bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibitory 5‐hydroxytryptamine receptors involved in pressor effects obtained by stimulation of sympathetic outflow from spinal cord in pithed rats
Authors: Morán A. , Velasco C. , Salvador T. , Martín M.L. , Román L. San
Published: July 2012

A study was made of the effects of 5‐hydroxytryptamine (5‐HT) on pressor response induced in vivo by electrical stimulation of the sympathetic outflow from the spinal cord of pithed rats. All animals had been pretreated with atropine. Intravenous infusion of 5‐hydroxytryptamine at doses of 10 and 20 μg kg−1 min−1 reduced the pressor effects obtained by electrical stimulation at intervals of 10 min over the 1 h of infusion.

This inhibitory action of 5‐HT was depressed by cyproheptadine and methiothepin but was not modified by ketanserin or MDL‐72222. By contrast, the inhibitory action of 5‐HT was lost in pithed rats that had been pretreated with exogenous noradrenaline.

The 5‐HT1 receptor agonist 5‐carboxamidotryptamine (5‐CT) caused an inhibition of the pressor response, whereas the 5‐HT3 receptor agonist, 1‐phenylbiguanide, produced a variable but significant increase in the pressor response. The 5‐HT2 receptor agonist, m‐CPP, did not modify the pressor sympathetic response.

Our results suggest that 5‐hydroxytryptamine interferes with sympathetic neurotransmission by inhibiting pressor effects as a result of stimulation of the complete sympathetic outflow, and that this inhibition is mainly through a presynaptic 5‐HT1 mechanism.
Characterization of the adenosine receptors mediating hypothermia in the conscious mouse
Authors: Anderson R. , Sheehan M.J. , Strong P.
Published: July 2012

The effects of a range of adenosine receptor‐selective ligands on body temperature were investigated following intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) injection in conscious mice. The compounds tested were the non‐selective adenosine receptor agonist 5′‐N‐ethyl‐carboxamidoadenosine (NECA), the adenosine A1 receptor‐selective agonists cyclopentyl‐adenosine (CPA), N6‐(9R‐phenyl‐isopropyl)‐adenosine (R‐PIA) and N‐(1S,trans)‐[2‐hydroxycyclopentyl]‐adenosine (GR79236), the A2a receptor selective agonist 2‐[p‐(2‐carboxyethyl)phenethylamino]‐5′‐N‐ethylcarboxamidoadenosine (CGS‐21680), the A2b receptor agonist N‐[(2‐methylphenyl)methyl]adenosine (metrifudil) and the A3 receptor agonist N6‐(4‐aminophenylethyl)adenosine (APNEA).

NECA (0.01‐1 μg, i.c.v.), all of the A1‐selective agonists (0.01‐1 μg, i.c.v.) and APNEA (0.1–3 μg i.c.v.) produced profound and dose‐related hypothermia and sedation. However, CGS‐21680 (0.1–10 μg i.c.v.) and metrifudil (0.01‐1 μg i.c.v.), produced only mild hypothermia at the highest doses tested.

The hypothermic response to the A1 receptor‐selective agonists, GR79236 and R‐PIA was dose‐dependently antagonized by peripheral administration of either the non‐selective adenosine receptor antagonist, 8‐phenyltheophylline (8‐PT, approximately 40 and 30 fold rightward shifts of the dose‐response curves respectively at 10 mg kg−1, i.p.), or the adenosine A1 receptor‐selective antagonist, 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX, approximately 20 fold shift of the GR79236 dose‐response curve at 1 mg kg−1, i.p.). The hypothermic response to APNEA was similarly dose‐dependently antagonized by the A1 receptor‐selective antagonist, DPCPX (5 fold shift at 0.1 mg kg−1, i.p.).

8(p‐Sulphophenyl)theophylline (8‐SPT, 10 and 30 mg kg−1, i.p.), a non‐selective adenosine receptor antagonist that penetrates the blood brain barrier poorly, produced only modest antagonism (approximately 2 fold shift at 30 mg kg−1, i.p.) of the hypothermic response to GR79236.

These data suggest that hypothermia induced by adenosine analogues in the conscious mouse is mediated via adenosine Ai receptors, which are probably located in the CNS.
Variable potency of nitrergic‐nitrovasodilator relaxations of the mouse anococcygeus against different forms of induced tone
Authors: Gibson A. , McFadzean I. , Tucker J.F. , Wayman C.
Published: July 2012

U46619 (thromboxane A2 receptors; 0.002‐1 μm), carbachol (muscarinic M3 receptors; 0.1–100μm), cyclopiazonic acid (CPA; Ca2+‐ATPase inhibitor; 0.1–30 μm) and K+ (5‐100mM) produced concentration‐dependent contractions of the mouse isolated anococcygeus muscle. Equi‐effective, sub‐maximal concentrations of each agent were used in further experiments (40 nm U46619; 5 μm carbachol; 5μm CPA; 70 mm K+).

Nifedipine (1 μm) totally abolished contractile responses to K+; those to U46619, carbachol and CPA were reduced by only 20–30% in the presence of nifedipine, but were greatly reduced (>90%) by a combination of nifedipine and SKF 96365 (0.1–40 μm).

In Ca2+‐free medium, contractions to K+ and CPA were abolished. Small residual responses remained to both carbachol and U46619; those to carbachol were transient, could not be repeated in the continued absence of Ca2+ and were prevented by pre‐incubation with CPA, but unaffected by SKF 96365; those to U46619 were sustained, could be repeated in the absence of Ca2+, and were resistant to CPA and SKF 96365.

Tone induced by all four agents could be relaxed by sodium nitroprusside (SNP), but with a clear order of potency. SNP (pIC40) was most effective against U46619 (7.92), less so against carbachol (6.80) and CPA (6.68), and least potent against K+ (5.94). A similar order of potency was observed with 8Br‐cyclic GMP (50 μm) and nitrergic field stimulation (1–20 Hz).

The relaxant potency of SNP was similar in normal Krebs solution and in high K+ (70 μm) Krebs containing 1 μm nifedipine.

Inclusion of SNP (0.01‐1 μm) or 8Br‐cyclic GMP (50 μm) in the Ca2+‐free medium inhibited the transient residual response to carbachol. Inclusion of similar concentrations of SNP or 8Br‐cyclic GMP, during Ca2+ re‐loading, increased the subsequent residual contraction to carbachol in Ca2+‐free medium.

