bluuebunny/crossref_metadata_2025 huggingface dataset:
Arterial chemoreceptor involvement in salicylate‐induced hyperventilation in rats
Authors: McQueen D.S. , Ritchie Isobel M. , Birrell G.J.
Published: July 2012

The extent to which peripheral arterial chemoreceptors are involved in the respiratory stimulant action of salicylates has been investigated in rats.

Injection of sodium salicylate (200 mg kg−1, single dose i.v.) caused a rapid transient hyperventilation that was not obtained when the carotid chemoreceptors were denervated by section of the carotid sinus nerves. A delayed (10 min) increase in respiration occurred regardless of whether or not the carotid nerves were sectioned.

Intravenous infusions of sodium salicylate (0.5 or 4 mg kg−1 min−1) caused hyperventilation in barbiturate‐anaesthetized rats. The threshold dose for respiratory stimulation was significantly lower when the carotid sinus nerves were intact than when they were bilaterally sectioned, and the same pattern was observed following intravenous injections of sodium salicylate (cumulative doses) in anaesthetized and conscious rats.

Bilateral sectioning of the vagosympathetic nerve trunks did not significantly affect hyperventilation evoked by salicylate, suggesting that this response does not involve actions of salicylate on sensory receptors innervated by these nerves.

Administration of salicylate close‐arterial to a carotid body, by local perfusion or crossperfusion of a carotid sinus, led to an increase in respiration when the ipsilateral carotid nerve was intact, but not when it was sectioned.

Neuropharmacological studies on anaesthetized rats showed that chemosensory discharge, recorded from a sectioned carotid nerve, increased in response to salicylate injections with a similar dose‐response pattern to the hyperventilation. Salicylate had no effect on baroreceptor discharge.

We conclude from our experiments that arterial chemoreceptors do contribute to salicylate‐induced hyperventilation, and are almost exclusively responsible for the initial phase of the response in rats. Later increases in breathing are independent of reflexes from arterial chemoreceptors and result from actions at other sites, including the CNS. The therapeutic implications of our results are discussed.
Cyclosporin therapy in vivo attenuates the response to vasodilators in the isolated perfused kidney of the rabbit
Authors: Cairns Hugh S. , Fairbanks Lynette D. , Westwick John , Neild Guy H.
Published: July 2012

The endothelium releases a number of vasoactive compounds, including the vasodilator prostaglandins, prostacyclin (PGI2) and prostaglandin E2 (PGE2) and endothelium‐derived relaxing factor (EDRF), which play an important role in the regulation of vascular tone in the microcirculation. Nephrotoxicity is the major complication of cyclosporin (CS) therapy and is related to an increase in intrarenal vascular tone. Endothelial cell generation of PGI2 is inhibited by CS although this cannot fully explain the changes in vascular tone observed. We have investigated the possibility that EDRF‐dependent vasodilatation is also affected by CS therapy in vivo.

CS nephrotoxicity was induced in rabbits with CS (15 mg kg−1 per day s.c. for 20 days (n = 6)); 6 rabbits were given CS vehicle (Veh) and 9 animals were studied without any treatment. Creatinine clearance fell significantly during treatment in the CS‐treated rabbits (11.78 ± 1.5 ml min−1, mean ± s.e.mean, to 7.79 ± 1.2 after 20 days treatment) but did not change in the vehicle‐treated animals.

The responses to the endothelium‐dependent (acetylcholine (ACh)) and endothelium‐independent (nitroprusside (NP) and PGI2) vasodilators were assessed in indomethacin‐treated isolated perfused kidneys (IPKs) from untreated, CS‐ and Veh‐treated animals. Vascular tone was induced with a constant infusion of noradrenaline 150 nM and the perfusion rate adjusted to produce a perfusion pressure of 90 mmHg. Perfusate flow rate (22.3 ± 4.6 vs 20.4 ± 3.1 ml min−1) and glomerular filtration rate (2.04 ± 0.37 vs 1.88 ± 0.16 nl min−1) did not differ between IPKs from CS‐ and Veh‐treated animals.

The vasodilator response to ACh was reduced in the kidneys from CS‐treated animals compared with those from untreated and Veh‐treated animals (mean reduction 35.3 ± 2.3% compared with Veh) as were the responses to both NP (42.8 ± 3.6%) and PGI2 (27.7 ± 7.4%).

This suggests that CS nephrotoxicity is not mediated via an effect on endothelium‐dependent responses and that it is more likely that CS has a direct effect on vascular smooth muscle.
Modulation of the vasodepressor actions of acetylcholine, bradykinin, substance P and endothelin in the rat by a specific inhibitor of nitric oxide formation
Authors: Whittle B.J.R. , Lopez‐Belmonte J. , Rees D.D.
Published: July 2012

The effects of the specific inhibitor of nitric oxide (NO) formation, NG‐monomethyl‐L‐arginine (L‐NMMA), on resting systemic arterial blood pressure (BP) and on the actions of both endothelium‐dependent and endothelium‐independent vasodilators were investigated in the anaesthetized, normotensive rat.

Intravenous administration of L‐NMMA (12.5–50 mg kg−1; 47–188 μmol kg−1) but not its enantiomer, D‐NMMA, induced a dose‐related increase in BP, which was reversed by the intravenous administration of L‐arginine (150–600 μmol kg−1), but not D‐arginine.

The vasodepressor responses to intravenous administration of the endothelium‐dependent vasodilators, acetylcholine, bradykinin and substance P were significantly inhibited by L‐NMMA (94 and 188 μmol kg−1 i.v.), but not by D‐NMMA.

The inhibition by L‐NMMA of these vasodepressor responses was reversed by administration of L‐arginine, but not D‐arginine.

Endothelin (ET‐1) induced dose‐related vasodepressor responses following bolus intravenous administration, which were significantly inhibited by L‐NMMA but not by D‐NMMA. This inhibition was reversed by administration of L‐arginine.

The vasodepressor effects of the endothelium‐independent vasodilators, glyceryl trinitrate or prostacyclin, were not significantly inhibited by L‐NMMA.

