the Ca2+ sensitivity of the contractile elements through the possible activation of protein kinase C.
Activation of the 5‐HT1c receptor expressed in Xenopus oocytes by the benzazepines SCH 23390 and SKF 38393
Authors: Briggs Clark A. , Pollock Nancy J. , Frail Donald E. , Paxson Cheryl L. , Rakowski Robert F. , Kang Chae Hee , Kebabian John W.
Published: July 2012

A cloned 5‐HT1C receptor expressed in Xenopus laevis oocytes was used to characterize the action of four dopamine D1‐selective benzazepines at the 5‐HT1C receptor. Additionally, the apparent binding of the D1‐selective benzazepines to 5‐HT1C receptors was measured in the choroid plexus of the pig.

In voltage‐clamped oocytes expressing the cloned 5‐HT1C receptor, 5‐hydroxytryptamine (5‐HT) elicited a characteristic inward current response with an EC50 of 13 nm. SCH 23390 acted as a stereoselective agonist (or partial agonist) with an EC50 of about 550 nm. SKF 38393 (1 μm–1 mm), SKF 77434 (100 μm), and SKF 82958 (100 μm) also acted as agonists (or partial agonists) at the cloned 5‐HT1C receptor. SKF 38393 was not stereoselective at the 5‐HT1C receptor.

The response to SCH 23390 activated slowly and, although the response contained many oscillations characteristic of the activation of the phosphatidylinositol signal transduction system, SCH 23390 rarely elicited the rapid spike‐like response seen routinely in response to 5‐HT. However, the responses to SKF 38393, SKF 77434, and SKF 82958 were identical in appearance to the response to 5‐HT, except that the responses to the benzazepines were smaller. These comparisons were made by applying both a benzazepine and 5‐HT to each individual oocyte expressing the cloned 5‐HT1C receptor.

Consistent with the responses measured in oocytes, SCH 23390 bound stereoselectively to 5‐HT1C receptors in the choroid plexus of the pig (Ki = 6.3 nm), and SKF 38393 bound non‐stereoselectively with lower affinity (Ki = 2.0–2.2 μm).

It is concluded that while these benzazepines demonstrate selectivity for the dopamine D1 receptor, they also can act as agonists or partial agonists at the 5‐HT1C receptor in situ and as expressed in Xenopus oocytes. The oocyte expression system is useful for studies of the functional pharmacology of these 5‐HT1C receptors. Information about the pharmacological actions and variations in stereoselectivity among dopamine and 5‐HT receptors should be of interest in modelling the interactions of ligands with these G‐protein coupled receptors, and in the testing of such models through receptor mutagenesis.;
Arterial and venous plasma concentrations of adenosine during haemorrhage
Authors: Zhang Yong , Lautt W. Wayne
Published: July 2012

A haemorrhage model was used to impose severe metabolic stress in anaesthetized cats by removing blood (15.3 ml min−1) to attain an arterial pressure of ca. 50 mmHg for a 2 h period. Adenosine levels in central venous blood rose by 5 min, reached a peak of about 3.5 times control levels by 15 min and then returned to the basal level (1 μm) by 60 min. However, the adenosine concentration in arterial blood remained unchanged for the entire 2 h period of hypotension. These data demonstrate that haemorrhage results in rapid adenosine release, but the released adenosine is not able to serve a role as a systemic circulating vasodilator even in this severe model.
Role of nitric oxide in non‐adrenergic, non‐cholinergic inhibitory junction potentials in canine ileocolonic sphincter
Authors: Ward Sean M. , McKeen Emma S. , Sanders Kenton M.
Published: July 2012

Electrical field stimulation causes neurally‐mediated relaxation of the ileocolonic sphincter that is due to activation of non‐adrenergic and non‐cholinergic (NANC) nerves. Recent studies have suggested that nitric oxide (NO) is the neurotransmitter that mediates relaxation.

Using intracellular recording techniques, we have tested whether NANC inhibitory junction potentials (i.j.ps) in the canine ileocolonic sphincter are also mediated by NO.

Electrical field stimulation elicited excitatory and inhibitory junction potentials: e.j.ps were blocked by atropine (10−6 m) and tetrodotoxin (TTX; 10−6 m); i.j.ps were also blocked by TTX and partially blocked by apamin (10−6 m). I.j.ps were unaffected by atropine, phentolamine and propranolol (all at 10−6 m).