At higher concentrations, SNP (0.1–10 μm) produced a partial relaxation of the sustained contraction to U46619 in Ca2+‐free medium.

Thus, the relaxant potency of the nitrergic stimuli was dependent on the agent and mechanism used to induce tone in the preparation. Examination of the contractile/relaxant interactions suggests that altered Ca2+ sequestration and inhibition of contractile protein function may underlie nitrergic relaxations of this tissue.
Nitric oxide formation from glyceryl trinitrate by rabbit aortic strip: detection by rabbit taenia coli concurrent with vasorelaxation
Authors: Hussain Aman S. , Poklewska‐Koziell Margo , Brien James F. , Marks Gerald S. , Nakatsu Kanji
Published: July 2012

The purpose of the present study was to assay NO formation from GTN biotransformation by the rabbit aortic strip (RAS) at times concurrent with its vasorelaxation. Such an assay is an important test of the prodrug hypothesis where it is postulated that glyceryl trinitrate (GTN) is biotransformed to nitric oxide (NO), the active species that initiates vascular smooth muscle relaxation. To test such a hypothesis, we propose that a sample of smooth muscle, poorly responsive to GTN, yet sensitive to the effects of NO could be used to detect RAS production of NO from GTN.

Muscle strips of rabbit taenia coli (RTCS) and RAS in close apposition, were mounted in tissue baths, and muscle relaxation was recorded with isometric force transducers. Tissues were submaximally precontracted with 30–35 mm K+ depolarizing solution and exposed to increasing concentrations of GTN (0.1 nm‐10 μm).

EC25 for GTN‐induced relaxation of RTCS in the presence of RAS was significantly decreased to that for RTCS in the absence of RAS (5.9 ± 3.0 × 10−8 m and 5.5 ± 3.7 × 10−6 m, respectively). Mean maximal levels of GTN‐induced relaxation of similarly precontracted RTCS also differed in the presence and absence of RAS, viz., 80.8 ± 2.1% and 29.8 ± 8.3% respectively.

RTCS was found to relax upon administration of NO gas bubbled through the incubation medium. Analysis of tissue bath medium revealed that the NO concentration to which RTCS was exposed attained a maximum of 33 nm. Relaxation of RTCS by NO gas was inhibited by 1 μm reduced haemoglobin.

For GTN‐incubation with intestinal and vascular smooth muscle preparations, NO formation was greater with RAS compared to RTCS. Thus, in the two‐issue bioassay, the RAS was the predominant source of NO formation from GTN.

Reduced deoxyhaemoglobin (1 μm), a potent extracellular NO scavenger, was found to decrease the augmented GTN‐induced relaxation in the RTCS‐RAS sandwich preparation from 17.3 ± 1.8% to 8.0 ± 0.8%. The augmented RTCS response was restored upon washout and subsequent addition of GTN, in the absence of reduced Hb.

These data indicate that nitric oxide or a closely related NO‐donor is produced by vascular biotransformation of GTN as seen by the increased sensitivity of RTCS to GTN when in the presence of RAS. The results of this bioassay thus support the GTN‐NO prodrug hypothesis.
Impairment of nitrergic‐mediated relaxation of rat isolated duodenum by experimental diabetes
Authors: Martinez‐Cuesta M.A. , Massuda H. , Whittle B.J.R. , Moncada S.
Published: July 2012

Diabetes mellitus is associated with changes in gastrointestinal motility. The effects of experimental diabetes, induced by streptozotocin administration to rats 3–4 weeks previously, on the nitric oxide (NO)‐mediated (nitrergic) relaxation of the duodenum have now been investigated.

The non‐adrenergic, non‐cholinergic (NANC) relaxation of the isolated duodenum induced by nicotine (0.3 – 10 μm) or the nicotinic agonist, 1,1‐dimethyl‐4‐phenylpiperazinium (DMPP; 10 μm) was inhibited by the NO synthase inhibitor, NG‐nitro‐l‐arginine (3–100 μm).

This nitrergic relaxation induced by nicotine or DMPP of the duodenum from diabetic rats was substantially smaller than that of the tissue from control rats.

By contrast, the relaxation of the duodenum from diabetic rats to the NO donor, nitroprusside (0.3–10 μm) was similar to that of control tissue, whereas the relaxation to ATP (0.1–3 μm) was enhanced to a small but significant degree.

Incubation of duodenal tissue from control rats at 4°C for 72 h, which leads to neuronal disruption, significantly attenuated the relaxation to nicotine or DMPP whereas the relaxation induced by nitroprusside or ATP was not affected. Comparable cold‐storage did not affect the endothelium‐dependent relaxation of rat aortic rings induced by acetylcholine (0.01–2 μm).

The calcium‐dependent NO synthase activity in duodenal tissue, determined by the conversion of radiolabelled l‐arginine to citrulline, was significantly reduced in cold‐stored tissue and in tissue obtained from diabetic rats.

These findings in the rat duodenum indicate that a reduction in intestinal NO synthase activity is associated with an impairment of the NANC relaxation. A defect in the intestinal nitrergic innervation could thus contribute to the motility dysfunction observed in diabetes.
Canine renovascular responses to sumatriptan and 5‐carboxamidotryptamine: modulation through endothelial 5‐HT1‐like receptors by endogenous nitric oxide
Authors: Whiting M.V. , Cambridge D.
Published: July 2012

In anaesthetized dogs, intra‐left atrial (i.l.a.) administration of the 5‐HT1‐like receptor agonists, sumatriptan (1 – 10 μg kg−1) and 5‐carboxamidotryptamine (0.03 – 0.3 μg kg−1) produced dose‐related reductions in renal blood flow and vascular conductance, which were characterized by their rapid onset and recovery.

In these animals, i.v. administration of the inhibitor of nitric oxide (NO) synthase, NG‐nitro‐l‐arginine methyl ester (l‐NAME; 10 mg kg−1) significantly augmented the renal vasoconstrictor responses to i.l.a. sumatriptan and 5‐carboxamidotryptamine.

