bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure‐activity studies on endothelin (16–21), the C‐terminal hexapeptide of the endothelins, in the guinea‐pig bronchus
Authors: Rovero Paolo , Patacchini Riccardo , Maggi Carlo Alberto
Published: July 2012

We describe the results of a structure‐activity study in which the C‐terminal hexapeptide of the endothelins, endothelin (16–21), is compared with shorter fragments; hexapeptides bearing amino‐acid substitutions and the corresponding C‐terminal fragments of sarafotoxins. The guinea‐pig bronchus was used in this study since it is the most sensitive preparation for endothelin (16–21) thus far developed.

The biological results obtained with endothelin (16–21) and analogues demonstrate that the contractile activity of the C‐terminal hexapeptide of endothelin on the guinea‐pig bronchus depends on quite close structural requirements, strongly suggestive of a receptor interaction. The following features appear to be essential for the biological activity: (a) the C‐terminal free carboxylic function; (b) the L‐configuration of Trp‐21; (c) the β‐carboxylic function of Asp‐18; (d) the presence of Leu‐17 and (e) the imidazole moiety of His‐16.

The hexapeptide corresponding to the C‐terminal portion of sarafotoxin, sarafotoxin (16–21), was devoid of biological activity. This behaviour might be related to the proposed existence of more than one receptor for the endothelin/sarafotoxin family in the guinea‐pig bronchus.
Electrical effects of okadaic acid extracted from black sponge on rabbit sinus node
Authors: Kondo Noriaki , Kodama Itsuo , Kotake Hiroshi , Shibata Shoji
Published: July 2012

Effects of okadaic acid on electrical responses and spontaneous activity in the dominant pacemaker cells of rabbit sinus node were investigated by use of microelectrode techniques.

Okadaic acid (10−5 m to 4 × 10−5 m) caused a shortening of cycle length of spontaneous firing (SPCL) accompanied by increases in both maximum upstroke velocity at phase 0 and amplitude of action potential.

All of the effects of okadaic acid were relatively well preserved in a low‐Ca2+ medium (0.12 mm). Okadaic acid restored the spontaneous activity of sinus node pacemaker cells even in a Ca2+‐deficient medium.

The effects of okadaic acid were markedly inhibited or abolished in a low Na+ medium (24 mm or 70 mm) and in the presence of a slow channel blocking agent, verapamil (10−6 m).

In voltage‐clamp experiments using a two‐microelectrode technique, okadaic acid (10−5 m) caused an increase in the slow inward current without affecting the outward current. At a higher concentration (4 × 10−5 m), the drug increased the outward current.

These results indicate that okadaic acid causes an increase in spontaneous activity of sinus node pacemaker cells mediated by an enhancement of slow inward current (Isi) through verapamil‐sensitive Ca2+ channels.
Thermal trauma alters myocardial cyclic nucleotides and protein content in mice
Authors: Tomera John F. , Martyn J.A. Jeevendra
Published: July 2012

This study tested the hypothesis that the systemic effects of burn include altered metabolic activity in the heart. Metabolic activity was studied by measuring alterations in cyclic nucleotide levels and protein concentrations in atrial and ventricular muscle in mice at 14 and 22 days after a 20% body surface area (BSA) burn. Thermal injury was produced on the dorsal surface of anesthetized male CD mice by immersion in water at 95°C for 8 s. This resulted in a full‐thickness, 3° scald burn. In atrial and ventricular tissues, levels of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) and guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) were analyzed by 125I‐radioimmunoassay.

The protein content (mg prot g−1 dry wt) increased in the atria. The cyclic AMP content (nmol g−1 dry wt) was significantly increased fourfold and ninefold at 14 and 22 days, respectively, in atria from burned animals compared to controls. The cyclic AMP/cyclic GMP ratios were similarly increased.

In the ventricle, the protein content and cyclic AMP levels were not altered, but the cyclic AMP/cyclic GMP ratios (nmol g−1 dry wt) were increased at both 14 and 22 days. These changes both in atria and ventricles were less prominent when cyclic nucleotide concentrations or ratios were expressed as pmol mg−1 protein.

The data confirm the hypothesis that a 20% BSA thermal injury evokes effects in sites remote from burn injury such as in the atria and ventricles. These effects include total body weight loss, elevated cyclic AMP, cyclic AMP/cyclic GMP ratios, and protein levels in the atria, and elevated cyclic AMP/cyclic GMP ratios in both atrial and ventricular tissues at 2 and 3 weeks after thermal injury. To prevent underestimation of cyclic nucleotide levels such changes should preferably be expressed on a prot g−1 dry weight basis.
Adrenalectomy abolishes antagonism of α‐adrenoceptor‐mediated hypotension by a β‐blocker in conscious rats
Authors: Tabrizchi R. , Pang C.C.Y.
Published: July 2012

The effects of a single bolus injection of propranolol, atenolol or ICI 118,551, non‐selective β‐, selective β1‐ and selective β2‐adrenoceptor antagonists, respectively, on mean arterial pressure (MAP) and plasma catecholamine concentrations were examined in seven groups of conscious and unrestrained adrenalectomized rats receiving a continuous infusion of the α‐adrenoceptor antagonist phentolamine. In all rats adrenaline was undetectable in the plasma four days after adrenalectomy.

In the first three groups, phentolamine significantly decreased MAP and increased the plasma concentrations of noradrenaline. The injection of propranolol, atenolol or ICI 118,551 in Groups I, II and III, respectively, caused a small increase in MAP and a small, but not significant, decrease in plasma noradrenaline concentrations.

Groups IV, V and VI were given a continuous infusion of adrenaline for 1 h prior to the infusion of phentolamine, followed by a bolus injection of propranolol, atenolol or ICI 118,551, respectively. Group VII was treated similarly to IV, but was also given daily cortisone replacement after adrenalectomy. Adrenaline slightly, but not significantly, decreased MAP while phentolamine significantly decreased MAP and increased plasma noradrenaline concentrations in all groups. A subsequent injection of a β‐blocker caused a significant increase in MAP in each group and a slight decrease in the plasma level of noradrenaline which reached statistical significance in group VII. The pressor effect of propranolol was significantly greater in the cortisone‐treated rats (Group VII) than in Group IV.