The arginine analogues, l‐NG‐nitroarginine methyl ester (l‐NAME) and NG‐monomethyl‐l‐arginine (l‐NMMA), decreased the amplitude of i.j.ps and l‐arginine, but not d‐arginine, partially restored the i.j.ps.

I.j.ps were also inhibited by oxyhaemoglobin (1%), but not by methaemoglobin.

Exogenous NO (10−7 m to 3 × 10−5 m) caused concentration‐dependent hyperpolarizations that were similar in amplitude to the NANC nerve‐evoked i.j.ps. Hyperpolarizations to NO were unaffected by l‐NAME, but were blocked by oxyhaemoglobin.

Tetrodotoxin, l‐NAME and oxyhaemoglobin all caused depolarization of resting membrane potential.

The specific guanosine 3′:5′‐cyclic monophosphate phosphodiesterase inhibitor, M&B 22948, caused hyperpolarization, increased the maximum level of hyperpolarization reached during i.j.ps, and increased the duration of i.j.ps.

These data further support the hypothesis that NANC neurotransmission in the ileocolonic sphincter is mediated by NO or an NO‐releasing compound. The data also suggest that tonic release of NO, possibly from spontaneous firing of NANC nerves, may regulate resting membrane potential and tone in this sphincter.
Investigation of the prostaglandin E (EP‐) receptor subtype mediating relaxation of the rabbit jugular vein
Authors: Lawrence Ruth A. , Jones R.L.
Published: July 2012

Prostaglandin E2 (PGE2) relaxes circular smooth muscle of the rabbit isolated jugular vein at very low concentrations (mean pIC50 against histamine‐induced contraction = 9.34). This effect is not blocked by the EP1‐receptor antagonist, AH 6809 (2 μm).

From a group of prostaglandin E analogues examined, 16,16‐dimethyl PGE2, misoprostol, 11‐deoxy PGE2‐1‐alcohol and 11‐deoxy PGE1 were highly potent relaxant agents, whereas 17‐phenyl‐ω‐trinor PGE2, MB 28767 and butaprost had low potency and sulprostone and oxoprostol were virtually inactive.

Comparison of the jugular vein data with published data for inhibitory agonist potencies on the cat trachea (EP2 preparation) and the field‐stimulated guinea‐pig vas deferens (EP3) indicates that the EP‐receptor in the rabbit jugular vein is closest to the EP2 subtype. However, the correlation is not entirely convincing. For example, butaprost, 16,16‐dimethyl PGE2 and 11‐deoxy PGE1 are of similar potency on the cat trachea, whereas butaprost is about 300 times less potent than the other two analogues on the jugular vein. The existence of more than one EP2‐receptor appears possible.

It was felt that the activity of butaprost required further investigation in view of the claim that it is a specific EP2‐receptor agonist. We have shown that butaprost has very low inhibitory activity on the guinea‐pig vas deferens, a very sensitive EP3‐receptor containing preparation. However, on the chick ileum, the original EP3 preparation, butaprost showed potent contractile activity (pEC25 ˜ 8.0). In addition, its maximum response was lower than that of PGE2; lower maxima were also found for sulprostone, MB 28767 and oxoprostol, but not for ICI 80205, 16,16‐dimethyl PGE2 and 17‐phenyl‐ω‐trinor PGE2. The maximal response to a combination of either sulprostone and butaprost or sulprostone and PGE2 was similar to that achieved by PGE2 alone. Analysis of the interaction between sulprostone and PGE2 appears to exclude a partial agonist action for sulprostone. Furthermore neither sulprostone nor butaprost appear to have inhibitory activity on the ileum. AH 6809 at 2 μm produced only a small shift of the PGE2 log concentration‐response curve.