The effects of l‐NAME upon these responses to sumatriptan and 5‐carboxamidotryptamine were significantly reversed by subsequent i.v. administration of l‐arginine (1000 mg kg−1).

l‐NAME significantly attenuated the systemic hypotensive responses to i.v. acetylcholine (0.3 – 3 μg kg−1) and this effect was also reversed by l‐arginine.

l‐NAME had no effect upon the renal vasoconstrictor response to i.l.a. administration of angiotensin II, nor did it affect the renal vascular conductance recovery response to brief mechanical occlusion of the renal artery.

These data suggest that sumatriptan and 5‐carboxamidotryptamine stimulate the release of NO through the activation of a 5‐HT1‐like receptor located on the endothelial cells.

It is concluded that in canine renal vasculature, 5‐HT1‐like agonists (and presumably endogenous 5‐hydroxytryptamine) can cause simultaneous activation of a 5‐HT1‐like receptor on both vascular smooth muscle and endothelial cells. The net renal vascular response to these agonists is therefore a function of both the vascular smooth muscle vasoconstriction and the concurrent vasodilator influence of NO released from the endothelium.
Interaction of β‐carboline inverse agonists for the benzodiazepine site with another site on GABAA receptors
Authors: Im Haesook K. , Im Wha Bin , Carter Donald B. , McKinley Denise D.
Published: July 2012

We examined the effects of methyl 6,7‐dimethoxy‐4‐ethyl‐β‐carboline‐3‐carboxylate (DMCM), a β‐carboline inverse agonist for the benzodiazepine site, on γ‐aminobutyric acid (GABA)‐induced Cl− currents in several cloned rat GABAA receptor subtypes expressed in human embryonic kidney cells. The Cl− currents were measured in the whole cell configuration of patch clamp techniques.

DMCM at low concentrations (<0.5 μm) occupying only the benzodiazepine site decreased GABA‐induced Cl currents in the α1β2γ2 and α3β2γ2 subtypes as expected from an inverse agonist, but produced no change in the α6β2γ2 subtype (perhaps a neutral antagonist). The drug at higher concentrations (> 0.5 μm) enhanced Cl− currents in all the subtypes, with a half maximal concentration of 6 to 20 μm, depending on the α isoform. In the α1β2 subtype, which is without the benzodiazepine site, DMCM monophasically increased Cl− currents with a half maximal concentration of 1.9 μm.

Ro 15–1788 (a classical benzodiazepine antagonist) had no effect on Cl− current enhancement by DMCM and, in fact, increased the current level through blocking current inhibition by DMCM via the benzodiazepine site. Also, Cl− current enhancement by pentobarbitone or by 3α, 21‐dihydroxy‐5α‐pregnan‐20‐one was additive to that by DMCM at saturating doses. It appears that the agonist site for DMCM is distinct from those for benzodiazepines, barbiturates and neurosteroids.

Among β‐carboline analogues, methyl‐β‐carboline‐3‐carboxylate and propyl‐β‐carboline‐3‐carboxylate markedly enhanced GABA‐induced Cl currents in the α1β2γ2 subtype, while N‐methyl‐β‐carboline‐3‐carboxamide and 1‐methyl‐7‐methoxy‐3,4‐dihydro‐β‐carboline did not. It appears that the 3‐carboxyl ester moiety is necessary for β‐carbolines to interact with a novel site on GABAA receptors as agonists.
Effect of the NMDA‐antagonist, MK 801, on benzodiazepine‐opioid interactions at the spinal and supraspinal level in rats
Authors: Luger Thomas J. , Lorenz Ingo H. , Grabner‐Weiss Christina , Hayashi Takahiko
Published: July 2012

Benzodiazepines potentiate morphine antinociception at the spinal level via GABAergic mechanisms. At the supraspinal level, the inhibitory effect of midazolam on morphine antinociception cannot be easily explained by GABAA receptor activation. Since excitatory amino acids play a role in central transmission, we investigated the effect of dizocilpine (MK 801) on this interaction in spinal cord and brain.

In rats with an intrathecal or intracerebroventricular catheter, the mecahnisms of the antinociceptive effect of benzodiazepine‐morphine combinations were tested during thermal nociceptive tests.

The principal findings of this study were that at the spinal level, midazolam potentiation of morphine antinociception can be antagonized by the NMDA antagonist, MK 801 (10 μg), as assessed by hot‐plate and tail‐flick tests. When drugs were administered supraspinally, midazolam inhibited morphine antinociception only in the hot‐plate test, an effect also inhibited by MK 801. In the tail‐flick assay, midazolam failed to influence the morphine response.

The NMDA antagonist significantly affected midazolam antinociception at the spinal level, but was not effective following i.c.v. administration of the drugs. MK 801 had no effect on morphine antinociception after i.t. and i.c.v. administration of the drugs.

The paradoxical effect of midazolam on morphine antinociception and its reversal by MK 801 might be due to modulation at various levels of the neuraxis and/or modulation of different pathways mediated via both GABAA and NMDA receptor mechanisms.
Role of angiotensin converting enzyme in the vascular effects of an endopeptidase 24.15 inhibitor
Authors: Telford Sarah E. , Smith A. Ian , Lew Rebecca A. , Perich Rose B. , Madden Anna C. , Evans Roger G.
Published: July 2012

1 We investigated the role of angiotensin converting enzyme (ACE) in the cardiovascular effects of N‐[1‐(R,S)‐carboxy‐3‐phenylpropyl]‐Ala‐Ala‐Tyr‐p‐aminobenzoate (cFP), a peptidase inhibitor selective for metalloendopeptidase (EP) E.C. 3.4.24.15.

2 In conscious rabbits, cFP (5 mg kg−1, i.v.) markedly slowed the degradation of [3H]‐bradykinin, potentiated the depressor response to right atrial administration of bradykinin (10–1000 ng kg−1), and inhibited the pressor response to right atrial angiotensin I (10–100 ng kg−1). In each of these respects, the effects of cFP were indistinguishable from those of the ACE inhibitor, captopril (0.5 mg plus 10 mg kg−1h−1 i.v.). Furthermore, the effects of combined administration of cFP and captopril were indistinguishable from those of captopril alone.

3 In experimentally naive anaesthetized rats, cFP administration (9.3 mg kg−1, i.v.) was followed by a moderate but sustained fall in arterial pressure of 13 mmHg. However, in rats pretreated with bradykinin (50 μg kg−1) a more pronounced fall of 30 mmHg was observed. Captopril (5 mg kg−1) had similar hypotensive effects to those of cFP, and cFP had no effect when it was administered after captopril.

