bluuebunny/crossref_metadata_2025 huggingface dataset:
Vasomotor responses of cerebral arterioles in situ to putative dopamine receptor agonists
Authors: Edvinsson Lars , McCulloch James , Sharkey John
Published: July 2012

The vasomotor responses of individual cerebral pial arterioles on the convexity of the cerebral cortex to subarachnoid perivascular micro‐injections of dopamine and the putative dopamine receptor agonists, apomorphine, SKF 38393 and LY 141865, have been examined in 38 anaesthetized cats.

The perivascular microapplication of dopamine (10−9–10−3 M) effected dose‐dependent reductions in pial arteriolar calibre, with the maximum reductions in calibre (22 ± 2% from preinjection levels: mean ± s.e.) being observed at 10−3 M. The cerebrovascular constriction produced by dopamine (10−5 M) could be significantly attenuated by the concomitant perivascular administration of phentolamine (10−6 M) or methysergide (10−6 M).

The perivascular microapplication of apomorphine (10−8–10−4 M) effected dose‐dependent increases in arteriolar calibre, with the maximum increase (31 ± 6%) being observed with apomorphine (10−5 M).

The perivascular administration of the putative dopamine D1‐receptor agonist, SKF 38393 (10−9–10−4 M) increased arteriolar calibre, with the maximum response (24 ± 3%) being observed with injection of 10−7 M. The putative dopamine D2‐receptor agonist, LY 141865, also increased cerebral arteriolar calibre, but only at high concentrations (maximum calibre increase 25 ± 6.1 with 10−4 M).

The cerebrovascular dilatations elicited by apomorphine and by SKF 38393 were markedly attenuated by the concomitant perivascular microapplication of the putative dopamine D1‐receptor antagonist, SCH 23390 (10−8 M). The perivascular administration of SCH 23390 (10−9–10−5 M) per se did not alter arteriolar calibre nor the arteriolar dilatation provoked by microinjections of acidic cerebrospinal fluid.

These results point to the presence on cat cerebral arterioles of dopamine receptors (probably of D1 subtype) mediating dilatation.
The mechanism of adenosine release from hypoxic rat liver cells
Authors: Belloni Francis L. , Elkin Peter L. , Giannotto Beverly
Published: July 2012

Uptake of [14C]‐adenosine into freshly dispersed rat hepatocytes was inhibited 44% by dipyridamole (50 μM) and 60% by nitrobenzylthioinosine (NBTI, 20 μM). The results are consistent with the known ability of these drugs to inhibit adenosine transport in other cell types.

The nucleotide analogue, α,β‐methylene adenosine diphosphate (AOPCP, 50 μM), inhibited by 84% the degradation of exogenous 5′ AMP that occurred rapidly when this substrate alone was presented to isolated hepatocytes. This confirms the ecto‐5′‐nucleotidase inhibitory properties of this analogue in isolated hepatocytes.

During hypoxic incubation, isolated hepatocytes released adenosine, which accumulated in the extracellular volume. Dipyridamole and NBTI each markedly attenuated this extracellular adenosine accumulation. In contrast, AOPCP had no inhibitory effect on net hypoxic adenosine release.

It is concluded that hypoxic rat hepatocytes produce adenosine intracellularly and that this adenosine is released via facilitated diffusion to the extracellular space, based on the inhibition observed with the transport inhibitors. The plasma membrane enzyme ecto‐5′‐nucleotidase does not appear to participate in hypoxic adenosine release from these cells as indicated by the lack of effect of the nucleotidase inhibitor, AOPCP.
Insensitivity of calcium‐dependent endothelial stimulation in rat isolated aorta to the calcium entry blocker, flunarizine
Authors: Miller R.C. , Schoeffter P. , Stoclet J.C.
Published: July 2012

In rat aortic segments complete with endothelium, acetylcholine (1 μM) relaxed noradrenaline, phenylephrine and prostaglandin F2α (PGF2α‐induced contractions of various magnitudes. Maximal 1 μM phenylephrine‐induced contractions were relaxed to a greater extent than were maximal contractions induced by the other two agonists.

Contractions elicited by various concentrations of phenylephrine and PGF2α in the presence of a maximal effective concentration of the calcium entry blocker flunarizine (3 μM) were relaxed by acetylcholine to about the same residual tension as were contractions elicited in the absence of flunarizine.

Acetylcholine (1 μM) and phenylephrine (1 μM) increased tissue levels of guanosine cyclic 3′5′‐monophosphate (cyclic GMP) by about 37 fold and 2 fold respectively. Preincubation of tissues in the absence of calcium abolished these agonist‐induced increases in cyclic GMP levels, but preincubation with flunarizine had no significant effect on the increase in cyclic GMP level induced by the agonists. Pretreatment with flunarizine had no significant effect on the basal tissue level of cyclic GMP, but pretreatment in calcium‐free solution reduced the basal tissue level of the cyclic nucleotide by about half.

It is concluded that in rat aorta, endothelium‐dependent acetylcholine‐induced relaxation and endothelium‐dependent acetylcholine and phenylephrine‐induced increases in tissue levels of cyclic GMP, are dependent on extracellular calcium, but are not antagonized by flunarizine. This may indicate that if calcium channels of endothelial cells are activated by these agonists, their characteristics are not identical with those of the calcium channels of the smooth muscle cells.
Action of agonists and antagonists at muscarinic receptors present on ileum and atria in vitro
Authors: Clague R.U. , Eglen R.M. , Strachan A.C. , Whiting R.L.
Published: July 2012

The action of ‘selective’ agonists and antagonists at muscarinic receptors mediating ileal contractions, and the rate and force of atrial contractions has been assessed.

The effect of nicotinic receptor stimulation, catecholamine release and acetylcholinesterase (AChE) action on muscarinic activity has also been assessed.