It is likely that contraction of the longitudinal smooth muscle of the chick ileum is mediated by (at least) two EP‐receptor subtypes; activation of only one receptor system does not induce the maximum response (i.e. the acetylcholine maximum) of the preparation. One receptor could be an EP3 subtype, at which sulprostone exerts a selective agonist action. The other receptor is unlikely to be an EP1 subtype, because of the high agonist potency of butaprost, the low agonist potency of iloprost, and the low antagonist potency of AH 6809. An alternative hypothesis is that the chick ileum contains a novel EP‐receptor subtype in addition to an EP3‐receptor.
Involvement of β2‐adrenoceptors in the regional haemodynamic responses to bradykinin in conscious rats
Authors: Gardiner S.M. , Kemp P.A. , Bennett T. , Bose C. , Foulkes R. , Hughes B.
Published: July 2012

Bradykinin can release neuronal calcitonin gene‐related peptide (CGRP) and adrenal medullary catecholamines, both of which could contribute to its cardiovascular effects in vivo. Therefore, in the main experiment, regional haemodynamic responses to bolus injections of bradykinin (3 nmol kg−1, i.v.) were assessed in the same chronically‐instrumented, conscious, Long Evans rats in the absence and in the presence of human α‐CGRP [8–37] or ICI 118551, antagonists of CGRP1‐receptors and β2‐adrenoceptors, respectively. The selected doses of these antagonists caused specific inhibition of responses mediated by exogenous human α‐CGRP and β2‐adrenoceptor agonists, respectively.

Bradykinin administered alone as an i.v. bolus had a slight pressor effect accompanied by a marked tachycardia. There were early (at about 30 s) increases in flow and conductance in the mesenteric vascular bed, and delayed (at about 90 s), but qualitatively similar, changes in the hindquarters vascular bed. There were only slight increases in flow and conductance in the renal vascular bed.

Human α‐CGRP [8–37] had no statistically significant effects on the responses to bolus doses of bradykinin. However, in the presence of ICI 118551, the pressor effect of bradykinin was significantly enhanced while its tachycardic effect was significantly suppressed. The hindquarters vasodilator effect of bradykinin was converted to a vasoconstriction and there was a slight renal vasoconstriction, but the mesenteric vasodilator effect of bradykinin was unchanged by ICI 118551.

In subsidiary experiments, in other animals, it was found that infusion of bradykinin (36 nmol kg−1 min−1) elicited a pattern of haemodynamic responses similar to that seen with bolus injections and, as in the latter case, the hindquarters hyperaemic vasodilatation was inhibited by ICI 118551. In the presence of mecamylamine (at a dose sufficient to block reflex heart rate responses to rises or falls in arterial blood pressure) bolus injection or infusion of bradykinin still elicited increases in renal, mesenteric and hindquarters blood flow. However, in additional experiments in adrenal demedullated rats (n = 4) the hindquarters hyperaemic effect of bradykinin was absent, although the mesenteric hyperaemic effect remained.

The results indicate that the increase in hindquarters blood flow following administration of bradykinin in vivo is largely due to activation of β2‐adrenoceptors by catecholamines released subsequent to direct stimulation of the adrenal medulla by the peptide. However, the bradykinin‐induced increase in mesenteric blood flow does not depend on this mechanism.
Neuroendocrine response to clonidine and 8‐OH‐DPAT in rats following chronic administration of desipramine or sertraline
Authors: O'Donnell J.M. , Grealy M.
Published: July 2012

Rats were administered either desipramine (DMI) or sertraline daily at doses 7.5 mg kg−1 or 10 mg kg−1, i.p., respectively and the effects on the functional state of hypothalamic neuroendocrine control mechanisms assessed by measurements of plasma hormones following acute drug challenge. The effects of treatment on gross behaviour and brain adrenoceptor density were also determined.

Both DMI and sertraline caused significant reduction in activity measured as ambulation and rearing at 14 days of treatment.

All animals were chronically cannulated after 14 days of treatment and tested for neuroendocrine response to acute i.v. clonidine (50 μg kg−1) or 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT, 250 μg kg−1) after 21 or more days of treatment.

Rats treated with DMI but not sertraline showed a virtually complete suppression of the growth hormone (GH) secretion elicited by clonidine in controls, while the secretion of corticosterone was augmented.

Treatment with DMI but not sertraline led to a significantly greater 8‐OH‐DPAT‐induced secretion of prolactin than in the control rats, while the plasma concentrations of corticosterone following 8‐OH‐DPAT were not influenced by either DMI or sertraline treatment.

The density (but not the affinity) of cerebral cortical binding of [3H]‐dihydroalprenolol was significantly reduced by DMI treatment.