4 CFP displaced the binding of [125I]‐351A (the p‐hydroxybenzamidine derivative of lisinopril) from preparations of rat plasma ACE and solubilized lung membrane ACE (KD = 1.2 and 0.14 μm respectively), and inhibited rat plasma ACE activity (KI = 2.4 μm). Addition of phosphoramidon (10 μm), an inhibitor of a range of metalloendopeptidases, including neutral endopeptidase (E.C.3.4.24.11), markedly reduced the potency of cFP in these systems.

5 Taken together these findings suggest that the actions of cFP in vivo are attributable to inhibition of ACE rather than EP 24.15. Given that cFP is a poor inhibitor of ACE in the presence of phosphoramidon in vitro, it is likely that cFP is cleaved by a phosphoramidon‐sensitive metallopeptidase in vivo to liberate N‐[1‐(R,S)‐carboxy‐3‐phenylpropyl]‐Ala‐Ala, a potent ACE inhibitor.
Comparative study of endotoxin‐induced hypotension in kininogen‐deficient rats with that in normal rats
Authors: Ueno Akinori , Ishida Hideki , Oh‐ishi Sachiko
Published: July 2012

1 The aim of this study was to clarify the role of endogenous bradykinin (BK) in the hypotensive response induced by lipopolysaccharide (LPS) by comparing the degree of hypotension caused by LPS in a strain of specific pathogen‐free (SPF) Brown Norway (B/N), kininogen‐deficient mutant Katholiek rats with that of B/N normal Kitasato rats.

2 The dose‐dependent hypotensive responses caused by intravenous injection of BK (1–100 nmol kg−1) or platelet‐activating factor (PAF, 0.003–1 μg kg−1), were not different in the two strains of rats used. However, there was a strong difference in the hypotensive response induced by LPS in kininogen‐deficient and normal rats; in normal rats the hypotensive response was composed of two phases (15 min and 70–80 min after LPS injection), but in kininogen‐deficient rats LPS caused a delayed (second phase), but not an acute (first phase) hypotension.

3 We demonstrate that Hoe 140 (1 mg kg−1, i.v.) is a potent, selective, and long‐lasting antagonist of the hypotensive effects of BK. Hoe 140 diminished the hypotension caused by LPS in normal rats to the level observed in kininogen‐deficient rats, but had no effect on the hypotension caused by LPS in kininogen‐deficient rats.

4 TCV309 (0.1 mg kg−1, i.v.) selectively inhibited the hypotension caused by repetitive injection of PAF for up to 180 min. Pretreatment with TCV309 caused a near complete inhibition of the LPS‐induced hypotension in kininogen‐deficient and normal B/N rats.

5 In the normal rats, dexamethasone (0.5 mg kg−1, i.p.) inhibited the second phase of the hypotension induced by LPS, but not the first phase of the hypotension.

6 A small amount of BK (0.1 nmol kg−1) potentiated the hypotensive action of PAF (0.01 μg kg−1), when they were injected simultaneously.

7 In conclusion, we demonstrate that formation of endogenous BK contributes primarily to the acute, but not to the delayed hypotension afforded by endotoxin in the rat. In contrast, formation of endogenous PAF contributes to both the acute and the delayed hypotension afforded by endotoxin in vivo.
Subgroups among μ‐opioid receptor agonists distinguished by ATP‐sensitive K+ channel‐acting drugs
Authors: Ocaña Maria , Del Pozo Esperanza , Barrios Manuel , Baeyens José M.
Published: July 2012

1 We evaluated the effects of the i.e.v. administration of different K+ channel blockers (gliquidone, 4‐aminopyridine and tetraethylammonium) and an opener of K+ channels (cromakalim) on the antinociception induced by several μ‐opioid receptor agonists in a tail flick test in mice.

2 The s.c. administration of all agonists of μ‐opioid receptors tested (morphine, 1–16 mg kg−1; methadone, 1–6 mg kg−1; buprenorphine, 0.04–0.64 mg kg−1; fentanyl, 0.02–0.32 mg kg−1 and levorphanol, 0.2–3.2 mg kg−1) elicited a dose‐dependent antinociceptive effect.

3 The ATP‐sensitive K+ channel blocker, gliquidone (0.06–16 μg per mouse, i.c.v.) antagonized the antinociception induced by buprenorphine, morphine and methadone. In contrast, gliquidone (0.25–160 μg per mouse) did not modify the antinociceptive effects of fentanyl and levorphanol.

4 Cromakalim (4–64 μg per mouse, i.c.v.), an opener of ATP‐sensitive K+ channels, enhanced the antinociception produced by buprenorphine, morphine, and methadone, and did not significantly modify the antinociceptive effects of fentanyl and levorphanol.

5 The i.c.v. administration of the K+ channel blockers tetraethylammonium (10 μg per mouse) or 4‐aminopyridine (25 ng per mouse) did not significantly modify the antinociception induced by any μ‐opioid receptor agonist tested.

6 These results suggest that the opening of ATP‐sensitive K+ channels is involved in the antinociceptive effect of morphine, buprenorphine and methadone, but not in that of fentanyl or levorphanol. Consequently, we suggest that at least two subgroups can be distinguished among μ‐opioid receptor agonists, each inducing antinociception through different effector mechanisms.
Neuroprotective profile of lifarizine (RS‐87476) in rat cerebrocortical neurones in culture
Authors: May Gillian R. , Rowand William S. , McCormack James G. , Sheridan Robert D.
Published: July 2012

1 The ability of the neuroprotective agent, lifarizine (RS‐87476), to mitigate veratridine‐, cyanide‐ and glutamate‐induced toxicity in rat embryonic cerebrocortical neurones in primary culture has been compared with that of tetrodotoxin (TTX), nitrendipine, (+)‐MK‐801 and (−)‐MK‐801. Lactate dehydrogenase (LDH) released into the culture medium was used as the indicator of cell viability.

2 Incubation of cultures for 16 h in a medium containing veratridine (10−4 M), sodium glutamate (10−3M) or sodium cyanide (10−3M) resulted in consistent elevations of LDH activity in the culture medium. The ability of compounds to attenuate these elevations was expressed as the concentration required to inhibit the increases in LDH release by 50% (IC50).

