bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of NG‐nitro‐l‐arginine methyl ester or indomethacin on differential regional and cardiac haemodynamic actions of arginine vasopressin and lysine vasopressin in conscious rats
Authors: Gardiner Sheila M. , Compton Alix M. , Kemp Philip A. , Bennett Terence
Published: July 2012

Measurements of changes in renal, mesenteric and hindquarters haemodynamics or cardiac haemodynamics in response to i.v. bolus doses of arginine vasopressin (AVP) or lysine vasopressin (LVP, 0.7 and 7.0 pmol) were made in conscious, chronically‐instrumented Long Evans rats.

In some experiments AVP and LVP were administered during an infusion of NG‐nitro‐l‐arginine methyl ester (l‐NAME; 1.0 or 0.3 mg kg−1 h−1) to determine whether or not inhibition of nitric oxide production influenced the cardiovascular effects of the peptides. In other experiments, indomethacin (bolus dose of 5 mg kg−1 followed by infusion at 5 mg kg−1 h−1) was given to determine the possible involvement of cyclo‐oxygenase products in the responses to AVP and LVP.

Under control conditions, the lower dose of LVP had significantly greater effects than AVP on heart rate, mean arterial blood pressure, renal, mesenteric and hindquarters conductances, total peripheral conductance, cardiac index, peak aortic flow and + dF/dtmax. The higher dose of LVP had significantly greater effects than AVP on all variables (i.e. including stroke index and central venous pressure).

In the presence of l‐NAME (1 mg kg−1 h−1) there was a sustained increase in mean arterial blood pressure (+ 23 ± 3 mmHg) and reductions in mesenteric (– 38 ± 4%) and hindquarters (–30 ± 6%) vascular conductances. Under these conditions the difference in the pressor effects of AVP and LVP was abolished, but their differential effects on regional and cardiac haemodynamics persisted. This dose of l‐NAME did not change cardiac baroreflex sensitivity.

During infusion of l‐NAME at a lower rate (0.3 mg kg−1 h−1), baseline cardiovascular status was unchanged and regional haemodynamic effects of AVP and LVP were enhanced, but the differences in the regional vasoconstrictor responses to the two peptides persisted.

Indomethacin (5 mg kg−1 bolus, then 5 mg kg−1 h−1 infusion) augmented the renal vasoconstrictor responses to AVP and LVP, but abolished the difference in the hindquarters vasoconstrictor responses to the two peptides. However, the differences in the pressor and the renal and mesenteric vasoconstrictor effects of AVP and LVP still occurred in the presence of indomethacin.

The results indicate that AVP normally has lesser cardiovascular effects than LVP but this difference does not seem to be due to more effective stimulation of nitric oxide‐mediated or cyclo‐oxygenase‐dependent vasodilator mechanisms by AVP than LVP.
Effect of endothelium removal on the vasoconstrictor response to neuronally released 5‐hydroxytryptamine and noradrenaline in the rat isolated mesenteric and femoral arteries
Authors: Urabe Masanobu , Kawasaki Hiromu , Takasaki Koichiro
Published: July 2012

The role of the vascular endothelium in the vasoconstrictor response to transmural nerve stimulation (TNS) was studied in isolated ring segments of rat mesenteric and femoral arteries.

In both types of artery, TNS (1 to 16 Hz) produced frequency‐dependent vasoconstriction, which was abolished by 100 nm tetrodotoxin, 10 μm guanethidine or 10 nm prazosin, indicating that the response was mediated by endogenous noradrenaline (NA) released from noradrenergic nerves. NA‐mediated vasoconstriction in response to TNS was significantly potentiated by removal of the endothelium.

In the presence of 10 nm prazosin, the reduced vasoconstriction in response to TNS was restored by incubation with 10 μm 5‐hydroxytryptamine (5‐HT) for 20 min. Restoration of the response to TNS was markedly attenuated by treatment with 10 nm ketanserin, 100 nm tetrodotoxin, or 10 μm guanethidine, indicating that the restored response was mediated by 5‐HT released from noradrenergic nerves. Vasoconstriction mediated by 5‐HT in response to TNS was not modified by removal of the endothelium.

In both types of artery with intact endothelium, treatment with 3μm methylene blue potentiated the NA‐mediated contractile response to TNS, but did not potentiate the 5‐HT‐mediated response to TNS.

In both types of artery, the contractile responses to exogenous NA and 5‐HT were potentiated by removal of the endothelium.

These results suggest that endothelial cells regulate neurogenic vasoconstriction by releasing endothelium‐derived relaxing factor. Furthermore, it appears likely that the response to neuronally released 5‐HT is not affected by the endothelium.
Further characterization, by use of tryptamine and benzamide derivatives, of the putative 5‐HT4 receptor mediating tachycardia in the pig
Authors: Villalón Carlos M. , den Boer Marien O. , Heiligers Jan P.C. , Saxena Pramod R.
Published: July 2012

It has recently been shown that the tachycardic response to 5‐hydroxytryptamine (5‐HT) in the anaesthetized pig, being mimicked by 5‐methoxytryptamine and renzapride and blocked by high doses of ICS 205–930, is mediated by the putative 5‐HT4 receptor. In the present investigation we have further characterized this receptor.

Intravenous bolus injections of the tryptamine derivatives, 5‐HT (3, 10 and 30 μg kg−1), 5‐methoxytryptamine (3, 10 and 30 μg kg−1) and α‐methyl‐5‐hydroxytryptamine (α‐methyl‐5‐HT; 3, 10, 30 and 100 μg kg−1), resulted in dose‐dependent increases in heart rate of, respectively, 25 ± 2, 48 + 3 and 68 ± 3 beats min−1 (5‐HT; n = 35); 15 ± 1, 32 ± 2 and 57 ± 3 beats min−1 (5‐methoxytryptamine; n = 30); 6 ± 4, 18 ± 6, 34 ± 6 and 64 ± 11 beats min−1 (α‐methyl‐5‐HT; n = 3).