These results show that DMI treatment blunted the sensitivity of post‐synaptic α2‐adrenoceptors, accompanied by complex interactions manifested as increased responsiveness of α1‐adrenoceptors and 5‐HT1A receptors. Sertraline had no significant neurendocrine effects at a dose which significantly reduced gross activity.
Effects of purines on the longitudinal muscle of the rat colon
Authors: Bailey S.J. , Hourani S.M.O.
Published: July 2012

Adenosine and adenosine 5′‐triphosphate (ATP) have been reported to cause relaxation of the rat colon longitudinal muscle preparation; the purinoceptors mediating this effect were investigated by use of a series of agonists and antagonists.

The tissue was precontracted with carbachol (1 μm), and the purines induced reversible relaxations with a potency order of 5′‐N‐ethylcarboxamidoadenosine (NECA) >N6‐cyclopentyladenosine (CPA) = adenosine 5′‐(α,β‐methylene) triphosphonate (AMPCPP) >adenosine = adenylyl 5′‐(β,γ‐methylene) disphosphonate (AMPPCP) = ATP. The P1‐selective antagonist 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX) (3 μm) shifted to the right the log concentration‐response curves of all these agonists except for AMPCPP, indicating that they all act via P1‐purinoceptors. The order of potency of the adenosine analogues and the relatively high concentrations of the antagonist required indicated that these receptors are of the A2 subtype. The P2‐selective antagonist suramin (300 μm) inhibited responses to AMPCPP, but not to the other agonists.

The dephosphorylation of the nucleotides was studied by high performance liquid chromatography following incubation with the longitudinal muscle preparation for up to 30 min. ATP was rapidly degraded, largely to adenosine, and AMPPCP and AMPCPP were also degraded, although more slowly, to adenosine and adenosine 5′‐(α,β‐methylene) diphosphonate (AMPCP) respectively. AMPCP, like AMPCPP, caused relaxations by acting on P2‐purinoceptors, as it was also inhibited by suramin (300 μm). Incubation of the tissue with adenosine deaminase abolished responses to adenosine, reduced those to ATP and AMPPCP, but had no effect on those to AMPCPP. ATP and AMPPCP therefore appear to be acting on the A2 receptors in this tissue largely via their degradation product adenosine.

The longitudinal muscle of the rat colon therefore contains both P1‐ and P2‐purinoceptors, which both mediate relaxation. The P1‐purinoceptors are of the A2 subtype and the P2‐purinoceptors are probably of the P2Y subtype, although the rapid degradation of the nucleotides means that it is difficult to classify them with certainty.
Correlation between airway epithelium‐induced relaxation of rat aorta in the co‐axial bioassay and cyclic nucleotide levels
Authors: Hay D.W.P. , Muccitelli R.M. , Page C.P. , Spina D.
Published: July 2012

In co‐axial bioassays, in the presence of indomethacin, addition of histamine (100 μm) or methacholine (100 μm) to guinea‐pig trachea produced an epithelium‐dependent relaxation of precontracted rat aorta which was associated with an approximately 2 fold elevation in tissue levels of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP). Removal of the airway epithelium abolished the histamine‐induced relaxation of rat aorta and the associated increase in intracellular cyclic GMP.

Epithelium‐dependent relaxation was not associated with altered adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) levels in rat aorta. Unstimulated intact or denuded guinea‐pig trachea also did not affect the levels of cyclic AMP or cyclic GMP in rat aorta.

Methylene blue (10 μm) abolished the methacholine‐induced, endothelium‐derived relaxing factor (EDRF)‐mediated rise in intracellular cyclic GMP in rat endothelium‐intact aorta alone. In contrast, methylene blue (10 μm) did not affect the methacholine‐induced epithelium‐dependent rise in intracellular cyclic GMP in rat endothelium‐denuded aorta in the co‐axial bioassay.

Relaxation of the rat aorta without endothelium was associated with increased levels of cyclic GMP (but not cyclic AMP) in response to sodium nitroprusside (5 nm) and of cyclic AMP (but not cyclic GMP) in response to isoprenaline (1 μm).

