bluuebunny/crossref_metadata_2025 huggingface dataset:
Actions mediated by P2‐purinoceptorsubtypes in the isolated perfused mesenteric bed of the rat
Authors: Ralevic V. , Burnstock G.
Published: July 2012

The effects of adenosine 5′‐triphosphate (ATP) and its analogues on the perfusion pressure of the isolated mesenteric bed of the rat were examined in preparations at resting tone, and with tone raised by noradrenaline.

In the preparations at resting tone, the effect of the analogues was to produce vasoconstriction, their rank order of potency being α,β‐methylene ATP > 2‐methylthio ATP > ATP.

In raised tone preparations, dose‐dependent vasodilatations were produced by ATP and 2‐methylthio ATP although, at the highest doses tested, responses decreased in magnitude. The rank order of potency of the analogues in eliciting this vasodilator response was 2‐methylthio ATP > ATP, while α,β‐methylene ATP was without effect.

Following desensitization of contractile responses to α,β‐methylene ATP, contractile responses to ATP and 2‐methylthio ATP were abolished while their relaxant responses were potentiated.

Removal of the endothelium with sodium deoxycholate totally abolished the vasodilator responses and enhanced the contractile responses.

It is concluded that, in the rat mesentery, ATP and its analogues cause vasoconstriction via P2x‐purinoceptors and vasodilatation via P2y‐purinoceptors and that these are located on the smooth muscle and on the endothelium, respectively.
Endothelium‐dependent modulation of the pressor activity of arginine vasopressin in the isolated superior mesenteric arterial bed of the rat
Authors: Randall Michael D. , Kay Alexander P. , Hiley C. Robin
Published: July 2012

Pressor responses to arginine vasopressin (AVP) were determined in the rat isolated superior mesenteric arterial bed perfused with Krebs‐Henseleit solution and compared with those to noradrenaline.

In control preparations the maximum pressor response to the peptide was 34 ± 3 mmHg and the ED50 was 21 ±4mu (n = 11). The maximal pressor response to noradrenaline (30 μg) was 100 ± 6 mmHg (n = 8). After removal of the functional endothelium with the detergent CHAPS, the maximum pressor response to AVP increased to 64 ± 4 mmHg and the ED50 decreased to 7.7 ± 2.0 mu (n = 11) but the response to 10 μg noradrenaline was unaffected.

Nordihydroguaiaretic acid (2.5 μm) significantly increased the maximum pressor response to AVP from 41 ±2 mmHg to 86 ±8 mmHg (n = 9); the ED50 was unchanged. Methylene blue (50 μm) also increased the maximum response from 41 ± 3 mmHg to 87 + 13 mmHg (n = 8) without affecting the ED50. Neither treatment significantly affected the response to 10 μg noradrenaline.

Neither indomethacin (10 μm) nor BW755C (10 μm) had significant effects upon either the maximal response or ED50 for AVP nor did they affect the response to 10 μg noradrenaline.

In 6 preparations SKF‐525A significantly increased both the ED50, from 9.8 ± 2.1 to 22 ± 2 mu, and the maximum response, from 36 ± 2 to 70 ± 3 mmHg.

It is concluded that the pressor response to AVP in this vascular bed is modulated, in the presence of functional endothelium, by the simultaneous release of endothelium‐derived relaxing factor.
Flunarizine inhibits endothelium‐dependent hypoxic facilitation in canine coronary arteries through an action on vascular smooth muscle
Authors: Iqbal Amjad , Vanhoutte Paul M.
Published: July 2012

Hypoxia augments contractile responses to several vasoactive agents in canine isolated coronary arteries with intact endothelium. Calcium antagonists inhibit the further increases in tension caused by hypoxia. The present experiments were designed to determine whether the calcium‐antagonist flunarizine would inhibit hypoxic contractions in isolated blood vessels through an action on the endothelium or on the vascular smooth muscle.

Rings of canine coronary arteries, with or without endothelium, were suspended at optimal length for isometric tension recording in organ chambers filled with modified Krebs‐Ringer bicarbonate solution.

Hypoxia (95% N2 and 5% CO2) augmented contractile responses to prostaglandin F2α (2 × 10−6m); removal of the endothelium abolished this hypoxic facilitation.

Flunarizine (5 × 10−5‐5 × 10−7 m) exerted a long‐lasting inhibition of the hypoxic facilitation in a concentration‐dependent manner. Flunarizine did not inhibit the response to prostaglandin F2α.

To differentiate between the response of smooth muscle and the endothelium, strips of coronary arteries without endothelium were layered with strips with or without endothelium. Hypoxia augmented contractions only in layered preparations with endothelium. Flunarizine prevented the hypoxic contractions in layered preparations in which only the smooth muscle was treated with flunarizine. In contrast, when only the endothelium was treated, no or minimal inhibition of the hypoxic contraction occurred with flunarizine (10−5 and 5 × 10−5 m, respectively).

These experiments indicate that the calcium antagonist flunarizine inhibits endothelium‐dependent hypoxic facilitation in canine coronary arteries primarily through its action on vascular smooth muscle.
Ventral tegmental area: site through which dopamine D2‐receptor agonists evoke behavioural and electrocortical sleep in rats
Authors: Bagetta Giacinto , de Sarro Giovambattista , Priolo Elisabetta , Nisticò Giuseppe
Published: July 2012

In freely moving rats the effects on behaviour and electrocortical (ECoG) spectrum power of some dopamine agonists, i.e. apomorphine and (+)−3PPP, given directly into different areas of the rat brain were studied. In particular, dopamine agonists were microinfused in the ventral tegmental area (VTA) and substantia nigra (SN) or into the caudate nucleus, n. accumbens and prefrontal cortex. The ECoG spectrum power effects were continuously analysed by means of a computerized Berg‐Fourier analyser as total spectrum power and power in preselected frequency bands.