The results suggest that adrenaline and adrenocortical steroids are both involved in the antagonism of α‐adrenoceptor‐induced hypotension by a β‐blocker.
Chronic β1‐adrenoceptor antagonist treatment sensitizes β2‐adrenoceptors, but desensitizes M2‐muscarinic receptors in the human right atrium
Authors: Motomura S. , Deighton N.M. , Zerkowski H.‐R. , Doetsch N. , Michel M.C. , Brodde O.‐E.
Published: July 2012

In 64 patients undergoing coronary artery bypass grafting the effects of chronic β1‐adrenoceptor antagonist (metoprolol, atenolol, bisoprolol) treatment on right atrial β‐adrenoceptor and muscarinic M2‐receptor number and functional responsiveness were investigated.

The β1‐adrenoceptor antagonists increased right atrial β1‐adrenoceptor number, did not affect β2‐adrenoceptor number, and decreased muscarinic M2‐receptor number.

Concomitantly, activation of right atrial adenylate cyclase by 10 μm GTP, 10 μm isoprenaline and 1 μm forskolin was enhanced and inhibition by 100 μm carbachol was diminished.

On isolated, electrically driven right atria the β1‐adrenoceptor‐mediated positive inotropic effect of noradrenaline was — even with β1‐adrenoceptor number increased — not altered, while the β2‐adrenoceptor‐mediated effect of procaterol was markedly enhanced. However, the carbachol‐induced negative inotropic effect was decreased.

It is concluded that chronic β1‐adrenoceptor antagonist treatment increases β1‐adrenoceptor number and concomitantly sensitizes β1‐adrenoceptor function, but desensitizes muscarinic M2‐receptor function in the human heart.
Methoxyphenamine inhibits basal and histamine‐induced nasal congestion in anaesthetized rats
Authors: Lau W.A.K. , King R.G. , Boura A.L.A.
Published: July 2012

Nasal resistance in anaesthetized rats was assessed by measuring air overflow during ventilation of the nasal passages at constant pressure. Nasal basal resistance was reduced in a dose‐dependent manner by methoxyphenamine hydrochloride (0.01–30 mg kg−1, i.v.), pseudoephedrine hydrochloride (0.03–3 mg kg−1, i.v.) and adrenaline bitartrate (0.01–3 μg kg−1, i.v.). Both methoxyphenamine and pseudoephedrine were less potent and less efficacious than adrenaline but caused longer‐lasting responses.

Nasal congestion induced by histamine (0.2% nebulised solution passed into the nasal passages for 15 s) was inhibited by i.v. administration of methoxyphenamine, pseudoephedrine, adrenaline, methoxamine or tyramine: the ID50s against 0.2% histamine‐induced nasal congestion were 1.16 (95% confidence limits; 0.5, 1.8) mg kg−1, 0.25 (0.19, 0.33)mg kg−1, 0.037 (0.018, 0.06) μg kg−1, 8.12 (6.74, 9.65) μg kg−1 and 30.6(26.1, 35.8) μg kg−1 respectively.

The inhibitory effects of both methoxyphenamine and tyramine on histamine‐induced nasal congestion were reduced after administration of desmethylimipramine (0.1 and 1 mg kg−1, i.v.) or prazosin (0.1 and 0.3 mg kg−1, i.v.). Similarly, the inhibitory effects of methoxamine were reduced after prazosin (0.1 and 0.3 mg kg−1).

These results indicate that methoxyphenamine (1 mg kg−1, i.v.) inhibits histamine‐induced nasal congestion in the rat. This action, at least in part, is probably indirect being mediated by release of neuronal noradrenaline which then acts on α1‐adrenoceptors.
Influence of N‐ethylmaleimide on action potential and force of contraction of guinea‐pig papillary muscles
Authors: von Poehl Corona , Iven H. , Brasch H.
Published: July 2012

Standard microelectrode techniques were used to investigate the influence of N‐ethylmaleimide on the action potential, slow response action potential and force of contraction of guinea‐pig papillary muscles.

N‐ethylmaleimide, 3 × 10−5 to 10−4 moll−1, concentration‐dependently increased the force of contraction. The positive inotropic effect developed quickly and, with the largest drug concentration, was followed by a progressive decline of the contractile force. The action potential duration was progressively shortened by N‐ethylmaleimide.

The effects of N‐ethylmaleimide were not prevented in the presence of tetrodotoxin 3 × 10−8 moll−1 and propranolol 4 × 10−6 moll−1 or by a reduction of the Na+‐concentration to 70 mmoll−1.

Verapamil, 10−6 moll−1, reduced the positive inotropic, but not the action potential shortening effect of N‐ethylmaleimide.

In K+‐depolarized muscles in the presence of propranolol and tetrodotoxin, N‐ethylmaleimide 10−4 moll−1 increased the maximum depolarization velocity and the duration of the slow response action potential. The latter effect was transient and was followed by a progressive reduction of the action potential duration.

The most likely explanation for the action potential shortening effect of N‐ethylmaleimide seems to be an increase of an outward potassium current while the transient inotropic effect of the drug may be caused, at least in part, by an increase of the slow inward calcium current.
The effect of capsaicin on voltage‐gated calcium currents and calcium signals in cultured dorsal root ganglion cells
Authors: Bleakman D. , Brorson J.R. , Miller R.J.
Published: July 2012

The effects of capsaicin on voltage‐gated Ca2+ currents (ICa), and intracellular Ca2+ concentrations ([Ca2+]i) in cultured dorsal root ganglion (DRG) neurones of the rat were examined in vitro by use of combined patch clamp‐microfluorometric recordings.