These results provide evidence that the postulated epithelium‐derived inhibitory factor (EpDIF) may produce relaxation of vascular tissue via elevation in cyclic GMP levels. Furthermore, some data suggest that EpDIF may act by stimulation of the particulate, rather than the soluble form of guanylate cyclase.
Bronchodilatation by tachykinins and capsaicin in the mouse main bronchus
Authors: Manzini Stefano
Published: July 2012

The effect of sensory neuropeptides and capsaicin on basal and stimulated tone of mouse bronchial smooth muscle has been evaluated.

In basal conditions neither sensory neuropeptides (subtance P, neurokinin A or calcitonin gene‐related peptide (CGRP)) nor capsaicin exerted any contractile effects. However, when a tonic contraction was induced with carbachol (1 μm) a prompt relaxation was induced by substance P (1– 100 nm) and by neurokinin A (1– 100 nm), with substance P being more potent. A second application of substance P was without effect. CGRP (10 nm) produced only a very small and erratic relaxation. Relaxation was also induced by capsaicin (1 μm), and this response could be evoked only once in each preparation. In 4 out of 6 preparations a cross‐desensitization between substance P and capsaicin was observed.

The selective NK1 tachykinin agonist, [Pro9]‐SP sulphone (1 μm), exerted potent bronchodilator actions on carbachol‐contracted mouse bronchial preparations. In contrast, neither [β Ala8]‐NKA (4–10) nor [MePhe7]‐NKB (both at a concentration of 1 μm), selective synthetic agonists for NK2 and NK3 receptors, exerted significant relaxant effects. Furthermore, the selective NK1 tachykinin antagonist, (±)‐CP 96,345 (1 μm), abolished substance P (1 nm)‐ but not isoprenaline (0.1 μm)‐induced relaxations.

Application of electrical field stimulation (EFS) (20 Hz, supramaximal voltage, 0.5 ms for 10 s) to carbachol‐contracted preparations evoked a transient contraction followed by a relaxation. The tetrodotoxin‐sensitive slow component of this relaxation was reduced following capsaicin desensitization.

In the presence of indomethacin (5 μm) the relaxation induced by substance P, capsaicin or EFS was suppressed.

In conclusion, the mouse main bronchus appears to be a monoreceptorial tissue containing only NK1 receptors which subserve bronchodilator functions. Such receptors could be activated by exogenous or endogenously (capsaicin or EFS) released tachykinins and the consequent relaxation is probably mediated by the generation of prostanoids.
The 5‐HT4 receptor subtype inhibits K+ current in colliculi neurones via activation of a cyclic AMP‐dependent protein kinase
Authors: Fagni L. , Dumuis A. , Sebben M. , Bockaert J.
Published: July 2012

The aim of the present study was to examine the effect of 5‐hydroxytryptamine (5‐HT) on K+ current in primary culture of mouse colliculi neurones and to identify the 5‐HT receptor subtype that could be involved in this effect.

The voltage‐activated K+ current of the neurones was partially blocked by 8‐bromo adenosine 3′:5′‐cyclic monophosphate (8‐bromo‐cyclic AMP). This effect was mimicked by 5‐HT and the action of 5‐HT could be antagonized by H7, a non specific protein kinase inhibitor, and by PKI, the specific cyclic AMP‐dependent protein kinase blocker.

A similar cyclic AMP‐dependent blockade of the K+ current was found with renzapride (BRL 24 924) and other 5‐HT4 receptor agonists such as cisapride, BIMU 8, zacopride and 5‐methoxytryptamine (5‐MeOT). ICS 205 930, the classical 5‐HT4 receptor blocker, could not be used in this study because it inhibited the studied K+ current by itself. However, the novel 5‐HT4 receptor antagonist, DAU 6285 blocked the effects of 5‐HT and renzapride on the K+ current.

The current was insensitive to the 5‐HT1 and 5‐HT3 receptor agonists (8‐hydroxy‐2‐(di‐n‐propylamino) tetralin, RU 24 969, carboxamidotryptamine, 2‐CH3‐5‐HT) as well as to 5‐HT1, 5‐HT2 and 5‐HT3 antagonists (methiothepin, ketanserin, ondansetron [GR 38 032]). Moreover, these antagonists did not affect the actions of the tested 5‐HT4 receptor agonists.