The nicotinic actions of carbachol did not affect its agonist potency nor the antagonist affinity data obtained when this agonist was used in atrial and ileal preparations.

Antagonist data indicated that muscarinic receptors mediating the rate and force of atrial contractions did not differ. Differences in agonist potencies at these two muscarinic receptors were attributable to either differences in intrinsic efficacy or susceptibility to the action of acetylcholinesterase. The small differences in agonist potency observed between atrial and ileal muscarinic receptors were considered not sufficient to indicate receptor heterogeneity.

The pirenzepine affinity data indicated that all three receptors are of the M2 type. Affinity data using secoverine and 4‐diphenyl‐acetoxy‐N‐methyl piperidine methiodide indicated that ileal and atrial muscarinic receptors differ. Data obtained using gallamine, pancuronium and stercuronium cannot be regarded as indicative of receptor affinity since the antagonism is not competitive; it did nonetheless corroborate the conclusion that ileal and atrial muscarinic receptors are different.
Stimulation and inhibition of gastrointestinal propulsion induced by substance P and substance K in the rat
Authors: Holzer P.
Published: July 2012

Substance P and substance K (neurokinin A) (dose range: 0.08–80 nmol kg−1) were tested for their effects on gastrointestinal propulsion in the rat. The peptides were given by intraperitoneal injection concurrently with the intragastric administration of a test meal containing charcoal and 51Cr.

Examination 3 min after the test meal showed that high doses of substance P (> 0.74 nmol kg−1) and substance K (> 8.8 nmol kg−1) inhibited gastric emptying and gastrointestinal transit. This inhibitory effect was changed to a stimulant effect by pretreatment of the rats with atropine (3.5 μmol kg−1). Guanethidine pretreatment (67 μmol kg−1) revealed a facilitatory effect of low doses of the two tachykinins (about 1 nmol kg−1) on gastrointestinal propulsion.

Examination 15 min after the test meal demonstrated that substance P (> 0.74 nmol kg−1) dose‐dependently enhanced gastrointestinal propulsion, an effect that was also seen after atropine pretreatment. Low doses of substance K (about 1 nmol kg−1) also stimulated gastrointestinal propulsion but this effect was abolished by atropine. In addition, atropine pretreatment revealed a stimulant effect of high doses of substance K (88 nmol kg−1) on gastric emptying.

These results show that the effects of substance P and substance K on gastrointestinal propulsion vary with dose and time and involve, at least partly, activation of the autonomic nervous system.
Pharmacological activity of ACC‐7513, a selective α‐adrenoceptor and 5‐hydroxytryptamine receptor blocking agent
Authors: Anderson William G. , Kam Sheung‐Tsam
Published: July 2012

The pharmacological activity of N‐ [2‐(2,6‐dimethoxyphenoxy) ethyl]‐2‐(2‐methoxyphenoxy) ethanaminium chloride (ACC‐7513) was determined in isolated smooth and cardiac muscle and its effect on blood pressure and heart rate assessed in the spontaneously hypertensive rat (SHR).

ACC‐7513 was found to be a potent α‐adrenoceptor blocking agent (pA2:8.33) and a 5‐hydroxytryptamine (5‐HT) antagonist (pA2:7.01), both in rabbit aortic strips. The affinity for α‐adrenoceptors was about 20 times greater than that for 5‐HT‐receptors.

High concentrations of ACC‐7513 did not block histamine in rabbit aortic strips, or β1‐ or β2‐adrenoceptor responses induced by isoprenaline in guinea‐pig right atria and trachea, respectively, but did block cholinoceptor responses induced by carbachol in rat uterus, non‐competitively.

High concentrations of ACC‐7513 also produced sino‐atrial depression in guinea‐pig right atria and direct relaxation of depolarized rabbit aortic strips.

ACC‐7513 depressed blood pressure of conscious SHRs and produced a reflex increase in heart rate. The reductions in pressure were modest and of short duration.

It is concluded that: (a) ACC‐7513 is a potent, selective α‐adrenoceptor and 5‐HT receptor antagonist; and (b) ACC‐7513 is not likely to be useful in the treatment of hypertension.
Changes in the behavioural response to a TRH analogue following chronic amitriptyline treatment and repeated electroconvulsive shock in the rat
Authors: Bennett G.W. , Green A.R. , Lighton Celia , Marsden C.A.
Published: July 2012

The arousal elicited in rats by injection into the nucelus accumbens of the thyrotrophin‐releasing hormone analogue CG 3509 (orotyl‐histidyl‐prolineamide) was used to assess the responsiveness to thyrotrophin‐releasing hormone following repeated treatment with amitriptyline or electroconvulsive shock.

Fourteen day administration of amitriptyline (15 mg kg−1 i.p. twice daily) reduced the behavioural response to bilateral intra‐accumbens injection of CG 3509 (2 × 2.5 μg). CG 3509‐induced hyperactivity, recovery from pentobarbitone‐induced anaesthesia and the reversal of both pentobarbitone‐induced hypothermia and decreased respiration, were all significantly reduced compared to either the response of the animals prior to amitriptyline administration or that observed in rats following chronic saline administration.

Repeated administration of electroconvulsive shock (5 shocks over 10 days) significantly increased CG 3509‐induced hyperactivity and the degree of reversal of pentobarbitone‐induced hypothermia and respiratory depression following CG 3509 administration.

The results demonstrate that chronic antidepressant treatments alter the central functional responsiveness to thyrotrophin‐releasing hormone. These changes are discussed with respect to the effects of antidepressant treatments on 5‐hydroxytryptamine receptors and possible thyrotrophin‐releasing hormone ‐ aminergic interactions.
The relaxant action of nicorandil in guinea‐pig isolated trachealis
Authors: Allen S.L. , Foster R.W. , Morgan G.P. , Small R.C.
Published: July 2012

Nicorandil (1–1000 μmol 1–1) caused concentration‐dependent relaxation of guinea‐pig isolated trachealis.