Under voltage‐clamp conditions, capsaicin (0.1–10 μm) caused a concentration‐dependent decrease in the magnitude of the ICa, an elevation in the holding current (Ih) and a concomitant rise in the [Ca2+]i in most cells examined. Repeated application of capsaicin produced marked desensitization.

Some decrease in the ICa produced by capsaicin was also observed when the rise in [Ca2+]i was buffered with EGTA or BAPTA and when Ba2+ was used as the charge carrier; under these conditions the desensitization previously observed was smaller.

The decrement in voltage‐gated current was smaller in Ba2+ containing solutions than in Ca2+ containing solutions suggesting that the capsaicin‐induced influx of Ca2+ partially mediated the observed decrease in the voltage‐gated current. In cells which showed a marked response to capsaicin an outward (positive) current was sometimes observed upon depolarization from −80 to 0mV. This effect was consistent with an outward movement of cations through the capsaicin conductance pathway which may also account, in part, for the apparent reduction in ICa by capsaicin.

The effects of capsaicin under voltage‐clamp conditions were prevented by ruthenium red (1 μm).

Under current clamp conditions, capsaicin depolarized and caused a rise in [Ca2+]i in the majority of DRG cells examined. Both of these effects could be prevented by ruthenium red (500 nm).

It is concluded that capsaicin reduces the ICa of rat DRG neurones primarily by indirect mechanisms.
Protein kinase C‐mediated contractile responses of arteries from diabetic rats
Authors: Abebe W. , MacLeod K.M.
Published: July 2012

The role of protein kinase C (PKC) in mediating enhanced contractile responses of aortae and mesenteric arteries from male rats with 12–14 week streptozotocin‐induced diabetes to noradrenaline (NA) was investigated using the PKC activator, phorbol 12,13‐dibutyrate (PDB), and the PKC inhibitor, staurosporine.

Maximum contractile responses of aortae and mesenteric arteries from diabetic rats to NA were significantly enhanced compared with responses of arteries from age‐matched control animals. The maximum NA responses were increased by 59.6 ± 7.9% in aortae and by 54.9 ± 7.4% in mesenteric arteries from diabetic animals, compared to their respective controls.

Pretreatment of aortae and mesenteric arteries from both control and diabetic animals with staurosporine (5 × 10−8 m) caused marked inhibition of contractile responses to a maximum concentration of NA (10−5 m in aortae; 3 × 10−5 m in mesenteric arteries). In the presence of staurosporine, no difference was observed in the magnitude of contractile responses of arteries from control and diabetic rats to NA.

Maximum contractile responses of mesenteric arteries from diabetic rats to PDB were significantly increased (by 45.0 ± 4.9%) compared to responses of arteries from control animals. In contrast, no significant difference was found in the magnitude of contractile responses of aortae from control and diabetic rats to PDB.

Staurosporine (5 × 10−8 m) caused marked attenuation of contractile responses of arteries from control and diabetic rats to a maximum concentration of PDB (3 × 10−6 m). In the presence of staurosporine, the difference in magnitude of contractile responses of mesenteric arteries from control and diabetic rats to PDB was abolished.

Contractile responses of aortae and mesenteric arteries from control and diabetic rats to PDB were reduced in the absence of extracellular Ca2+, and in the presence of the Ca2+ channel blockers, nifedipine (3 × 10−6 m) or verapamil (3 × 10−6 m). Under these conditions, no difference was found in the magnitude of contractile responses of mesenteric arteries from control and diabetic rats to PDB.

These data suggest that enhanced contractile responses of aortae and mesenteric arteries from streptozotocin‐induced diabetic rats to NA may result, at least in part, from increased activation of PKC. In addition, increased activation of PKC‐mediated processes, which are dependent on the presence of extracellular Ca2+, may further contribute to the enhanced contractile responses of diabetic mesenteric arteries to NA.
Stereoselective inhibition of muscarinic receptor subtypes by the enantiomers of hexahydro‐difenidol and acetylenic analogues
Authors: Feifel R. , Wagner‐Röder M. , Strohmann C. , Tacke R. , Waelbroeck M. , Christophe J. , Mutschler E. , Lambrecht G.
Published: July 2012

The affinities of the (R)‐ and (S)‐enantiomers of hexahydro‐difenidol (1) and its acetylenic analogues hexbutinol (2), hexbutinol methiodide (3) and p‐fluoro‐hexbutinol (4) (stereochemical purity > 99.8%) for muscarinic receptors in rabbit vas deferens (M1), guinea‐pig atria (M2) and guinea‐pig ileum (M3) were measured by dose‐ratio experiments.

The (R)‐enantiomers consistently showed higher affinities than the (S)‐isomers. The stereoselectivity ratios [(R)/(S)] were greatest with the enantiomers of 1 (vas deferens: 550; ileum: 191; atria: 17) and least with those of the p‐Fluoro‐analogue 4 (vas deferens: 34; ileum: 8.5; atria: 1.7).

The enantiomeric potency ratios for compounds 1–4 were highest in rabbit vas deferens, intermediate in guinea‐pig ileum and much less in guinea‐pig atria. Thus, these ratios may serve as a predictor of muscarinic receptor subtype identity.

(S)‐p‐Fluoro‐hexbutinol [(S)‐4] showed a novel receptor selectivity profile with preference for M3 receptors: M3 > M2 ≥ M1.

These results do not conform to Pfeiffer's rule that activity differences between enantiomers are greater with more potent compounds.
Mediation of bradykinin‐induced contraction in canine veins via thromboxane/prostaglandin endoperoxide receptor activation
Authors: Aksoy Mark O. , Harakal Concetta , Smith J. Bryan , Stewart Gwendolyn J. , Zerweck Charles R.
Published: July 2012

Canine jugular and femoral veins were studied to determine the possible importance of thromboxane (TXA2) and prostaglandin endoperoxides (prostaglandin H2, PGH2) in mediating bradykinin(BK)‐induced contraction.