These findings with L‐NMMA suggest that resting blood pressure in the rat is modulated by endogenous NO biosynthesis and that endothelium‐dependent vasodilators act through the formation of endogenous NO to exert their actions in vivo.
Effect of cromakalim on bronchoconstriction evoked by cholinergic nerve stimulation in guinea‐pig isolated trachea
Authors: McCaig Dorothy J. , De Jonckheere B.
Published: July 2012

Cromakalim reduced intraluminal pressure in the guinea‐pig isolated, innervated trachea.

Preganglionic stimulation of the cervical vagus nerve elicited a frequency‐dependent increase in intraluminal pressure. Cromakalim attenuated responses to vagal stimulation in a concentration‐dependent manner at all frequencies tested.

Field stimulation caused a frequency‐dependent increase in intraluminal pressure mediated by muscarinic cholinoceptors. Cromakalim did not affect the amplitude of responses at any frequency of stimulation, even at high concentrations.

Acetylcholine, added to the Krebs solution bathing the adventitial surface of the trachea, evoked a concentration‐dependent increase in intraluminal pressure. The concentration‐effect curve for acetylcholine was unaltered in the presence of cromakalim.

It is concluded that cromakalim modulates cholinergic neuroeffector transmission in the trachea chiefly by a prejunctional mechanism. However, cromakalim probably does not interfere with acetylcholine release from postganglionic cholinergic neurones.
Arachidonic acid‐induced bronchomotor responses are partially mediated by release of sensory neuropeptides from capsaicin‐sensitive structures
Authors: Manzini Stefano , Ballati Lido , Geppetti Pierangelo , Rubini Ilaria , Meini Stefania , Perretti Francesca
Published: July 2012

Administration of arachidonic acid (AA) both in vitro and in vivo elicited prominent contractile responses in guinea‐pig airways, which were markedly reduced after capsaicin desensitization. Furthermore, AA superfusion elicited a significant calcitonin gene‐related peptide‐like immunoreactivity release from isolated bronchi. It is suggested that at least part of the bronchomotor actions of AA rely upon stimulation of capsaicin‐sensitive primary afferents.
The cholinergic pharmacology of tetrahydroaminoacridine in vivo and in vitro
Authors: Hunter A.J. , Murray T.K. , Jones J.A. , Cross A.J. , Green A.R.
Published: July 2012

The effect of tetrahydroaminoacridine (THA) on cholinergically mediated behaviour in the rat and mouse has been investigated. In addition the actions of this compound on cholinesterase activity and on muscarinic and nicotinic receptors has also been examined.

Administration of THA (5–20 mg kg−1, i.p.) produced a dose‐dependent increase in tremor, hypothermia and salivation in both rats and mice. A similar profile of activity was seen following physostigmine (0.1‐0.6 mg kg−1) administration.

THA was approximately fifty fold less potent than physostigmine in inducing behavioural change but its effects persisted for over twice as long as those of physostigmine. For example THA‐induced hypothermia was still present at 4 h in the mouse and 8 h in the rat.

In vitro THA was a potent non‐competitive inhibitor of rat brain cholinesterase (IC50: 57 + 6 nM) and bovine erythrocyte acetylcholinesterase (IC50: 50 + 10 nM) but was a more potent inhibitor of horse serum butyrylcholinesterase (IC50: 7.2 + 1.4 nM).

Radioligand binding studies indicated that THA binds non‐selectively but with moderate potency to both M1 (Ki: 600 nM) and M2 (Ki: 880 nM) muscarinic receptors. THA also interacted with the allosteric site present on cardiac M2 receptors.

It is concluded that THA is a reversible non‐competitive inhibitor of cholinesterase with a long half life (compared with physostigmine). It also may antagonize muscarinic receptors at high doses. The long half life may account for its reported efficacy in the treatment of Alzheimer's disease.
Effects of yohimbine on submaxillary salivation in dogs
Authors: Montastruc Paul , Berlan Michel , Montastruc Jean‐Louis
Published: July 2012

The effects of yohimbine (0.5 mg kg−1 i.v.) on both resting and parasympathetic and sympathetic stimulation‐induced submaxillary salivary responses were investigated in the anaesthetized dog.

Salivary secretion was increased significantly for a period of 45 min following an injection of yohimbine.

Sectioning of the chorda tympani (but not the cervical sympathetic) nerve abolished the yohimbine‐induced increase in resting salivary secretion and potentiated that elicited by electrical stimulation of the chorda tympani nerve.

These results show that yohimbine increases submaxillary secretion by inhibition of presynaptic α2‐adrenoceptors located on the chorda tympani, which inhibit cholinergic transmission.
The mechanism of amphetamine‐induced inhibition of rat substantia nigra compacta neurones investigated with intracellular recording in vitro
Authors: Mercuri Nicola B. , Calabresi Paolo , Bernardi Giorgio
Published: July 2012

The effects of (+)‐amphetamine (1–300 μm) applied by superfusion, on substantia nigra zona compacta neurones were studied in slices of the rat mesencephalon with intracellular recording techniques (current and voltage clamp mode).

Amphetamine inhibited the action potential discharge, hyperpolarized the cells and increased the membrane conductance. Under voltage clamp it produced an outward current.

The amphetamine outward current reversed at potentials negative to −100 mV (2.5 mM extracellular potassium) and was reduced by barium, (1 mM) suggesting an increased potassium conductance.

In slices treated with tetrodotoxin and calcium‐free solution and added cobalt, amphetamine was still effective.

(−)‐Sulpiride, (1 μm) a D2 antagonist, blocked the effects of both amphetamine and dopamine.

In slices treated for more than 3 h with 30 μm α‐methyl‐DL‐tyrosine, an agent known to block the synthesis of dopamine, the action of amphetamine was attenuated, while dopamine was still effective.

Responses to applied dopamine were potentiated by cocaine (10 μm) but unaffected by amphetamine (1–3 μm).