Propranolol (1 μmol 1−1) did not modify the relaxant action of nicorandil but antagonized isoprenaline.

Among K+‐channel inhibitors tested, apamin (0.1 μmol 1−1) and procaine (5 mmol 1−1) did not modify the relaxant action of nicorandil. In contrast, tetraethylammonium (TEA, 8 mmol 1−1) caused five fold antagonism.

Trachealis exposed to K+‐rich (120 mmol 1−1) Krebs solution developed near‐maximal tension. Nicorandil relaxed the K+‐depolarized tissue though its concentration‐effect curve was shifted markedly to the right.

In tissues in which tone was induced by histamine, methylene blue (100 μmol 1−1) antagonized nicorandil and sodium nitroprusside but did not modify the relaxant action of aminophylline.

Intracellular electrophysiological recording showed that nicorandil (1 μmol 1−1) could evoke some relaxation in the absence of electrical changes. Higher concentrations (10–1000 μmol 1−1) reduced the amplitude and frequency of spontaneous electrical slow waves. Nicorandil also caused concentration‐dependent hyperpolarization and relaxation. When the hyperpolarization was sufficiently pronounced slow wave activity was abolished.

TEA (8 mmol 1−1) induced slow waves which were surmounted by a spike potential. TEA slightly reduced the maximal hyperpolarization induced by nicorandil and increased the time required for nicorandil to abolish slow wave discharge.

Procaine (5 mmol 1−1) induced slow waves of relatively low frequency. Sometimes these were surmounted by a spike potential. Procaine markedly reduced the hyperpolarization induced by nicorandil and increased the time required for abolition of slow waves.

In studies of the efflux of 86Rb+ from muscle‐rich strips of trachea, nicorandil (1000 μmol 1−1) increased the efflux rate constant, whereas isoprenaline (1 μmol 1−1) was without effect.

It is concluded that nicorandil‐induced relaxation does not involve the activation of β‐adrenoceptors but is partly attributable to the formation of nitric oxide from the nitrate moiety in its molecular structure. Nicorandil can evoke relaxation in the absence of membrane potential change but towards the upper end of its effective concentration range, nicorandil increases membrane K+ conductance and thereby evokes hyperpolarization of trachealis cells. The K+ channels opened by nicorandil are permeable to 86Rb, insensitive to apamin and TEA but may be inhibited by procaine.
Role of the endothelium on the facilitatory effects of angiotensin I and angiotensin II on noradrenergic transmission in the caudal artery of the rat
Authors: Story D.F. , Ziogas J.
Published: July 2012

Perfusion of carbogen gas through the lumen of the rat caudal artery abolished the dilator response to acetylcholine (1 μmol 1−1) in artery segments which had been precontracted with noradrenaline (50 nmol 1−1). Hence, it was assumed that gas perfusion was effective in removing the vascular endothelium.

Angiotensin I (30 nmol 1−1) and angiotensin II (10 nmol 1−1) enhanced the responses of artery segments to field stimulation of their sympathetic nerves (0.5 Hz, 10 s). In arteries with an intact endothelium the ability of each peptide to enhance responses to stimulation was the same whether applied through the lumen or to the adventitial surface.

Removal of the endothelium, by gas perfusion, did not significantly alter the facilitatory effects of extraluminally or intraluminally applied angiotensin I or angiotensin II.

The converting enzyme inhibitor enalaprilat was equally effective in inhibiting the facilitatory effect of angiotensin I in the presence and absence of an intact endothelium.

It is concluded that in the rat caudal artery, conversion of angiotensin I to angiotensin II does not depend on an intact endothelium and that the facilitatory effect of angiotensin II on noradrenergic neuroeffector transmission is not modified by, or dependent on, an intact endothelium.
Pharmacological analysis of the interaction between Bay K 8644 and 5‐HT in rabbit aorta
Authors: Barrett V.J. , Leff P. , Martin G.R. , Richardson P.J.
Published: July 2012

Bay K 8644 potentiated and augmented 5‐hydroxytryptamine (5‐HT)‐induced contractions in the rabbit, isolated aorta preparation, as manifested in leftward shift and increase in the asymptote of 5‐HT E/[A] (effect vs concentration) curves.

The operational model of agonism (Black & Leff, 1983) was used to analyse this interaction and the concomitant effects of irreversible receptor alkylation by phenoxybenzamine. The competitive effects of spiperone in the presence and absence of Bay K 8644 were also examined.

From these analyses it is concluded that Bay K 8644 elicits its potentiating effects by increasing the efficacy of 5‐HT at the 5‐HT2 receptor with no alteration in affinity. This is consistent with the known effect of Bay K 8644 of causing an increase in the functional concentration of plasmalemmal calcium channels coupled to the 5‐HT2 receptors in this preparation.

The positively co‐operative shape of the 5‐HT E/[A] curves obtained in the aorta and the quantitative nature of their potentiation by Bay K 8644 indicated that the coupling of 5‐HT2 receptor occupancy to intracellular calcium concentration is linear and that the co‐operativity resides in the subsequent relation between intracellular calcium and pharmacological effect.

Bay K 8644 may serve as a probe for differentiating between the types of calcium channels that transduce 5‐HT receptor‐mediated effects in different systems. Such information would be useful in the classification of agonist interactions with 5‐HT receptors.
The influence of epithelium on the responsiveness of guinea‐pig isolated trachea
Authors: Holroyde Martin C.
Published: July 2012

This study was designed to investigate the possibility that tracheal epithelium generates a relaxant factor analogous to the endothelial‐derived relaxant factor (EDRF) of vascular tissue. The absence of such a factor following epithelial damage in diseases such as asthma might help to explain the airway hyperreactivity characteristic of such diseases.