The present results show that part of the voltage‐activated K+ current in mouse colliculi neurones is cyclic AMP‐sensitive and the blockade of the current by 5‐HT involves the 5‐HT4 receptor subtype. The putative implication of 5‐HT4 receptors in neuronal plasticity, via a blockade of K+ channels, is discussed.
Inhibitory effects of certain enantiomeric cannabinoids in the mouse vas deferens and the myenteric plexus preparation of guinea‐pig small intestine
Authors: Pertwee R.G. , Stevenson L.A. , Elrick D.B. , Mechoulam R. , Corbett A.D.
Published: July 2012

The psychoactive cannabinoids (−)‐Δ9‐tetrahydrocannabinol ((−)‐Δ9‐THC) and the 1,1‐dimethylheptyl homologue of (−)‐11‐hydroxy‐Δ8‐tetrahydrocannabinol ((−)‐DMH) both inhibited electrically‐evoked contractions of the mouse isolated vas deferens and the myenteric plexus‐longitudinal muscle preparation of the guinea‐pig small intestine.

Concentrations of (−)‐Δ9‐THC and (−)‐DMH that decreased twitch heights by 50% were 6.3 and 0.15 nm respectively in the mouse vas deferens and 60 nm and 1.4 nm respectively in the myenteric plexus preparation. (−)‐DMH was about 40 times more potent than (−)‐Δ9‐THC in both preparations, supporting the notion that their mode of action in each tissue is the same.

The psychically inactive cannabinoid, (+)‐DMH, had no inhibitory effect in the mouse vas deferens at a concentration of 30 nm, showing it to be at least 1000 times less potent than (−)‐DMH. In the myenteric plexus preparation, (+)‐DMH was about 500 times less potent than its (−)‐enantiomer.

The inhibitory effects of sub‐maximal concentrations of (−)‐Δ9‐THC were not attenuated by 300 nm naloxone.

The findings that (−)‐Δ9‐THC and (−)‐DMH are highly potent as inhibitors of the twitch response of the mouse vas deferens and guinea‐pig myenteric plexus preparation and that DMH shows considerable stereoselectivity suggest that the inhibitory effects of cannabinoids in these preparations are mediated by cannabinoid receptors.
Comparative effects of BRL 38227, nitrendipine and isoprenaline on carbachol‐ and histamine‐stimulated phosphoinositide metabolism in airway smooth muscle
Authors: Challiss R.A. John , Patel Neela , Arch Jonathan R.S.
Published: July 2012

The ability of BRL 38227 and nitrendipine to affect muscarinic agonist and histamine‐stimulated [3H]‐inositol phosphate accumulation in slices of bovine tracheal smooth muscle has been studied and compared with the established inhibitory effects of isoprenaline on this pathway.

Pre‐addition of BRL 38227 (5 μm), nitrendipine (1 μm) or isoprenaline (10 μm) significantly inhibited the subsequent inositol phosphate response to histamine at all concentrations studied (10– 1000 μm). BRL 38227 and nitrendipine also significantly inhibited the [3H]‐inositol phosphate response to low (1 μm), but not high (100 μm) concentrations of carbachol. Isoprenaline had no effect at any concentration of carbachol studied.

Nitrendipine (IC50 = 95 nm) and BRL 38227 (IC50 = 322 nm) caused concentration‐related inhibitions of the inositol phosphate response to histamine (100 μm). Similar maximal inhibitions were caused by each agent (55– 58%). Inhibitory effect of BRL 38227 was reduced in potency (IC50 = 5.5 μm), but not magnitude, in the presence of glibenclamide (0.5 μm).

Time‐course studies comparing the effects of BRL 38227 addition 15 min before, and 10 min after histamine challenge showed that for pre‐addition a distinct (< 2 min) lag occurred following histamine addition before the inhibitory effect of BRL 38227 was manifest. In contrast, when BRL 38227 was added 10 min after histamine, an inhibitory effect was immediately apparent.

Further evidence for an initial, ‘protected’ phase of inositol phosphate accumulation was provided by the finding that BRL 38227 pre‐addition had no effect on the early (0–300 s) time‐course of inositol 1,4,5‐trisphosphate mass accumulation.

The inhibitory effect of BRL 38227, but not that of nitrendipine or isoprenaline, on histamine‐stimulated [3H]‐inositol phosphate accumulation was completely prevented in the presence of an elevated extracellular K+ (65 mm) concentration.