Isolated vein rings incubated in modified Krebs solution contracted to TXA2/PGH2 analogs SQ26655 and U44069 with potency of contraction exceeding that for BK. The potency ranking for both veins was SQ26655 > U44069 > BK > PGF2α > TXB2 > PGD2.

The cyclo‐oxygenase inhibitors indomethacin (3 × 10−7 m) and flufenamic acid (10−5 m) reduced BK contractions without affecting those induced by noradrenaline (NA).

TXA2/PGH2 receptor antagonists SQ29548 (10−8 m) and BM13177 (10−6 m) strongly inhibited BK‐induced tension. The action of antagonists was reversible with negligible influence on NA‐elicited contraction. Selective removal of endothelium had no effect on BK‐induced contraction or the action of the antagonists.

The thromboxane synthase inhibitors dazoxiben (10−4 m) and CGS 12970 (10−5 m) had no significant inhibitory effect on BK‐induced tension.

These results suggest that in canine jugular and femoral vein, the action of BK is largely dependent upon stimulation of the cyclo‐oxygenase pathway to produce PGH2 and possibly TXA2, which can activate a smooth muscle TXA2/PGH2 receptor to elicit vasoconstriction.
Suppression by neuropeptide Y of capsaicin‐sensitive sensory nerve‐mediated contraction in guinea‐pig airways
Authors: Grundemar Lars , Grundström Nils , Johansson Irene G.M. , Andersson Rolf G.G. , Håkanson Rolf
Published: July 2012

In the present study we have examined whether neuropeptide Y (NPY) interferes with non‐adrenergic, non‐cholinergic nerve‐mediated contractions and relaxations in the guinea‐pig airways. In these experiments we have used ring preparations of bronchi and trachea, incubated in the presence of atropine, propranolol and indomethacin (each 1 μm).

The contractile response to electrical stimulation of non‐adrenergic, non‐cholinergic nerve fibres was suppressed by NPY and NPY 13–36 in a concentration‐dependent manner, these agents having similar inhibitory potencies. NPY caused a more complete inhibition than the C‐terminal fragment.

NPY affected neither the basal tension nor the substance P‐evoked contraction in the bronchi and trachea and did not interfere with nerve‐mediated, non‐adrenergic relaxation in the trachea.

On the basis of these results, it is suggested that NPY may act on the terminals of sensory neurones in the airways to prevent antidromic, excitatory neurotransmission by inhibiting transmitter release.
A bradykinin (BK)1 receptor antagonist blocks capsaicin‐induced ear inflammation in mice
Authors: Mantione Charles R. , Rodriguez Richard
Published: July 2012

The effect of various peptide antagonists on capsaicin‐induced (250 μg per ear) ear inflammation has been examined.

Co‐administration of the substance P (SP) antagonist [d‐Pro2,d‐Trp7,9]SP at 100 and 300 μg per ear with capsaicin markedly attenuated oedema, whereas a vasopressin antagonist was ineffective.

Using the same scheme, the mixed BK2 and BK1 bradykinin (BK) antagonist NPC 567 (d‐Arg[Hyp3, d‐Phe7]BK) did not inhibit oedema at 100 μg per ear, but did inhibit at a higher dose (300 μg). The BK1 antagonist [Leu8,desArg9]BK produced significant inhibition at both doses.

When BK was used to induce ear inflammation (30 μg per ear), the SP antagonist inhibited ear oedema. Both BK receptor subtype antagonists inhibited inflammation with the BK1 being more potent than the BK2 antagonist.

These results suggest that BK1 along with BK2 receptors are located on capsaicin‐sensitive fibres, where they may modulate the degree of neurogenic inflammation.
Vascular effects of helodermin, helospectin I and helospectin II: a comparison with vasoactive intestinal peptide (VIP)
Authors: Grundemar Lars , Högestätt Edward D.
Published: July 2012

Helodermin, helospectin I and helospectin II, peptides recently isolated from the salivary gland venom of Heloderma suspectum, were compared to vasoactive intestinal peptide (VIP) with respect to effects on systemic blood pressure and on isolated femoral arteries in the rat.

They all reduced blood pressure in a dose‐dependent manner; helodermin was less effective than VIP. However, at doses higher than 1 nmol kg−1 all four peptides reduced blood pressure to about the same extent.

The half‐life of the hypotensive effect of VIP was longer than that of helodermin and the helospectins.

VIP and helodermin were equally potent in relaxing femoral arteries precontracted with phenylephrine or prostaglandin F2α.

Helospectin I and II relaxed phenylephrine‐contracted vessels to the same extent as VIP but with a lower potency.

Addition of VIP 1 μm to preparations exposed to helodermin 1 μm or to either of the helospectins did not produce a further relaxation.

The findings indicate that VIP, helodermin and helospectin I and II have a similar profile of action and therefore may act on a common receptor.
Effect of quinine on the release of catecholamines from bovine cultured chromaffin cells
Authors: Tang R. , Novas M.L. , Glavinović M.I. , Trifaró J.‐M.
Published: July 2012

The effects of quinine on catecholamine release from cultured bovine chromaffin cells were studied.

Quinine (25–400 μm) produced a dose‐related inhibition of catecholamine release in response to depolarizing concentrations (12.5–50 mm) of K+.

The inhibition of the secretory response to high K+ produced by quinine decreased with the increase in the extracellular concentration of Ca2+.

Stimulation of cultured chromaffin cells with 50 mm K+ produced a significant increase in Ca2+ influx. In the presence of 100 μm quinine a 54% inhibition of the K+‐induced Ca2+ influx was observed.

Quinine treatment of chromaffin cell cultures produced a small but significant decrease in membrane resting potential and a less pronounced depolarization in response to 50 mm K+.

