bluuebunny/crossref_metadata_2025 huggingface dataset:
Sympathoinhibitory effects of rilmenidine may be mediated by sites located below the brainstem
Authors: Sannajust Frédéric , Barrès Christian , Koenig‐Bérard Elisabeth , Sassard Jean
Published: July 2012

To determine the site of action of rilmenidine, we examined its effects on arterial blood pressure (BP), heart rate (HR) and postganglionic renal sympathetic nerve activity (RSNA) after intracerebroventricular (i.c.v.) administration (300 μg kg−1), in groups (all n = 6) of conscious and freely moving, pentobarbitone‐anaesthetized and pentobarbitone‐anaesthetized and spinally transected, fifteen week‐old male spontaneously hypertensive rats (SHRs).

In conscious SHRs, which exhibited a low sympathetic nerve activity (RSNA: 3.4 ± 0.9 μV), rilmenidine was inactive on systolic BP (SBP), diastolic BP (DBP), HR and RSNA.

In intact pentobarbitone‐anaesthetized SHRs, which exhibited an elevated sympathetic nerve activity (RSNA: 10.6 ± 0.9 μV), rilmenidine exerted potent antihypertensive (ΔSBP: −37 ± 4%; ΔDBP: −43 ± 6%), bradycardic (ΔHR: −32 ± 3%) and sympathoinhibitory (ΔRSNA: −68 ± 9%) activities.

In pentobarbitone‐anaesthetized SHRs with cervical spinal cord transection, BP was markedly decreased and sympathetic nerve activity (RSNA: 10.3 ± 3.1 μV) returned to the level observed in conscious SHRs (RSNA: 3.6 ± 0.5 μV). In these conditions, rilmenidine remained sympathoinhibitory (ARSNA: −74 ± 5%).

In conclusion, we have shown that pentobarbitone‐anaesthesia enhances the peripheral sympathetic tone by a central action, as the spinal cord transection allows RSNA to return to normal levels and that, spinal or ganglionic structures could be a major site of the sympathoinhibitory action of rilmenidine.
Influence of anaesthesia on the cardiovascular effects of rilmenidine and clonidine in spontaneously hypertensive rats
Authors: Sannajust Frédéric , Cerutti Catherine , Koenig‐Bérard Elisabeth , Sassard Jean
Published: July 2012

The acute cardiovascular effects of two α2‐adrenoceptor agonists, rilmenidine and clonidine, were studied in 15‐week‐old male spontaneously hypertensive rats (SHRs). The effects of these drugs were compared with intravenous (i.v.) and intracerebroventricular (i.c.v.) administration in conscious and pentobarbitone‐anaesthetized SHRs, in which aortic blood pressure (BP) was continuously recorded.

In conscious SHRs, i.v. doses of either rilmenidine (30, 100, 300 μg kg−1) or clonidine (3, 10, 30 μg kg−1) induced dose‐dependent short‐lasting increases in BP followed by moderate decreases associated with bradycardia, while the same three doses of both drugs given i.c.v. were devoid of BP and heart rate (HR) effects.

Pentobarbitone‐anaesthesia increased the sympathetic control of BP and suppressed the cardiac baroreflex sensitivity.

In anaesthetized SHRs, i.v. injections of the same 3 doses of rilmenidine and clonidine induced a slight increase in BP, rapidly followed by profound and long‐lasting BP and HR decreases. Surprisingly, when given i.c.v., these 3 doses lowered BP and HR to the same extent but in a more progressive manner.

The lack of efficacy of both drugs in conscious SHRs after the i.c.v. administration of i.v. active doses and the lack of more marked and rapid effects in anaesthetized SHRs, after i.c.v. than after i.v. injections, question the involvement of a major central site of action for these antihypertensive α2‐adrenoceptor agonists. Moreover, these results show that the cardiovascular effects of these drugs are profoundly influenced by baseline sympathetic nervous system activity which is enhanced by pentobarbitone‐anaesthesia.
CI988, a selective antagonist of cholecystokininB receptors, prevents morphine tolerance in the rat
Authors: Xu X.‐J. , Wiesenfeld‐Hallin Z. , Hughes J. , Horwell D.C. , Hökfelt T.
Published: July 2012

The effect of chronic treatment with CI988, a recently developed selective antagonist of cholecystokinin type‐B receptors (CCKB receptors) on the tolerance to morphine analgesia was studied in rats with the hot plate test.

Morphine tolerance was induced with the use of two paradigms. Morphine was injected i.p. either in a schedule of increasing doses (1–32 mg kg−1) twice daily for 6 days or at a fixed dose (3 mg kg−1) daily for 29 days.

In both series of experiments, tolerance to the analgesic effect of morphine was prevented by simultaneous treatment with i.p. CI988. Chronic treatment with only CI988 daily for up to 29 days did not reduce the analgesic effect of a weekly injection of morphine.

CI988 did not diminish the physical dependence to morphine, as examined with naloxone precipitated withdrawal.

The present results provide evidence that chronic treatment with a selective CCKB receptor antagonist could prevent tolerance to the analgesic effect of morphine without affecting morphine‐induced physical dependence. Application of CCK antagonists may be clinically important in treating chronic pain patients by preventing morphine tolerance and by eliminating the need to increase morphine doses to unacceptable levels.
Pharmacological and histological examinations of regional differences of guinea‐pig lung: a role of pleural surface smooth muscle in lung strip contraction
Authors: Wong Wai‐shiu Fred , Bloomquist Shari L. , Bendele Alison M. , Fleisch Jerome H.
Published: July 2012

Parenchymal lung strip preparations have been widely used as an in vitro model of peripheral airway smooth muscle. The present study examined functional responses of 4 consecutive guinea‐pig lung parenchymal strips isolated from the central region (segment 1) to the distal edge (segment 4) of the lower lung lobe. The middle two segments were designated as segments 2 and 3.

Lung segments 1 and 4 exhibited significantly greater contraction than the other 2 segments to KCl when responses were expressed as mg force per mg tissue weight. Contractile responses to bronchospastic agents including histamine, carbachol, endothelin‐1, leukotrienes (LT) B4 and D4, and the thromboxane A2‐mimetic U46619 demonstrated no significant difference in EC50 values among the 4 lung segments.