Apomorphine and (+)−3PPP (0.01, 0.1 and 1.0 nmol) given bilaterally into the VTA produced behavioural and ECoG sleep in a dose‐dependent fashion. A statistically significant (P < 0.01) increase in ECoG total spectrum power with a predominant increase in the lower frequency bands (0.25–3, 3–6 and 6–9 Hz) occurred. No behavioural and ECoG changes were evoked by the same doses of apomorphine bilaterally microinfused into the SN or into the caudate nucleus or by (+)−3PPP (1.0 nml) microinjected into the n. accumbens or applied onto the prefrontal cortex.

Behavioural and ECoG sleep was also induced in rats after systemic administration of apomorphine (263 nmol kg−1, i.p.).

The behavioural and ECoG spectrum power effects of apomorphine (1.0 nmol) bilaterally microinfused into the VTA were prevented by a previous microinjection into the same site of (−)‐sulpiride (9.8 nmol). Similarly, behavioural and ECoG effects evoked by (+)−3PPP (0.1 nmol) given bilaterally into the VTA, were completely antagonized by a previous injection into the same site of haloperidol (16 pmol given 10 min before). In contrast, pretreatment with SCH 23390 (50 μg kg−1, s.c.), a selective antagonist at dopamine D1‐receptors, was unable to antagonize the behavioural and ECoG spectrum power effects of (+)−3PPP.

Soporific effects induced by systemic administration of apomorphine were antagonized by (−)‐sulpiride (9.8 nmol) given bilaterally into the VTA 10 min before, whereas, yohimbine (1.3 nmol), (an antagonist at α2‐adrenoceptors) bilaterally microinfused into the VTA, was ineffective in this respect.

The present experiments provide evidence suggesting that stimulation of dopamine D2‐receptors located at the cell body level and/or the dendrites of dopaminergic neurones in the VTA may represent the mechanism through which apomorphine or (+)−3PPP exert their soporific effects in rats.
Centrally acting hypotensive agents with affinity for 5‐HT1A binding sites inhibit forskolin‐stimulated adenylate cyclase activity in calf hippocampus
Authors: Schoeffter Philippe , Hoyer Daniel
Published: July 2012

A number of centrally acting hypotensive agents and other ligands with high affinity for 5‐hydroxytryptamine1A (5‐HT1A) recognition sites have been tested on forskolin‐stimulated adenylate cyclase activity in calf hippocampus, a functional model for 5‐HT1A‐receptors.

Concentration‐dependent inhibition of forskolin‐stimulated adenylate cyclase activity was elicited by the reference 5‐HT1‐receptor agonists (mean EC50 value, nm): 5‐HT (22), 5‐carboxamidotryptamine (5‐CT, 3.2), 8‐hydroxy‐2‐(di‐n‐propylamino)‐tetralin (8‐OH‐DPAT, 8.6), N,N‐dipropyl‐5‐carboxamidotryptamine (DP‐5‐CT, 2.3), l‐[2‐(4‐aminophenyl)ethyl]‐4‐(3‐trifluoromethylphenyl)‐piperazine (PAPP or LY 165163, 20), 5‐methoxy‐3‐(l,2,3,6‐tetrahydro‐4‐pyridinyl)−1H indole (RU 24969, 20), buspirone (65) and ipsapirone (56). amounted to 18–20% inhibition for all but the latter two agonists (14%).

The following hypotensive agents with high affinity for 5‐HT1A sites were potent agonists in this system (mean EC50 value, nm): flesinoxan (24), indorenate (99), erythro‐l‐(1‐[2‐(l,4‐benzodioxan‐2‐yl)−2‐hydroxyethyl]‐4‐piperidyl)−2‐benzimidazolinone (R 28935, 2.5), urapidil (390) and 5‐methylurapidil (3.5). The first two agents were full agonists, whereas the latter three acted as partial agonists with 60–80% efficacy.

Metergoline and methysergide behaved as full agonists and cyanopindolol as a partial agonist with low efficacy. Spiroxatrine and 2‐(2,6‐dimethoxyphenoxyethyl)aminomethyl‐l,4‐benzodioxane (WB 4101) which bind to 5‐HT1A sites with nanomolar affinity, were agonists and inhibited potently forskolin‐stimulated adenylate cyclase in calf hippocampus, showing mean EC50 values of 23 and 15 nM, respectively. Spiroxatrine and WB 4101 yielded 90% and 50% efficacy, respectively.

Spiperone and methiothepin (each 1 μm) caused rightward shifts of the concentration‐effect curve to 8‐OH‐DPAT, without loss of the maximal effect, as did the partial agonist cyanopindolol (0.1 μm) and the (−)− and (+)‐enantiomers of pindolol (1 μm and 0.1 mM, respectively).

There was an excellent correlation (r = 0.90, P = 0.0001) between the pEC50 values (ranging from 6.4 to 8.7) of the 19 agonists tested at adenylate cyclase and their pKD for 5‐HT1A recognition sites. Apparent pKB values of antagonists at adenylate cyclase and their pKD values for 5‐HT1A binding sites were also significantly correlated.