Removal of epithelium by rubbing enhanced the sensitivity of guinea‐pig isolated tracheal chains to 5‐hydroxytryptamine, histamine, acetylcholine, adenosine, isoprenaline and also minimally to KC1. Responses to LaCl3 and electrical field stimulation were not affected. Low concentrations of adenosine produced contractions only in tissues denuded of epithelium.

In the presence of indomethacin 1.4 μM or dithiothreitol (DTT) 1 μM, dose‐response curves to histamine were moved to the left in both control and rubbed tissues, and the maximum response was increased. The difference in sensitivity between tissues with and without epithelium was not affected by indomethacin, but was slightly reduced by DTT. Phenidone (0.1 mM) also increased the maximum responses, but increased the sensitivity only of the tissues with intact epithelium, to the same level as that seen in the tissues denuded of epithelium.

Superfusion cascade studies provided no evidence for the generation of a relaxant factor from tracheal epithelium.

It is suggested that the supersensitivity produced by removal of the epithelium is not due to the removal of a relaxant factor, but rather to the removal of a permeability barrier, allowing a greater concentration of agonist at the level of the underlying smooth muscle.
Characterization of α‐adrenoceptors in the vasculature of the canine nasal mucosa
Authors: Berridge T.L. , Roach A.G.
Published: July 2012

α‐Adrenoceptors present in the vasculature of the nasal mucosa in β‐adrenoceptor blocked dogs have been characterized pharmacologically using selective α1‐ and α2‐adrenoceptor agonists and antagonists.

In pentobarbitone‐anaesthetized dogs, intra‐arterial (i.a.) administration of the selective α1‐agonists cirazoline and phenylephrine, the selective α2‐agonist UK‐14,304 and the mixed α1/α2‐agonists adrenaline, noradrenaline and oxymetazoline produced dose‐related nasal vasoconstrictor responses (as measured by decreases in nasal cavity pressure). The rank order of agonist potency was adrenaline > oxymetazoline = UK‐14,304 > noradrenaline > cirazoline > phenylephrine.

The nasal response to cirazoline was inhibited by the selective α1‐adrenoceptor antagonist prazosin but not by the new, potent selective α2‐adrenoceptor antagonist RX 811059. In contrast, UK‐14,304 was inhibited only by RX 811059. Either prazosin or RX 811059 reduced the effect of the mixed agonist adrenaline.

In spinal dogs, the noradrenaline‐evoked fall in nasal cavity pressure was reduced by either prazosin or RX 811059. Prazosin attenuated markedly the nasal vasoconstrictor response to electrical stimulation of postganglionic fibres emerging from the superior cervical ganglion (SNS) whereas RX 811059 was ineffective. Administration of the neuronal re‐uptake inhibitor cocaine potentiated the effect of i.a. noradrenaline but reduced marginally the maximal response to SNS. After cocaine, RX 811059 enhanced the effect of SNS and attenuated the response to noradrenaline. Prazosin reduced effectively the responses to both SNS and noradrenaline after cocaine. Pretreatment with the α2‐agonist UK‐14,304 did not affect the response to noradrenaline in the nasal cavity but evoked a persistent (up to 2 h) reduction in the response to SNS. RX 811059 antagonized the inhibitory effect of UK‐14,304.

These results demonstrate that both postjunctional α1‐ and α2‐adrenoceptors mediating vasoconstriction are present in the canine nasal mucosa. In addition, sympathetic neurones innervating the nasal mucosa are characterized by a very efficient re‐uptake process and contain prejunctional α2‐adrenoceptors.
A study in the rat of the renal actions of nitrendipine and diltiazem on the adrenergic regulation of calcium and sodium reabsorption
Authors: Johns Edward J. , Manitius Jacek
Published: July 2012

In pentobarbitone‐anaesthetized rats, intravenous administration of diltiazem at 5 μg kg−1min−1did not change blood pressure or renal blood flow but increased glomerular filtration rate by approximately 16%, urine flow by 85%, calcium excretion by 151% and absolute and fractional sodium excretions by 100% and 69%, respectively. A similar pattern of responses was obtained in renally denervated animals, except that calcium excretion did not change statistically. Diltiazem given at 20 μg kg−1min−1into renally innervated and denervated groups of animals depressed blood pressure between 15–17 mmHg but had no effect on renal haemodynamic or tubular function.

Nitrendipine administered at 0.5 μg kg−1min−1to renally innervated and denervated animals significantly depressed blood pressure in intact animals by 6 mmHg and in both groups did not change renal haemodynamics but caused similar increases in urine flow of between 79–98%, calcium excretion of between 87 and 125%, absolute sodium excretion of between 108 and 140% and fractional sodium excretion of between 83 and 170%. Infusion of nitrendipine at 1.0 μg kg−1min−1into intact or renally denervated animals decreased blood pressure by 18–20 mmHg and increased urine flow by 84–111%, calcium excretion by 85%, absolute sodium excretion by 81–137% and fractional sodium excretion by 52–102%.

Stimulation of the renal nerves at low frequencies (0.8 to 1.5 Hz) caused minimal changes in renal haemodynamics but decreased urine flow by 27%, calcium excretion by 35%, absolute and fractional sodium excretions 32% and 36%, respectively. In different groups of animals given either diltiazem at 20 μg kg−1min−1or nitrendipine at 0.5 μg kg−1min−1or l.0 μg kg−1min−1, a similar degree of renal nerve stimulation caused an identical pattern of excretory responses of similar magnitude to those obtained in the absence of drug.