Contractile responses of segments 1 and 4 to antigen‐challenge (ovalbumin), ionophore A23187 and substance P were significantly greater than the other 2 segments with respect to either sensitivity or maximum responsiveness.

U46619‐induced contractions of the 4 lung segments were relaxed in similar manner by papaverine and theophylline up to 100%, salbutamol up to 80%, and sodium nitroprusside by only 20%. In contrast, sodium nitroprusside markedly reversed U46619‐induced contraction of pulmonary arterial rings and bronchial rings.

Histological studies identified 2–4 layers of smooth muscle cells underlying the lung pleural surface. Mast cells were prominent in this area. Moreover, morphometric studies showed that segment 4 possessed the least amount of smooth muscle structures from bronchial/bronchiolar wall and vasculatures as compared to the other 3 segments, and a significant difference in this respect was evident between segment 1 and segment 4.

Since lung segments 1 and 4 are covered with larger surface area of lung pleura, the present results suggest that the significantly greater intrinsic contractile responses of segments 1 and 4 are associated with the presence of increased lung pleural surface possibly together with more mast cells. Thus, a primary contribution to the net contraction of the lung parenchymal strips may be smooth muscle from the lung pleura, alveolar ducts and interstitial contractile cells rather than from bronchi/bronchioles and micro‐vasculatures.
Increased secretion of glandular‐kallikrein in the bronchial washings induced by intravenous injection of leukotriene C4 in guinea‐pigs
Authors: Jin Hong Yong , Katori Makoto , Majima Masataka , Sunahara Noriyuki
Published: July 2012

Intravenous administration of leukotriene C4 (LTC4) and LTD4 (1–10 nmol kg−1) caused a dose‐dependent increase in secretion of glandular‐kallikrein in the bronchial washings of guinea‐pigs, as measured by cleavage of a synthetic substrate and the formation of kinin. LTC4 was more potent than LTD4 and pilocarpine was much less potent than peptide leukotrienes on a molecular basis.

The increases in levels of glandular‐kallikrein in the bronchial washings that were induced by LTC4 (3 nmol kg−1, i.v.) were almost completely inhibited by pretreatment with an antagonist of leukotrienes (ONO‐1078), with an antagonist of thromboxane (S‐1452), with an inhibitor of thromboxane synthetase (OKY‐046), with indomethacin, with atropine or with scopolamine. These results indicate that the LTC4‐induced increase in levels of glandular‐kallikrein may have been mediated by the formation of thromboxane and the release of acetylcholine.

The increases in levels of glandular‐kallikrein in the bronchial washings induced by STA2 (20 pmol kg−1, i.v.), a stable analogue of thromboxane A2, were completely blocked by pretreatment with atropine, whereas increases induced by pilocarpine (41 μmol kg−1, i.v.) were not blocked by pretreatment with indomethacin, although such increases were inhibited by atropine. This result indicates that secretion of kallikrein stimulated by LTC4 may have been mediated by the successive formation of thromboxane A2 and release of acetylcholine.

Intravenous administration of bradykinin (3–30 nmol kg−1) caused a dose‐dependent increase in levels of glandular‐kallikrein in the bronchial washings. This increase was completely inhibited by pretreatment with atropine, with indomethacin or with an antagonist of thromboxane.

The increases in levels of glandular‐kallikrein in the bronchial washings induced by LTC4 (3 nmol kg−1, i.v.) and pilocarpine (41 μmol kg−1, i.v.) were significantly inhibited by pretreatment with an antagonist of bradykinin. These results suggest that intravenous LTC4 may increase secretion of glandular‐kallikrein via formation of thromboxane A2 and release of acetylcholine in that order, and kinin released by kallikrein may enhance the rate of secretion of glandular‐kallikrein.
Sustained decreases in weight and serum insulin, glucose, triacylglycerol and cholesterol in JCR: LA‐corpulent rats treated with d‐fenfluramine
Authors: Brindley David N. , Hales Paul , Al‐Sieni Abdulbasit I.I. , Russell James C.
Published: July 2012

The effects of d‐fenfluramine were studied in the JCR: LA‐corpulent rat that is grossly obese, hyperphagic, hyperlipidaemic, hyperinsulinaemic and atherosclerosis‐prone.

Daily doses of 1, 2.5 and 5 mg kg−1 of d‐fenfluramine produced sustained decreases in body weight and food intake over a period of 30 days in 6 month old female rats fed ad libitum. This was accompanied by decreases in the circulating concentrations of glucose, triacylglycerol, free cholesterol and insulin.

Food restriction imposed by meal feeding also decreased circulating glucose, triacylglycerols, cholesterol and insulin and diminished the effect of d‐fenfluramine on these parameters in male and female rats.

Addition of d‐fenfluramine to drinking water to give a dose of about 0.25 mg kg−1 daily produced a sustained decrease in body weight and food intake of male and female rats over a nine week period.

The results show that the JCR: LA‐corpulent rat is very sensitive to the pharmacological effects of d‐fenfluramine. These rats should provide an appropriate animal model for determining the mechanisms of action of this antiobesity agent and whether apparently beneficial changes in metabolism translate into long‐term protection against premature atherosclerosis.
Release of vasoactive intestinal polypeptide from the rat gastric fundus
Authors: D'Amato M. , Currò D. , Montuschi P. , Ciabattoni G. , Ragazzoni E. , Lefebvre R.A.
Published: July 2012

Auxotonic responses and release of vasoactive intestinal polypeptide‐like immunoreactivity (VIP‐LI) induced by electrical field stimulation (EFS) were studied in longitudinal muscle strips from the gastric fundus of reserpinized rats suspended between parallel platinum electrodes in Krebs solution containing atropine (1 μm), 5‐hydroxytryptamine (3 μm) and bovine serum albumin (50 mg l−1).

EFS (supramaximal voltage, 1 ms, 0.25–32.0 Hz, trains of 2 min) induced frequency‐dependent relaxations.

EFS at frequencies ≥ 8 Hz also produced significant increases in VIP‐LI release.