3 Neurotoxicity induced by veratridine was inhibited by lifarizine (IC50 = 4× 10−7M), TTX (IC50 = 3 × 10−8 M) and nitrendipine (IC50 = 3 × 10−5 M). In contrast, (+)‐MK‐801 (up to 3 × 10−5 M) was ineffective against this insult.

4 Glutamate‐induced neurotoxicity was inhibited by (+)‐MK‐801 (IC50 = 1.4 × 10 −8 M) and to a lesser extent by (−)‐MK‐801 (IC50 = 1 × 10−7 M), but was unaffected by lifarizine, TTX or nitrendipine (up to 10−6M).

5 (+)‐MK‐801 was effective against sodium cyanide‐induced neurotoxicity (IC50= 1.9 × 10−8M), whereas lifarizine and TTX (up to 10−6 m) and nitrendipine (up to 3 × 10−6 m) were without protective activity against this insult.

6 The results demonstrate that lifarizine potently protects rat cortical neurones in vitro against a neurotoxic insult that requires activation of sodium channels for its expression, and that the compound is ineffective against insults mediated by N‐methyl‐D‐aspartate receptor activation. The weak efficacy of nitrendipine against veratridine‐induced cell death argues against the involvement of L‐type calcium channels in this insult. These data are consistent with the notion that the neuroprotective activity of lifarizine observed in vivo may be mediated by inhibition of neuronal sodium currents.
Sustained contraction produced by caffeine after ryanodine treatment in the circular muscle of the guinea‐pig gastric antrum and rabbit portal vein
Authors: Chowdhury J.U. , Pang Y.‐W. , Huang S.‐M. , Tsugeno M. , Tomita T.
Published: July 2012

1 Caffeine inhibited spontaneous mechanical activity at 0.3‐1 mM, but produced a tonic contraction at concentrations higher than 3 mM in the circular muscle of the guinea‐pig gastric antrum. In the circular muscle of the rabbit portal vein, caffeine at concentrations higher than 1 mM produced an early phasic contraction followed by a small tonic component. The caffeine‐induced contraction was abolished by removal of the external Ca2+ more rapidly in the gastric antrum than the portal vein.

2 When the preparations were pretreated with ryanodine (1 μm) a sustained contraction developed on wash‐out of caffeine (10 mM) both in the gastric antrum and portal vein. This contraction was not affected by nicardipine (3 μm) or verapamil (3 μm), but was readily abolished by removal of the external Ca2+ or by addition of cobalt (1 mM). Spontaneous electrical activity, the slow wave, in gastric muscles was blocked in the presence of 10 mM caffeine, but reappeared during the sustained contraction.

3 Both the contractions induced directly by caffeine and those produced following caffeine wash‐out after ryanodine treatment were accompanied by a maintained increase in intracellular Ca2+ concentration measured with fura‐2.

4 The presence or absence of Ca2+ during the application of ryanodine did not affect the ability of caffeine to initiate sustained contractions, provided Ca2+ was present during the exposure to caffeine.

5 It is concluded that caffeine can induce a sustained contraction after ryanodine treatment both in the guinea‐pig gastric antrum and rabbit portal vein, by activating a Ca2+ influx pathway insensitive to organic Ca2+ channel blockers. No clear evidence was obtained for involvement of the Ca2+ influx pathway activated through depletion of intracellular Ca2+ stores. A hypothesis is proposed that the plasma membrane of these preparations is similar to the sarcoplasmic reticulum membrane in that Ca2+ permeability can be increased almost irreversibly by a combination of caffeine and ryanodine in the presence of the external Ca2+.
Comparison of the transplacental transfer of enalapril, captopril and losartan in sheep
Authors: Stevenson Kathleen M. , Gibson Karen J. , Lumbers Eugenie R.
Published: July 2012

1 The transplacental transfers of three drugs (enalapril, captopril and losartan) which block the renin angiotensin system and have different lipophilicities were studied in chronically catheterized foetal sheep (125–139 days gestation).

2 The ability of the foeto‐placental unit to convert enalapril to enalaprilat was studied in two chronically catheterized foetuses. Enalapril (3 mg kg−1, 7.9 fimol kg−1 given i.v. to the foetuses abolished the foetal pressor response to 5 μg angiotensin I (AI) in one foetus and attenuated the pressor response in the other.

3 Enalapril (100 mg, 5.7 fimol kg−1) given i.v. to the ewe (n = 5) abolished the maternal pressor response to 2.5 μg AI (n = 1) and attenuated the maternal pressor response to 5 μg AI (n = 5, P< 0.001). The foetal pressor response to 5 μg AI (n = 2) and 10 μg AI (n = 3) did not change. The maternal and foetal pressor responses to angiotensin II (All; n = 5) did not change.

4 Foetal pressor responses to 5 μg AI (n = 1) and 10 μg AI (n = 2) were attenuated within 11 min of their mothers (n = 3) being given i.v. captopril (15 mg, 1.5 fimol kg‐1). Foetal pressor responses to 5 μg All (n = 1) and to 10 μg All (n = 2) did not change.

5 Losartan (10 mg kg−1, 21.7 fimol kg‐1) given i.v. to the foetus (n = 9) attenuated the foetal pressor response to 5 μg All (P< 0.001) but the maternal pressor response to 5 μg All did not change.

6 Losartan (100 mg, 21.7 μmol kg‐1) given i.v. to the ewe (n = 5) attenuated the maternal pressor response to 5 μg All (P< 0.002) but the foetal pressor response to 5 μg All did not change.

7 It is concluded that the foeto‐placental unit of the sheep can metabolize enalapril to enalaprilat. Captopril readily crosses the sheep placenta but enalapril and losartan do not. Thus, the transplacental transfer of these drugs does not parallel their lipid solubilities. Furthermore the results show that AT1 receptors are important in mediating the vasoconstrictor effects of All in the foetus.
Modulation of acetylcholine release at mouse neuromuscular junctions by interaction of three homologous scorpion toxins with K+ channels
Authors: Vatanpour H. , Harvey A.L.
Published: July 2012

1 The effects of three scorpion toxins, charybdotoxin (CTX), iberiotoxin (IbTX), and noxiustoxin (NTX) have been studied on acetylcholine release and on K+ channels by means of twitch tension and electrophysiological recording techniques using isolated skeletal muscle preparations and by a radioligand binding assay using 125I‐labelled dendrotoxin I (DpI) and rat brain synaptosomal membranes.