It is suggested that the inhibition of substantia nigra compacta neurones by amphetamine is mainly due to the release of endogenous dopamine.
Native and oxidized low‐density lipoproteins have different inhibitory effects on endothelium‐derived relaxing factor in the rabbit aorta
Authors: Jacobs Michael , Plane Frances , Bruckdorfer K. Richard
Published: July 2012

The effect of native low‐density lipoproteins (LDL) and oxidized LDL (OXLDL) on the relaxations to endothelium‐derived relaxing factor (EDRF) in isolated, intact aortic rings of the rabbit were investigated.

Native LDL induced a concentration‐dependent reversible inhibition of the relaxations elicited by acetylcholine (ACh) or A23187, in rings pre‐contracted by noradrenaline (NA), adrenaline (Ad) and 5‐hydroxytryptamine (5‐HT), but not phenylephrine (PE), which was not influenced by indomethacin.

The inhibition was surmountable in the rings pre‐contracted with NA and Ad and only partially in those pre‐contracted with 5‐HT.

OXLDL induced an inhibition of the relaxations elicited by ACh and A23187 which was independent of the contractile agonist. The extent of inhibition and its reversibility varied with the LDL from individual donors, but was unaffected by indomethacin.

Native and oxidized LDL inhibited relaxations evoked by exogenous nitric oxide (NO) to the same extent. Higher concentrations of NO overcame the inhibition. The inhibition was independent of the contractile agonist and the preparation of LDL from individual donors.

Only OXLDL inhibited reversibly relaxations evoked by glyceryl trinitrate (GTN) and the inhibition was independent of the LDL preparation from individual donors.

This study demonstrates that native and OXLDL influence the response to EDRF in isolated aorta. We suggest that these lipoproteins may contribute to the attenuation of responses to EDRF found in isolated arteries from hypercholesterolaemic and atherosclerotic animals.
Enhanced coronary vasoconstrictor responses to 5‐hydroxytryptamine in the presence of a coronary artery stenosis in anaesthetized dogs
Authors: Woodman Owen L.
Published: July 2012

In the anaesthetized dog, left circumflex coronary artery blood flow and external diameter were measured and the vascular responses to an injection of 5‐hydroxytryptamine (5‐HT, 0.02–2 μg kg−1) assessed, before and after a screw clamp had been placed on the artery to produce a severe stenosis.

In the normal coronary circulation, intra‐coronary (i.c.) injection of 5‐HT increased coronary blood flow (CBF) but decreased the external diameter of the large coronary artery (CD), without affecting systemic mean arterial pressure or heart rate.

In the normal coronary circulation, the 5‐HT‐induced increases in CBF were unaffected by blockade of 5‐HT2‐receptors with ketanserin (0.1 mg kg−1 i.c.) but were significantly attenuated by blockade of 5‐HT1‐like receptors with methysergide (0.1 mg kg−1 i.c.).

In the presence of a severe stenosis, the increase in CBF produced by 5‐HT was markedly attenuated and a secondary decrease in CBF was revealed. The stenosis also caused a marked enhancement of the 5‐HT‐induced constriction of the large artery, such that the reduction of the CD was approximately doubled at all doses of 5‐HT tested. The enhanced 5‐HT‐induced reduction in CD was similar with placement of the stenosis either proximal or distal to the site of diameter measurement.

In the presence of the stenosis, blockade of 5‐HT2‐receptors with ketanserin (0.1 mg kg−1 i.c.) significantly attenuated the 5‐HT‐induced decreases in CD and CBF.

These results demonstrate that, in the anaesthetized dog, placement of a severe, flow‐limiting stenosis enhances 5‐HT‐induced constriction of the large coronary arteries and reveals a reduction in coronary blood flow. These observations support suggestions that, in the presence of coronary artery disease, 5‐HT could contribute to reductions in coronary blood flow leading to myocardial ischaemia.
Contractile activity of three endothelins (ET‐1, ET‐2 and ET‐3) on the human isolated bronchus
Authors: Advenier C. , Sarria B. , Naline E. , Puybasset L. , Lagente V.
Published: July 2012

The effects of three endothelins: (i) the classical or human/porcine endothelin (ET‐1); (ii) [Trp6, Leu7] endothelin (ET‐2) and (iii) [Thr2, Phe4, Thr5, Tyr6, Lys7, Tyr14] endothelin or rat endothelin (ET‐3) were tested on the human isolated bronchus.

ET‐1 produced a concentration‐dependent contraction of the human isolated bronchus that proceeded in two different steps. The first step was observed at very low concentrations (pD2 = 11.01 ± 0.17, n = 10) but corresponded to a low intrinsic activity (Emax = 15.6 ± 1.8% of Emax induced by acetylcholine (ACh) 3 × 10−3 m, n = 10). This effect was potentiated by Bay K 8644 10−7 m (Emax = 26.1 ± 2.9% of ACh 3 × 10−3 m, n = 5, P < 0.05), reduced by nicardipine 10−6 m (Emax = 6.0 ± 2.6% of ACh 3 × 10−3 m, n = 5, P < 0.05) and strongly inhibited in calcium‐free medium. The second step of the action of ET‐1 corresponded to a lesser potency (pD2 = 7.90 ± 0.17, n = 9) but a higher intrinsic activity (Emax = 82.5 ± 4.7% of ACh 3 × 10−3 m). This effect was not significantly modified by nicardipine 10−6 m or by Bay K 8644 10−7 m. Neither of the two effects was modified by indomethacin 3 × 10−6m.

The effects of ET‐2 and ET‐3 were qualitatively similar to those of ET‐1 but quantitatively different; for these two steps of contracting activity and for potency and efficacy the ranking was: ET‐1 > ET‐2 = ET‐3.

Thus, ET‐1 appears to be the most potent of these three substances in its effect on the human isolated bronchus. Its activity seems to involve the action of voltage‐dependent calcium channels at low concentrations (10−12 to 10−9 m), whereas other mechanisms are involved at higher concentrations (10−8 to 3 × 10−7 m).
Evidence that an atypical β‐adrenoceptor mediates the inhibition of spontaneous rhythmical contractions of rabbit isolated jejunum induced by ritodrine and salbutamol
Authors: Norman Bernard J. , Leathard Helen L.
Published: July 2012

The nature of the adrenoceptors mediating the inhibitory action of noradrenaline, ritodrine and salbutamol on the spontaneous activity of longitudinal muscle of the rabbit jejunum in vitro was investigated by use of a range of adrenoceptor antagonists.