The results demonstrate that membrane hyperpolarization, and/or blockade of voltage‐operated Ca2+‐channels can regulate agonist‐stimulated phosphoinositide metabolism in airway smooth muscle. The possible contribution of this regulatory mechanism to the relaxant properties of these agents is discussed.
Noradrenaline modulates smooth muscle activity of the isolated intravesical ureter of the pig through different types of adrenoceptors
Authors: Hernández M. , Prieto D. , Simonsen U. , Rivera L. , Barahona M.V. , García‐Sacristán A.
Published: July 2012

We have studied the effects of α‐ and β‐adrenoceptor agonists and antagonists on both phasic peristaltic activity and basal tone of the isolated intravesical ureter of the pig by means of isometric techniques in vitro.

Spontaneous phasic activity was exhibited by 21% of pig intravesical ureter preparations manifested as rhythmic contractions with average frequency and amplitude of 2.54 ± 0.18 min−1 and 1.48 ± 0.16 g (n = 31), respectively.

Adrenaline, noradrenaline and phenylephrine induced concentration‐dependent increases in both phasic activity and basal tone of ureteral preparations, all three agonists being more potent in modifying ureteral phasic activity than baseline tone. B‐HT 920, B‐HT 933 and clonidine had no significant effect.

Phentolamine (10−9 − 10−7 m) and prazosin (3 × 10−11 − 3 × 10−8 m) significantly inhibited increases in both frequency of phasic activity and baseline tone induced by a submaximal dose of noradrenaline. Rauwolscine (10−9 − 10−7 m) affected only the tone evoked by noradrenaline and higher concentrations of this antagonist were needed to block phasic activity.

Pretreatment of ureteral strips with the β‐adrenoceptor antagonist, propranolol (10−6 m), significantly increased the maximum contraction evoked by noradrenaline. After incubation with phentolamine (10−6 m), noradrenaline (10−7 − 10−6 m) decreased phasic activity induced by prostaglandin F2α (10−5 m). Isoprenaline and salbutamol also abolished PGF2α‐induced phasic activity. Pafenolol (10−6 m) and butoxamine (10−6 m) blocked the inhibitory effect of noradrenaline, isoprenaline, and salbutamol on PGF2α‐induced phasic activity.

These results suggest that noradrenaline may modulate both phasic peristaltic activity and basal tone of pig intravesical ureter through both α‐ and β‐adrenoceptors.
Guinea‐pig treatment with pertussis toxin suppresses macrophage‐dependent bronchoconstriction by fMLP and fails to inhibit the effects of PAF
Authors: Kadiri Chakir , Leduc Dominique , Lefort Jean , Imaizumi Atsushi , Vargaftig B. Boris
Published: July 2012

Bronchoconstriction and thromboxane B2 (TxB2) release following the intra‐tracheal administration of the secretagogue N‐formyl‐l‐methionyl‐l‐leucyl‐l‐phenylalanine (fMLP) to lungs from pertussis toxin‐treated guinea‐pigs in vivo and in vitro were inhibited as compared to saline‐treated animals, under conditions where the responses to PAF were modified less effectively.

The cell target accounting for bronchoconstriction by fMLP and for inhibition by pertussis toxin is located in the airways and is probably the alveolar macrophage. Indeed (a) fMLP‐induced superoxide anions and TxB2 formation by alveolar macrophages were inhibited by pertussis toxin given in vivo; (b) Gi proteins of membranes from alveolar macrophages were ADP‐ribosylated in vivo by pertussis toxin and (c) bronchoconstriction and TxB2 release in response to the intra‐tracheal administration of fMLP to lungs from pertussis toxin‐treated animals were restored when alveolar macrophages from control guinea‐pigs were transferred into the airways of pertussis toxin‐treated animals before lung isolation.

Pertussis toxin administered to guinea‐pigs in vivo, reduced the subsequent TxB2 formation and superoxide anion release by alveolar macrophages stimulated with PAF, but failed to inhibit PAF‐induced bronchoconstriction.