2 On chick biventer cervicis preparations, CTX and IbTX (125 nM) augmented the twitch responses to indirect muscle stimulation. Further, the increase (about 70–80% of control twitch height) was fast in onset, reaching a maximum within 25–30 min. NTX at 125 nM produced a slower augmentation of the twitch responses to indirect muscle stimulation, with the maximum response being seen after 40–50 min.

3 On mouse triangularis sterni preparations, CTX (300 nM after 35–40 min) and IbTX (100 nM after 15 min) increased quantal content of the evoked endplate potentials (e.p.p.) by about two fold. However, NTX (300 nM) caused only a small increase in e.p.p. amplitude, which was followed by repetitive e.p.ps in response to single shock nerve stimulation after 40–50 min.

4 Extracellular recording of nerve terminal current waveforms in triangularis sterni preparations revealed that CTX and IbTX (3‐100nM), but not NTX (100 nM), blocked the Ca2+‐activated K+ current, 7K.ca‐ However, there was no major change in the portion of the nerve terminal waveform associated with voltage‐dependent K+ currents, IKv.

5 In the radioligand binding assay, NTX potently displaced labelled [125I]‐DpI, whereas CTX produced only partial displacement. However, IbTX did not displace [125I]‐DpI from its binding sites on rat brain synaptosomal membranes.

6 We conclude that these three structurally homologous scorpion toxins act on different K+ channels and that this leads to different patterns of facilitation of acetylcholine release. IbTX acts selectively on high conductance Ca2+‐activated K+ channels, leading to an increase in the amplitude of e.p.ps without any other changes. NTX acts on voltage‐dependent K+ channels that are sensitive to dendrotoxin and causes repetitive e.p.ps. CTX shares amino acid residues that exist in the structures of IbTX and NTX; CTX acts on both Ca2+‐ and voltage‐dependent K+ channels.
In vitro characterization of tripitramine, a polymethylene tetraamine displaying high selectivity and affinity for muscarinic M2 receptors
Authors: Chiarini A. , Budriesi R. , Bolognesi M.L. , Minarini A. , Melchiorre C.
Published: July 2012

1 The antimuscarinic effects of tripitramine were investigated in vitro in isolated driven left (force) and spontaneously beating right (force and rate) atria as well as in the ileum of guinea‐pig and rat and in the trachea and lung strip of guinea‐pig and compared with the effects of methoctramine.

2 Tripitramine was a potent competitive antagonist of muscarinic M2 receptors in right and left atria. The pA2 values ranged from 9.14 to 9.85. However, in the guinea‐pig and rat left atria but not in guinea‐pig right atria, tripitramine at lower concentrations (3–10 nM) produced a less than proportional displacement to the right of agonist‐induced responses owing to the presence of a possible saturable removal process.

3 Tripitramine was about three orders of magnitude less potent in ileal and tracheal than in atrial preparations (pA2 values ranging from 6.34 to 6.81) which makes it more potent and more selective than methoctramine.

4 Another intriguing finding was the observation that the pA2 value of 7.91 observed for tripitramine in guinea‐pig lung does not correlate with that found at both muscarinic M2 and M3 receptor subtypes, which clearly indicates that the contraction of guinea‐pig lung strip is not mediated by these muscarinic receptor subtypes.

5 A combination of tripitramine with atropine resulted in addition of the dose‐ratios for left atria as required for two antagonists interacting competitively with the same receptor site, whereas the same combination gave a supra‐additive antagonism on guinea‐pig ileum which suggests that tripitramine interacts with a second interdependent site.

6 Tripitramine was more specific than methoctramine since, in addition to muscarinic receptors, it inhibited only frog rectus abdominis muscular (pIC50 value of 6.14) and rat duodenum neuronal (pIC50 value of 4.87) nicotinic receptors among receptor systems investigated, namely α1‐, α1‐, and β1‐ adrenoceptors, H1‐ and H2‐histamine receptors, and muscular and neuronal nicotinic receptors.
Receptors for endothelin‐1 in asthmatic human peripheral lung
Authors: Knott Patrick G. , D'Aprile Angela C. , Henry Peter J. , Hay Douglas W.P. , Goldie Roy G.
Published: July 2012

[125I]‐endothelin‐1 ([125I]‐ET‐1) binding was assessed by autoradiography in peripheral airway smooth muscle and alveolar wall tissue in human non‐asthmatic and asthmatic peripheral lung. Levels of specific binding to these structures were similar in both non‐asthmatic and asthmatic lung. The use of the receptor subtype‐selective ligands, BQ‐123 (ETA) and sarafotoxin S6c (ETB), demonstrated the existence of both ETA and ETB sites in airway smooth muscle and in alveoli. In airway smooth muscle from both sources, the great majority of sites were of the ETB subtype. Quantitative analyses of asthmatic and non‐asthmatic alveolar wall tissue demonstrated that 29–32% of specific [125I]‐ET‐1 binding was to ETA sites and 68–71% was to ETB sites. Thus, asthma was not associated with any significant alteration in the densities of ETA and ETB receptors in peripheral human lung.
Endotoxin inhibition of distension‐stimulated gastric acid secretion in rat: mediation by NO in the central nervous system
Authors: Barrachina M.D. , Whittle B.J.R. , Moncada S. , Esplugues J.V.
Published: July 2012

The involvement of nitric oxide in the acute inhibitory effects of low doses of endotoxin, following intracerebroventricular (i.c.v.) or intravenous (i.v.) administration, on gastric acid secretion stimulated by distension or i.v. infusion of pentagastrin has been investigated in the continuously perfused stomach of the anaesthetized rat.

The i.c.v. administration of E. coli endotoxin (800 ng kg−1) abolished the acid secretory response induced by gastric distension (20 cm water intragastric pressure) within 30 min of administration.

By contrast, submaximal rates of acid secretion induced by i.v. infusion of pentagastrin (8 μg kg−1 h−1) were not inhibited by i.c.v. administration of endotoxin (800 ng kg−1).