The actions of ritodrine and salbutamol were antagonized competitively by propranolol. The pA2 values of 6.4 and 6.6 respectively were smaller than those found elsewhere for β1‐ and β2‐adrenoceptors.

In contrast, the responses to ritodrine and salbutamol were antagonized only by high concentrations (>2.7 μm) of phentolamine and were unaffected by yohimbine (2.6 μm), mepyramine (2.5 μm) or cimetidine (4.0 μm).

Ritodrine which is less potent than salbutamol in tissues with typical β2‐adrenoceptors was found to be 8 times more potent than salbutamol in the rabbit jejunum.

It is suggested that in the rabbit jejunum ritodrine and salbutamol may act at an atypical β‐adrenoceptor, at which propranolol is a competitive but not very potent antagonist.
PAF‐induced bronchial hyperresponsiveness in the rabbit: contribution of platelets and airway smooth muscle
Authors: Coyle A.J. , Spina D. , Page C.P.
Published: July 2012

Aerosol administration of platelet activating factor (PAF) to normal rabbits induced an enhanced airway responsiveness to inhaled histamine, 6 and 24 h after exposure. Following exposure to bovine serum albumin (BSA) as the carrier molecule for PAF, there was an increase in airway responsiveness to histamine 6h after challenge, although by 24 h this was not significantly different from the responsiveness of airways to histamine before BSA.

PAF‐induced bronchial hyperresponsiveness at 24 h was associated with a substantial increase in the number of neutrophils and mononuclear cells and a small, but significant increase in the number of eosinophils in the lungs as assessed by bronchoalveolar lavage. BSA exposure failed to alter the total number of cells in the lungs, although there was a significant increase in the number of neutrophils in the bronchoalveolar lavage fluid.

Selective platelet depletion with a guinea‐pig anti‐rabbit platelet serum inhibited PAF‐induced bronchial hyperresponsiveness. In addition, there was an attenuation of PAF‐induced airway inflammation in animals rendered thrombocytopenic.

The contractile potency to histamine, methacholine and carbachol was similar in intrapulmonary bronchi taken from rabbits exposed to an aerosol of BSA or PAF. Furthermore, the relaxant potency to the non‐selective β‐adrenoceptor agonist isoprenaline, was unaltered in PAF‐treated rabbits. In contrast, there was a 2.58 fold reduction in the relaxant potency to theophylline in rabbits exposed to PAF compared with rabbits exposed to BSA.

These results suggest that in the rabbit, PAF‐induced bronchial hyperresponsiveness at 24 h is associated with airways inflammation and is dependent upon platelet activation, but is not related to changes in airway smooth muscle function.
Investigation into atropine‐induced antinociception
Authors: Ghelardini C. , Malmberg‐Aiello P. , Giotti A. , Malcangio M. , Bartolini A.
Published: July 2012

The effect of atropine on the nociceptive system was examined in mice and rats by use of the hot‐plate, writhing and tail‐flick tests.

Atropine dose‐dependently produced analgesia, no effect and hyperalgesia. Analgesia was observed in both species with doses ranging from 1 to 100 μg kg−1 while hyperalgesia was obtained with 5 mg kg−1.

Atropine antinociception was prevented by pirenzepine (0.1 μg per mouse, i.c.v.), dicyclomine (10 mg kg−1, i.p.), atropine‐methylbromide (0.5 μg per mouse, i.c.v.) and hemicholinium‐3 (1 μg per mouse, i.c.v.). Naloxone (1 mg kg−1, i.p.), α‐methyl‐p‐tyrosine (100 mg kg−1, s.c.) and reserpine (2 mg kg−1, i.p.) were ineffective.

The site of atropine analgesia is in the CNS since it exerts its antinociceptive effect also when injected i.c.v. (1–10 ng per mouse). Moreover drugs which do not cross the blood‐brain barrier, such as hemicholinium‐3, pirenzepine and atropine methylbromide, were unable to antagonize atropine analgesia if administered i.p.

Atropine also in vitro, showed a biphasic action on electrically‐evoked guinea‐pig ileum contractions. Concentrations between 10−14 and 10−12m increased electrically and nicotine‐evoked contractions but did not affect acetylcholine‐ and oxotremorine‐evoked contractions. Concentrations above 10−9m inhibited both electrically‐ and drug (acetylcholine, nicotine and oxotremorine)‐evoked contractions while they were ineffective on unstimulated ileum.

On the basis of the above findings, amplification of cholinergic transmission by very low doses of atropine is postulated, through a selective blockade of presynaptic muscarinic autoreceptors, as the likely mechanism of action.

Atropine antinociception, unlike oxotremorine antinociception, was obtained without any impairment of mouse rota‐rod performance.

The antagonism by pirenzepine and dicyclomine of oxotremorine and atropine antinociception suggests that M1 muscarinic receptor subtypes are responsible for cholinergic analgesia.
Actions of 5‐HT1 ligands on excitatory synaptic transmission in the hippocampus of alert rats
Authors: O'Connor J.J. , Rowan M.J. , Anwyl R.
Published: July 2012

The effects of 5‐hydroxytryptamine1 (5‐HT1) ligands on excitatory synaptic transmission were examined in the stratum radiatum of the CA1 region of the dorsal hippocampus of alert, gently restrained, rats.

5‐HT produced a dose‐dependent reduction in the amplitude of the electrically evoked population excitatory postsynaptic potential (e.p.s.p.) when injected directly into the hippocampus via a cannula (dose producing 50% maximum inhibition, ED50 = 0.46 μg).

Direct intrahippocampal (i.h.) application of buspirone (ED50 = 0.29 μg), gepirone (1 μg), ipsapirone (1 μg), BMY 7378 (0.1 μg) and 5‐carboxamidotryptamine (5‐CT, 0.02 μg) mimicked the inhibitory effect of 5‐HT.