This study further indicates that the 5‐HT1A recognition site and the 5‐HT receptor mediating inhibition of adenylate cyclase in hippocampus are the same. The data show that a number of centrally acting hypotensive agents with high affinity for the 5‐HT1A site are potent agonists in this model, suggesting an involvement of central 5‐HT1A‐receptors in the control of blood pressure.
Activation of a bradykinin receptor in peripheral nerve and spinal cord in the neonatal rat in vitro
Authors: Dray A. , Bettaney J. , Forster P. , Perkins M.N.
Published: July 2012

In an in vitro preparation of the neonatal rat spinal cord with attached tail, administration of bradykinin (Bk) to the spinal cord or to the tail produced depolarization of a ventral root (L3‐L5). The effect of Bk at each site was selectively and reversibly antagonized by D‐Arg [Hyp2, Thi5,8 D‐Phe7]‐Bk but could not be mimicked or antagonized by the B1‐receptorligands [des‐Arg9]‐Bk or Leu8[des‐Arg9]‐Bk, respectively. Peripherally evoked noxious responses produced by capsaicin or heat, were unaffected by either antagonist administered to the spinal cord. These data suggest that Bk‐evoked responses in the spinal cord and at peripheral nociceptors were mediated via a receptor which by definition is of the B2‐type. Additionally Bk is unlikely to be a physiological mediator of acute nociception in the spinal cord.
Induction of rat gastric damage by the endothelium‐derived peptide, endothelin
Authors: Whittle B.J.R. , Esplugues J.V.
Published: July 2012

The effect of the endogenous vasoconstrictor peptide, endothelin, on gastric mucosal integrity has been investigated in the rat. Local intra‐arterial infusion of endothelin, in picomole doses, dose‐dependently induced haemorrhagic and necrotic damage in the gastric mucosa. Such injury was not prevented by atropine, cimetidine, adrenoceptor antagonists, indomethacin, or the 5‐lipoxygenase inhibitor BW A4C. These results suggest a potential pro‐ulcerogenic role of endothelin in the pathogenesis of gastric damage and ulceration.
Age‐associated decrease in histamine‐induced vasodilatation may be due to reduction of cyclic GMP formation
Authors: Moritoki Hideki , Tanioka Asao , Maeshiba Yoshihiro , Iwamoto Takeshi , Ishida Yukio , Araki Hiromasa
Published: July 2012

The effects of aging on histamine‐induced vasodilatation and cyclic GMP production in rat thoracic aorta were investigated.

This histamine‐induced dilatation of the aorta was mediated by H1‐receptors and was dependent on the endothelium.

Histamine induced the greatest dilatation of arteries of 3–4 week old rats, progressively less of those of rats of 8 to 56 weeks old, and scarcely detectable dilatation of those of 100 week old rats.

Histamine induced cyclic GMP production in aorta from rats of 4 weeks old, with no change in the cyclic AMP level. This increase in the cyclic GMP level induced by histamine also decreased with age, being about 70% as great at 8 weeks, 50% as great at 50–60 weeks, and 10% as great at 130 weeks of age.

Removal of the endothelium completely abolished the histamine‐induced increase in cyclic GMP.

The dilator effect of nitroprusside, which enhances cyclic GMP production by stimulating guanylate cyclase directly (not indirectly via the endothelium derived relaxing factor, EDRF), also snowed age‐related attenuation.

The dilator effect of 8‐bromo cyclic GMP, which stimulates cyclic GMP‐dependent protein kinase, also decreased during aging.

These results suggest that aging reduces the ability of the endothelium to produce EDRF, which stimulates guanylate cyclase, and so decreases cyclic GMP production. Thus the decreased dilator response of the arteries to histamine during aging is probably due to both loss of endothelial function and reduction of guanylate cyclase activity. Alteration of cyclic GMP‐dependent protein kinase activity may also participate in the age‐related changes.
Noradrenaline release evoked by a physiological irregular sympathetic discharge pattern is modulated by prejunctional α‐ and β‐adrenoceptors in vivo
Authors: Kahan Thomas , Pernow John , Schwieler Jonas , Wallin B. Gunnar , Lundberg Jan M. , Hjemdahl Paul
Published: July 2012

Sympathetic nerve stimulation‐evoked overflow of endogenous noradrenaline (NA) and vasoconstriction were studied in canine blood‐perfused gracilis muscle in situ. Nerves were stimulated at an average frequency of 2 Hz (240 pulses, 120 s) with impulses derived from a recording of the normal irregular sympathetic discharge to human skeletal muscle, with regular bursts of impulses, or with the conventional continuous stimulus mode.

Variations in impulse activity were closely paralleled by changes in vascular tone. However, all stimulation patterns evoked the same integrated NA overflow and the same degree of vasoconstriction.

Blockade of β‐adrenoceptors by propranolol (0.5mgkg−1 i.v.) significantly reduced NA overflow and vasoconstriction evoked both by continuous and irregular nerve stimulation, by approximately 15–20%.

The enhancement of NA overflow following α‐adrenoceptor blockade by phenoxybenzamine (0.5mgkg−1 local i.a.) was significantly greater when evoked by continuous than by irregular nerve discharge (24 vs 14 fold). Effects were similar with irregular and regular burst activity. Half of this enhancement has been shown to be due to blockade of neuronal uptake of NA by phenoxybenzamine. Vasoconstrictor responses to all stimulation patterns were similarly reduced, but not abolished, by phenoxybenzamine.

The normal irregular sympathetic discharge seems to evoke a similar integrated NA release and equally pronounced vasoconstriction as stimulation with regular bursts or at constant frequency. We provide additional evidence for a physiological prejunctional α‐adrenoceptor‐mediated inhibition of NA release. This mechanism may be influenced by the discharge pattern. Also prejunctional β‐adrenoceptors seem to modulate NA release under physiological conditions. However, the α‐adrenoceptor‐mediated mechanism is quantitatively more important.
Effects and interactions of sensory neuropeptides on airway microvascular leakage in guinea‐pigs
Authors: Rogers Duncan F. , Belvisi Maria G. , Aursudkij Boonrut , Evans Timothy W. , Barnes Peter J.
Published: July 2012

We have studied the effect of the sensory neuropeptides substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and calcitonin gene‐related peptide (CGRP) on microvascular permeability in guinea‐pig airways in vivo and investigated whether CGRP would potentiate the effect of SP. We used the extravasation of intravenously‐injected Evans blue dye as an index of permeability.