VIP‐LI release induced by EFS at 16 Hz no longer occurred in the presence of tetrodotoxin (1 μm) or a Ca2+‐free medium.

Detection of VIP‐LI upon activation of inhibitory non‐adrenergic, non‐cholinergic neurones indicates that VIP meets the ‘detectable release’ criterion for an inhibitory neurotransmitter in the rat gastric fundus.
Participation of endothelium‐derived nitric oxide but not prostacyclin in the gastric mucosal hyperaemia due to acid back‐diffusion
Authors: Lippe Irmgard Th. , Holzer Peter
Published: July 2012

The possible participation of prostacyclin and nitric oxide (NO) in the gastric mucosal hyperaemic response to acid back‐diffusion through a disrupted gastric mucosal barrier was examined. The experiments were carried out on anaesthetized rats in which acid back‐diffusion was elicited by gastric perfusion with dilute ethanol in 0.15 m HCl and gastric mucosal blood flow (MBF) was measured by the hydrogen gas clearance technique.

Indomethacin (28 μmol kg−1, s.c.), an inhibitor of the formation of cyclo‐oxygenase products including prostacyclin, failed to alter mean arterial blood pressure (MAP), basal MBF and the hyperaemic response to acid back‐diffusion in urethane‐anaesthetized rats.

NG‐nitro‐l‐arginine methyl ester (l‐NAME; 13 and 43 μmol kg−1, i.v.), an inhibitor of endothelium‐derived NO formation, increased MAP in a dose‐dependent manner. Whilst basal MBF in urethane‐anaesthetized rats was not changed, the increase in MBF caused by gastric perfusion with dilute ethanol in acid was dose‐dependently depressed by l‐NAME. The loss of H+ ions from the gastric lumen, an indirect measure of acid back‐diffusion, was significantly enhanced by 43 μmol kg−1 l‐NAME. In contrast, d‐NAME (13 and 43 μmol kg−1) was without effect on MAP, basal and stimulated MBF, and acid back‐diffusion.

Unlike in urethane‐anaesthetized rats, l‐NAME led to a significant reduction of basal MBF in phenobarbitone‐anaesthetized rats. MAP in the phenobarbitone‐anaesthetized rats was significantly higher than in urethane‐anaesthetized rats, and the hypertensive effect of l‐NAME under phenobarbitone anaesthesia was significantly smaller than under urethane anaesthesia.

The rise in MBF brought about by acid back‐diffusion was blocked by l‐NAME administered to phenobarbitone‐anaesthetized rats. Infusion of l‐arginine (120 μmol kg−1 min−1, i.v.) led to a partial, but significant, reversal of the effects of l‐NAME on MAP and the hyperaemia due to acid back‐diffusion.

These findings indicate that endothelium‐derived NO plays an important mediator role in the gastric mucosal vasodilatation caused by back‐diffusion whilst vasodilator prostanoids such as prostacyclin are not involved.
Differential cardiovascular and neuroendocrine effects of epinine and dopamine in conscious pigs before and after adrenoceptor blockade
Authors: van Woerkens L.J. , Boomsma F. , in 't Veld A.J. Man , Bevers M.M. , Verdouw P.D.
Published: July 2012

The effects of epinine or dopamine (both 1–10 μg kg−1 min−1) on systemic haemodynamics and plasma concentrations of catecholamines and prolactin were studied in conscious pigs before and after combined non‐selective α‐ and β‐adrenoceptor blockade.

The plasma concentrations of the two compounds did not differ from each other over the entire dose‐range.

Epinine increased aortic blood flow (AoBF, 24 ± 6%), which was due to an increase in heart rate (HR) for doses less than 10 μg kg−1 min−1. At 10 μg kg−1 min−1, HR decreased slightly (10 ± 3%, as compared to the value obtained at 5 μg kg−1 min−1) and stroke volume increased up to 15% (P < 0.05). Mean arterial pressure (MAP, 99 ± 3 mmHg at baseline) decreased dose‐dependently (14 ± 2%, P < 0.05) up to the infusion rate of 5 μg kg−1 min−1, but increased by 4.0 ± 1.8 mmHg during infusion of 10 μg kg−1 min−1. Systemic vascular resistance (SVR) decreased up to 23 ± 3% for doses less than 10 μg kg−1 min−1, but did not change further during infusion of the highest dose. LVdP/dtmax increased during the two highest infusion rates up to 22 ± 6% (P < 0.05). After the infusion was stopped there was an abrupt increase in HR (18 ± 4%, P < 0.05) and a further decrease in SVR before all parameters returned to baseline.

Dopamine caused increases in AoBF (27 ± 3%) similar to epinine, the only difference being that HR continued to increase (32 ± 5%) and MAP (13 ± 3%) and SVR continued to decrease (31 ± 3%) over the entire dose‐range. The increase in LVdP/dtmax at the highest dose (48 ± 4%, P < 0.05) was more pronounced than with epinine.

Adrenoceptor blockade inhibited all epinine‐induced changes, but did not affect the dopamine‐induced changes in AoBF, SVR and MAP, but attenuated the increases in HR and LVdP/dtmax.

6 Noradrenaline (NA) and adrenaline (Ad) concentrations did not change during infusion of epinine or dopamine, but NA increased by 50% within 2.5 min after stopping the infusion of epinine. After adrenoceptor blockade NA and Ad concentrations did not change during infusion of dopamine, which contrasted with a decrease of 55 ± 5% (P < 0.05) in NA during infusion of epinine.

7 Prolactin concentrations decreased gradually from 480 ± 40 pg ml−1 to 270 ± 50 pg ml−1 (P < 0.05) during infusion of epinine, but did not change significantly during dopamine infusion.

8 The differential effects of epinine and dopamine on MAP, SVR, plasma NA (before and after adrenoceptor blockade) and prolactin, leads us to conclude that in conscious pigs, epinine is a more potent α, β2 and D2‐receptor agonist, but a weaker D1‐receptor agonist than dopamine.
Inhibition of sympathetic hypertensive responses in the guinea‐pig by prejunctional histamine H3‐receptors
Authors: Hey J.A. , del Prado M. , Egan R.W. , Kreutner W. , Chapman R.W.
Published: July 2012

The effect of (R)‐α‐methylhistamine, a selective H3‐histamine receptor agonist, was examined on the neurogenic hypertension and tachycardia that is induced by stimulation of areas in the medulla oblongata of guinea‐pigs. Electrical medullary stimulation (32 Hz, 3–5 s trains, 0.5–1.0 ms square pulse, 25–400 μA) produced intensity‐dependent increases in blood pressure and a more variable tachycardia.