Prior i.c.v. administration of the NO synthase inhibitor, NG‐nitro‐l‐arginine methyl ester (l‐NAME, 800 μg kg−1) restored the acid secretory responses to distension in rats treated with endotoxin (i.c.v.).

Likewise, i.v. administration of endotoxin (5 μg kg−1) abolished the acid secretory response induced by gastric distension within 30 min of administration. Prior i.c.v injection of l‐NAME (800 μg kg−1) or its i.v. administration (10 mg kg−1) restored acid secretory responses in rats receiving i.v. endotoxin.

The reversal by l‐NAME (i.v.) of the acid inhibitory effects of endotoxin (i.v.) was prevented by l‐arginine (12 mg kg−1, i.c.v. or 100 mg kg−1, i.v), but not by its enantiomer d‐arginine.

The present results imply the existence of an acute response to endotoxin involving NO synthesis in the brain. NO may act as a neuromodulator or neurotransmitter in a nervous reflex leading to the inhibition of acid secretion stimulated by gastric distension.
Pharmacological characterization of bradykinin receptors in canine cultured tracheal smooth muscle cells
Authors: Yang Chuen Mao , Luo Shue‐Fen , Hsia Hui‐Chuan
Published: July 2012

[3H]‐bradykinin was used to characterize the bradykinin receptors associated with canine cultured tracheal smooth muscle cells (TSMCs). Receptor binding assay showed that TSMCs had specific, saturable, high‐affinity binding sites for [3H]‐bradykinin.

The specific [3H]‐bradykinin binding increased linearly with increasing cell concentrations. The equilibrium for association of [3H]‐bradykinin with the bradykinin receptors was attained within 2 h at 4°C and 1 h at room temperature, respectively.

Analysis of binding isotherms yielded an apparent equilibrium dissociation constant (KD) of 2.5 ± 0.3 nm and a maximum receptor density (Bmax) of 25.1 ± 0.3 fmol mg−1 protein. The Hill coefficient for [3H]‐bradykinin binding was 1.00 ± 0.02. The association (K1) and dissociation (K‐1) rate constants were (8.67 ± 2.60) × 106 m−1 min−1 and 0.024 ± 0.005 min−1, respectively. KD, calculated from the ratio of K‐1 and K1 was 2.8 ± 0.5 nm, a value close to that of KD calculated from Scatchard plots of binding isotherms.

The B1 receptor selective agonist, (des‐Arg9‐bradykinin, 0.1 nm–10 μm) and antagonist ([Leu8, des‐Arg9]‐bradykinin, 0.1 nm–10 μm) did not inhibit the [3H]‐bradykinin binding to TSMCs, which excludes the presence of B1 receptors in canine TSMCs.

The specific binding of [3H]‐bradykinin to canine TSMCs was inhibited by B2 receptor selective antagonists ([d‐Arg0, Hyp3, Thi5, d‐Tic7, Oic8]‐bradykinin, Hoe 140, 0.1 nm–10 μm and [d‐Arg0, Hyp3, Thi5,8, d‐Phe7]‐bradykinin, 0.1 nm–10 μm) and agonists (bradykinin and kallidin, 0.1 nm–10 μm) with a best fit by a one‐binding site model. The order of potency for the inhibition of [3H]‐bradykinin binding was kallidin = bradykinin = Hoe 140>[d‐Arg0, Hyp3, Thi5,8, d‐Phe7]‐bradykinin.

Preincubation of TSMCs with forskolin for 24 h led to an up‐regulation of B2 receptors, increasing in Bmax from 25.1 ± 0.3 to 218 ± 24 fmol mg−1 protein without changing the KD values. [3H]‐bradykinin binding to TSMCs was inhibited by the B2 receptor selective antagonists and agonists, but not by the B1 receptor selective reagents. The up‐regulation of the B2 receptor by forskolin was mediated through protein synthesis, since cycloheximide blocked this response.

It is concluded that the pharmacological characteristics of the bradykinin receptors in canine cultured TSMCs are primarily of the B2 receptor subtype.
Reduction of carrageenin oedema and the associated c‐Fos expression in the rat lumbar spinal cord by nitric oxide synthase inhibitor
Authors: Honoré Prisca , Chapman Victoria , Buritova Jaroslava , Besson Jean‐Marie
Published: July 2012

Three hours after intraplantar carrageenin (6 mg/150 μl of saline) Fos‐like immunoreactivity (Fos‐LI) was mainly observed in L4 and L5 segments of the dorsal horn. Both superficial (I–II) and deep laminae (V–VI) neurones were labelled.

We have studied the effect of systemic administration of a nitric oxide synthase inhibitor, NG‐nitro‐l‐arginine methyl ester (l‐NAME) on carrageenin evoked c‐Fos expression and thus the contribution of nitric oxide to this expression.

Pre‐administration of l‐NAME (10, 25, 50, 100 mg kg−1, i.v.) dose‐dependently reduced the number of superficial and deep laminae Fos‐LI neurones, 100 mg kg−1 produced a 63 ± 2% and 72 ± 4% reduction of Fos‐LI neurones respectively, P < 0.0001 for both superficial and deep neurones.

Pre‐administered l‐NAME dose‐relatedly reduced the carrageenin‐evoked paw and ankle oedema, with 100 mg kg−1 of l‐NAME resulting in a 74 ± 2% and 103 ± 2% reduction respectively.

Post‐administration of l‐NAME (10 mg kg−1, i.v.) reduced the number of superficial and deep laminae Fos‐LI neurones (65 ± 7% and 53 ± 8% reduction respectively, P <0.01 for both superficial and deep neurones).

Post‐administered l‐NAME reduced both the paw and ankle oedema (52 ± 8% and 62 ± 10% reduction respectively, P<0.0001 for both paw and ankle).

Pre‐administered d‐NAME (100 mg kg−1, i.v.), the inactive isomer of l‐NAME, produced a weak reduction of the number of superficial laminae Fos‐LI neurones (26 ± 8% reduction, P<0.05), without influencing the deep Fos‐LI neurones (5 ± 8% enhancement) or the oedema.

Systemic l‐arginine (1200 mg kg−1) did not reverse the reduction of the total number of Fos‐LI neurones induced by 100 mg kg−1 of l‐NAME, or the effect of l‐NAME on the paw and ankle oedema.