The results suggest that the inhibition of the K+‐evoked release of catecholamines produced by quinine is at least partly due to a decrease in Ca2+ influx. Ca2+ influx is lower because quinine reduces the sensitivity of the membrane potential to changes in extracellular K+ but direct effects of quinine on Ca2+ channels cannot be excluded.
Assessment of imiloxan as a selective α2B‐adrenoceptor antagonist
Authors: Michel Anton D. , Loury Dana N. , Whiting Roger L.
Published: July 2012

The α2‐adrenoceptor binding sites of rabbit spleen and rat kidney, labelled with [3H]‐rauwolscine, were characterized using a range of subtype selective ligands.

In rabbit spleen, the α‐2‐adrenoceptor binding sites displayed high affinity for oxymetazoline and WB 4101 and low affinity for prazosin and chlorpromazine suggesting the presence of an α2A subtype.

There was evidence for heterogeneity of the α2‐adrenoceptor binding sites present in rabbit spleen. The results obtained with oxymetazoline and WB 4101 indicated that at least 75% of the [3H]‐rauwolscine binding sites in this preparation displayed a pharmacology consistent with the presence of an α2A subtype.

In rat kidney, the α2‐adrenoceptor binding sites displayed high affinity for prazosin and chlorpromazine and low affinity for oxymetazoline and WB 4101 suggesting the presence of an α2B subtype.

The inclusion of guanylylimidodiphosphate (Gpp(NH)p, 0.1 mm) did not modify the pharmacology of the α2‐adrenoceptor binding sites present in the two preparations. Furthermore, when the two membrane preparations were combined, the resultant pharmacology was still consistent with the presence of two receptors that retained the characteristics of the α2A and α2B subtypes.

Imiloxan was identified as a selective α2B ligand while benoxathian displayed a high degree of selectivity for the α2A‐adrenoceptor binding site. The selectivity of imiloxan for the α2B‐adrenoceptor binding site, coupled with its specificity for α2‐adrenoceptors, should make it a valuable tool in the classification of α2‐adrenoceptor subtypes.
l‐NG‐monomethyl arginine and l‐NG‐nitro arginine inhibit non‐adrenergic, non‐cholinergic relaxation of the mouse anococcygeus muscle
Authors: Gibson A. , Mirzazadeh Shokoufeh , Hobbs A.J. , Moore P.K.
Published: July 2012

The effects of l‐NG‐monomethyl arginine (l‐NMMA) and l‐NG‐nitro arginine (l‐NOARG) on non‐adrenergic, non‐cholinergic (NANC) relaxations of the mouse anococcygeus were investigated.

l‐NMMA (10–200 μm) produced a concentration‐related inhibition of the NANC response; the inhibitory effect of 50 μm l‐NMMA was completely reversed by l‐arginine but not d‐arginine (both 100 μm).

l‐NOARG (1–50 μm) also produced a concentration‐related inhibition of the NANC response and was some 30–50 times more potent than l‐NMMA; again, the effects of 10 μm l‐NOARG were reversed by 100 μm l‐, but not d‐, arginine. By itself 100 μm l‐arginine did not relax the tissue, but did cause a slight potentiation of the NANC response.

Sodium nitroprusside (0.01–10 μm), hydroxylamine (0.1–100 μm), sodium azide (1–100 μm) and nitric oxide (3–120 μm) all relaxed carbachol‐induced tone; relaxations to submaximal concentrations of these nitrovasodilators were unaffected by either 50 μm l‐NMMA or 10 μm l‐NOARG.

l‐NOARG 10 μm did not inhibit, but rather potentiated, contractions of the mouse anococcygeus due to stimulation of its sympathetic nerves.

The inhibitory effects of 10 μm l‐NOARG on NANC relaxations were reversed by l‐arginine (by 131%), l‐citrulline (by 75%), l‐arginine methyl ester (by 46%) and l‐homoarginine (by 22%), but were unaffected by a variety of other amino acids and their derivatives (all at 100 μm).

The results provide strong evidence that NANC relaxations of the mouse anococcygeus are mediated by an endogenous nitrate material, probably derived from l‐arginine, and confirm that l‐NOARG provides a very useful and potent drug for the investigation of endogenous nitrate function.
Effects on renal sympathetic axons in dog of acute 6‐hydroxydopamine treatment in combination with selective neuronal uptake inhibitors
Authors: Sunn N. , Harris P.J. , Bell C.
Published: July 2012

In anaesthetized dogs, we have investigated the effect on renal responses to sympathetic nerve stimulation of acute treatment with the catecholaminergic neurotoxin 6‐hydroxydopamine (2 mg kg−1 i.v.), administered alone or after blockade of neuronal catecholamine uptake pathways for noradrenaline (NA) or dopamine with desmethylimipramine or benztropine, respectively.

Under control conditions, renal nerve stimulation caused renal vasoconstriction, reduced glomerular filtration and sodium and water excretion and caused net efflux of NA and dopamine into the renal venous plasma. Two h after administration of 6‐hydroxydopamine alone, there was abolition of both functional responses and catecholamine efflux during nerve stimulation.

In animals pretreated with desmethylimipramine (1 mg kg−1), 6‐hydroxydopamine had no significant effect on functional responses to renal nerve stimulation and nerve‐evoked efflux of NA was only moderately reduced. Efflux of dopamine was still markedly reduced by 6‐hydroxydopamine, but more variably than occurred without desmethylimipramine treatment.

In animals pretreated with benztropine (0.2 mg kg−1), nerve‐evoked efflux of dopamine, but not that of NA, was protected against reduction by 6‐hydroxydopamine. A higher dose of benztropine (1 mg kg−1) protected efflux of both NA and dopamine against 6‐hydroxydopamine.