The tachykinins SP, NKA and NKB (0.025–5.0 nmol kg−1, i.v.) significantly (P < 0.05) increased extravasation of dye in a dose‐related manner and with a similar pattern of distribution; they were most potent in the trachea and main bronchi, less potent in the larynx and intrapulmonary airways, and had little significant effect in the bladder.

SP was significantly more potent in causing extravasation of dye than NKA or NKB with ED50 values (nmol kg−1) in the range 0.04–0.1, depending on the airway level, compared with values in the range 0.3–0.7 for the neurokinins.

CGRP (0.0025–2.5 nmol kg−1, i.v.) had no significant effect on microvascular permeability and did not potentiate SP‐induced extravasation of dye.

Each neuropeptide decreased mean arterial blood pressure, indicating vasodilatation, in a dose‐related manner. Co‐injection of CGRP and SP produced additive decreases in arterial pressure.

We conclude that, in guinea‐pig airways, tachykinins increase microvascular permeability via tachykinin receptors of the NK‐1 sub‐type (indicated by an order of potency of SP > NKA = NKB) on endothelial cells. The response appears to be related to mechanisms in addition to vasodilatation. The relevance of the responses to the tachykinins in asthma is discussed.
The effects of nitroglycerin on regional myocardial contractile dysfunction produced by treadmill exercise or isoprenaline stimulation in dogs
Authors: Schneider W. , Grohs J.G. , Krumpl G. , Mayer N. , Raberger G.
Published: July 2012

To compare different methods of cardiac stress testing that are clinically applied in the management of coronary heart disease, 2 groups of dogs each were chronically instrumented and subjected to treadmill exercise or isoprenaline infusion in the presence of coronary stenosis.

It was of interest to determine differences in haemodynamic and regional myocardial contractile parameters, the response to antianginal therapy (nitroglycerin 15μgkg−1 15min−1, i.v.), and, in particular, whether this response differed according to the mode of cardiac stimulation, i.e. treadmill exercise or isoprenaline infusion.

After stenosis of the circumflex branch of the left coronary artery which affected resting myocardial function only minimally, treadmill exercise or isoprenaline infusion induced transient regional contractile dysfunction. Heart rate, arterial blood pressure, left ventricular end‐diastolic pressure and left ventricular dp/dtmax were registered and myocardial oxygen demand was calculated. Regional contractile performance was assessed by ultrasonic distance measurement in the underperfused and in a normally perfused area.

Treadmill exercise led to an increase in systolic arterial and left ventricular end‐diastolic pressure. In contrast, isoprenaline‐induced stimulation led to a decrease in diastolic arterial and left ventricular end‐diastolic pressure. Regional contractile function in the critically underperfused area showed a deterioration during both modes of stress. Nitroglycerin completely abolished stress‐induced contractile dysfunction only in the group where treadmill exercise was employed for stimulation.

The inability of nitroglycerin to prevent myocardial dysfunction in the isoprenaline group may be due to exhaustion of the arterial and/or venous vasodilator potency of nitroglycerin in the presence of adrenoceptor vasodilatation induced by isoprenaline.

These findings indicate that clinical antianginal drug testing and the evaluation of the course of disease in patients with coronary heart disease may be highly dependent on the test method chosen.
Dietary ω3 polyunsaturated fatty acids augment endothelium‐dependent relaxation to bradykinin in coronary micro vessels of the pig
Authors: Shimokawa Hiroaki , Aarhus Lawrence L. , Vanhoutte Paul M.
Published: July 2012

The effects of chronic dietary supplementation with ω3 polyunsaturated fatty acids on endothelium‐dependent relaxations were examined in isolated coronary microvessels of the pig.

Animals were maintained for four weeks with or without dietary supplementation of purified eicosapentaenoic acid (3.5 g daily) and docosahexaenoic acid (1.5 g daily). Fatty acid profiles of plasma lipids showed that only the fraction of eicosapentaenoic acid increased by the treatment, together with a decrease of that of arachidonic acid.

In the treated group, endothelium‐dependent relaxations to bradykinin were significantly augmented, while contractions to acetylcholine or relaxations to nitroprusside were unaltered.

These results indicate that dietary ω3 polyunsaturated fatty acids (mainly eicosapentaenoic acid) augment endothelium‐dependent relaxations in coronary microvessels of the pig, without changing the ability of vascular smooth muscle to contract or relax.
Interactions between angiotensin II, sympathetic nerve‐mediated pressor response and cyclo‐oxygenase products in the pithed rat
Authors: Grant T.L. , McGrath J.C.
Published: July 2012

The influence of angiotensin II (AII) on resting blood pressure and on sympathetic nerve‐mediated pressor responses in the pithed rat was investigated either by inhibiting the renin‐angiotensin system or by infusing AII.

Plasma AII levels in the pithed rat were approximately 20 fold higher than in normotensive rats.

Infusion of a subpressor dose of AII (50ngkg−1 min−1) had no effect on sympathetic nerve mediated pressor responses but a pressor dose of AII, (200ngkg−1min−1) facilitated nerve‐mediated pressor responses.

The angiotensin converting enzyme inhibitor, teprotide, and the AII‐receptor antagonist, saralasin, lowered the diastolic blood pressure and attenuated sympathetic nerve‐mediated pressor responses. There was no difference in the effects of teprotide at 1 mgkg1‐ and 10mgkg−1. Infusion of sodium nitroprusside at concentrations producing a fall in diastolic blood pressure of similar magnitude to that produced by teprotide and saralasin significantly attenuated nerve‐mediated pressor responses.