The calciuretic, diuretic and natriuretic activities of diltiazem and nitrendipine were not dependent on renal nerves and probably represented a direct action on the tubular reabsorptive processes of these ions. The renal nerve‐induced increases in tubular calcium and sodium reabsorption indicate that these α‐adrenoceptor‐mediated responses are not dependent on the inward movement of calcium
Effects of calcium channel antagonists on action potential conduction and transmitter release in the guinea‐pig vas deferens
Authors: Beattie D.T. , Cunnane T.C. , Muir T.C.
Published: July 2012

The effects of the Ca2+ channel antagonists amlodipine, cobalt, diltiazem, nifedipine and verapamil and the local anaesthetic lignocaine were investigated on action potential conduction in and on evoked transmitter release from sympathetic nerves in the guinea‐pig isolated vas deferens. Transmitter release was investigated by measurement of (a) evoked (trains of pulses at 1 and 2 Hz, 0.1‐0.5 ms supramaximal voltage) excitatory junction potentials (e.j.ps) using microelectrodes; tension was recorded simultaneously; (b) tritium (3H) overflow from vasa preincubated (37°C, 30 min) in Krebs solution containing either [3H]‐noradrenaline (NA, 25 μCi ml−1, 2 × 10−6 M NA) or [3H]‐adenosine (50 μCi ml−1, 1 × 10−6 M adenosine).

Amlodipine (0.5–2 × 10−4 M), verapamil (0.5‐2 × 10−4 M), diltiazem (1–8 × 10−4 M), lignocaine (0.1–2 × 10−3 M) and cobalt (2–6 × 10−2 M) in descending order of potency, but not nifedipine (1–5 × 10−3 M), increased the latency and inhibited, then abolished, the amplitude and number of action potentials in a concentration‐dependent manner.

Amlodipine (0.5–1 × 10−4 M), verapamil (1–2 × 10−4 M), diltiazem (1–5 × 10−4 M) and cobalt (1 × 10−3 M), in descending order of potency, but not nifedipine (5 × 10−4 M), inhibited then abolished evoked e.j.ps in a concentration‐dependent manner. Cobalt inhibited e.j.ps at a lower concentration than that (2–6 × 10−2 M) required to block action potential conduction.

In unstimulated tissues, the resting 3H overflow following preincubation with [3H]‐NA consisted largely of 4‐hydroxy 3‐methoxymandelic acid (VMA), 4‐hydroxy 3‐methoxy phenylglycol (MOPEG), 3,4 dihydroxyphenylglycol (DOPEG) and NA; stimulated tissues (300 pulses at 20 Hz, 0.5 ms supramaximal voltage) released mainly NA. Verapamil (0.1–1 × 10−4 M), amlodipine (0.05–1 × 10−4 M) and nifedipine (1–5 × 10−4 M), but not cobalt (2 × 10−3 M), increased, significantly, the resting overflow of 3H comprising mainly DOPEG. Cobalt (2 × 10−3 M) inhibited, significantly, the stimulation‐evoked overflow of 3H.

Verapamil (1 × 10−4 M) had little effect on the resting overflow of 3H following preincubation with [3H]‐adenosine. Diltiazem (5 × 10−4 M) and cobalt (2 × 10−3 M) both inhibited evoked 3H overflow. Nifedipine (5 × 10−4 M) was ineffective.

The effectiveness of Ca2+ channel antagonists at pre‐ and postjunctional sites differ; the results are discussed in terms of the selectivity of these drugs for each site and their differential effects on transmitter release.
Regional differences of reactivity to stimulants in the dog portal tree
Authors: Fujii Kazutoshi , Fujiwara Motohatsu , Kumada Kaoru , Kurahashi Kazuyoshi , Usui Hachiro
Published: July 2012

We studied the regional differences both of reactivity to various stimulants and of neurogenic responses elicited by transmural stimulation in the longitudinal and circular muscles of the truncal portal vein, mesenteric vein, splenic vein and gastric vein of the dog portal tree.

Strong spontaneous activity appeared in the longitudinal muscle of the truncal portal vein (96% of preparations tested). Weak spontaneous activity sometimes appeared in the circular muscle of the truncal portal vein (41%) and rarely in the longitudinal muscle of the mesenteric vein (12%). It did not appear in other segments.

The splenic vein and the gastric vein showed similar patterns in the relationship between resting tension and response to noradrenaline; that is, the responsiveness of either longitudinal or circular muscle of these two veins increased and then decreased almost parallel as resting tension increased and reached a maximum under the same resting tension.

The longitudinal muscle of both the truncal portal vein and the mesenteric vein was more responsive to noradrenaline, acetylcholine, histamine and KCl than the circular muscle; for example 2.02 and 1.44 times more responsive to noradrenaline, respectively. On the other hand, the longitudinal muscle of the splenic vein and the gastric vein responded less well than the circular muscle; for example 0.36 and 0.16 times as responsive to noradrenaline, respectively.

Acetylcholine and histamine caused marked contractions which were comparable to those elicited by noradrenaline in the longitudinal muscle of the truncal portal vein. Acetylcholine also elicited similar contractions in the longitudinal muscle of the mesenteric vein but the responses induced in preparations of other segments were small.

The longitudinal muscle of the truncal portal vein responded well even to low‐frequency stimulation of 2 Hz, while the circular muscles of the truncal portal and splenic veins gave marked responses only to high‐frequency stimulation of 10 or 20 Hz or more. These contractile responses were attenuated by phentolamine (10−6 m) or atropine (10−6 m). The longitudinal muscle of the splenic vein showed no significant response to stimuli of any frequency.

It seems that the portal tree receives not only adrenergic but also cholinergic innervation. In addition, the longitudinal muscle of the truncal portal vein may receive non‐adrenergic, non‐cholinergic innervation as well.