We conclude that acute treatment with a low dose of 6‐hydroxydopamine is an effective method of inactivating peripheral sympathetic nerves. The differential effects of desmethylimipramine and benztropine in preserving nerve‐evoked efflux of NA and dopamine after 6‐hydroxydopamine support the view that these catecholamines originate predominantly from different intrarenal axons. However, neither uptake blocker appears to be completely specific in its actions.
Influence of two β‐adrenoceptor antagonists, propranolol and pindolol, on cold adaptation in the rat
Authors: Kortelainen Marja‐Leena , Huttunen Pirkko , Lapinlampi Tuomo
Published: July 2012

Adult male rats were treated with propranolol (2.0 mg kg−1 day−1 i.p.), pindolol (0.2 mg kg−1 May−1 i.p.) or 0.9% NaCl day−1 i.p. and exposed to +4°C for 42 days, or treated with 0.9% NaCl day−1 i.p. and kept at +23°C for 42 days. They were weighed once a week, when a 24 h urine sample was also collected and colon temperature measured.

Urinary noradrenaline (NA), adrenaline (Ad) and dopamine were analysed by high‐performance liquid chromatography with an electrochemical detector. After the acclimatization period the interscapular brown adipose tissue was excised and weighed and the activity of the oxidative enzymes succinate dehydrogenase and cytochrome oxidase measured.

The pindolol‐treated and propranolol‐treated rats gained weight during the cold‐acclimatization period. The amount of interscapular brown adipose tissue increased in the cold, but the increase was lowest in the pindolol‐treated group. No changes were seen in the other brown adipose tissue parameters in cold‐exposed animals. The excretion of catecholamines followed the same pattern in all three cold‐exposed groups, with an initial rise in noradrenaline and adrenaline excretion and a slight rise in dopamine excretion.

The results suggest possible connections between β‐adrenoceptor antagonists, weight gain and cold acclimatization. Pindolol had a slight inhibitory effect on cold‐induced brown adipose tissue hypertrophy in rats.
RS 30026: a potent and effective calcium channel agonist
Authors: Patmore Leslie , Duncan Greig P. , Clarke Brendan , Anderson Amanda J. , Greenhouse Robert , Pfister Jürg R.
Published: July 2012

A series of dihydropyridine derivatives has been evaluated for calcium channel agonist activity using reversal of nisoldipine‐induced inhibition of beating of aggregates of embryonic chick myocytes. This test appears to be specific for calcium channel agonists since isoprenaline and cardiac glycosides are inactive.

RS 30026 was the most potent of the series, was significantly more potent than CGP 28392 and of similar potency to Bay K 8644 (pEC50 = 7.45, 6.16 and 7.20, respectively). RS 30026 increased edge movement of individual aggregates, in the absence of nisoldipine, by 50% at 2nm.

Compounds were also evaluated for their effects on guinea‐pig papillary muscle and porcine coronary artery rings. RS 30026 displayed positive inotropism at concentrations between 10−9 and 10−6 m (pEC200 = 8.21), but was a much more powerful inotrope than Bay K 8644, increasing contractility to 1300% of control at 10−6 m (compared to 350% of control for Bay K 8644). RS 30026 caused vasoconstriction at concentrations between 10−10 and 10−7 m.

Calcium channel currents in single embryonic chick myocytes were recorded by whole‐cell voltage clamp techniques. RS 30026 (100 nm‐500 nm) produced large increases in peak current amplitude and shifted the voltage for threshold and maximal currents to more negative values. RS 30026 (500 nm) also produced large increases in the inward tail currents evoked upon repolarization. The effects of Bay K 8644 (50 and 500 nm) were much less marked.

Analysis of the activation characteristics of currents showed parallel shifts in the activation curve to more negative potentials in the presence of 50 nm Bay K 8644, with a much smaller shift in the presence of 500 nm Bay K 8644. RS 30026 (100 and 500 nm) caused concentration‐dependent shifts in the activation of the calcium channel currents with an increase of the slope of the curve.

RS 30026 appears to be the most potent and effective calcium channel agonist described to date.
Ciguatoxin enhances quantal transmitter release from frog motor nerve terminals
Authors: Molgó Jordi , Cornelia Joan X. , Legrand Anne Marie
Published: July 2012

Ciguatoxin (CTX), a marine toxin produced by the benthic dinoflagellate Gambierdiscus toxicus, is responsible for a complex endemic disease in man known as ciguatera fish poisoning. In the present study we have investigated the effects of purified CTX extracted for Gymnothorax javanicus moray‐eel liver on frog isolated neuromuscular preparations with conventional electrophysiological techniques.

CTX (1–2.5 nm) applied to cutaneous pectoris nerve‐muscle preparations induced, after a short delay, spontaneous fibrillations of the muscle fibres that could be suppressed with 1 μm tetrodotoxin (TTX) or by formamide to uncouple excitation‐contraction.

In preparations treated with formamide, CTX (1–2.5 nm) caused either spontaneous or repetitive muscle action potentials (up to frequencies of 60–100 Hz) in response to a single nerve stimulus. Recordings performed at extrajunctional regions of the muscle membrane revealed that during the repetitive firing a prolongation of the repolarizing phase of the action potential occurred. At junctional sites the repetitive action potentials were triggered by repetitive endplate potentials (e.p.ps).

CTX (2.5 nm) caused a TTX‐sensitive depolarization of the muscle membrane.

In junctions equilibrated in solutions containing high Mg2+ + low Ca2+, addition of CTX (1.5 nm) first induced an average increase of 239 ± 36% in the mean quantal content of e.p.ps. Subsequently CTX reduced and finally blocked nerve‐evoked transmitter release irreversibly.

CTX (1.5–2.5 nm) increased the frequency of miniature endplate potentials (m.e.p.ps) in junctions bathed either in normal Ringer, low Ca2+‐high Mg2+ medium or in a nominally Ca2+‐free solution containing EGTA. Extensive washing with toxin‐free solutions did not reverse the effect. Furthermore, Cd2+ (0.1 mm), a potent calcium channel blocker, neither antagonized nor abolished the increase in transmitter release caused by CTX.

TTX (1 μm) completely prevented the effect of CTX (2.5 nm) on m.e.p.p. frequency. This effect was independent of the presence of extracellular Ca2+. TTX, when added after CTX (2.5 nm) exposure, antagonized the increase in m.e.p.p. frequency. The antagonism was complete in Ca2+‐free medium. These results strongly suggest that increased permeability of the nerve terminal to Na+ is responsible for the increase in m.e.p.p. frequency caused by CTX. It is likely that CTX may trigger calcium release from internal stores due to an increase of intraterminal Na+ concentration.