The increases in heart rate following i.v. administration of certain substituted benzamide derivatives were genereally less marked and not dose‐dependent: 1 ± 5, 11 ± 3 and 10 ± 5 beats min−1 after 300, 1000 and 3000 μg kg−1 of metoclopramide, respectively, (n = 8); 21 ± 4, 19 ± 2 and 2 ± 2 beats min−1 after 100, 300 and 1000 μg kg−1 of cisapride, respectively, (n = 5); 6 ± 2, 14 ± 2, 37 ± 6, 43 ± 8 and 34 ± 10 beats min−1 after 10, 30, 100, 300 and 1000 μg kg−1 of zacopride, respectively, (n = 6); and 1 ± 1, 2 ± 1 and 5 ± 2 beats min−1 after 300, 1000 and 3000 μg kg−1 of dazopride, respectively, (n = 4). These drugs behaved as partial agonists, antagonizing the responses to 5‐HT and 5‐methoxytryptamine dose‐dependently.

The 5‐HT3 receptor agonist 1‐phenyl‐biguanide (100, 300 and 1000 μg kg−1) induced only slight increases in heart rate of 1 ± 1, 6 ± 2 and 11 + 1 beats min−1, respectively, (n = 3). These effects were not antagonized by the selective 5‐HT3 receptor antagonist granisetron (3 mg kg−1). In addition, 1‐phenyl‐biguanide (1000 μg kg−1) did not modify the tachycardia induced by either 5‐HT‐ or 5‐methoxytryptamine.

High doses (3 mg kg−1) of ICS 205–930, a 5‐HT3 receptor antagonist with an indole group and devoid of effects on porcine heart rate per se, antagonized the stimulatory effects of 5‐HT, 5‐methoxytryptamine, α‐Me‐5‐HT, metoclopramide, cisapride, zacopride, dazopride and 1‐phenyl‐biguanide. However, the 5‐HT2 receptor antagonist ketanserin (0.5 mg kg−1), the 5‐HT3 receptor antagonists granisetron (3 mg kg−1) and MDL 72222 (3 mg kg−1) and the dopamine D2 receptor antagonist domperidone (3 mg kg−1) had no antagonist activity.

The above results support our contention that 5‐HT, 5‐methoxytryptamine, α‐Me‐5‐HT and the substituted benzamide derivatives increase porcine heart rate by a direct action on the cardiac pacemaker, via the activation of a putative 5‐HT4 receptor. The pharmacological profile of this novel 5‐HT receptor is similar (neurones from mouse brain colliculi and human heart) or, perhaps, even identical (guinea‐pig cholinergic neurones) to other putative 5‐HT4 receptors.
Effects of glibenclamide on cytosolic calcium concentrations and on contraction of the rabbit aorta
Authors: Yoshitake Kiyonobu , Hirano Katsuya , Kanaide Hideo
Published: July 2012

Using fluorometry of fura‐2 and rabbit aortic strips, we studied the effects of glibenclamide (GLB), a sulphonylurea anti‐diabetic drug and an inhibitor of opening of K+ channels, on cytosolic calcium concentrations ([Ca2+]i) and on force development.

Both high K+‐depolarization and noradrenaline (NA) increased [Ca2+]i and force, in a concentration‐dependent manner, in the presence of extracellular Ca2+ (1.25 mm). However, force development in relation to [Ca2+]i ([Ca2+]i‐force relationship) observed with NA was much greater than that observed with K+‐depolarization.

Pretreatment with GLB (10−6–10−4 m) for 10 min partially inhibited, in a concentration‐dependent manner, both [Ca2+]i elevation and the force development induced by 118 mm K+‐depolarization or NA 10−5 m in the presence of extracellular Ca2+. The [Ca2+]i‐force relationship induced by both 118 mm K+ physiological salt solutions and by NA 10−5 m in the GLB‐treated strips overlapped that obtained in the non‐treated strips, thereby suggesting that GLB has no effect on the Ca2+‐sensitivity of the intracellular contractile apparatus. Only high concentrations (10−4 m) of GLB decreased [Ca2+]i and the force, when applied after the force induced by 118 mm K+ PSS or NA 10−5 m reached the maximum level.

In the absence of extracellular Ca2+, NA induced a transient increase in [Ca2+]i and in the force and these increases were inhibited when the vascular strips were pretreated with GLB for 10 min. The [Ca2+]i‐force relationship obtained in the GLB‐treated strips overlapped that in the non‐treated ones.

An ATP‐sensitive K+ channel opener, cromakalim (10−5 m) reduced the increased [Ca2+]i and force induced by 25 mm K+‐depolarization and NA 10−5 m. Subsequent application of GLB concentration‐dependently reversed this relaxant effect of cromakalim on the NA‐induced contraction (IC50 = 2 × 10−7 m). Complete reversal of the effect was observed with 10−5 m GLB.

We suggest that GLB inhibits both high K+‐depolarization‐ and NA‐induced contraction of the rabbit aorta, by decreasing [Ca2+]i and with no effect on the [Ca2+]i‐force relationship. However, when NA‐induced contractions were inhibited by a K+‐channel opener, GLB reversed this inhibitory effect by inhibiting K+‐channel opening and increasing [Ca2+]i.
l‐NG‐nitro arginine methyl ester exhibits antinociceptive activity in the mouse
Authors: Moore P.K. , Oluyomi A.O. , Babbedge R.C. , Wallace P. , Hart S.L.
Published: July 2012

l‐NG‐nitro arginine methyl ester (l‐NAME, 1–75 mg kg−1) administered intraperitoneally (i.p.) elicits dose‐related antinociception in the mouse assessed by the formalin‐induced paw licking procedure. Antinociceptive activity is still present 24 h after injection. l‐NAME (75 mg kg−1, i.p.) is also antinociceptive in the acetic acid‐induced abdominal constriction and hot plate procedures.

l‐NAME additionally produces a dose‐related inhibition of formalin‐induced paw licking following intracerebroventricular (i.c.v., 0.1–100 μg per mouse) and oral (p.o., 75–150 mg kg−1) administration.

l‐Arginine (600 mg kg−1, i.p.) but not d‐arginine (600 mg kg−1) or naloxone (5 mg kg−1) reverses the antinociceptive effect of l‐NAME in the formalin test.