(R)‐α‐methylhistamine inhibited the hypertension and tachycardia due to submaximal CNS stimulation. The inhibition of hypertension by (R)‐α‐methylhistamine was dose‐dependent (10–300 μg kg−1, i.v.) and was not seen at high intensities of stimulation.

(R)‐α‐methylhistamine (300 μg kg−1, i.v.) did not attenuate the pressor response to adrenaline (1 and 3 μg kg−1, i.v.), indicating that the effect of (R)‐α‐methylhistamine was not mediated by a postjunctional action on smooth muscle.

The inhibition of CNS‐induced hypertension by (R)‐α‐methylhistamine (300 μg kg−1, i.v.) was blocked by the H3 antagonists, thioperamide (ID50 = 0.39 mg kg−1, i.v.), impromidine (ID50 = 0.22 mg kg−1, i.v.) and burimamide (ID50 = 6 mg kg−1, i.v.). The rank order potency of these antagonists is consistent with activity at the H3B receptor subtype. Chlorpheniramine (30 μg kg−1, i.v.) and cimetidine (3 mg kg−1, i.v.) did not antagonize the inhibition of CNS‐hypertension by (R)‐α‐methylhistamine.

These results suggest that (R)‐α‐methylhistamine inhibits sympathetic hypertensive responses in guinea‐pigs by activation of prejunctional H3‐receptors, possibly located on postganglionic nerve terminals. Furthermore, on the basis of the rank order potency to different H3‐antagonists, it appears that the H3B‐receptor subtype is involved with H3‐receptor responses on vascular sympathetic nerves.
Evidence for a noradrenergic innervation to α1A‐adrenoceptors in rat kidney
Authors: Blue David R. , Vimont Rachel L. , Clarke David E.
Published: July 2012

Experiments were undertaken to characterize the α1‐adrenoceptor subtype mediating vasoconstrictor responses to periarterial noradrenergic nerve stimulation (PNS) in the isolated perfused kidney of the rat.

Vasoconstrictor responses to nerve stimulation were inhibited by prazosin (10 nm), 5‐methyl‐urapidil (30 nm), and nitrendipine (1 μm) but were resistant to inhibition by chloroethylclonidine (100 μm).

5‐Methyl‐urapidil (30 nm), chloroethylclonidine (100 μm) and nitrendipine (1 μm) did not inhibit the neuronal release of tritium from nerves loaded with [3H]‐noradrenaline.

The results suggest that renovascular α1A‐adrenoceptors receive a noradrenergic innervation and that the innervated receptors are coupled to dihydropyridine‐sensitive calcium channels.
Bradykinin B2 receptor‐mediated phosphoinositide hydrolysis in bovine cultured tracheal smooth muscle cells
Authors: Marsh Katrina A. , Hill Stephen J.
Published: July 2012

Bovine tracheal smooth muscle cells were established in culture to study agonist‐induced phosphoinositide (PI) hydrolysis in this tissue.

Bradykinin (0.1 nm‐10 μm) evoked a concentration‐dependent increase (log EC50 (m) = −9.4 ±0.2; n = 8) in the accumulation of total [3H]‐inositol phosphates in cultured tracheal smooth muscle cells whereas the selective B1 receptor agonist des‐Arg9‐bradykinin (10 μm) was significantly less effective (16% of bradykinin maximal response; relative potency = 0.2 with respect to bradykinin = 100).

The bradykinin‐induced increase in PI hydrolysis was unaffected by the B1 receptor antagonist des‐Arg9[Leu8]‐bradykinin (1 nm‐1 μm) but showed marked attenuation in the presence of the B2 receptor antagonists d‐Arg,[Hyp3,d‐Phe7]‐bradykinin (10 nm‐10 μm) or d‐Arg[Hyp3,Thi5,8,d‐Phe7]‐bradykinin (10 nm‐10 μm). The estimated KB values obtained for these two compounds, assuming competitive antagonism, were 40 ± 14 nm and 8.6 ± 2.8 nm for d‐Arg,[Hyp3,d‐Phe7]‐bradykinin and d‐Arg[Hyp3,Thi5,8,d‐Phe7]‐bradykinin respectively.

We conclude that bradykinin B2 receptors are expressed in cultured bovine tracheal smooth muscle cells and are coupled to PI hydrolysis mechanisms.
Involvement of multiple receptors in the biological effects of calcitonin gene‐related peptide and amylin in rat and guinea‐pig preparations
Authors: Giuliani Sandro , Wimalawansa Sunil J. , Maggi Carlo Alberto
Published: July 2012

The activity of rat α and β calcitonin gene‐related peptide (CGRP) as compared to the structurally related peptide, rat amylin, has been investigated in the guinea‐pig isolated left atrium (electrically driven), in mucosa‐free strips from the base of the guinea‐pig urinary bladder and in the rat isolated vas deferens (pars prostatica). The antagonist activity of the C‐terminal fragment of human αCGRP, αCGRP(8–37), was also investigated.

In the guinea‐pig isolated left atrium the three peptides produced a concentration‐related positive inotropic effect, amylin being about 16 and 31 times less potent than α or βCGRP, respectively. Human αCGRP(8–37) produced a rightward displacement of the log concentration‐response curve to the three agonists tested, without depression of maximal response attainable. Apparent pKB values calculated on the basis of the displacement produced by 1 μm human αCGRP(8–37) indicated an agonist‐independent affinity of the antagonist (6.66 ± 0.11 for αCGRP, 6.42 ± 0.17 for βCGRP and 6.95 ± 0.11 for amylin).