Systemic injection of buspirone (ED50 = 0.88 mg kg−1, i.p.), BMY 7378 (0.01 mg kg−1, i.p.) and RU 24969 (1 mg kg−1 s.c.) also had an inhibitory effect on the amplitude of the e.p.s.p.

Injection of 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT, 2 μg) and spiroxatrine (1 μg) i.h. alone had no effect on the e.p.s.p. amplitude but prevented the inhibitory effect of 5‐HT.

Systemic injection (i.p.) of methysergide (5 mg kg−1) and spiroxatrine (1mg kg−1) antagonized the inhibitory effect of buspirone whereas pretreatment with ketanserin (1mg kg−1), trifluoperazine (1 mg kg−l) and idazoxan (1 mg kg−l) had no effect on the response to buspirone.

It is concluded that hippocampal synaptic transmission is highly sensitive to the agonist and antagonist properties of 5‐HT1 ligands in the alert rat.
Effects of pre‐contraction with endothelin‐1 on α2‐adrenoceptor‐and (endothelium‐dependent) neuropeptide Y‐mediated contractions in the isolated vascular bed of the rat tail
Authors: MacLean Margaret R. , McGrath J. C.
Published: July 2012

The pressor effects to bolus doses of the α2‐adrenoceptor agonist UK‐14,304 were studied in the isolated vascular bed of the perfused rat tail before and after increasing the perfusion pressure with infusions of endothelin‐1. Those of neuropeptide Y were studied before and after pre‐constriction with endothelin‐1 or 5‐hydroxytryptamine. The pressor effects of neuropeptide Y were studied before and after functional disruption of the endothelium with the detergent CHAPS.

Endothelin‐1 and the α1‐adrenoceptor agonist phenylephrine induced dose‐dependent vasoconstriction, endothelin‐1 being some 104 times more potent than phenylephrine [log dose (mol) of the ED50 for endothelin‐1 and phenylephrine: −11.8 ± 0.2 (n = 7), −8.2 ± 0.2 (n = 5) respectively].

Under control conditions, at basal perfusion pressures, UK‐14,304 and neuropeptide Y were virtually inactive as vasoconstrictors. Following a sustained increase in perfusion pressure by infusions of endothelin‐1 (2.5–10 nM at 0.8 ml min−1), however, both UK‐14,304 and neuropeptide Y induced dose‐dependent pressor responses and both were some 102 times more potent than phenylephrine [log dose (mol) of the ED50 for UK‐14304 and neuropeptide Y: −10 ± 0.5 (n = 6), −10.3 ± 0.4 (n = 6) respectively]. Responses to neuropeptide Y also were uncovered when vascular tone was increased with 5‐hydroxytryptamine (5–20 nm) [log dose (mol) of the ED50 for neuropeptide Y: −10.2 ± 0.2 (n = 6)].

Pre‐constriction‐induced pressor responses to UK‐14,304 were inhibited by 1 μm rauwolscine whilst those to neuropeptide Y were inhibited by disruption of the endothelium. Removal of the endothelium had no significant effect on the pressor responses to 4 pmol or 8 pmol endothelin‐1 and had no effect on the increase in perfusion pressure induced by the endothelin‐1 infusions but did decrease the time‐course of pressor responses to bolus injections of endothelin‐1. Endothelial disruption had no significant effect on the vasoconstriction induced by all but one of the doses of phenylephrine administered [log dose (mol) of the ED50 for phenylephrine after CHAPS: −8.6 ± 0.2 (n = 5)], indicating that the responsiveness of the vascular smooth muscle was not destroyed by CHAPS. This treatment did, however, slow the onset and prolong the time course of the phenylephrine‐induced responses.

These results indicate that, in the isolated vascular bed of the rat tail, pressor responses to both α2‐adrenoceptor‐ and neuropeptide Y receptor‐activation are uncovered by agonist‐induced preconstriction including that to endothelin‐1. Neuropeptide Y‐induced vasoconstriction was endothelium‐dependent.
Evidence for the presynaptic action of 5‐hydroxytryptamine and the involvement of purinergic innervation in the rabbit lower urinary tract
Authors: Chen Hong‐I
Published: July 2012

The effects of 5‐hydroxytryptamine (5‐HT) were studied in vitro on bladder and urethral muscle strips from the rabbit. 5‐HT produced dose‐dependent contraction in the detrusor and urethra.

The 5‐HT‐induced contraction could be dose‐dependently inhibited by the 5‐HT3 antagonists MDL 72222, ICS 205–930 and BRL 43694. No effect of ketanserin, methysergide or metitepine was observed on the contractile response to 5‐HT.

Atropine and α,β‐methylene ATP both partially blocked the contractile response to 5‐HT. Together they caused more inhibition than either alone.

Atropine and α,β‐methylene ATP also inhibited the contractile response to electrical field stimulation. The 5‐HT3 antagonist MDL 72222 had no effect on the contraction to field stimulation.

The atropine‐ and α,β‐methylene ATP‐resistant components of 5‐HT‐induced contraction were not affected by the 5‐HT1 antagonists metitepine, the 5‐HT2 antagonists ketanserin and methysergide or the 5‐HT3 antagonists MDL 72222, ICS 205–930 and BRL 43694.

Tetrodotoxin, hexamethonium, phentolamine and prazosin had no effect on the contractile response to 5‐HT.

These results suggest that in the rabbit lower urinary tract (i) there are 5‐HT3 receptors, (ii) the contractile response to 5‐HT is mediated by presynaptic stimulation, (iii) there is non‐adrenergic, non‐cholinergic excitatory neurotransmission.
General anaesthetics and field currents in unclamped, unmyelinated axons of rat olfactory cortex
Authors: McGivern J. , Scholfield C.N.
Published: July 2012

The effects of seven general anaesthetics and one local anaesthetic having a wide range of physical and chemical properties were studied on nerve terminal Na‐ and K‐mediated currents in slices of olfactory cortex. These currents were measured from the groups of fine unmyelinated axons traversing the surface of the olfactory cortex and which give off synapses en passant. The amplitude of the K‐current was visualized by depolarizing the axons via an electrode polarization.