High doses of l‐NAME (37.5–600 mg kg−1) but not d‐NAME (75 mg kg−1) administered i.p. produce dose‐related increases in blood pressure of the urethane‐anaesthetized mouse whilst i.c.v. injected l‐NAME (0.1 and 100 μg per mouse) is inactive.

l‐NAME (75 mg kg−1, i.p.) did not inhibit oedema formation in the formalin‐injected mouse hindpaw.

l‐NAME (75 mg kg−1) did not produce any overt behavioural changes in treated mice and failed to influence locomotor activity or the incidence of dipping, crossing, rearing or circling behaviour assessed by a modified ‘head‐dipping’ board procedure. A high dose of l‐NAME (600 mg kg−1) reduced dipping behaviour and locomotor activity suggesting a possible sedative effect. d‐NAME (600 mg kg−1) was inactive.

These results suggest that l‐NAME produces an opioid‐independent and long‐lasting antinociception in the mouse most probably by a direct effect within the central nervous system.
Effects of hypoxia and metabolic inhibitors on production of prostacyclin and endothelium‐derived relaxing factor by pig aortic endothelial cells
Authors: Richards Joanna M. , Gibson Ian F. , Martin William
Published: July 2012

The content of adenosine triphosphate (ATP) and basal and bradykinin‐stimulated production of prostacyclin and endothelium‐derived relaxing factor (EDRF) was measured in primary cultures of porcine aortic endothelial cells under normoxic (14.4% O2) and hypoxic (2.8% O2) conditions, and following treatment with rotenone and 2‐deoxy glucose, which inhibit oxidative and glycolytic metabolism, respectively.

ATP content and basal and bradykinin‐stimulated production of prostacyclin were similar under normoxic and hypoxic conditions. EDRF production, assessed as endothelial guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) content, was also similar under both conditions.

Treatment with rotenone (0.3 μm) had no effect on ATP content or basal or bradykinin‐stimulated production of prostacyclin or of EDRF, measured as endothelial cyclic GMP content. Elevation of cyclic GMP content by atriopeptin II was also unaffected.

Treatment with 2‐deoxy glucose (20 mm) in glucose‐free Krebs solution lowered ATP content, reduced bradykinin‐stimulated production of prostacyclin and abolished the bradykinin‐stimulated elevation of cyclic GMP content. Resting production of prostacyclin was unaffected but basal content of cyclic GMP was lowered in some experiments. Elevation of cyclic GMP content by atriopeptin II was abolished.

Combined treatment with rotenone (0.3 μm) and 2‐deoxy glucose (20 mm) lowered ATP content more than with 2‐deoxy glucose alone. Basal production of prostacyclin rose slightly and bradykinin‐stimulated production was powerfully inhibited. Basal content of cyclic GMP was unaffected, but bradykinin‐stimulated production was abolished. Elevation of cyclic GMP by atriopeptin II was also abolished.

Cascade bioassay experiments using endothelium‐denuded rings of rabbit aorta as a detector system confirmed that bradykinin‐stimulated production of EDRF was blocked by 2‐deoxy glucose, but not by rotenone.

These data indicate that porcine aortic endothelial cells in culture operate under mainly glycolytic metabolism and this probably explains why production of prostacyclin and EDRF is unaffected under hypoxic conditions. They also indicate that glycolytic metabolism is required for agonist‐stimulated production of prostacyclin and EDRF by these cells.
Modulation of the hypothermic and hyperglycaemic effects of 8‐OH‐DPAT by α2‐adrenoceptor antagonists
Authors: Durcan Michael J. , Wozniak Krystyna M. , Linnoila Markku
Published: July 2012

The effects of pretreatment with two novel and relatively specific α2‐adrenoceptor antagonists on the hypothermic and hyperglycaemic responses induced by the 5‐HT1A receptor agonist 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) were investigated in mice. The α2‐adrenoceptor antagonists used were, atipamezole, which occupies both central and peripheral receptors, and L 659,066, which poorly penetrates the blood brain barrier.

Atipamezole (1 and 3 mg kg−1) alone had no effect on body temperature but significantly attenuated the 8‐OH‐DPAT‐induced hypothermic response. The hyperglycaemic effect of 8‐OH‐DPAT was also attenuated by pretreatment with atipamezole; however, 3 mg kg−1 atipamezole did cause some hypoglycaemia when administered alone.

Pretreatment with L 659,066 (3–30 mg kg−1) failed to alter the hypothermic effects of 8‐OH‐DPAT. All doses of L 659,066 tested attenuated 8‐OH‐DPAT‐induced hyperglycaemia, but the highest dose (30 mg kg−1) produced hypoglycaemia when administered alone.

The results suggest that the attenuation of 8‐OH‐DPAT‐induced hypothermia by α2‐adrenoceptor antagonists may be centrally mediated whereas the blockade of 8‐OH‐DPAT‐induced hyperglycaemia may involve peripheral mechanisms.
Stimulation of neutrophil adherence to vascular endothelial cells by histamine and thrombin and its inhibition by PAF antagonists and dexamethasone
Authors: Watanabe Masako , Yagi Mikio , Omata Mitsugu , Hirasawa Noriyasu , Mue Suetsugu , Tsurufuji Susumu , Ohuchi Kazuo
Published: July 2012

In order to clarify the roles of platelet‐activating factor (PAF) in histamine‐ and thrombin‐induced neutrophil adhesion to vascular endothelial cells, the effects of several PAF antagonists were examined. The effects of the glucocorticoid dexamethasone were also examined in order to gain further insight into the anti‐inflammatory actions of glucocorticoids.

In culture, histamine and thrombin stimulated the adherence of rat peritoneal neutrophils to human endothelial cells from the umbilical vein. They did not stimulate neutrophil adherence in the absence of endothelial cells, suggesting that the target cells for the histamine‐ and thrombin‐induced adherence of neutrophils were endothelial cells, not neutrophils.

Several PAF antagonists, such as CV‐3988, L‐652,731 and Y‐24,180 inhibited the histamine‐ and thrombin‐induced neutrophil adherence in a concentration‐dependent manner. Indomethacin failed to inhibit it.