The longitudinal muscle of the portal vein may be crucial to venous return in assisting movement of the blood it contains. If this is the case in man, then the regional differences in the portal tree demonstrated in this study may explain why varicose changes during portal hypertension occur preferentially in the oesophagogastric region and rarely in other regions, as blood stasis may occur more readily in the regions of the gastric and splenic veins where the longitudinal muscle is not very active.
The effects of the stable thromboxane A2‐mimetic, U46619, on gastric mucosal damage and gastric non‐parietal secretion in the rat
Authors: Bunce K.T. , Clayton N.M.
Published: July 2012

The effects of the thromboxane A2‐mimetic, U46619, and the thromboxane receptor antagonist, AH23848, on ethanol‐induced gastric mucosal damage and gastric non‐parietal secretion have been examined in the rat.

Oral dosing with U46619 or AH23848 produced a dose‐related inhibition of ethanol‐induced gastric mucosal damage in the conscious rat, and these effects were partially blocked by indomethacin treatment.

Intragastric application of U46619 or AH23848 to the stomach of the anaesthetized rat stimulated the gastric secretion of a juice which consisted principally of Na+ and Cl− ions. These secretagogue effects of both compounds were blocked by indomethacin treatment.

These results show that U46619 and AH23848 induce secretory and protective effects in the stomach of the rat, although these responses probably do not involve thromboxane receptors and are mediated, at least in part, by endogenous prostaglandins.

The results are discussed in relation to the role of endogenous thromboxane A2 in gastric mucosal protection, and of the possible protective function of non‐parietal secretion in the stomach.
Kinin antagonist activity of compounds from Mandevilla velutina in the rat isolated uterus
Authors: Calixto João B. , Nicolau Mauro , Pizzolatti Moacir G. , Yunes Rosendo A.
Published: July 2012

The effect of four semi‐purified compounds obtained from Mandevilla velutina crude extract by silica gel chromatography fractionization were analysed for their inhibitory effects on uterine contractions induced by bradykinin (BK), lysylbradykinin (L‐BK), acetylcholine (ACh) and oxytocin, in vitro.

None of the compounds tested affected uterine tone. Pre‐incubation for 20 min with fraction 12 (20 to 80 μg ml−1), isolated from M. velutina produced a parallel and concentration‐dependent displacement to the right of the concentration‐response curves for BK and L‐BK (1 to 1000 nM). Schild plots of these data were linear (correlation close to unity), and yielded a nominal pA2 value (as g ml−1) of 5.1 and 4.9, respectively, and the values of the slopes were not significantly different from unity. Fraction 11 (10 to 40 μg ml−1) also produced a parallel and concentration‐dependent displacement to the right of the BK concentration‐response curve. The Schild plot gave a mean pA2 value (g ml−1) of 5.4 and a slope not significantly different from unity.

Fraction 12 did not influence the uterine contractile responses induced by ACh (0.1 to 100 μm) and oxytocin (0.01 to 30 miu ml−1) at concentrations less than 80 μg ml−1.

Fraction 16 (20 to 80 μg ml−1) antagonized the action of BK only at concentrations greater than 40 μg ml−1, whereas fraction 5 (20 to 80 μg ml−1) was completely inactive against BK‐induced responses.

As observed previously with the crude extract, the onset of the BK antagonistic action of these compounds was rapid and completely reversible following intermittent washing of the preparation for 30–60 min.

These results indicate the existence of at least two compounds in the crude extract of Mandevilla velutina that act as competitive and selective kinin antagonists on the isolated uterus of the rat.
Antinociception induced by systemic administration of local anaesthetics depends on a central cholinergic mechanism
Authors: Bartolini A. , Galli A. , Ghelardini C. , Giotti A. , Malcangio M. , Malmberg‐Aiello P. , Zucchi P.L.
Published: July 2012

The antinociceptive effects of systemically‐administered procaine, lignocaine and bupivacaine were examined in mice and rats by using the hot‐plate, writhing and tail flick tests.

In both species all three local anaesthetics produced significant antinociception which was prevented by atropine (5 mg kg−1, i.p.) and by hemicholinium‐3 (1 μg per mouse, i.c.v.), but not by naloxone (3 mg kg−1, i.p.), α‐methyl‐p‐tyrosine (100 mg kg−1, s.c.), reserpine (2 mg kg−1, i.p.) or atropine methylbromide (5.5 mg kg−1, i.p.).

Atropine (5 mg kg−1, i.p.) which totally antagonized oxotremorine (40 μg kg−1, s.c.) antinociception did not modify morphine (5 mg kg−1, s.c.) or baclofen (4 mg kg−1, s.c.) antinociception. On the other hand, hemicholinium, which antagonized local anaesthetic antinociception, did not prevent oxotremorine, morphine or baclofen antinociception.

Intracerebroventricular injection in mice of procaine (200 μg), lignocaine (150 μg) and bupivacaine (25 μg), doses which were largely ineffective by parenteral routes, induced an antinociception whose intensity equalled that obtainable subcutaneously. Moreover, the i.c.v. injection of antinociceptive doses did not impair performance on the rota‐rod test.

Concentrations below 10−10 m of procaine, lignocaine and bupivacaine did not evoke any response on the isolated longitudinal muscle strip of guinea‐pig ileum, or modify acetylcholine (ACh)‐induced contractions. On the other hand, they always increased electrically‐evoked twitches.

The same concentrations of local anaesthetics which induced antinociception did not inhibit acetylcholinesterase (AChE) in vitro.

On the basis of the above findings and the existing literature, a facilitation of cholinergic transmission by the local anaesthetics is postulated; this could be due to blockade of presynaptic muscarinic receptors.
Direct binding studies on ileal and cardiac muscarinic receptors
Authors: Michel Anton D. , Whiting Roger L.
Published: July 2012

Functional studies have indicated that muscarinic receptors in cardiac tissue differ from those in the ileum. In the present study ileal and cardiac muscarinic receptors identified by [3H]‐N‐methyl scopolamine ([3H]‐NMS) were characterized and the selectivity of currently available ileal and atrial selective antagonists determined.