After teprotide, AII 50 mg kg−1 min −1 increased diastolic blood pressure. The inhibitory effect of teprotide on nerve‐mediated pressor responses was antagonized by this infusion of AII only if the rats were pretreated with the cyclo‐oxygenase inhibitor, flurbiprofen.

It is concluded that AII is a major determinant of vascular tone in the pithed rat and that inhibition of the renin‐angiotensin system attenuates sympathetic nerve‐mediated pressor responses at least in part through the fall in blood pressure per se. The demonstration of this is complicated by an excessive release of vasodilator prostaglandins possibly due to the infused AII. Since plasma AII levels are high, the effects of blockade of the renin‐angiotensin system will be exaggerated and so the importance of AII as a modulator of sympathetic responses will be overestimated in this model.
Microinfusion of clonidine and yohimbine into locus coeruleus alters EEG power spectrum: effects of aging and reversal by phosphatidylserine
Authors: de Sarro G.B. , Bagetta G. , Ascioti C. , Libri V. , Nisticò G.
Published: July 2012

The behavioural and electrocortical (ECoG) power spectrum effects of clonidine, and yohimbine, an agonist and an antagonist at α2‐adrenoceptors, after their unilateral microinfusion into the rat locus coeruleus (LC) in young (50–70 days old) and old (13–15 months old) rats were studied.

Clonidine (0.09, 0.19, 0.28 and 0.56 nmol) microinfused into the LC of young rats induced dose‐dependent behavioural and ECoG slow wave sleep (SWS) with a significant increase in total voltage power and power in the lower frequency bands. In contrast, yohimbine (1.3 and 2.6 nmol) infused into the LC of young rats produced ECoG desynchronization and a significant decrease in total voltage power.

In contrast to young rats, clonidine (0.19 and 0.28 nmol) given into the LC did not affect behaviour and the ECoG power spectrum in old rats. However, after higher doses of clonidine (0.56 and 1.2 nmol) a small and short‐lasting period of behavioural and ECoG SWS was still evident. Similarly, in old rats yohimbine, at a dose (1.3 nmol) which was stimulative in young animals, did not significantly affect behaviour and ECoG power spectrum. Higher doses of yohimbine (2.6 and 5.2 nmol) were required to induce behavioural and ECoG changes similar to those observed with lower doses of yohimbine in young rats.

Chronic treatment with phosphatidylserine (30mgkg−1, orally, daily for 21 and 30 days), was able gradually to restore in old rats, in comparison with a vehicle‐treated group, the responsiveness of α2‐adrenoceptors to clonidine and yohimbine given into the LC.
Biphasic effects of intra‐accumbens histamine administration on spontaneous motor activity in the rat; a role for central histamine receptors
Authors: Bristow L.J. , Bennett G.W.
Published: July 2012

The effect of intra‐accumbens injection of histamine and related compounds on the spontaneous motor activity of the rat has been investigated.

Microinjections of histamine (1–200μg) induced dose‐dependent, biphasic changes in rat activity consisting of an initial brief hypoactivity response followed by a marked hyperactivity phase. The histamine metabolite, n‐tele‐methylhistamine was without effect.

Pretreatment with the H1‐receptor antagonist mepyramine (10 μg) blocked the hypoactivity response and markedly attenuated histamine‐induced hyperactivity. In contrast, pretreatment with the H2‐receptor antagonist SKF93479 had no effect on histamine‐induced behaviour.

Microinjection of the H1‐receptor agonist 2‐thiazolylethylamine induced a marked hyperactivity response, but unlike the response to histamine, there was no initial hypoactivity. The H2‐receptor agonist dimaprit had no apparent behavioural effects following intra‐accumbens injection.

Intra‐accumbens injection of the non‐selective histamine agonists nα‐methylhistamine or nα, nα‐dimethylhistamine induced both marked hypoactivity and hyperactivity responses which were comparable with the effects of histamine.

The present results demonstrate a histamine, H1‐receptor‐mediated arousal in the nucleus accumbens which follows transitory hypoactivity, possibly due to activation of presynaptic H3‐receptors.
Nifedipine kinetics in the rat and relationship between its serum concentrations and uterine and cardiovascular effects
Authors: Downing Sandra J. , Hollingsworth M.
Published: July 2012

The kinetics of nifedipine and the relationship between its serum concentration and uterine and cardiovascular effects were investigated in 3 groups of animals. These were ovariectomized (ovx) anaesthetized non‐pregnant rats following bolus i.v. injection (400 μg kg−1) and during 300 min infusion (10 μg kg−1 min−1) and ovx, progesterone‐treated late pregnant rats during infusion. Also, the kinetics were determined in ovary‐intact late pregnant rats following bolus i.v. injection (400 μg kg−1).

Measurement of serum nifedipine concentrations after bolus i.v. injection in ovx non‐pregnant rats showed a biexponential decay with time from which the following parameters were calculated: Vβ= 300 ± 30 ml kg−1; rate constants k12 = 0.51 ± 0.18 min−1; k21 = 0.07 ± 0.02 min−1; kel = 0.10 ± 0.05 min−1; elimination clearance = 2.4 ± 0.2 (ml min−1)kg−1; t1/2α = 2.5 ± 1.0 min; t1/2β = 102 ± 15 min. In intact pregnant rats, a biexponential decay of serum nifedipine concentrations with time was also observed after bolus i.v. administration with similar parameters to non‐pregnant animals. These kinetic parameters, used to calculate serum nifedipine concentrations obtained during infusion, predicted values similar to experimental values for 180 min, but thereafter slightly underestimated experimental values.