Dexamethasone, a steroidal anti‐inflammatory drug, did not inhibit the histamine‐ and thrombin‐induced adherence of neutrophils to endothelial cells when the drug was present only during the 20 min incubation period for the adherence assay. When the endothelial cells were preincubated for 3 h with dexamethasone, the adherence of neutrophils to endothelial cells induced by histamine or thrombin was not inhibited.

When the neutrophils were preincubated for 3 h with dexamethasone, the histamine‐ and thrombin‐induced adherence of neutrophils to endothelial cells was inhibited.

Our studies indicate that: (a) adherence of neutrophils to endothelial cells induced by histamine and thrombin is mediated by PAF production since PAF antagonists inhibited the adherence of neutrophils; and (b) neutrophils, not endothelial cells, are the target cells through which dexamethasone acts to inhibit adherence.
Parainfluenza virus infection damages inhibitory M2 muscarinic receptors on pulmonary parasympathetic nerves in the guinea‐pig
Authors: Fryer Allison D. , Jacoby David B.
Published: July 2012

The effect of viral infection on the function of neuronal M2 muscarinic autoreceptors in the lungs was studied in anaesthetized guinea‐pigs.

Guinea‐pigs were inoculated intranasally with either parainfluenza type 3 or with a vehicle control. Four days later the animals were anaesthetized, paralysed and artificially ventilated. Pulmonary inflation pressure, tidal volume, blood pressure, and heart rate were recorded. Both vagus nerves were cut and electrical stimulation of the distal portions caused bronchoconstriction (measured as an increase in pulmonary inflation pressure) and bradycardia.

In control animals, pilocarpine (1–100 μg kg−1, i.v.) attenuated vagally‐induced bronchoconstriction by stimulating inhibitory M2 muscarinic receptors on parasympathetic nerves in the lungs. Conversely, blockade of these receptors with the antagonist gallamine (0.1–10 mg kg−1, i.v.) produced a marked potentiation of vagally‐induced bronchoconstriction. These results confirm previous findings.

In guinea‐pigs infected with parainfluenza virus, pilocarpine did not inhibit vagally‐induced bronchoconstriction. Furthermore, gallamine did not potentiate vagally‐induced bronchoconstriction to the same degree as in uninfected controls.

There was no increase in baseline pulmonary inflation pressure in the infected animals over the controls. Receptors on airway smooth muscle were unchanged by viral infection since large doses of pilocarpine caused equivalent bronchoconstriction in both groups of animals. Gallamine inhibited the vagally‐induced fall in heart rate equally in both groups of animals indicating that virus‐induced changes in M2 receptor function on pulmonary parasympathetic nerves are not part of a generalized decrease in M2 receptor function.

These results demonstrate that the M2 muscarinic receptor‐mediated inhibition of acetylcholine release from parasympathetic nerves in the lungs is decreased in animals infected with parainfluenza virus. Loss of this inhibition would result in increased release of acetylcholine from the parasympathetic nerves and may explain virus‐induced airway hyperresponsiveness.
Changes in brain striatum dopamine and acetylcholine receptors induced by chronic CDP‐choline treatment of aging mice
Authors: Giménez Rosa , Raïch Josep , Aguilar Juan
Published: July 2012

Spiroperidol binding (dopamine D2 receptors) and quinuclidinyl benzilate binding (muscarinic receptors) in striata of 19‐month old mice was analyzed for animals that had received chronic administration of cytidine 5′‐diphosphocholine (CDP‐choline) incorporated into the chow consumed (100 or 500 mg kg−1 added per day) for the 7 months before they were killed.

Treated animals displayed an increase in the dopamine receptor densities of 11% for those receiving 100 mg kg−1 and 18% for those receiving 500 mg kg−1 as compared to the control aged animals that had received no CDP‐choline. Control animals showed, from 2 months to 19 months of life, a 28% decrease in the receptor density. No change in the affinity of the receptors for spiroperidol was found in the treated or untreated animals.

Muscarinic acetylcholine receptor densities were also partially recovered by the same treatment in aged animals that showed a 14% decrease of these receptors in this case. The muscarinic receptor density increased 6% for the animals that received 100 mg kg−1 and 17% for the animals that received 500 mg kg−1 without any change in the affinity of the receptor for quinuclidinyl benzilate.

Aged animals displayed a slight increase in brain membrane fluidity as indicated by a decrease in the polarization value of the non‐polar fluorophore 1,6‐diphenyl‐1,3,5‐hexatriene. Interestingly, in the treated animals a greater increase in membrane fluidity was determined and found to be very similar for the two doses.

It is concluded that chronic administration of CDP‐choline to aged animals promoted a partial recovery of the striatum dopamine and acetylcholine receptor function normally reduced with aging, which might be explicable in terms of mechanisms involving fluidity of the brain neuronal membrane.
Delineation of three pharmacological subtypes of α2‐adrenoceptor in the rat kidney
Authors: Uhlén Staffan , Wikberg Jarl E.S.
Published: July 2012

Simultaneous computer modelling of plain and ARC 239‐ and guanoxabenz‐masked [3H]‐RX821002 saturation curves, plain ARC 239 and guanoxabenz competition curves as well as ARC 239‐masked guanoxabenz competition curves revealed that the drugs bound to three α2‐adrenoceptor subtypes in the rat kidney with grossly differing selectivities. These α2‐adrenoceptor subtypes were termed α2A, α2B1 and α2B2. The order of affinities for [3H]‐RX821002 for the adrenoceptor sites was α2A > α2B1 > α2B2, the Kd s being 0.62 ± 0.05, 2.52 ± 0.11 and 6.74 ± 1.21 nm, respectively. The order of affinities for ARC 239 was α2B1 > α2B2 ≫ α2A with Kd s 4.78 ± 1.04, 28.8 ± 4.1 and 1460 ± 270 nm, respectively. For guanoxabenz the order of affinities was α2A > α2B1 ≫ α2B2 with Kd s 99.7 ± 15.1, 508 ± 135 and 25,400 ± 2400 nm, respectively.