In terms of the current functional classification of muscarinic receptors both ileal and cardiac muscarinic receptors were of the M2 subtype based upon their low affinity for pirenzepine.

Cyclohexylphenyl(2‐piperidinoethyl)silanol (CPPS), a highly ileal selective antagonist in functional studies, was unable to distinguish between ileal and atrial muscarinic receptors identified in binding studies. Furthermore, although AF‐DX 116 and dicyclomine were able to differentiate atrial and ileal muscarinic receptors, neither compound was more than 2 fold selective. These data indicate that it is not possible to subclassify ileal and atrial muscarinic receptors using direct ligand binding studies with these antagonists.

In circular ileal smooth muscle, apparent heterogeneity of the M2 muscarinic receptor population was observed. Thus AF‐DX 116 identified two populations of sites with affinities differing by 30 fold. These two populations of M2 muscarinic receptors may represent the typical M2 muscarinic receptors identified in cardiac tissue and the more recently discovered ‘gland type’ M2 muscarinic receptors.

The circular ileal smooth muscle tissue homogenate was able to decrease dramatically the apparent affinity of adiphenine. This activity, which appeared to result from a phenylmethylsulphonylfluoride (PMSF) sensitive protease effect, should be considered when conducting studies using this tissue preparation and compounds of similar structure to adiphenine.
Actions of amiloride analogues on prostacyclin synthesis by rat aortic rings
Authors: Ritter J.M. , Aksoy A. , Cragoe E.J. , Taylor G.W.
Published: July 2012

Fresh rat aortic rings were incubated in HEPES‐buffered salt solutions (pH 8.0) in the presence or absence of amiloride analogues. The effect of these drugs on prostacyclin (PGI2) synthesis was determined by radioimmunoassay of the stable hydrolysis product 6‐oxo‐prostaglandin (PG)F1α.

Amiloride and phenamil (potent inhibitors of epithelial Na+ transport) had no significant effect on basal or Ca2+‐stimulated PGI2 synthesis.

Several analogues previously reported to inhibit Na+/Ca2+ exchange caused a dose‐related increase in 6‐oxo‐PGF1α production in media containing NaCl 120 mm and CaCl2 2.5 mm. 2′,3′‐Benzobenzamil was the most potent analogue with a maximum stimulation of 4.51 ± 0.89 fold, and an EC50 of 3 × 10−5 m.

Amiloride analogues bearing substituents on the 5‐amino group of the pyrazine ring have been reported to inhibit Na+/H+ exchange more potently than Na+/Ca2+ exchange. Three of these compounds inhibited Ca2+‐stimulated 6‐oxo‐PGF1α production at concentrations that did not significantly influence basal 6‐oxo‐PGF1α production.
Metabolic requirements for release of endogenous noradrenaline during myocardial ischaemia and anoxia
Authors: Dart A.M. , Riemersma R.A. , Schömig A. , Ungar A.
Published: July 2012

The metabolic conditions required for noradrenaline (NA) release from ischaemic and anoxic perfused hearts of the rat were studied.

Forty minutes of flow reduction to approximately 0.25 ml g−1 min−1 did not elicit enhanced noradrenaline overflow from the isolated heart perfused with normoxic perfusate even in the absence of added substrate. Enhanced overflow did occur when substrate‐free ischaemia was induced after a 60 min period of substrate‐free perfusion.

Noradrenaline overflow was enhanced by perfusion at normal flow rates with an anoxic (PO2<1 mmHg) perfusate containing no substrate. Such enhanced overflow occurred in the absence of calcium in the perfusate and was almost completely abolished by the addition of 11 mm glucose.

Enhanced noradrenaline overflow occurring either during low flow ischaemia after substrate deprivation or during anoxic substrate‐free perfusion at normal flow rates was markedly suppressed by desipramine.

Exocytotic noradrenaline overflow induced by electrical stimulation of the left cervico‐thoracic ganglion continued unchanged during 60 min of anoxia if the perfusate contained 11 mm glucose. In the absence of added substrate there was a decline in the overflow induced by such stimulation which was more rapid with anoxic than normoxic perfusate.

Re‐introduction of calcium, oxygen and substrate after 10, 20 or 30 min of calcium‐free, substrate‐free, anoxic perfusion was associated with a massive overflow of the intracellular enzyme lactate dehydrogenase. At 10 min there was an associated transient minor increase in NA overflow but at 20 and 30 min the overflow of NA, elevated as a result of anoxic perfusion, returned to pre‐anoxic levels on the re‐introduction of substrate and oxygen.

These studies demonstrate a central role for the metabolic status of the sympathetic nerve terminal in determining the magnitude of exocytotic and nerve‐impulse independent noradrenaline release from the heart. During the course of myocardial ischaemia in vivo nerve‐impulse independent release would be expected to occur only in regions of severe flow reduction. This may produce heterogeneous stimulation of the myocardium.
Triazolodiazepines: dissociation of their Paf (platelet activating factor) antagonistic and CNS activity
Authors: Casals‐Stenzel J. , Weber K.H.
Published: July 2012

The relationship between the activity of thieno‐ or benzo‐triazolodiazepines on platelet‐activating factor (Paf)‐induced effects and on the CNS (central nervous system) was studied in vitro and in vivo.

Brotizolam and triazolam inhibited Paf‐induced human platelet aggregation. The IC50 ‐ values were 0.54 and 7.6 μm, respectively. This inhibitory effect was not blocked by the specific central‐type benzodiazepine (BDZ) antagonist, Ro 15–1788, or the specific peripheral‐type BDZ ligand, Ro 5–4846. These BDZ ligands also showed an inhibitory effect on Paf‐induced platelet aggregation (IC50 = 200 and 560 μm, respectively). Ro 15–1788 or Ro 5–4846 in combination with brotizolam or triazolam enhanced the Paf inhibitory effect of these triazolodiazepines.