Immediate reductions in uterine contractions, mean blood pressure and heart rate were observed following bolus i.v. injection of nifedipine to ovx non‐pregnant rats, with returns towards control values as serum nifedipine concentrations declined. IC15 values (15% change from baseline), calculated from log10 serum concentration‐response curves, of 0.3 ± 0.05 μg ml−1 for inhibition of uterine contractions, 0.8 ± 0.3 μg ml−1 for depression of blood pressure and 3.8 ± 1.0 μg ml−1 for reduction in heart rate were obtained.

In ovx non‐pregnant rats, nifedipine infusion produced a maximum reduction in integral of uterine contractions of 70% by 120 min and a maximum reduction of 15% in heart rate. Mean blood pressure was not significantly different from vehicle‐treated rats. IC15 values were 0.7 ± 0.1 μg ml−1 and 2.8 ± 0.6 μg ml−1 for inhibition of uterine contractions and heart rate respectively.

In ovx, progesterone‐treated late pregnant rats, nifedipine infusion produced similar serum concentrations to those of non‐pregnant rats but completely abolished uterine contractions by 70 min. Maximum reductions of 30% in heart rate and blood pressure were observed. IC15 values were 0.5 ± 0.1 μg ml−1 for uterine contractions, 0.9 ± 0.3 μg ml−1 for blood pressure and 1.2 ± 0.3 μg ml−1 for heart rate.

The findings suggest that the kinetics of nifedipine are similar in pregnant and non‐pregnant rats and support the idea that the drug exerts a slight selectivity for uterine inhibition relative to cardiovascular effects. The uterus of the late pregnant rat appears to be more sensitive to nifedipine than that of the non‐pregnant animal.
Tricyclic antidepressants block N‐methyl‐D‐aspartate receptors: similarities to the action of zinc
Authors: Reynolds Ian J. , Miller Richard J.
Published: July 2012

Using the radioligand [3 H]‐MK801, we have examined drug interactions with the phencyclidine recognition site of the N‐methyl‐D‐aspartate receptor.

The trycyclic antidepressants desmethylimipramine and imipramine inhibited [3 H]‐MK801 binding with IC50 values of 7.4 and 22.5 μM, respectively. Other related tricyclic antidepressants and neuroleptics were also effective but less potent.

Desmethylimipramine, imipramine and chlorimipramine slowed the dissociation rate of [3 H]‐MK801 in a similar manner to Zn2+. Phencyclidine and related compounds had no effect on the dissociation rate of [3 H]‐MK801.

Desmethylimipramine, imipramine and ketamine also prevented the Ca2+ influx into cultured cortical neurones of the rat produced by N‐methyl‐D‐aspartate.

As the actions of tricyclic antidepressants in this system are not competitive with respect to N‐methyl‐D‐aspartate, glycine or MK‐801, and as they slow the dissociation of [3 H]‐MK801, we conclude that tricyclic antidepressants may be acting at the Zn2+ recognition site on the N‐methyl‐D‐aspartate receptor.
Stimulatory and inhibitory actions of excitatory amino acids on inositol phospholipid metabolism in rat cerebral cortex
Authors: Godfrey Philip P. , Wilkins C. Jason , Tyler Wendy , Watson Stephen P.
Published: July 2012

The effects of excitatory amino acids on [3 H]‐inositol phosphate levels have been examined in rat cortical slices under basal conditions or following agonist stimulation.

Ibotenate and quisqualate provoked a substantial dose‐dependent (EC50, 30 μM and 20 μM respectively) increase in inositol phosphates; these responses were not additive suggesting a common site of action for the two amino acids. The responses to maximally effective concentrations of ibotenate and quisqualate were not blocked by verapamil, tetrodotoxin or Cd2+, indicating that these effects are not indirect. Small, but significant, increases in inositol phosphates were also seen with glutamate and N‐methyl‐DL‐aspartate (NMDLA); kainate and aspartate were ineffective.

Each excitatory amino acid tested reduced carbachol (1 mM) stimulated inositol phosphate formation. Kainate (IC50, 20 μM) and NMDLA (IC50, 20 μM) were the most effective inhibitors. Kainate also reduced the responses to noradrenaline, 5‐hydroxytryptamine and 20 mM K+.

The inhibitory action of NMDLA, but not kainate, could be reversed with the NMDA antagonists, DL‐2‐amino‐5‐phosphonovalerate (APV) and MK‐801; DL‐2‐amino‐4‐phosphonobutyrate (APB) was without effect. Since MK‐801 blocks the ion channels associated with the NMDA receptor, it appears that inhibition requires the entry of ions into the cell.

APV and MK‐801 potentiated the stimulatory response to ibotenate but had no effect on the response to quisqualate. Potentiation was presumably the result of blocking the inhibition by ibotenate mediated through NMDA receptors.

In conclusion, excitatory amino acids appear to reduce agonist‐mediated inositol phosphate formation in rat cerebral cortex by a non‐specific action, possibly including the influx of Na+ ions. In addition ibotenate and quisqualate substantially enhance inositol phosphate production: the pharmacology of the response suggests that it is mediated by a receptor distinct from previously defined excitatory amino acid receptor subtypes.
Evidence for dopaminergic co‐transmission in dog mesenteric arterial vessels
Authors: Soares‐da‐Silva P.
Published: July 2012

The overflow of dopamine and noradrenaline (NA) from the main trunk of the dog mesenteric artery and its proximal branches during prolonged depolarization (120 min) by K+ (52 mM) was quantified by high performance liquid chromatography with electrochemical detection.

K+‐induced depolarization resulted in release of both dopamine and NA. The amount of NA released from both blood vessels declined progressively throughout the experiment. In the main trunk the same pattern of release was observed for dopamine, whereas in the proximal branches the overflow of dopamine increased throughout the experiment.

The addition of phentolamine (0.2 μM) to the perifusion fluid increased the overflow of both amines. In the presence of sulpiride (1 μM) the overflow of dopamine and NA was found to be increased in the proximal branches, but not in the main trunk. The addition of phentolamine to sulpiride caused a further increase in amine overflow in proximal branches, but not in the main trunk.