Binding constants for 14 compounds for the three rat kidney α2‐adrenoceptor subtypes were determined by the simultaneous computer modelling of plain and ARC 239‐ and guanoxabenz‐masked drug competition curves, plain ARC 239 and guanoxabenz competition curves as well as ARC 239‐masked guanoxabenz competition curves. Of the 14 compounds tested, oxymetazoline and guanfacine were found to bind with low affinities to both of the α2B1‐ and α2B2‐adrenoceptors but with high affinity to the α2A‐adrenoceptor. Prazosin instead bound with high affinities to the α2B1‐ and α2B2‐adrenoceptors but with low affinity to the α2A‐adrenoceptor. By contrast, guanoxabenz and ARC 239 delineated clearly between all the three α2‐adrenoceptor subtypes. Notably the affinities of guanoxabenz for α2B1‐ and α2B2‐adrenoceptors differed 72 fold and for α2A‐ and α2B2‐adrenoceptors 380 fold. The selectivities of a number of other drugs were less marked but their Kd s were consistent with all three sites being α2‐adrenoceptors.

(−)‐Adrenaline and (−)‐noradrenaline showed dissimilar order of affinities for the three α2‐adrenoceptors. For (−)‐adrenaline the order of affinities was α2B1 ≥ α2A > α2B2 and for (−)‐noradrenaline α2B2 ≥ α2B1 > α2A. All three α2‐adrenoceptors showed the expected stereoselective binding for adrenaline enantiomers, the (+)‐form being 7–10 fold less potent than the (−)‐form.

[3H]‐yohimbine was also used as radioligand. The data with this ligand were fully compatible with the [3H]‐RX821002 data. However, [3H]‐yohimbine appeared to label only α2B1‐ and α2B2‐adrenoceptors presumably because it had too low an affinity for α2A‐adrenoceptors.

We conclude that three pharmacological subtypes of α2‐adrenoceptors are labelled by [3H]‐RX821002 in the rat kidney. Guanoxabenz and ARC 239 may be used in competition studies to delineate between these three α2‐adrenoceptor subtypes. Moreoever, we here present a method allowing the determination of binding constants for an arbitrary drug to the three α2‐adrenoceptor subtypes.
The control of the contraction of myocytes from guinea‐pig heart by the resting membrane potential
Authors: Mermi J. , Yajima M. , Ebner F.
Published: July 2012

The influence of different holding potentials (− 120 to − 70 mV) on the contraction of enzymatically dispersed myocytes from guinea‐pig hearts was evaluated. Contractions were elicited by repetitive depolarizations to 0 mV at 0.5 Hz.

While ineffective at 140 and 5 mmol 1−1 [Na+]o and pipette Na+, respectively, depolarization of the resting membrane with the holding potential increased myocyte shortening at reduced Na+ gradients ([Na+]o 70 or [Na+]i 10–15 mmol 1−1). Elevated intracellular Na+ after Na+‐pump inhibition with ouabain 1–10 μmol 1−1 was similarly effective with regard to the inotropic response to different holding potentials.

At − 70 mV holding potential, reduction of [Na+]o from 140 to 70 mmol 1−1 increased myocyte shortening and induced an inwardly directed component of the holding current which peaked at − 44 ± 10 pA and declined thereafter in parallel with the inotropic effect. The relation of this inward current to [Ca2+]i was confirmed by experiments at high Ca2+ buffer capacity where [Na+]o reduction induced a Ni2+‐insensitive, outwardly directed component (36 ± 15 pA) of the holding current. The observed inward current is suggested to reflect the extrusion of [Ca2+]i in exchange for [Na+]o as a counter‐regulatory mechanism which limits the increase of [Ca2+]i.

The interventions which increased the strength of the contraction also enhanced the transient tail current after repolarization, suggesting its close relation to [Ca2+]i. This finding confirmed the pattern found with cell shortening.

It is concluded that under certain conditions, voltage‐dependent and Na+‐dependent Na+‐Ca2+ exchange during the interval between the contractions is relevant to the diastolic concentration of [Ca2+]i which in turn determines the accumulation of Ca2+ in the sarcoplasmic reticulum and the magnitude of the subsequent contraction.
A calcitonin gene‐related peptide (CGRP) antagonist (CGRP8–37) inhibits microvascular responses induced by CGRP and capsaicin in skin
Authors: Hughes S.R. , Brain S.D.
Published: July 2012

The effect of the calcitonin gene‐related peptide (CGRP) antagonist CGRP8–37 on responses to CGRP and other mediators was investigated in rabbit dorsal skin.

Blood flow changes at intradermally‐injected sites were measured by a multiple site 133xenon clearance technique. CGRP8–37 had little effect on blood flow at doses up to 0.3 nmol/site, when injected alone, although a significant increase in blood flow was observed at the highest dose tested (1 nmol/site).

CGRP8–37 dose‐dependently inhibited the increased blood flow induced by human αCGRP and human βCGRP, but had no effect on equivalent vasodilator responses induced by vasoactive intestinal peptide (VIP) and prostaglandin E1 (PGE1). CGRP8–37 showed a preferential ability to inhibit αCGRP (IC50 0.04 nmol), when compared with βCGKP (IC50 ≥ 0.3 nmol).

Capsaicin, which selectively activates sensory nerves, caused a dose‐dependent increase in blood flow when injected intradermally into rabbit skin. The effects of capsaicin (0.01–0.1 μmol/site) were inhibited by CGRP8–37 (0.3 nmol/site), with a partial but significant attenuation of blood flow induced by the highest dose of capsaicin.

Oedema formation, induced by intradermal histamine injection (3 nmol/site), was measured in rabbit skin by the local accumulation of intravenously‐injected 125I‐labelled albumin. Vasodilator doses of CGRP, PGE1 and capsaicin potentiated, in a synergistic manner, oedema formation induced by histamine. CGRP8–37 totally inhibited the potentiating effect of CGRP, partially inhibited the synergistic effect of capsaicin, but did not affect PGE1‐induced responses.

The results suggest that capsaicin acts to release a rabbit form of CGRP in skin and that CGRP8–37 is a useful antagonist for investigating the potential of CGRP as a neurogenic mediator of inflammation.
The effect of inhibitors of nitric oxide biosynthesis and cyclic GMP formation on nerve‐evoked relaxation of human cavernosal smooth muscle
Authors: Pickard R.S. , Powell P.H. , Zar M.A.
Published: July 2012

The inhibitory transmission in isolated preparations of cavernosal smooth muscle from human penis has been studied.