Intraplantar l‐arginine (30 mg) did not reverse the effect of l‐NAME (100 < mg kg−1) on the total number of Fos‐LI neurones. However, the inhibitory effects of l‐NAME on the paw and ankle oedema were partially reversed by intraplantar l‐Arginine (34 ± 9% and 45 ± 11% reduction of carrageenin oedema respectively) with these effects being significant as compared to the effect of l‐NAME alone (P<0.05 for both).

There is a strong correlation between the reduction of the number of Fos‐LI neurones and the oedema by l‐NAME, clearly demonstrating a predominant role of peripheral NO in the development of one of the signs of carrageenin inflammation.
Interaction between gallopamil and cardiac ryanodine receptors
Authors: Zucchi Riccardo , Ronca‐Testoni Simonetta , Yu Gongyuan , Galbani Paola , Ronca Giovanni , Mariani Mario
Published: July 2012

In a sarcoplasmic reticulum fraction obtained from rat hearts, the analysis of equilibrium [3H]‐ryanodine binding showed high and low affinity sites (KD = 1.3 nm and 2.8 μm, Bmax = 2.2 pmol mg−1 and 27.8 pmol mg−1). The dissociation rate constant increased at 1 μm VS 4 nm [3H]‐ryanodine concentration, and micromolar ryanodine slowed the dissociation of nanomolar ryanodine.

The binding of 4 nm [3H]‐ryanodine was not affected by gallopamil, while the binding of 100 nm to 18 μm [3H]‐ryanodine was partly displaced. Data analysis suggested that gallopamil inhibited low affinity [3H]‐ryanodine binding, with IC50 in the micromolar range.

Gallopamil decreased the dissociation rate constant of 1 μm [3H]‐ryanodine. While gallopamil alone did not affect the dissociation of 4 nm [3H]‐ryanodine, gallopamil and micromolar ryanodine slowed it to a greater extent than micromolar ryanodine alone.

Our results are consistent with the hypothesis that the ryanodine receptor is a negatively cooperative oligomer, which undergoes a sequential alteration after ryanodine binding. Gallopamil has complex actions: it inhibits ryanodine binding to its low affinity site(s), and probably modulates the cooperativity of ryanodine binding and/or the transition to a receptor state characterized by slow ryanodine dissociation. These molecular actions could account for the previously reported effect of gallopamil on the sarcoplasmic reticulum calcium release channel.
Cytochrome P450‐dependent effects of bradykinin in the rat heart
Authors: Fulton D. , Mahboubi K. , McGiff J.C. , Quilley J.
Published: July 2012

Vasodilator responses to bradykinin (BK) in the rat heart are reported to be independent of NO and cyclo‐oxygenase/lipoxygenase products of arachidonic acid (AA).

We verified that inhibition of NO synthase with l‐nitroarginine (50 μm) and cyclo‐oxygenase with indomethacin (2.8 μm) were without effect on vasodilator responses to BK (10–1000 ng) in the Langendorff rat heart preparation.

l‐Nitroarginine elevated perfusion pressure, signifying a crucial role of NO in the maintenance of basal vasculature tone.

In hearts treated with l‐nitroarginine to eliminate NO and elevate perfusion pressure, vasodilator responses were reduced by inhibitors of cytochrome P450 (P450), clotrimazole (1 μm) and 7‐ethoxyresorufin (1 μm). 17‐Octadecynoic acid (17‐ODYA 2 μm), a mechanism based inhibitor of P450‐dependent metabolism of fatty acids, also reduced vasodilator responses to BK.

These results confirm that NO and prostaglandins do not mediate vasodilator responses to BK in the rat heart but suggest a major role for a P450‐dependent mechanism via AA metabolism.
Evidence that nitric oxide from the endothelium attenuates inherent tone in isolated pulmonary arteries from rats with hypoxic pulmonary hypertension
Authors: Wanstall Janet C. , Hughes Ian E. , O'Donnell Stella R.
Published: July 2012

The inherent contractile tone, and its modulation by the endothelium, have been studied in isolated pulmonary artery preparations taken from rats in which pulmonary hypertension was induced by exposure to a hypoxic environment (10% O2) for 14 days. Control rats were housed in room air.

All preparations in which the endothelium was left intact relaxed in response to acetylcholine (43 ± 4% and 54 ± 9%, reversal of the noradrenaline‐induced contraction in control and hypoxic rats, respectively) indicating that the endothelium was functional in both groups of rats.

Exposure of the preparations to Ca2+‐free physiological salt solution containing 2 mm EGTA for 30–40 min had no effect on preparations from control rats but caused relaxation in preparations from hypoxic rats. The relaxation (taken as a measure of the inherent tone in the preparations) was larger in preparations without endothelium (14.5 ± 1.9 mn mm−2; n = 5) than in preparations with endothelium (9.1 ± 1.2 mn mm−2; n = 5).

In preparations from hypoxic rats the magnitudes of the contractions to 80 mm K+ and to noradrenaline (0.1 μm) were less than in preparations from control rats. This may have been because the preparations from hypoxic rats were already partially contracted due to the inherent tone.

The nitric oxide (NO) synthase inhibitor, NG‐nitro‐l‐arginine methyl ester (l‐NAME, 0.1–100 μm) had negligible effect on preparations from control rats or on endothelium‐denuded preparations from hypoxic rats, but produced concentration‐dependent contractions (maximum contraction 7.4 ± 0.7 mn mm−2 (n = 4) with 100 μm) in endothelium‐intact preparations from hypoxic rats. This effect of l‐NAME was prevented by l‐arginine (1 mm) but not by d‐arginine (1 mm).

Contractions to l‐NAME were also seen in endothelium‐intact arteries from control rats if the preparations were first partially contracted by exposure to K+, endothelin, U46619 (thromboxanemimetic) or noradrenaline.

It is concluded that isolated pulmonary artery rings from hypoxic rats, but not those from control rats, have substantial inherent tone. This inherent tone is normally attenuated by the generation of an endothelium‐derived factor that is probably NO. A stimulus for the release of NO from the endothelium may be the contraction of the underlying smooth muscle, whether the contraction is inherent in the tissue, as in preparations from hypoxic rats, or is induced by a vasoconstrictor spasmogen.