It is concluded that CTX exerts, in the nanomolar concentration range, a selective action on sodium channels of the neuromuscular junction causing both pre‐ and postsynaptic effects.
Different effects of prostaglandins on adrenergic neurotransmission in atrial and ventricular preparations
Authors: Mantelli Laura , Amerini Sandra , Ledda Fabrizio
Published: July 2012

The effects of prostaglandin E2 (PGE2) and iloprost on the cardiac response to adrenergic nerve stimulation in guinea‐pig atrial and ventricular preparations have been studied.

In guinea‐pig isolated atria both PGE2 (0.1–10 nm) and iloprost (0.1–3 μm) concentration‐dependently reduced the cardiac response to adrenergic nerve stimulation.

The inhibition of cyclo‐oxygenase by indomethacin and acetylsalicylic acid potentiated the response to nerve stimulation in the atrial preparations.

Arachidonic acid (1–10 μm) reduced the response to nerve stimulation in atria. This effect was prevented by indomethacin and acetylsalicylic acid.

In guinea‐pig ventricles PGE2 and iloprost were found to be effective at higher concentrations than in atrial preparations: arachidonic acid, indomethacin or acetylsalicylic acid did not modify the cardiac response to adrenergic nerve stimulation.

These results suggest a different modulator role for endogenous prostaglandins in atrial and ventricular tissue.
(+)‐Hydrastine, a potent competitive antagonist at mammalian GABAA receptors
Authors: Huang Jun‐Hua , Johnston Graham A.R.
Published: July 2012

(+)‐Hydrastine is a phthalide isoquinoline alkaloid, isolated from Corydalis stricta. It has the same 1S,9R configuration as the competitive GABAA receptor antagonist bicuculline and is the enantiomer of the commercially available (−)‐hydrastine.

(+)‐Hydrastine (CD50 0.16 mg kg−1, i.v.) was twice as potent as bicuculline (CD50 0.32 mg kg−1, i.v.) as a convulsant in mice. This action was stereoselective in that (+)‐hydrastine was 180 times as potent as (−)‐hydrastine.

(+)‐Hydrastine was a selective antagonist at bicuculline‐sensitive GABAA receptors in the guinea‐pig isolated ileum. It did not influence phaclofen‐sensitive GABAB receptors or acetylcholine receptors in this tissue. (+)‐Hydrastine was a competitive antagonist of GABAA responses (pA2 6.5) more potent than bicuculline (pA2 6.1).

When tested against the binding of [3H]‐muscimol to high affinity GABAA binding sites in rat brain membranes, (+)‐hydrastine (IC50 2.37 μm) was 8 times more potent than bicuculline (IC50 19.7 μm).

As an antagonist of the activation of low affinity GABAA receptors as measured by the stimulation by GABA of [3H]‐diazepam binding to rat brain membranes, (+)‐hydrastine (IC50 0.4 μm) was more potent than bicuculline (IC50 2.3 μm).

(+)‐Hydrastine, 10 nm to 1 mm, did not inhibit the binding of [3H]‐(−)‐baclofen to GABAB binding sites in rat brain membranes.
Actions of cocaine on rat nucleus accumbens neurones in vitro
Authors: Uchimura N. , North R.A.
Published: July 2012

Intracellular recordings were made from 103 neurones of the rat nucleus accumbens in vitro.

Dopamine (3–100 μm; in sulpiride, 1 μm) hyperpolarized neurones (79%) by acting at D1 receptors: dopamine (3–100 μm; in SCH23390, 1 μm) depolarized neurones (55%) by acting at D2 receptors. 5‐Hydroxytryptamine (1–100 μm) depolarized 86% neurones.

Both actions of dopamine as well as the effect of 5‐hydroxytryptamine were potentiated by cocaine (0.3–30 μm), which had no effect of its own on membrane potential.

Dose‐ratio was computed as [(concentration of agonist causing a 4 mV potential change in cocaine)/(concentration of agonist causing a 4 mV potential change without cocaine)]. Cocaine (1–30 μm) caused the same dose‐ratio whether dopamine depolarizations (D2) or hyperpolarizations (D1) were measured; the dose‐ratio ranged from 2 (1 μm) to 50 (30 μm).

Responses to 5‐hydroxytryptamine were increased more than responses to dopamine; cocaine 1 μm gave a dose‐ratio of 13.4 and at 30 μm gave a dose‐ratio of 118.

It is concluded that cocaine acts to inhibit the uptake of dopamine and 5‐hydroxytryptamine in slices of rat nucleus accumbens; lower concentrations of cocaine (0.3 to 1 μm) are particularly effective in potentiating the action of 5‐hydroxytryptamine.
Effect of cyclo‐oxygenase blockade on the renal actions of vasopressin and SK&F 105494 in the rhesus monkey
Authors: Brooks David P. , Caldwell Nancy C. , Koster Paul F. , Albrightson‐Winslow Christine R. , Kinter Lewis B.
Published: July 2012

Vasopressin administration to pentobarbitone‐anaesthetized, hydrated female rhesus monkeys resulted in dose‐dependent increases in urine osmolality and decreases in urine flow. Treatment with indomethacin at a dose (5 mg kg−1, i.v.) that reduced urinary prostaglandin E2 (PGE2) excretion by at least 70% did not alter these responses.

The vasopressin antagonist, SK&F 105494 (Pas1,6d‐Tyr(Et)2Val4Arg7d‐Arg8desGly9 arginine vasopressin; 10 μg kg−1), caused significant rightward shifts (P < 0.05) of both the vasopressin‐urine osmolality and the vasopressin‐urine flow dose‐response curves. Treatment with indomethacin did not alter these responses.