Electrical field stimulation (EFS; 2–64 pulses/train, 0.8 ms pulse duration, 10 Hz) evoked relaxation of preparations treated with guanethidine (50 μm). The EFS‐evoked relaxations were atropine‐resistant and tetrodotoxin‐sensitive indicating their origin to be non‐adrenergic, non‐cholinergic (NANC) nerve stimulation.

EFS‐evoked relaxation was attenuated dose‐dependently by the nitric oxide (NO)‐synthase inhibitor, l‐NG‐nitro arginine (l‐NOARG; 0.3–100 μm) but not by d‐NG‐nitro arginine. The inhibitory effect of l‐NOARG on transmission was antagonized by l‐arginine (100 μm), a NO precursor, but not by d‐arginine.

Incubation with methylene blue (10–50 μm), a known inhibitor of guanylate cyclase activation by NO, caused a concentration‐related inhibition of EFS‐evoked relaxation.

It is concluded that NANC nerve‐evoked relaxation of human cavernosal smooth muscle is mediated by NO or a NO‐like substance.
Effects of the glycine prodrug milacemide (2‐N‐pentylaminoacetamide) on catecholamine secretion from isolated adrenal medulla chromaffin cells
Authors: Yadid Gal , Zinder Oren , Youdim Moussa B.H.
Published: July 2012

Milacemide (2‐n‐pentylaminoacetamide) is a glycine prodrug which readily crosses the blood brain barrier and increases brain glycine and glycineamide. In vitro and in vivo studies, with numerous tissues, including adrenal chromaffin cells, have clearly shown that the formation of the latter metabolites is exclusively mediated by monoamine oxidase B for which milacemide is a substrate.

Milacemide, glycineamide and glycine caused a time‐ and dose‐dependent release of catecholamines from bovine isolated chromaffin cells.

Milacemide (10−4 m) induced catecholamine release was roughly 30% of that initiated by acetylcholine (10−4 m), the natural secretagogue.

The combined effects of milacemide (10−4 m) and acetylcholine (10−4 m) on catecholamine secretion from chromaffin cells is additive, suggesting that milacemide does not act through the normal nicotinic receptor release mechanism.

The release of catecholamines from chromaffin cells in response to milacemide (10−4 m) was partially inhibited by the selective MAO‐B inhibitors (−)‐deprenyl (10−7 m) and AGN 1135 (10−6 m). This indicates that the MAO‐B derived metabolites, glycineamide and glycine, contribute to the secretion of catecholamines as does milacemide itself.

It is apparent that release of catecholamines by glycine is mediated by its uptake into the cells since [3H]‐glycine uptake and catecholamine release showed a higly significant correlation (r = 0.96).
Differential actions of platelet‐activating factor (PAF) receptor antagonists on the vasodilator and vasoconstrictor effects of PAF in the rat perfused heart
Authors: Hu Weimin , Man Ricky Y.K.
Published: July 2012

Selectivity for blocking the coronary vasodilator and vasoconstrictor effects of platelet‐activating factor (PAF) in the rat perfused heart was observed with different PAF antagonists. CV‐6209 showed selectivity for blocking the vasodilator effect of PAF and a higher concentration (10 fold) was required to block the vasoconstrictor effect. The remaining PAF antagonists (FR‐900452, WEB 2086 and BN‐50739) showed selectivity for blocking the vasoconstrictor effect of PAF (10, 200 and 1000 fold respectively). A combination of low concentrations of CV‐6209 (10 nm) with FR‐900452 (5 μm) or WEB 2086 (0.5 μm) was effective in blocking both the vasodilator and vasoconstrictor effects of PAF. CV‐6209 and WEB 2086 did not affect the vasodilator action of leukotriene B4 (LTB4) and the vasoconstrictor action of LTC4 and LTD4. Our results support the hypothesis that the functionally opposite effects of PAF in the rat perfused heart may be mediated by different PAF receptor subtypes.
Beneficial effect of beraprost, a prostacyclin‐mimetic agent, on post‐hypoxic recovery of cardiac function and metabolism in rabbit isolated hearts
Authors: Tanonaka Kouchi , Maruyama Youichi , Takeo Satoshi
Published: July 2012

The present study was undertaken to determine whether beraprost, a stable prostacyclin‐mimetic agent, may exert a beneficial effect on post‐hypoxic recovery of cardiac function and metabolism. Isolated rabbit hearts were perfused by the Langendorff method for 20 min under glucose‐free hypoxic conditions, followed by 45 min reoxygenation in the presence of glucose, and their functional and metabolic changes with or without beraprost‐treatment were examined.

Hypoxic insult induced cessation of cardiac contractile force, depletion of myocardial high‐energy phosphates, accumulation of tissue calcium, and release of creatine kinase and ATP metabolites. Subsequent reoxygenation resulted in a poor recovery of cardiac contractile force (less than 10% of the pre‐hypoxic value), a poor restoration of high‐energy phosphates, and increase in calcium content. A further release of creatine kinase and ATP metabolites from the heart was observed during reoxygenation.

Treatment with 0.45 μm beraprost during the whole hypoxic period resulted in a significant suppression of the increase in tissue calcium, and the release of creatine kinase and ATP metabolites during hypoxic perfusion. This treatment also elicited a significant post‐hypoxic recovery of the cardiac contractile force and the tissue high‐energy phosphates. Reoxygenation‐induced release of creatine kinase and ATP metabolites was also prevented by treatment with beraprost.

When hearts were treated with prostacyclin sodium (0.50 μm) in the same manner for the purpose of comparison, similar improvement of post‐hypoxic contractile and metabolic recovery were observed.