Formation of TxB2 by alveolar macrophages following the intra‐tracheal administration of fMLP accounts for bronchoconstriction and requires pertussis toxin‐sensitive Gi proteins. PAF operates via a different mechanism, which is independent of Gi‐like protein and involves mediators other than TxB2 and superoxide anions.
Cardiovascular selectivity of adenosine receptor agonists in anaesthetized dogs
Authors: Gerencer R.Z. , Finegan B.A. , Clanachan A.S.
Published: July 2012

In order to determine the relevance of adenosine (Ado) receptor classification obtained from in vitro methods to the cardiovascular actions of Ado agonists in vivo, the cardiovascular effects of adenosine 5′‐monophosphate (AMP), N6‐cyclohexyladenosine (CHA, 400 fold A1‐selective), 5′‐N‐ethylcarboxamidoadenosine (NECA, A1 ≅ A2) and 2‐phenylaminoadenosine (PAA, 5 fold A2‐selective) were compared in open‐chest, fentanyl‐pentobarbitone anaesthetized dogs.

Graded doses of CHA (10 to 1000 μg kg−1), NECA (0.5 to 100 μg kg−1) or PAA (0.1 to 20 μg kg−1) were administered intravenously and changes in haemodynamics and myocardial contractility were assessed 10 min following each dose. The effects of graded infusions of AMP (200 to 1000 μg kg−1 min−1) were also evaluated.

AMP and each of the Ado analogues (NECA > PAA > CHA) increased the systemic vascular conductance index (SVCI) in a dose‐dependent manner and reduced mean arterial pressure (MAP). At doses causing similar increases in SVCI, these agonists caused (i) similar reflex increases in heart rate (HR) and cardiac index (CI) and decreases in AV conduction interval (AVi) and (ii) similar increases in coronary vascular conductance (CVC).

After cardiac autonomic blockade with atropine (0.2 mg kg−1) and propranolol (1 mg kg−1), AMP, CHA and PAA still increased SVCI and CVC and decreased MAP. CHA and PAA had no marked effects on HR, CI or AVi. As in the absence of cardiac autonomic blockade, equieffective vasodilator doses of CHA and PAA had identical effects on CVC, CI and AVi.

Myocardial contractility, as assessed by Emax measurements, was stimulated by AMP in control animals. Following cardiac autonomic blockade, PAA increased contractility while AMP and CHA had no significant effects.

Despite marked differences in receptor selectivity in vitro, no marked differences between the actions of these A1‐ and A2‐selective Ado receptor agonists on the cardiovascular system in vivo were apparent. Difficulties therefore exist in the application of in vitro Ado receptor selectivity data to the prediction of the cardiovascular effects of Ado agonists in vivo.
Pterins inhibit nitric oxide synthase activity in rat alveolar macrophages
Authors: Jorens Philippe G. , van Overveld Frans J. , Bult Hidde , Vermeire Paul A. , Herman Arnold G.
Published: July 2012

The synthesis of nitrite and citrulline from l‐arginine by immune‐stimulated rat alveolar macrophages and the modulation of this synthesis were studied. 2,4‐Diamino‐6‐hydroxypyrimidine (DAHP), 6R‐5,6,7,8‐tetrahydro‐l‐biopterin (BH4) and l‐sepiapterin were potent inhibitors of the recombinant interferon‐γ induced production of nitrogen oxides in intact cultured cells with I50 values for BH4 and l‐sepiapterin of approximately 10 μm. They were equally effective in inhibiting the induced production of citrulline. This inhibitory effect was concentration‐dependent for all three modulators investigated.

The inhibitory effects were not dependent on incubation times of either 24 or 48 h, on the immune‐stimulus used (lipopolysaccharide, interferon‐γ), or whether these stimuli were added during or after the induction period.

Pterin‐6‐carboxylic acid (PCA), which cannot be converted into BH4, and methotrexate (MTX), which inhibits dihydrofolatereductase but not de novo biosynthesis of BH4, did not change the production of nitrite.

The data indicate that DAHP, an inhibitor of the de novo biosynthesis of the co‐factor BH4, blocks the nitric oxide synthase activity in intact cells. Since the pterins BH4 and l‐sepiapterin blocked the l‐arginine dependent production of nitrite and citrulline, the activity of nitric oxide synthase in phagocytic cells may be regulated by metabolic endproducts of the de novo biosynthesis of BH4.