The anaesthetics tested were ketamine (0.1–2 mm), pentobarbitone (0.1–5 mm), urethane (5–200 mm), halothane (0.5–5 mm), ether (10–200 mm), alphaxalone (0.001–0.05 mm), diisopropylphenol (0.05–0.5 mm) and lignocaine (0.01–0.5 mm). All had depressant effects on the axonal Na‐current (at the higher concentrations tested) and on the K‐current (at slightly lower concentrations). The apparent lower potency on the Na‐current was considered to be due to a masking of effect as a consequence of the reduction in the K‐mediated membrane rectification rather than any real difference in the susceptibilities of the Na and K‐currents.

Some of the depressant effect of pentobarbitone and alphaxalone was γ‐aminobutyric acid (GABA)‐mediated as indicated by the reduced potency in the presence of bicuculline. The actions of ketamine and halothane were unaffected by bicuculline.

For some anaesthetics these axonal depressant effects might contribute to general anaesthesia, while for other substances the relatively high concentrations necessary would suggest that this mode of action does not produce effective anaesthesia in vivo.
Inhibition by l‐glutamine of the release of endothelium‐derived relaxing factor from cultured endothelial cells
Authors: Hecker Markus , Mitchell Jane A. , Swierkosz Tomasz A. , Sessa William C. , Vane John R.
Published: July 2012

l‐Glutamine (0.02–2 mm) but not d‐glutamine (0.2 mm and 2 mm) inhibited the release of endothelium‐derived relaxing factor (EDRF) from bovine aortic endothelial cells cultured in the presence or absence of l‐arginine. Inhibition was maximal at a concentration of 200 μm, and was reversed by l‐arginine (50 μm) but not d‐arginine (100 μm). l‐Glutamic acid (2 mm) or ammonium chloride (1 mm), putative products of the metabolism of l‐glutamine in endothelial cells, had no effect on EDRF release. l‐Glutamine (0.2 mm and 2 mm) but not d‐glutamine (2 mm), l‐glutamic acid (2 mm) or ammonium chloride (1 mm) also inhibited the generation of l‐arginine in endothelial cells. Thus, l‐glutamine inhibits EDRF release by preventing the generation of l‐arginine.
Effects of galanin, its analogues and fragments on rat isolated fundus strips
Authors: Katsoulis Stavros , Schmidt Wolfgang E. , Schwörer Harald , Creutzfeldt Werner
Published: July 2012

Rat and porcine galanin (rGal and pGal) produced dose‐dependent contraction of rat fundus strips in a concentration range of 6 nm–100 nm.

The stimulatory effect of rGal on rat fundus strips was not modified in the presence of somatostatin (250 nm), naloxone (1 μm), guanethidine (10 μm), a mixture of propranolol (3 μm) and phentolamine (3 μm), tetrodotoxin (1 μm), indomethacin (10 μm), atropine (1 μm), a mixture of methysergide (2.5 μm) and ketanserin (2.5 μm), a mixture of mepyramine (10 μm) and cimetidine (10 μm), and saralasin (10 μm) or when strips were desensitized to substance P and neurotensin.

These results suggest the localization of specific Gal receptors on the surface of smooth muscle cells of rat fundus.

The galanin analogues [d‐Trp2]‐rGal, [NLe4]‐rGal, [d‐Ala7]‐rGal, [d‐Trp2‐NLe4‐d‐Ala7]‐rGal and fragments [Cys23]‐Gal (1–23), Gal (1–18) were fully active. In contrast, rGal (3–29) was completely inactive and showed no antagonistic properties to the contractile effect of intact galanin.

The order of potency of the galanin peptides, analogues and fragments to contract rat fundus strips was: pGal > rGal > [NLe4]‐rGal > [Cys23]‐Gal (1–23) > Gal (1–18) > [d‐Ala7]‐rGal > [Trp2]‐rGal > [d‐Trp2‐NLe4‐d‐Ala7]‐rGal.

The data originating from our structure‐activity study suggest that the C‐terminal portion of Gal contributes mainly to the affinity of Gal receptors whereas the N‐terminal portion of Gal is responsible for the full activation of Gal receptors in this tissue. In particular the amino acids in position 1 and 2 of Gal (Gly‐Trp) appear to be essential for binding and intrinsic activity.
Reserpine induces vascular α2‐adrenergic supersensitivity and platelet α2‐adrenoceptor up‐regulation in dog
Authors: Estan Luis , Senard Jean‐Michel , Tran Marie‐Antoinette , Montastruc Jean‐Louis , Berlan Michel
Published: July 2012

The aim of the present study was to investigate the influence of catecholamine levels on the regulation of α2‐adrenoceptor sensitivity in dogs.

Blood pressure and heart rate values at rest, plasma catecholamine levels, platelet and adipocyte α2‐adrenoceptors as well as the α2‐mediated cardiovascular responses to clonidine (10 μg kg−1 i.v., after α1‐, β‐adrenoceptor plus muscarinic blockade) or noradrenaline (0.5, 1, 2 and 4 μg kg−1 i.v. after α1‐ and β‐adrenoceptor blockade) were measured before and after reserpine treatment (0.1 mg kg−1 day−1 s.c. over 15 days).

Reserpine induced a significant decrease in resting systolic and diastolic blood pressures (213 ± 2/87 ± 6 mmHg before vs 158 ± 5/59 ± 3mmHg after treatment) as well as in heart rate (91 ± 2 beats min−1 before vs 76 ± 3 beats min−1 after treatment).

A 5 min tilt test performed under chloralose anesthesia, failed to modify blood pressure before treatment whereas it induced a significant fall in the same animals after the 15 day treatment. Plasma levels of noradrenaline significantly decreased (262 ± 58 vs 66 ± 31 pg ml−1) whereas plasma adrenaline levels were unchanged.

The α2‐mediated pressor responses to noradrenaline were significantly increased after reserpine. Clonidine induced a marked pressor effect (+72 and +45% in systolic and diastolic blood pressures respectively) after reserpine treatment. This effect was suppressed by administration of RX‐821002, a new specific α2‐adrenoceptor antagonist.