These results demonstrate that treatment with either beraprost or prostacyclin is beneficial for post‐hypoxic recovery of cardiac function and metabolism. Since the observed effects on post‐hypoxic contractile recovery were exerted at a concentration of approximately 0.50 μm of these agents (a concentration far from the physiological range) the underlying mechanism appears to be different from the physiological action of prostacyclin.
Effects of selective D1 and D2 dopamine agonists on cockroach salivary gland acinar cells in vitro
Authors: Evans A.M. , Green K.L.
Published: July 2012

The ability of the selective dopamine receptor agonists, fenoldopam and SKF38393 (D1) and quinpirole and LY163502 (D2), to mimic the effect of dopamine on cockroach salivary gland acinar cells has been investigated.

Intracellular recordings of the membrane potential established that all the agonists mimicked dopamine (i.e. they induced a hyperpolarization which was occasionally followed by a depolarization), whether applied by addition to the superfusate or locally by pressure ejection.

The rank order of potency of the agonists to induce a hyperpolarization was (equipotent molar ratio relative to dopamine in parentheses): dopamine (1) ≫ fenoldopam (1000) > SKF38393 (3500) > LY163502 (13750) > quinpirole (35000).

The agonists also elicited secretion from the salivary gland when superfused onto the preparation. SKF38393 and quinpirole did not induce the same maximum rate of secretion as dopamine. The rank order of potency of the agonists was (minimum effective concentration in parentheses): dopamine (0.03 μm) > fenoldopam (4.8 μm) > SKF38393 (40.8 μm) > quinpirole (132 μm).

Both the hyperpolarizing and secretory responses to all the agonists were antagonized by the selective D1 antagonist, (+)‐SCH23390, but not the selective D2 antagonist, (±)‐sulpiride.

These results support the idea that the same receptors mediate both the hyperpolarizing and secretory responses, and that they are similar to the mammalian D1 receptor.
Novel kainate derivatives: potent depolarizing actions on spinal motoneurones and dorsal root fibres in newborn rats
Authors: Ishida M. , Shinozaki H.
Published: July 2012

Neuropharmacological actions of several kainate derivatives (kainoids) were examined for electrophysiological effects in the isolated spinal cord and the dorsal root fibre of the newborn rat.

Some kainoids caused depolarization of the motoneurone much more effectively than kainic acid or domoic acid and others were weaker. The rank order of the depolarizing activities of the kainoids tested here is as follows: 4‐(2‐methoxyphenyl)‐2‐carboxy‐3‐pyrrolidineacetic acid (MFPA) > acromelic acid A > domoic acid ≧ 4‐(2‐hydroxyphenyl)‐2‐carboxy‐3‐pyrrolidineacetic acid (HFPA) ≧ acromelic acid B > kainic acid.

In the isolated dorsal root fibre, domoic acid caused the most significant depolarization. There were distinct differences with regard to the rank order of the depolarizing activity between the motoneurone and the dorsal root fibre. The rank order in the dorsal root fibre is domoic acid > acromelic acid B > 5‐bromowillardiine ≧ MFPA > acromelic acid A > HFPA > kainic acid.

Significant desensitization of kainate receptors was observed in the isolated dorsal root fibre during prolonged application of l‐glutamate, kainate and its derivatives. Cross desensitization was also observed among these excitatory amino acids. Receptors desensitized by kainate did not respond to MFPA, HFPA and acromelic acids, suggesting that these kainate derivatives activated common kainate receptors in the dorsal root fibre.

In both motoneurones and dorsal root fibres, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) effectively depressed the depolarization induced by kainoids, and neither 3‐[(±)‐2‐carboxypiperazin‐4‐yl]propyl‐1‐phosphonic acid (CPP) nor picrotoxin blocked or affected the depolarization, but there were some differences in pharmacological potencies of glutamate antagonists between both preparations.

MFPA, HFPA and acromelic acids should provide valuable pharmacological tools for analysis of physiological functions of excitatory amino acids, in particular, as specific agonists for some subtypes of kainate receptors.
Chronic treatment with the angiotensin I converting enzyme inhibitor, perindopril, protects in vitro carbachol‐induced vasorelaxation in a rat model of vascular calcium overload
Authors: Henrion Daniel , Chillon Jean‐Marc , Capdeville‐Atkinson Christine , Vinceneux‐Feugier Marion , Atkinson Jeffrey
Published: July 2012

Treatment of young rats with vitamin D3 plus nicotine produced 31 and 4 fold increases in the calcium content of the aorta and the mesenteric arterial bed, respectively.

Aortic rings and perfused mesenteric arterial beds from vitamin D3/nicotine‐treated animals showed a diminished contractile response to noradrenaline in vitro.

In vascular preparations from vitamin D3/nicotine‐treated animals, precontracted with noradrenaline, relaxation by the endothelium‐dependent vasodilator, carbachol, was attenuated but responses to sodium nitroprusside were not modified.

Prolonged treatment with the angiotensin I converting enzyme inhibitor, perindopril, at a dose (1 mg kg−1) which did not significantly modify blood pressure, failed to prevent vascular calcium overload.

Perindopril treatment diminished noradrenaline‐evoked vasoconstrictor responses of aortic rings in both groups, but restored responses in mesenteric arterial beds of vitamin D3/nicotine‐treated rats.

Perindopril treatment also restored the maximal responses to carbachol of both aortic rings and mesenteric arterial beds of vitamin D3/nicotine‐treated rats.

In conclusion, in the vitamin D3 plus nicotine model of calcium overload, reduced endothelial‐mediated relaxation can be prevented by perindopril treatment.
Characterization of the effects of the new inotropic agent BDF 9148 in isolated papillary muscles and myocytes of the guinea‐pig heart
Authors: Ravens Ursula , Wettwer Erich , Pfeifer Thomas , Himmel Herbert , Armah Benjamin
Published: July 2012

The cardiotonic agent BDF 9148 (4‐[3′‐(1″‐benzhydryl‐azetidine‐3″‐oxy)‐2′‐hydroxypropoxy]‐1H‐indole‐2‐carbonitrile) is structurally related to DPI 201‐106 (4‐[3′‐(4″‐benzhydryl‐1″‐piperazinyl)‐2′‐hydroxypropoxy]‐1H‐indole‐2‐carbonitrile) which is known to modify cardiac sodium channels. In guinea‐pig papillary muscles, both compounds increase force of contraction with similar concentration‐response curves. Like DPI 201‐106, BDF 9148 prolongs the action potential duration in a tetrodotoxin‐sensitive manner. With high concentrations (> 3 μm), however, the action potential duration shortens again. In order to elucidate the underlying changes in membrane currents, we have investigated the effects of BDF 9148 in isolated ventricular myocytes of the guinea‐pig heart.