In the guinea‐pig isolated urinary bladder, α or βCGRP or amylin produced a concentration‐related inhibition of twitch contractions evoked by train electrical field stimulation (10 Hz frequency, 0.25 ms duration at 100 V for 0.5 s every 60 s). Amylin was about 100 times less potent than α or βCGRP. Human αCGRP(8–37) (3 μm) did not significantly affect the inhibitory action of the three agonists tested.

In the rat isolated vas deferens, α or βCGRP or amylin produced a concentration‐related inhibition of twitch contractions evoked by electrical field stimulation (0.2 Hz frequency, 0.5 ms duration at 60 volts). Amylin was about 100 times less potent than α or βCGRP. Human αCGRP(8–37) at 3 μm did not significantly affect the inhibitory action of amylin and at 3 μm antagonized the responses to rat α and βCGRP with apparent pKB values of 5.86 ± 0.15 and 6.11 ± 0.13, respectively.

These findings indicate that multiple receptors mediate the actions of peptides of the CGRP/amylin family in the preparations investigated. In the guinea‐pig atrium both α and β forms of rat CGRP as well as amylin act by stimulating a single class of receptors which are sensitive to the inhibitory action of human αCGRP(8–37). In rat isolated vas deferens, at least two receptors could be present, one activated by α and βCGRP and partially sensitive to human αCGRP(8–37) and another which is sensitive to amylin but not recognised by human αCGRP(8–37). This latter type of receptor could be entirely responsible for the action of the agonists in the guinea‐pig urinary bladder.
Electrophysiological effects of CRE‐1087 in guinea‐pig ventricular muscles
Authors: Delpón Eva , Valenzuela Carmen , Pérez Onésima , Tamargo Juan
Published: July 2012

The electrophysiological effects of CRE‐1087, a new antiarrhythmic drug, were studied in guinea‐pig papillary muscles.

CRE‐1087 (10−7 m‐10−4 m) produced a concentration‐dependent decrease in the action potential amplitude and Vmax of the upstroke without altering the action potential duration or the resting membrane potential.

At 5 × 10−6 m, CRE‐1087 produced a 5.0 ± 1.0% tonic Vmax block and this value was not modified at the different rates of stimulation tested. In the presence of CRE‐1087, trains of stimuli at rates between 0.5 and 3 Hz led to an exponential decline in Vmax (frequency‐dependent Vmax block) which augmented at higher rates of stimulation. At 2 Hz the onset kinetics of the frequency‐dependent Vmax block was fitted by a monoexponential function being the K value 0.099 ± 0.012 AP−1. The time constant for the recovery of Vmax from the frequency‐dependent block was prolonged to 18.3 ± 1.5 s.

CRE‐1087 (5 × 10−6 m) did not shift the membrane responsiveness curve.

CRE‐1087 had no effect on the characteristics of the slow action potentials elicited by isoprenaline in ventricular fibres depolarized by 27 mm KCl, which suggested that CRE‐1087 did not exhibit class IV (Ca antagonist) antiarrhythmic actions.

6 The slow onset and the slow offset kinetics of frequency‐dependent Vmax block during repetitive activity suggested that in guinea‐pig ventricular muscle fibres CRE‐1087 exhibited class Ic antiarrhythmic actions.
Possible mechanisms of inhibition with atropine against noradrenaline‐induced contraction in the rabbit aorta
Authors: Satake Nobuhiro , Kiyoto Sumio , Shibata Shoji , Gandhi Vijayalakshmi , Jones David J. , Morikawa Masako
Published: July 2012

In the rabbit isolated aorta, atropine (3 × 10−6 m‐10−4 m) inhibited contractile response to noradrenaline without affecting contraction to KCl.

In the presence of contraction to noradrenaline, atropine (3 × 10−7 m‐10−4 m) caused concentration‐dependent relaxation. Pretreatment with theophylline (10−3 m) potentiated the relaxant action of atropine. Relaxation to atropine was not affected by the specific guanosine 3′:5′‐cyclic monophosphate phosphodiesterase inhibitor, M & B 22,948 (10‐4 m), tetraethylammonium (10 mm), indomethacin (10−5 m), propranolol (10−7 m), nifedipine (10−6 m) or removal of the endothelium.

Relaxation to either atropine or prazosin was not affected by preincubation with prazosin and atropine, respectively.

In Ca2+‐free medium containing EGTA and nifedipine, atropine (10−7 m‐10−4 m) inhibited the residual noradrenaline response more than the subsequent Ca2+‐induced contraction. Pretreatment with either theophylline (10−3 m), forskolin (3 × 10−7 m) or a low concentration of prazosin (3 × 10−9 m) also inhibited the residual contraction to noradrenaline and Ca2+. The effect of combined treatment of atropine and any of these agents was much greater than with each individual agent.

Atropine (10−6 m‐10−4 m) also inhibited increases in the level of inositol monophosphates (IP) in response to noradrenaline. Theophylline (10−3 m) and a low concentration of prazosin (3 × 10−9 m) also inhibited IP formation. Combined with atropine, the effect was much greater than with each of these agents individually.

6 Atropine did not affect adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) levels in the aorta and also failed to displace specific [3H]‐prazosin binding.

7 These results suggest the possibility that smooth muscle relaxation to atropine may be due to the inhibition of phosphoinositide metabolism. The relaxation is not apparently due to an action of atropine on α1‐adrenoceptors, or a change in the level of cyclic AMP.
Thimerosal blocks stimulated but not basal release of endothelium‐derived relaxing factor (EDRF) in dog isolated coronary artery
Authors: Crack Peter , Cocks Thomas
Published: July 2012

The effect of an acetly‐coA lysolecithin acyltransferase inhibitor, thimerosal, on the release of endothelium‐derived relaxing factor (EDRF) was examined in the greyhound isolated coronary artery.

Thimerosal (1–10 μm) relaxed fully, ring segments of coronary artery which were contracted with the thromboxane A2‐mimetic, U46619 (30 nm). The response was endothelium‐dependent, slow in both onset and time to reach maximum. The maximum relaxation to the highest concentration of thimerosal (10 μm) was maintained for 10–20 min before the tissue slowly regained active force (1–2 h) to the same or higher level as that prior to the addition of thimerosal. At this time the endothelium‐dependent relaxation responses to acetylcholine (ACh), substance P (SP), bradykinin (BK) and the calcium ionophores, ionomycin and A23187 were abolished. The endothelium‐dependent contractions to the nitric oxide synthase inhibitors, NG‐nitro‐l‐arginine (l‐NNA; 10–100 μm) and NG‐monomethyl‐l‐arginine (l‐NMMA: 10–100 μm), however, were unaffected.