SK&F 105494 alone or after indomethacin treatment had minimal effects on urine osmolality and urine flow.

The data indicate that indomethacin does not alter the antidiuretic activity of vasopressin in the rhesus monkey and that SK&F 105494 is a potent antagonist of exogenous vasopressin with minimal agonist activity.
Rat hippocampal muscarinic autoreceptors are similar to the M2 (cardiac) subtype: comparison with hippocampal M1, atrial M2 and ileal M3 receptors
Authors: Richards M.H.
Published: July 2012

Affinity constants for 15 non‐selective or putatively selective muscarinic antagonists were determined at muscarinic autoreceptors and postsynaptic receptors (linked to phosphatidylinositol (PI) hydrolysis) in rat hippocampal slices, at muscarinic receptors mediating contractility in guinea‐pig atria or ileal smooth muscle and at binding sites in rat cerebral cortical membranes labelled with [3H]‐1‐quinuclidinyl benzilate or [3H]‐pirenzepine.

Comparison of the affinities of these antagonists at central M1 receptors (inositol‐monophosphate formation in rat hippocampal slices) with their affinities at peripheral M1 receptors (inhibition by McN‐A‐343 of electrically stimulated twitches in rabbit vas deferens) provides support for the suggestion that these receptors may differ pharmacologically.

Comparison of affinity constants obtained by displacement of specifically bound [3H]‐pirenzepine from rat cerebral cortical membranes with those obtained in functional tests showed poor correlations between affinities for binding sites and for functional atrial receptors or for hippocampal autoreceptors. A significant correlation was found between affinities for [3H]‐pirenzepine binding and those determined at muscarinic receptors linked to PI turnover in rat hippocampus. A significant correlation was also obtained between the affinities for specific [3H]‐pirenzepine binding sites in cortical membranes and the affinities at ileal receptors.

Comparison of the affinity values for muscarinic autoreceptors in rat hippocampus with affinity values obtained from in vitro models of muscarinic receptor subtypes showed no significant correlations between these autoreceptors and either M1 or M3 receptors. A significant correlation was found between antagonist affinities for hippocampal autoreceptors and muscarinic receptors in the heart. Therefore, muscarinic autoreceptors in rat hippocampus are pharmacologically similar to the M2 (cardiac) muscarinic receptor subtype.
The role of the epithelium in modulating the responses of guinea‐pig trachea induced by bradykinin in vitro
Authors: Bramley Andrew M. , Samhoun Marwa N. , Piper Priscilla J.
Published: July 2012

The effect of removing the epithelium on the responses of the guinea‐pig isolated trachea (GPT) to bradykinin (BK) and prostaglandin E2 (PGE2) was investigated.

BK (3 pmol–10 nmol) induced dose‐related relaxations of the intact (with epithelium), and contracted the rubbed (without epithelium) preparation of GPT. Similar responses were also obtained with PGE2 (0.3–3.0 nmol).

Indomethacin (1.4 μm) modified the BK‐induced response of intact GPT, from a relaxation to a contraction, but inhibited the BK‐induced contraction of the rubbed GPT.

There was a significant increase in PGE2 release from the intact GPT following stimulation with BK.

Removal of the epithelium from the GPT significantly reduced both basal and BK‐induced generation of PGE2.

The induction of tone in the rubbed GPT by addition of acetylcholine (ACh) caused BK and PGE2 (0.3 nmol–3 nmol) to produce relaxations of the tissue.

Salbutamol (10−8 m‐10−6 m) reduced the relaxations induced by BK on intact GPT, in a concentration‐dependent manner.

These results suggest that both tone and an epithelial‐dependent cyclo‐oxygenase mechanism are important in modulating BK‐induced responses of GPT.
Pharmacological analysis of [3H]‐senktide binding to NK3 tachykinin receptors in guinea‐pig ileum longitudinal muscle‐myenteric plexus and cerebral cortex membranes
Authors: Guard Steven , Watson Stephen P. , Maggio John E. , Too H. Phon , Watling Keith J.
Published: July 2012

The binding properties and pharmacological specificity of the selective NK3 tachykinin receptor agonist [3H]‐senktide ([3H]‐succinyl[Asp6,MePhe8] substance P (6–11)) have been examined in homogenates of guinea‐pig ileum longitudinal muscle‐myenteric plexus (LM/MP) and cerebral cortex.

Scatchard analysis of saturation binding studies in guinea‐pig ileum LM/MP and cerebral cortex membranes indicated that [3H]‐senktide bound to a single site with apparent high affinity, KD = 2.21 ± 0.65 nm; Bmax = 13.49 ± 0.04 fmol mg−1 protein in ileum and KD = 8.52 ± 0.45 nm; Bmax = 76.3 ± 1.6 fmol mg−1 protein in cortex (values are means ± ranges; n = 2).

The pharmacological profile for tachykinins and analogues in displacing [3H]‐senktide from ileum membranes was: [MePhe7] neurokinin B > neurokinin B (NKB) ≃ senktide > eledoisin > substance P (SP) > neurokinin A(NKA) > physalaemin > [Sar9,Met(O2)11]SP > [Nle10]NKA(4–10) = [Glp6,L‐Pro9]‐SP(6–11) > substance P methyl ester, consistent with [3H]‐senktide binding to an NK3 subtype of tachykinin receptor. A similar rank order of affinity was obtained for these peptides in displacing [3H]‐senktide from cortex membranes

Several tachykinin receptor agonists were tested for their ability to displace [3H]‐senktide from ileal and cortical NK3 binding sites and were found to be either weak displacers (pIC50 < 5.00) or inactive.

The binding of [3H]‐senktide to cortex membranes was inhibited by GTP (pIC50 = 6.49)and GTP‐γ‐S (pIC50 = 6.67) with ATP being at least three orders of magnitude less potent (pIC50 = 3.55).

These results indicate that both central and peripheral NK3 receptors share a similar pharmacological specificity and that they may be labelled selectively with the NK3 receptor agonist [3H]‐senktide.