In isolated cells, a concentration of 1 μm BDF 9148 prolonged the action potential duration and markedly enhanced unloaded cell shortening, indicating that the procedure of cell isolation does not abolish the effect of the drug.

Membrane currents were studied with the single electrode voltage clamp technique. With clamp steps from −80 mV to −40 mV, BDF 9148 (1 μm) induced a slowly decaying inward current which was suppressed by tetrodotoxin. Therefore, like DPI 201‐106, BDF 9148 slows the inactivation of the sodium channels.

In order to quantify the effects of BDF 9148 and DPI 201‐106 on sodium current inactivation, we have measured the inward current amplitude still present at 100 ms after a depolarizing clamp step from −80 mV to −30 mV. Both drugs increased this current component in a concentration‐dependent manner; however, BDF 9148 had a larger effect in the low concentration range.

The calcium current was inhibited by BDF 9148 and DPI 201‐106 in a concentration‐dependent manner; the pD2 values were 5.70 and 5.95, respectively.

The two compounds are thought to produce similar positive inotropic effects by imposing a sodium load on the muscle cells via modification of the sodium channels. The differences in action potential duration could be due to different contributions of ionic currents other than sodium or calcium currents and of pump and exchange currents. At present, there is not sufficient data to identify clearly distinct current components responsible for the differences in action potential prolongation.;
Amelioration of cisplatin‐induced acute renal failure with 8‐cyclopentyl‐1,3‐dipropylxanthine
Authors: Knight R.J. , Collis M.G. , Yates M.S. , Bowmer C.J.
Published: July 2012

The effect of the selective adenosine A1‐receptor antagonist, 8‐cyclopentyl‐1,3‐dipropylxanthine (CPX), on the development of cisplatin‐induced acute renal failure was investigated in the rat.

CPX at doses of 0.03, 0.1 and 0.3 mg kg−1, i.v. caused increasing degrees of antagonism of adenosine‐induced bradycardia in anaesthetized rats. The magnitude of antagonism was not directly proportional to the increment in dose, but for each dose, it was similar in rats injected with either saline or cisplatin. CPX at a dose of 0.03 mg kg−1 significantly antagonized adenosine‐induced bradycardia for up to 2.5 h, while doses of 0.1 and 0.3 mg kg−1 produced significant blockade for periods longer than 5 h.

Administration of cisplatin (6 mg kg−1, i.v.) caused acute renal failure characterized by decreased inulin and p‐aminohippurate clearances, increased urine volume but decreased excretion of Na+, K+ and Cl− ions and by increased plasma levels of urea and creatinine. Kidney weight was increased in cisplatin‐treated rats and renal tubule necrosis occurred.

Administration of CPX (0.03 mg kg−1, i.v.; twice daily for two days) to rats given cisplatin did not reduce the severity of the resultant renal failure. However, treatment with 0.1 mg kg−1 CPX attenuated the increases in plasma creatinine/urea levels observed in rats on days 3 and 7 after induction of renal failure. In addition, this dose significantly reduced renal tubule damage and increased inulin and p‐aminohippurate clearances. A similar pattern of protection was noted with CPX at a dose of 0.3 mg kg−1 although the increase in inulin clearance was not statistically significant. However, this higher dose of CPX significantly increased Na+ and K+ excretion compared to vehicle‐treated rats.

CPX at doses of 0.03, 0.1 and 0.3 mg kg−1 produced blockade of an A1‐receptor mediated response i.e. adenosine‐induced bradycardia, but only treatment with the higher doses of CPX (0.1 and 0.3 mg kg−1) ameliorated nephrotoxicity produced by cisplatin. The lack of any protective effect afforded by the lowest dose of CPX could be a result of its shorter duration of action.

This study indicates that adenosine plays a significant role in the pathophysiology of cisplatin‐induced acute renal failure.;
Evidence that epithelium‐dependent relaxation of vascular smooth muscle detected by co‐axial bioassays is not attributable to hypoxia
Authors: Spina D. , Fernandes L.B. , Preuss J.M.H. , Hay D.W.P. , Muccitelli R.M. , Page C.P. , Goldie R.G.
Published: July 2012

The present study was undertaken to examine further the contribution of hypoxia to airway epithelium‐dependent relaxation of rat aorta in the co‐axial bioassay.

Endothelium‐denuded rat aorta contracted with phenylephrine (0.05 μm) relaxed in a time‐dependent manner (t½ = 8.3 ± 0.4 min, n = 38) when the bathing solution was bubbled with 95% N2 and 5% CO2. In co‐axial bioassays, the t½ for histamine (100 μm; guinea‐pig trachea)‐ and methacholine (100 μm; rabbit bronchus)‐ induced relaxation was 1.9 ± 0.2 min (n = 14) and 1.2 ± 0.1 min (n = 26), respectively.

Hypoxia‐induced relaxation was not associated with a rise in intracellular guanosine 3′:5′‐cyclic monophosphate (cyclic GMP). This contrasts with previous findings of an elevation in cyclic GMP associated with epithelium‐dependent relaxation of rat aorta in co‐axial bioassays.

Hypoxia‐induced vascular relaxation was antagonized by the ATP‐sensitive K+ channel blocker, glibenclamide (100 μm). In contrast, glibenclamide (100 μm) failed to inhibit histamine (100 μm; guinea‐pig trachea)‐ and methacholine (0.1–100 μm; rabbit bronchus)‐induced release of epithelium‐derived inhibitory factor (EpDIF), in co‐axial bioassays. Glibenclamide (100 μm) antagonized BRL 38227 (lemakalin), but not isoprenaline‐induced relaxation of phenylephrine‐contracted rat aorta.

These data strongly suggest that the airway epithelium‐dependent relaxant responses observed in co‐axial bioassays cannot be attributed to hypoxia.