In guinea‐pigs, Ro 15–1788, 100 mg kg‐1p.o. and 10 mg kg‐1 i.v. completely inhibited the hypnogenic effect of 10 mg kg−1 p.o. and 1 mg kg−1 i.v. of brotizolam, respectively. Similar results were obtained with triazolam but at higher doses.

In anaesthetized guinea‐pigs, a dose of 100 mg kg‐1 p.o. of Ro 15–1788 did not inhibit bronchoconstriction and hypotension caused by Paf (30 ngkg−1 min−1 i.v.). The combination of brotizolam (10 mg kg−1 p.o.) or triazolam (200 mg kg−1 p.o.) with this BDZ antagonist (100 and 400 mg kg‐1 p.o., respectively) did not affect the Paf inhibitory activity of these triazolodiazepines.

These results show that the Paf antagonistic properties of the triazolodiazepines can be dissociated from their CNS activity. It is conceivable that compounds of this structural type could be the forerunners of a novel series of potent Paf antagonists.
Anticonvulsant effects of some calcium entry blockers in DBA/2 mice
Authors: De Sarro G.B. , Meldrum B.S. , Nisticó G.
Published: July 2012

The behavioural and anticonvulsant effects of several drugs acting by various mechanisms on calcium‐channels or affecting intracellular Ca2+ concentrations were studied after both systemic and intracerebroventricular administration in DBA/2 mice, a strain genetically susceptible to sound‐induced seizures.

The anticonvulsant effects were evaluated on seizures evoked by means of auditory stimulation (109 dB) in animals placed singly under a perspex dome.

Flunarizine and dihydropyridine derivatives, belonging to class I of calcium entry blockers, administered intraperitoneally, were the most potent compounds.

Diltiazem, a benzothiazepine derivative belonging to class III, and HA 1004, a calcium antagonist, acting by inhibiting Ca2+ mobilization from intracellular stores, injected intraperitoneally, were 3–7.6 fold and 5.8–10.7 fold less potent than flunarizine respectively.

Verapamil and methoxyverapamil, two phenylalkylamine derivatives, given intraperitoneally, were completely ineffective in preventing sound‐induced seizures in DBA/2 mice. In addition, high doses of verapamil and its methoxyderivative occasionally produced spontaneous tonic‐clonic seizures.

After intracerebroventricular administration of the hydrosoluble calcium entry blockers, belonging to different classes, the anticonvulsant effects were similar to those observed after systemic administration.

The systemic administration of Bay K 8644, a dihydropyridine analogue, having the ability to stimulate calcium entry into cells produced a dose‐dependent increase in clonic and tonic convulsions and other neurological side effects.

The present results strongly support the idea that some Ca2+ antagonists may be useful in human epilepsy.
Lysophosphatidylcholine‐induced arrhythmias and its accumulation in the rat perfused heart
Authors: Man Ricky Y.K.
Published: July 2012

The tissue level of lysophosphatidylcholine (LPC) was determined in rat hearts perfused with a solution containing 5 μm LPC. The relationship between LPC accumulation and the severity of arrhythmias produced was examined.

The accumulation of LPC was dependent on the perfusion time and this accumulation was associated with the occurrence of severe arrhythmias. A positive correlation between the tissue LPC content and the arrhythmia score was found (P < 0.01).

No consistent alteration in total phospholipid, phosphatidylcholine or cholesterol content was found. This suggests that LPC‐induced arrhythmias are not associated with alterations of major lipid components in the heart.

When severe arrhythmias occurred in the presence of LPC in the rat perfused heart, less than 2% of total tissue phospholipid was in the form of LPC.

The positive correlation between LPC accumulation and the occurrence of arrhythmias suggests a cause and effect relationship of LPC with cardiac arrhythmias in the rat perfused heart. However, in the ischaemic heart, other biochemical factors can contribute, to different degrees, to ischaemia‐induced cardiac arrhythmias.
A study of the actions of P1‐purinoceptor agonists and antagonists in the mouse vas deferens in vitro
Authors: Blakeley A.G.H. , Dunn P.M. , Petersen S.A.
Published: July 2012

We have examined the effects of purinoceptor agonists and antagonists on the mechanical ‘twitch’ response, excitatory junction potential (e.j.p.) amplitude and [3H]‐noradrenaline overflow in the mouse vas deferens.

The agonist profile for inhibition of the mechanical response was N6‐([R]‐2‐phenylisopropyl)adenosine (l‐PIA) ⋍ N6‐cyclohexyladenosine (CHA) > 5′ N‐ethylcarboxamidoadenosine (NECA) > 2‐chloroadenosine (2ClA) ⋍ N6‐([S]‐2‐phenylisopropyl)adenosine (d‐PIA).

The P1‐purinoceptor agonists inhibited the e.j.p. with an agonist profile of CHA > l‐PIA NECA > 2ClA.

2ClA inhibited [3H]‐noradrenaline overflow with an EC50 of 1.2 μm which was not significantly different from the values for inhibition of the e.j.p. and the mechanical response.

The inhibitory action of 2ClA on the mechanical response was antagonized by 5 μm 8‐phenyltheophylline (8‐PT). However, neither blockade of P1‐purinoceptors by 8‐PT nor increasing the rate of degradation of endogenous adenosine by addition of adenosine deaminase had any effect on the mechanical response per se. 8‐PT (5 μm) also failed to alter the e.j.p. amplitude or [3H]‐noradrenaline overflow.

These results indicate that there are P1‐purinoceptors present on sympathetic nerve terminals of the mouse vas deferens which are more like A1‐ than A2‐receptors, but may be better classified as being of the A3‐subtype (Ribeiro & Sebastiao, 1986). These receptors are not normally involved in the feedback regulation of transmitter release in this tissue.