Thimerosal (10 μm) did not affect the relaxation curve to sodium nitroprusside (SNP) nor the contraction curve to the thromboxane A2‐mimetic, U46619.

Both the relaxation response to thimerosal and the selective block of the relaxation responses to stimulated EDRF release were unaffected by either indomethacin (10 μm) or superoxide dismutase (150 u ml−1).

l‐NNA (100 μm) significantly blocked the relaxation curves to thimerosal and A23187 but not that to SNP.

6 Abolition of stimulated EDRF‐mediated responses with thimerosal was unlikely to result from maximal and maintained stimulation of EDRF release even when active U46619‐induced force had returned to pre‐thimerosal levels, since the relaxation curves to glyceryl trinitrate (GTN) and SNP were markedly attenuated in the presence of SNP and GTN respectively when active force was restored with endothelin‐1 (ET‐1).

7 Melittin (1 μm), ionomycin (1 μm) and A23187 (1 μm) each had selective effects on stimulated but not basal EDRF responses, similar to those of thimerosal.

8 We propose that stimulated but not ‘basal’ release of EDRF is dependent on the release of arachidonic acid or one of its non‐cyclo‐oxygenase metabolites, possibly by Ca2+‐dependent activation of phospholipase A2.
Effects of nitric oxide synthase inhibitors, l‐NG‐nitroarginine and l‐NG‐nitroarginine methyl ester, on responses to vasodilators of the guinea‐pig coronary vasculature
Authors: Vials Amanda , Burnstock Geoffrey
Published: July 2012

The effects of l‐NG‐nitroarginine (l‐NOARG) and l‐NG‐nitroarginine methyl ester (l‐NAME) on vasodilatation induced by ATP, substance P, 5‐hydroxytryptamine (5‐HT), bradykinin and sodium nitroprusside (SNP) were examined in the guinea‐pig coronary bed, by use of a Langendorff technique. The effects of these inhibitors of nitric oxide synthesis were assessed on their ability to inhibit both the amplitude and the area of the vasodilator response.

The vasodilator responses evoked by low doses of 5‐HT (5 × 10−10−5 × 10−8 mol) were almost abolished by l‐NAME and l‐NOARG (both at 10−5, 3 × 10−5 and 10−4 m), although l‐NOARG (3 × 10−5 m) was significantly less potent than l‐NAME (3 × 10−5 m) as an inhibitor of vasodilator responses to 5‐HT (5 × 10−8 mol).

The vasodilator responses evoked by substance P (5 × 10−12−5 × 10−9 mol) were reduced in the presence of l‐NAME and l‐NOARG (both at 10−5 and 3 × 10−5 m). The response to substance P was almost abolished by l‐NAME and l‐NOARG (both at 10−4 m).

The amplitude of the vasodilator responses to ATP (5 × 10−11 and 5 × 10−9−5 × 10−7 mol) was little affected by either l‐NAME or l‐NOARG (both at 10−5, 3 × 10−5 and 10−4 m). However, the area of the response to ATP (5 × 10−10‐5 × 10−7 mol) was inhibited by l‐NAME (10−5, 3 × 10−5 and 10−4 m) and to a lesser extent by l‐NOARG (10−5 and 10−4 m).

The amplitude and area of the vasodilator responses to bradykinin (5 × 10−12−5 × 10−11 mol) were reduced, but not abolished, by l‐NOARG and l‐NAME.

6 Neither the amplitude nor area of the responses to sodium nitroprusside (5 × 10−10−5 × 10−7 mol) were inhibited by either l‐NAME or l‐NOARG (both at 10−5 and 3 × 10−5 m).

7 It is concluded that in the guinea‐pig coronary vasculature, the vasodilatation evoked by substance P and low doses of 5‐HT is mediated almost exclusively via nitric oxide, whereas the vasodilatations evoked by ATP and bradykinin appear to involve other mechanisms in addition to the release of nitric oxide. l‐NAME was a more effective agent than l‐NOARG in inhibiting the vasodilator actions of 5‐HT and ATP in this preparation.
Endothelium‐dependent modulation of resistance vessel contraction: studies with NG‐nitro‐l‐arginine methyl ester and NG‐nitro‐l‐arginine
Authors: Bennett Michael A. , Watt Pamela A.C. , Thurston Herbert
Published: July 2012

The effect of NG‐nitro‐l‐arginine methyl ester (l‐NAME) and NG‐nitro‐l‐arginine (l‐NOARG) on noradrenaline (NA)‐induced contractility and acetylcholine (ACh)‐induced endothelium‐dependent relaxation was studied in rat mesenteric resistance arteries.

Third order branches of mesenteric arteries were dissected and mounted on two forty micron wires in a Mulvany myograph.

Incubation with l‐NAME and l‐NOARG (10 μm) caused a time‐dependent shift in the 50% response to NA (ED50) (0.01 μm‐10 μm) but was not associated with an increase in the maximum contractile response.

l‐NAME and l‐NOARG (10 μm) caused a time‐dependent inhibition of ACh (1 μm)‐induced relaxation with a maximum effect after 120 min.

Following endothelium removal, incubation with either l‐NAME or l‐NOARG caused no significant shift in the ED50, although the residual relaxation response to ACh (1 μm) was further attenuated.

6 Incubation with the cylco‐oxygenase inhibitor, indomethacin, enhanced the relaxation to ACh and reduced the inhibitory effects of l‐NAME and l‐NOARG.