Reserpine treatment significantly increased platelet α2‐adrenoceptor number (identified with [3H]‐yohimbine or [3H]‐RX821002) with no change in Kd values. α2‐Adrenoceptor number remained unchanged in adipocytes (identified with [3H]‐RX821002).

These results show that a 15 day treatment with reserpine induces a vascular α2‐adrenergic supersensitivity and an up‐regulation in platelet α2‐adrenoceptors. In contrast, this phenomenon does not involve all the tissues since adipocyte α2‐adrenoceptors escape the effect of reserpine. We suggest that the levels of plasma noradrenaline play an important role in the regulation of the platelet and vascular α2‐adrenoceptors. In contrast, adipocyte α2‐adrenoceptors are not affected by changes in plasma noradrenaline levels.
Factors influencing the onset of ouabain inhibition of Na,K‐ATPase from guinea‐pig myocardium
Authors: Ebner F.
Published: July 2012

The onset of ouabain inhibition was quantified by analysis with an integrated rate equation from experiments in which the activity of Na,K‐ATPase from guinea‐pig myocardium had been altered with adenosine 5′‐triphosphate (ATP, 0.3–9 mmoll−1) in the absence and presence of a detergent.

Under control conditions with increasing ouabain (0.1–100 μmoll−1) and ATP (0.3–1 mmoll−1) concentrations, inhibition developed faster. The acceleration by ouabain became less effective at saturating concentrations leading to a non‐linear relationship between pseudo‐first‐order rate constants of inhibition and ouabain concentration. With a rise of ATP to 3 and 9 mmoll−1, i.e., near total Mg concentration (5 mmoll−1), inhibition was retarded presumably because the free concentrations of Mg and uncomplexed ATP changed. Varying the ATP concentration had little effect on ouabain potency at steady state; Hill coefficients were < 1.

The detergent alamethicin (23 μg ml−1) neither interfered with Na,K‐ATPase activity nor with inhibition at steady state but accelerated its onset. This supports a role for a lipid barrier in the development of inhibition.

While the reaction of low concentrations of ouabain with the receptors seemed to govern inhibition rate, with an increase in steroid concentration in the presence of alamethicin, ATP‐dependent enzyme activity interfered with the onset of inhibition. The transition of the enzyme between ouabain‐sensitive and ATP‐hydrolytic conformations consequently causes the non‐linear concentration‐dependence of pseudo‐first‐order rate constants. As the Hill coefficient was < 1, a reaction of ouabain with two receptors also could have contributed to the special concentration‐dependence of inhibition rates.
The inhibitory adenosine receptor at the neuromuscular junction and hippocampus of the rat: antagonism by 1,3,8‐substituted xanthines
Authors: Sebastião A.M. , Stone T.W. , Ribeiro J.A.
Published: July 2012

The ability of 1,3,8‐substituted xanthines to antagonize the inhibitory effects of adenosine receptor agonists on the amplitude of nerve‐evoked twitches of the rat phrenic‐diaphragm and on the amplitude of orthodromically‐evoked population spikes, recorded from the CA1 pyramidal cells of rat hippocampal slices, was investigated.

1,3‐Dipropyl‐8‐cyclopenthylxanthine (DPCPX), 1,3‐dipropyl‐8‐(carboxymethyloxyphenyl)xanthine (XCC), 1,3‐dipropyl‐8‐(4‐((2‐aminoethyl)amino)carbonylmethyloxyphenyl)xanthine (XAC), 1,3‐dipropyl‐8‐(2‐amino‐4‐chlorophenyl)xanthine (PACPX), 8‐phenyltheophylline (8‐PT), 1,3‐diethyl‐8‐phenylxanthine (DPX) and PD 115,199, in concentrations virtually devoid of effect on neuromuscular transmission, shifted to the right in a near parallel manner the log concentration‐response curve for the inhibitory effect of 2‐chloroadenosine (CADO) on nerve‐evoked twitches of the phrenic‐diaphragm. Linear Schild plots with slopes near to unity were obtained for all the xanthines.

The order of potency of the xanthines as antagonists of the effect of CADO in the phrenic‐diaphragm was DPCPX (Ki = 0.54 nm) > XCC (Ki = 10 nm), XAC (Ki = 11 nm), PACPX (Ki = 13 nm) > DPX (Ki = 22 nm), 8‐PT (Ki = 25 nm) > PD 115,199 (Ki = 57 nm). The potency of DPCPX in antagonizing the inhibitory effects of R‐N6‐phenylisopropyladenosine (R‐PIA) and 5′‐N‐ethylcarboxamide adenosine (NECA) on nerve‐evoked twitch responses was not statistically different from its potency in antagonizing the inhibitory effect on CADO.

In the hippocampal slices, DPCPX, XCC and XAC, used in concentrations virtually devoid of effect on population spike amplitude, shifted to the right in a near parallel manner the log concentration‐response curve for the inhibitory effect of CADO on the amplitude of the population spikes. The Schild plots were linear with slopes near unity.

The potencies of DPCPX (Ki = 0.45 nm) and XAC (Ki = 11 nm) in antagonizing the inhibitory adenosine receptor at the hippocampus were similar to their potencies for antagonism of the inhibitory adenosine receptor at the phrenic‐diaphragm. XCC was only slightly more potent (Ki = 5.4 nm) as an antagonist of the adenosine receptor in the hippocampus than in the phrenic‐diaphragm.

The results suggest that the inhibitory adenosine receptors in the phrenic‐diaphragm and in the hippocampus of the rat are similar, and that according to the antagonist potencies, these receptors belong to the A1‐adenosine receptor subtype.
The effects of novel vasodilator long chain acyl carnitine esters in the isolated perfused heart of the rat
Authors: Criddle D.N. , Dewar G.H. , Wathey W.B. , Woodward B.
Published: July 2012

The effects of palmitoyl carnitine (PC) and novel derivatives were examined on the isolated Langendorff perfused heart of the rat.

Bolus injections of PC (1–300 nmol) produced coronary constriction accompanied by a cumulative irreversible depression of contractility.