The addition of α‐methyl‐p‐tyrosine (50 μM) to the perifusion fluid caused a decrease in the amounts of dopamine and NA released from both preparations. In α‐methyl‐p‐tyrosine‐treated preparations phentolamine increased amine overflow to the same extent as in experiments without tyrosine hydroxylase inhibition. The increasing effect of sulpiride on the overflow of dopamine and NA from the proximal branches was completely abolished after α‐methyl‐p‐tyrosine.

The results presented suggest that in the proximal branches of the dog mesenteric artery, dopamine β‐hydroxylase represents a rate limiting step in the synthesis of NA; dopamine, through activation of prejunctional dopamine receptors acts like a prejunctional co‐transmitter in the control of transmitter release, but only newly‐synthesized dopamine appears to be responsible for this effect.
Role of stimulatory GTP‐binding protein (Gs) in reduced β‐adrenoceptor coupling in the femoral artery of spontaneously hypertensive rats
Authors: Asano Masahisa , Masuzawa Kaoru , Matsuda Tomohiro
Published: July 2012

Arterial relaxant responses to β‐adrenoceptor agonists are decreased in spontaneously hypertensive rats (SHR) when compared with normotensive Wistar‐Kyoto rats (WKY). To establish which component of the β‐adrenoceptor · adenylate cyclase (AC) system is impaired in the SHR arteries, effects of two activators of AC ‐ cholera toxin (CTX) and forskolin ‐ and of dibutyryl cyclic AMP (db cyclic AMP) were compared between strips of femoral arteries isolated from 13 week‐old SHR and age‐matched WKY.

In the absence of timolol, a β‐adrenoceptor antagonist, contractile responses of the strips to noradrenaline (NA) were significantly greater in the SHR than in the WKY. Timolol augmented the contractile responses to NA to a smaller extent in the SHR than in the WKY.

After blockade by timolol of β‐adrenoceptors, contractile responses of the strips to NA through the activation of α‐adrenoceptors were not significantly different between the two strains.

Pre‐treatment of the strips with CTX, an activator of the stimulatory GTP‐binding protein (Gs), produced a slow‐onset and long‐lived antagonism of the α‐adrenoceptor‐mediated contractions. The antagonism was much smaller in the SHR than in the WKY.

The dose‐response curves of the strips from both strains for α‐adrenoceptor stimulation with NA determined after pretreatment with CTX were comparable to those determined in the absence of timolol.

Forskolin, an activator of the catalytic subunit of AC, and DB cyclic AMP also antagonized the α‐adrenoceptor‐mediated contractions. However, these antagonisms were not significantly different between the two strains.

Isobutyl methylxanthine (IBMX), an inhibitor of cyclic AMP phosphodiesterase, produced a similar antagonism of the α‐adrenoceptor‐mediated contractions between the two strains.

These results suggest that a reduced function of Gs is the main factor responsible for the decreased responsiveness to β‐adrenoceptor stimulation in the SHR femoral artery.
Selective modulation by membrane potential of the interaction of some calcium entry blockers with calcium channels in rat mesenteric artery
Authors: Morel Nicole , Godfraind Théophile
Published: July 2012

The effects of flunarizine, (+)‐PN 200‐110 and nifedipine on [3 H]‐(+)‐PN 200‐110 specific binding were investigated in intact rat mesenteric arteries bathed in physiological solution or in KCl‐depolarizing solution, and in a membrane fraction from rat mesenteric arteries.

Unlabelled dihydropyridines, (+)‐PN 200‐110 and nifedipine, inhibited [3 H]‐(+)‐PN 200‐110 specific binding concentration‐dependently in polarized as well as in depolarized intact arteries. The Ki value of (+)‐PN 200‐110 was decreased in arteries bathed in KCl‐depolarizing solution compared to arteries bathed in physiological solution, while the Ki value of nifedipine was not significantly changed. Ki values measured in depolarized arteries were close to the IC50 values (concentrations inhibiting by 50% the KCl‐contraction of rat mesenteric artery).

Flunarizine (10−6 M) was unable to displace the specific binding of [3 H]‐(+)‐PN 200‐110 in intact arteries bathed in physiological solution. At 10−7 M‐10−6 M, it inhibited the binding in depolarized arteries, suggesting that prolonged depolarization is required for the interaction of flunarizine with the dihydropyridine receptor.

In a membrane fraction isolated from rat mesenteric arteries, (+)‐PN 200‐110, nifedipine and flunarizine were all able to displace completely the specific binding of [3 H]‐(+)‐PN 200‐110. Displacement curves were parallel and Hill coefficients were close to unity. Ki values were close to the values obtained in depolarized intact arteries.

These results revealed a good correlation between the data obtained from binding tests and from pharmacological studies for dihydropyridine calcium entry blocking drugs, taking into account the time‐dependence associated with their action on KCl‐contraction compared to their binding properties. There was an important discrepancy between the concentrations of flunarizine active in binding studies and those active in pharmacological studies, which could be accounted for by the existence of multiple binding sites for calcium entry blockers in calcium channels.
A quantitative study of the actions of excitatory amino acids and antagonists in rat hippocampal slices
Authors: Blake J.F. , Brown M.W. , Collingridge G.L.
Published: July 2012

A quantitative pharmacological investigation of the actions of excitatory amino acids on hippocampal CA1 neurones has been made using a new slice preparation developed for grease gap recording; d.c. potential was measured across a grease barrier placed between alvear fibres and the bathing medium.

In Mg2+‐free perfusate, N‐methyl‐D‐aspartate (NMDA, 1–100 μM), quisqualate (1–500 μM), kainate (1–200 μM) and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA, 1–100 μM) caused dose‐dependent depolarizations.