7 In conclusion, l‐NAME and l‐NOARG are potent inhibitors of acetylcholine‐induced endothelium‐dependent relaxation in mesenteric resistance arteries. The shift in ED50 associated wtih these inhibitors suggests a probable role for the endothelium in modulating the contractility of the resistance vasculature.
Evidence for the absence of a functional role for muscarinic M2 inhibitory receptors in cat trachea in vivo: contrast with in vitro results
Authors: Killingsworth C.R. , Yu Mingfu , Robinson N.E.
Published: July 2012

. The effect of the selective muscarinic M2 receptor antagonist, gallamine and the selective M2 receptor agonist, pilocarpine, on airway constriction induced by vagal stimulation was studied in anaesthetized cats. In addition, the effect of gallamine on contraction of cat isolated tracheal and bronchi preparations induced by electrical field stimulation was also investigated.

. In in vivo experiments, extrathoracic airway constriction was measured with an electromechanical caliper that was attached to the outer surface of tracheal ring 4. Intrathoracic airway constriction was determined by measuring the changes in total lung resistance and dynamic compliance during vagal stimulation.

. Intravenous gallamine (0.1, 1, and 10 mg kg−1) augmented the rise in total lung resistance induced by vagal stimulation in a dose‐ and frequency‐dependent manner. At stimulation frequencies of 8 and 12 Hz the fall in dynamic compliance provoked by vagal stimulation was also significantly increased by gallamine (10 mg kg−1). Gallamine was without effect on airway constriction induced by acetylcholine.

. Vagal stimulation at 4 Hz produced significant tracheal constriction, but the amount of constriction did not change following injection of increasing doses of gallamine. Similarly, there was no difference in tracheal constriction at any frequency of stimulation (0.5–16 Hz) when frequency‐response curves before and after gallamine injection (10 mg kg−1) were compared.

. Pilocarpine (0.01–10 μg kg−1, i.v.) diminished changes in total lung resistance and dynamic compliance induced by vagal stimulation, an effect that was reversed by gallamine (10 mg kg−1, i.v.). Vagally‐induced tracheal constriction was not significantly affected by any dose of pilocarpine, nor was it modified by gallamine (10 mg kg−1) given subsequently.

. Atropine (0.5 mg kg−1) completely blocked tracheal constriction induced by vagal stimulation, indicating that the changes in tracheal ring diameter provoked by stimulation were mediated by muscarinic receptors and that intravenous drugs could reach the cervical trachealis muscle.

. In vitro tissue bath studies demonstrated a significant leftward shift of the frequency‐response curve to electrical field stimulation in both tracheal strips and bronchial rings following gallamine (10−1m) administration.

. Although the functional presence of muscarinic M2 autoreceptors was demonstrated in feline isolated tracheal and bronchial preparations, a corresponding functional role was not detected in cat trachea in vivo. This was despite repeated demonstration of muscarinic M2 receptor‐mediated limitation of airway constriction of intrathoracic airways in vivo.
Characterization of receptors involved in the direct and indirect actions of prostaglandins E and I on the guinea‐pig ileum
Authors: Lawrence Ruth A. , Jones R.L. , Wilson N.H.
Published: July 2012

. A study of the effects of prostaglandin E2 (PGE2) and eleven synthetic analogues on the guinea‐pig isolated ileum preparation has revealed three distinct contractile actions, each associated with a different prostaglandin E (EP‐) receptor subtype. In addition, PGI2 (prostacyclin) and its stable analogues can activate prostaglandin I (IP‐) receptors to elicit both contraction and relaxation of the ileum.

. Two of the PGE actions involve direct stimulation of the smooth muscle, being unaffected by 1 μm morphine treatment. One action is blocked by AH 6809 at micromolar concentrations and ICI 80205 and 16,16‐dimethyl PGE2 are particularly potent agonists. Activation of EP1‐receptors appears to be involved. The second action is unaffected by AH 6809; sulprostone and MB 28767 are potent agonists. Comparison with agonist potency rankings on the guinea‐pig vas deferens indicates that EP3‐receptors may be involved.

. The third PGE effect and the stimulant PGI effect are blocked by morphine, indicating enteric neurones and/or sensory nerve terminals as sites of action. EP2‐receptors may be involved in the PGE action, in view of the marked effect of morphine on the contractile actions of misoprostol, 11‐deoxy PGE2‐1‐alcohol, 11‐deoxy PGE1 and butaprost, all of which show some selectivity for EP2‐receptors. The PGI action is most easily studied with cicaprost (EC25 = 1.3 nm), since iloprost, carbacyclin and to a lesser extent PGI2 also have agonist activity at EP1‐receptors.

. The contractile action of 17‐phenyl‐ω‐trinor PGE2 on the ileum is unaffected by morphine. Since this analogue shows only weak agonist activity on the rabbit jugular vein (EP2 preparation) and guinea‐pig vas deferens (EP3), it may be a more useful standard agonist than PGE2 in EP1‐receptor studies.

. In the presence of morphine and AH 6809, cicaprost inhibits histamine‐induced contractions (IC25 = 22 nm). PGI2 and iloprost show mixed inhibitory/potentiating actions, whereas carbacyclin only potentiates histamine contractions. This IP‐receptor‐mediated inhibition may account for the bell‐shaped log concentration‐response curve of cicaprost (no inhibitors present) and the very marked block of iloprost‐induced contractions by AH 6809.

. We have found no evidence for either IP‐receptors mediating direct contraction or EP‐receptors mediating inhibition of the ileum longitudinal smooth muscle, as has been suggested in the literature.

. In view of the complexity of prostanoid action on the guinea‐pig ileum we feel that the preparation must be used with caution to ascertain the EP1 agonist or antagonist potencies of novel compounds.
The effects of chronic treatment with the dihydropyridine, Bay K 8644, on hyperexcitability due to ethanol withdrawal, in vivo and in vitro
Authors: Whittington M.A. , Butterworth A.R. , Dolin S.J. , Patch T.L. , Little H.J.
Published: July 2012

. The effects of chronic treatment with the dihydropyridine, Bay K 8644, were studied on the ethanol withdrawal syndrome, in vivo and in vitro.

. Addition of racemic Bay K 8644 to the drinking mixture, throughout the chronic ethanol treatment, decreased the behavioural excitability seen during ethanol withdrawal in vivo.

. All the signs of hyperexcitability in field potentials in the isolated hippocampal slice, caused by ethanol withdrawal, were decreased by the chronic administration of Bay K 8644.