Prior storage of PC in chloroform containing 2% ethanol in heat‐sealed ampoules resulted in production of the ethyl ester of the compound (PCE). This compound was isolated and also synthesized (P1E). In contrast to PC, both PCE and P1E exhibited potent vasodilator activity.

Increasing the fatty acid chain length from palmitoyl to stearoyl resulted in a significant reduction in coronary dilator activity of the ester compound, whereas different ester groups did not affect the vasodilator action appreciably. Complete removal of the fatty acid chain abolished all vascular effects at the doses used.

The vasodilatation produced by these acyl carnitine esters was comparable to that produced by several known vasodilator drugs including verapamil, cromakalim, amyl nitrate and iloprost; however, the duration of the vasodilator response was more prolonged with the carnitate derivatives.
Relationships between tumour necrosis factor, eicosanoids and platelet‐activating factor as mediators of endotoxin‐induced shock in mice
Authors: Myers Adam K. , Robey James W. , Price Ray M.
Published: July 2012

The toxicity of intravenous recombinant human tumour necrosis factor (rhTNF), a TNF fragment (TNF114–130), endotoxin and combinations of rhTNF or TNF114–130 were tested in mice. Neither rhTNF nor TNF114–130 was lethal alone, but when combined with a non‐lethal dose of endotoxin, rhTNF provoked dose‐dependent mortality, as did higher doses of endotoxin alone.

Both the toxicity and the vasopermeability changes induced by endotoxin alone were blocked by the platelet‐activating factor (PAF) antagonist BN52021, indomethacin or the dual cyclo‐oxygenase/lipoxygenase inhibitor BW755C.

The lethality of the combined low dose endotoxin/rhTNF challenge was unaffected by pretreatment with BN52021, indomethacin or BW755C, or by treatment at 6h intervals with BN52021 or BW755C.

The results of these studies suggest that TNF, a putative, early mediator of septic or endotoxin shock, cannot by itself mimic all of the effects of bacterial endotoxin in the model used in this study. Apparently, TNF works synergistically with other mediators whose release is stimulated by endotoxin.

The results also suggest that the mechanism of shock production by the rhTNF/endotoxin combination in mice is not dependent on the early stimulation of eicosanoid or PAF synthesis by rhTNF.
Central inhibition by γ‐aminobutyric acid and muscimol of the release of vasopressin and oxytocin by an osmotic stimulus in the rat
Authors: Bisset G.W. , Chowdrey H.S. , Fairhall K.M. , Gunn L.K.
Published: July 2012

In water‐loaded rats under ethanol anaesthesia, the injection of 2–4 μl 1.54 m NaCl solution (hypertonic saline: HS) into a lateral cerebral ventricle (i.c.v.) produced an antidiuretic and a pressor response, together with increased urinary excretion of vasopressin and ‘oxytocin‐like radioimmunoreactivity’ (OLRI). In lactating rats HS also produced a milk‐ejection response which was shown to be due to the release of oxytocin.

The injection of 20–40 μg γ‐aminobutyric acid (GABA) or 40–80 ng muscimol i.c.v. 2 min before HS inhibited the antidiuretic, pressor and milk‐ejection responses and reduced the urinary excretion of vasopressin and OLRI.

The pressor response to HS was abolished by a ganglion blocking agent but it was not reduced by a vasopressin antagonist. After the antagonist, the antidiuretic response to HS was abolished and the pressor response was accompanied by a diuresis both of which were blocked by muscimol.

The threshold dose of HS for an antidiuretic response was 4–8 times higher on injection into the cisterna magna (i.cist.) than when injected i.c.v. GABA, i.v. or i.cist, did not inhibit the response to HS i.c.v.

The results confirm other evidence that, in the rat, in contrast some other species, an osmotic stimulus causes release of both vasopressin and oxytocin. This release is blocked by GABA and muscimol. These drugs and HS act at a site reached not from the subarachnoid space but from the cerebral ventricles, probably the hypothalamus. The pressor response to HS under the experimental conditions used is due entirely to central sympathetic stimulation and this effect, as well as the release of vasopressin and oxytocin, is blocked by muscimol.
Inhibitory action of α‐human atrial natriuretic peptide on noradrenaline‐induced synthesis of myo‐inositol 1,4,5‐trisphosphate in the smooth muscle cells of rabbit aorta
Authors: Kajikuri Junko , Kuriyama Hirosi
Published: July 2012

Interactions between the synthesis of myo‐inositol 1,4,5‐trisphosphate (IP3) and guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) in the smooth muscle cells of the rabbit aorta were investigated.

In the presence or absence of vascular endothelium, noradrenaline (NA; 5 μm) consistently reduced the amount of phosphatidylinositol 4,5‐bisphosphate (PI‐P2) and increased both phosphatidic acid (PA) and IP3.

In the presence or absence of endothelium, acetylcholine (ACh; 100 μm but not 5 μm) slightly increased the amount of IP3, but exposure to ACh (100 μm) 4 min after application of NA did not modify NA‐induced synthesis of IP3.

ACh (100 μm) markedly enhanced the synthesis of cyclic GMP in the presence of endothelium but not in the endothelium‐denuded tissues.

Prazosin (5 μm) but not dibutyryl cyclic GMP (db‐cyclic GMP; 100 μm) blocked the hydrolysis of PI‐P2 induced by 5 μm NA. Synthesis of IP3 induced by NA, as estimated with [3H]‐inositol was not modified by application of 100 μm db‐cyclic AMP or db‐cyclic GMP.

α‐Human atrial natriuretic peptide (α‐hANP; 0.1 μm) increased cyclic GMP in the presence or absence of endothelium. α‐hANP (0.1 μm) consistently inhibited the hydrolysis of PI‐P2 induced by 5 μm NA.

The results indicate that synthesis of IP3 is inhibited neither by the synthesis of cyclic GMP in the cytosol nor by cyclic GMP itself. However, synthesis of IP3 through hydrolysis of PI‐P2 may be inhibited by an interaction between some steps in the IP3 synthetic process and by the activation of the α‐hANP‐guanylate cyclase process at the sarcolemma.