The dose‐response relationships were fitted to logistic expressions. The maximum responses to AMPA, NMDA and kainate were similar; their respective EC50 values were 5, 13 and 23 μM. Quisqualate had a smaller maximum; its EC50 value was 10 μM. The slopes of the dose‐response relationships were different for the 4 agonists; the order of steepness of the slopes was NMDA > AMPA > kainate > quisqualate.

Similar amino acid‐induced depolarizations were observed in slices of just the CA1 region or in whole slices bathed in tetrodotoxin. Isolated alvear fibres, however, were insensitive to the excitatory amino acids.

D‐2‐Amino‐5‐phosphonovalerate (APV, 50 μM) selectively and reversibly antagonized responses induced by NMDA (apparent pA2 = 5.21).

Kynurenic acid (1 mM) reversibly depressed responses to the three agonists tested. The doseratios for antagonism of AMPA, kainate and quisqualate were 6.9, 5.6 and 4.6 respectively.

This preparation has a different sensitivity profile to agonists from those of previously reported preparations of spinal cord, neocortex and cerebellum. The greater sensitivity to NMDA may be due to the higher density of NMDA receptors in the hippocampus. The effects of the antagonists, APV and kynurenate, are similar to those found in other brain areas.
Noradrenaline (gamma) and ATP responses of innervated and non‐innervated rat cerebral arteries
Authors: Edwards F.R. , Hards Daphne , Hirst G.D.S. , Silverberg G.D.
Published: July 2012

The distribution of sympathetic adrenergic nerves on the rat middle cerebral artery and on the arterioles which originated from it was determined by use of gloxylic histochemistry.

Whereas the middle cerebral artery and proximal arterioles arising from this artery received a sympathetic innervation, the distal regions of the same arterioles were devoid of innervation.

The arteries and arterioles which were innervated were depolarized by noradrenaline in the combined presence of α‐ and β‐adrenoceptor antagonists. Those which were not innervated were not depolarized by noradrenaline.

ATP depolarized all arteries and arterioles examined.

These observations are discussed with respect to the similarities and differences between γ‐adrenoceptors and P2 purinoceptors.
Interactions of drugs acting on central dopamine receptors and cholinoceptors on yawning responses in the rat induced by apomorphine, bromocriptine or physostigmine
Authors: Zarrindast M.R. , Poursoltan M.
Published: July 2012

Yawning was induced by subcutaneous (s.c.) injection of low doses of apomorphine to rats. This effect decreased with increasing doses of the drug.

Intraperitoneal (i.p.) pretreatment of animals with sulpiride (D2‐receptor blocker) reduced the frequency of the yawns induced by apomorphine, while SCH 23390 (D1‐receptor blocker, s.c.) pretreatment increased the small number of yawns which was induced by higher doses of apomorphine. Administration of SCH 23390 alone to rats also produced a low degree of yawning.

Apomorphine‐induced yawning was decreased in animals treated with SK&F 38393 (D1 ‐agonist, i.p.), atropine (i.p.) or theophylline (i.p.).

Intraperitoneal injection of bromocriptine (D2‐agonist) in rats also induced dose‐dependent yawning. The effect was decreased in animals pretreated with sulpiride, while SCH 23390 pretreatment did not change bromocriptine‐induced yawning significantly. Pretreatment of animals with SK&F 38393, atropine or theophylline reduced the number of yawns induced by bromocriptine.

Physostigmine (i.p.) but not neostigmine (i.p.) also induced yawning. The effect was antagonized by atropine or theophylline but not by sulpiride. Administration of SK&F 38393 decreased yawning induced by physostigmine. This inhibitory influence of SK&F 38393 was reduced by SCH 23390 in pretreated animals. Treatment of animals with SCH 23390 or bromocriptine increased the frequency of yawns induced by physostigmine.

It is concluded that D2‐receptor activation elicits yawning through influence on cholinergic mechanisms, whereas D1‐receptor stimulation decreases yawning behaviour by a negative influence on the cholinergic system.
Effects of hydroxyethyl rutosides upon the permeability of single capillaries in the frog mesentery
Authors: Blumberg Sara , Clough Geraldine , Michel Charles
Published: July 2012

We have investigated the effects of a standardised mixture of hydroxyethyl rutosides (HR) upon the permeability of the walls of single capillaries and venules of the frog mesentery.

In each experiment a single vessel was perfused via a micropipette with frog Ringer solutions containing bovine serum albumin (10 mg ml−1) and Ficoll 70 (40 mg ml−1) first in the absence of HR and then with HR added to the perfusate. The permeability of the vessel walls was assessed during each perfusion by using a development of the Landis micro‐occlusion technique to estimate their hydraulic permeability (Lp) and the effective osmotic pressure (σΔπ) exerted across them by the perfusate macromolecules.

Measurements were made both in vessels which appeared to be healthy and in vessels showing signs of stasis or inflammation before perfusion.

HR at concentrations of 1.0, 0.1 and 0.01 mg ml−1 reduced hydraulic permeability to approximately half of its value in the absence of HR. It increased σδπ to macromolecules at concentrations of 10, 1.0, 0.1, 0.01 and 0.001 mg ml−1. The effects of HR upon permeability were not reversed within 10 min of perfusion with an HR‐free solution.

Ultrastructural examination of a number of vessels in which initial high values of permeability were reduced to values within the normal range of permeabilities by HR, showed clear signs of damage to the endothelium, with large gaps between adjacent endothelial cells.

These observations suggest that HR does reduce microvascular permeability both in healthy vessels and vessels showing signs of inflammation. The reduction in permeability of inflamed vessels does not appear to be the result of closure of the gaps between adjacent endothelial cells.