. These effects resembled those previously reported for chronic administration of calcium channel antagonists; racemic Bay K 8644 has both calcium channel activating and antagonist properties.

. Measurement of brain levels of Bay K 8644 at the end of the chronic treatment showed that the compound reached micromolar concentrations during the treatment, but none could be detected in the tissues at the time of the above measurements.

. It is possible that the results might be explained by predominance of the calcium channel antagonist properties of this compound, owing to the high central concentrations achieved during the treatment. Tolerance to the calcium channel activating properties of Bay K 8644 may also have occurred during the chronic treatment.
Bradykinin receptors in the guinea‐pig taenia caeci are similar to proposed BK3 receptors in the guinea‐pig trachea, and are blocked by HOE 140
Authors: Field Julie L. , Hall Judith M. , Morton Ian K.M.
Published: July 2012

. Bradykinin (BK) receptors of the guinea‐pig taenia caeci were compared with those of the guinea‐pig trachea, a preparation proposed to possess novel BK3 receptors.

. Bradykinin‐evoked contractile responses were unaffected in both preparations by the selective BK1 receptor antagonist [des‐Arg9,Leu8]‐BK (1 μm−10 μm). The BK2 receptor antagonists, d‐Arg‐[Hyp3,d‐Phe7]‐BK and d‐Arg‐[Hyp3,Thi5,8,d‐Phe7]‐BK, both had low affinities (apparent pKB estimates < 6) which did not differ significantly between the two preparations (P > 0.05). In contrast, the novel bradykinin receptor antagonist d‐Arg‐[Hyp3,Thi5,d‐Tic7,Oic8]‐BK (HOE 140) potently antagonized responses to bradykinin with relatively high affinity (apparent pKB = 8.42 ± 0.15 and 8.94 ± 0.16 in the taenia caeci, and trachea, respectively).

. We conclude that the bradykinin receptors in the guinea‐pig taenia caeci have similar recognition properties to those present in the guinea‐pig trachea, and in this respect the taenia caeci represents a useful preparation for the further study of proposed novel BK3 receptors.
Influence of NG‐nitro‐l‐arginine methyl ester on vagally induced gastric relaxation in the anaesthetized rat
Authors: Lefebvre R.A. , Hasrat J. , Gobert A.
Published: July 2012

. The influence of the nitric oxide (NO) biosynthesis inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME) on the gastric relaxation induced by peripheral vagal stimulation was investigated in the anaesthetized rat.

. Peripheral vagal stimulation (10 Hz, 10 V, 1 ms for 20 s) induced a reproducible biphasic response: a short‐lasting increase followed by a more pronounced decrease in intragastric pressure. This response also occurred in reserpinized animals (5 mg kg−1, i.p., 24 h before the experiment) while atropine (1 mg kg−1, i.v.) abolished the initial increase in intragastric pressure.

. l‐NAME (1–30 mg kg−1, i.v.) induced an increase in arterial blood pressure. l‐NAME (1 mg kg−1, i.v.) had no influence on the vagally induced gastric response while l‐NAME (10 and 30 mg kg−1 i.v.) significantly changed it: the initial increase in intragastric pressure was enhanced while the decrease in intragastric pressure was reduced or abolished. NG‐nitro‐l‐arginine (l‐NNA, 10 mg kg−1, i.v.) had the same effect.

. An i.v. infusion of phenylephrine (10 μg kg−1 min−1) inducing a pressor response similar to that produced by l‐NAME (30 mg kg−1, i.v.) did not influence the vagal gastric response. Infusion of l‐arginine (300 mg kg−1 bolus, then 100 mg kg−1 h−1) starting 30 min beforehand, reduced the pressor effect and prevented the influence of l‐NAME (10 mg kg−1, i.v.) on the vagal gastric response. After injection of both atropine (1 mg kg−1, i.v.) and l‐NAME (30 mg kg−1, i.v.), the vagally induced decrease in intragastric pressure was similar to that obtained under control conditions.

. These results are consistent with NO being released and inducing gastric relaxation during peripheral vagal stimulation. In addition to NO, another inhibitory non‐adrenergic non‐cholinergic neurotransmitter is released.
Effect of dihydropyridines on calcium channels in isolated smooth muscle cells from rat vena cava
Authors: Mironneau J. , Yamamoto T. , Sayet I. , Arnaudeau S. , Rakotoarisoa L. , Mironneau C.
Published: July 2012

. Whole‐cell patch‐clamp method was applied to single smooth muscle cells freshly isolated from the rat inferior vena cava.

. Depolarizing pulses, applied from a holding potential of − 90 mV, activated both Na+ and Ca2+ channels. The fast Na+ current was inhibited by nanomolar concentrations of tetrodotoxin (TTX). The slow Ba2+ current (measured in 5 mm Ba2+ solution) was inhibited by Cd2+ and modulated by dihydropyridine derivatives. When the cells were held at a holding potential of −80 mV, racemic Bay K 8644 increased the Ba2+ current (ED50 = 10 nm) while racemic isradipine inhibited the current (IC50 = 21 nm).

. The voltage‐dependency of isradipine blockade was assessed by determining the steady‐state availability of the Ca2+ channels. From the shift of the inactivation curve in the presence of isradipine, we calculated a dissociation constant of 1.11 nm for inactivated Ca2+ channels. Scatchard plots of the specific binding of (+)‐[3H]‐isradipine obtained in intact strips incubated in 5.6 mm or 135 mm K+ solutions confirmed the voltage‐dependency of isradipine binding.

. Specific binding of (+)‐[3H]‐isradipine was completely displaced by unlabelled (±)‐isradipine, with an IC50 of 15.1 nm. This value is similar to the IC50 for inhibition of the Ba2+ current (21 nm) in cells maintained at a holding potential of −80 mV.

. Bay K 8644 had no effects on the Ba2+ current kinetics during a depolarizing test pulse. The steady‐state inactivation‐activation curves of Ba2+ current were not significantly shifted along the voltage axis.

. The present data suggest the existence of two distinct dihydropyridine binding sites which can be bound preferentially by agonist or antagonist derivatives.