bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of cholesteryl ester deposition in macrophages by calcium entry blockers: an effect dissociable from calcium entry blockade
Authors: Daugherty Alan , Rateri Debra L. , Schonfeld Gustav , Sobel Burton E.
Published: July 2012

The effects of calcium entry blockers on stimulated cholesteryl [3H]‐oleate deposition in cultured macrophages were characterized in order to elucidate mechanisms underlying possible antiatheros‐clerotic effects. Stimulation of intracellular cholesteryl [3H]‐oleate deposition was initiated by incubation of macrophages with β‐very low density lipoproteins (β‐VLDL).

Nifedipine (Class I) markedly reduced cholesteryl [3H]‐oleate deposition at all concentrations tested. However, Bay K 8644, a dihydropyridine which is known to stimulate calcium entry, also reduced cholesteryl [3H]‐oleate deposition with a similar potency to nifedipine.

The effects of three Class II calcium entry blockers were evaluated: verapamil, methoxyverapamil, and diltiazem. Verapamil inhibited cholesteryl [3H]‐oleate deposition in a concentration‐dependent manner. Similarly, methoxyverapamil reduced cholesteryl [3H]‐oleate deposition in a concentration‐dependent manner although the reduction was not as great as that produced by verapamil. In contrast, diltiazem at any concentration tested did not inhibit cholesteryl [3H]‐oleate deposition.

Flunarizine (a Class III calcium entry blocker) produced a modest stimulation of cholesteryl [3H]‐oleate deposition at the lowest concentration used (10−7 m) but marked depression at the highest concentration (10−5 m).

The results indicate calcium entry blockers may exert protective effects on the development of atherosclerosis in animal models of diet‐induced hyperlipidaemia by inhibiting intracellular cholesteryl ester deposition, but this effect may not be related to their calcium entry‐blocking effects.
Cytoprotective effects of disodium cromoglycate on rat stomach mucosa
Authors: Goossens J. , Van Reempts J. , Van Wauwe J.P.
Published: July 2012

The cytoprotective effects of the anti‐asthmatic drug, disodium cromoglycate (DSCG), on gastric mucosal necrosis induced by ethanol in rats were studied. Subcutaneous, but not oral, DSCG prevented the formation of gastric lesions and this effect was dose‐dependent between 1.25 and 40 mg kg−1, with an ED50 value of 6.8 mg kg−1. Maximal cytoprotection occurred 15–30 min after DSCG treatment.

Histological examination revealed that DSCG effectively protected the gastric mucosa against ethanol‐induced vascular congestion, haemorrhage, epithelial desquamation and mucosal oedema.

Enhanced production of endogenous prostaglandins, which are known cytoprotective compounds, could not explain the mucosal protection. At a dose of 40 mg kg−1, DSCG did not change prostaglandin E2 or 6‐keto‐prostaglandin F1α concentrations in gastric mucosal tissue, although its cytoprotective activity was partially inhibited by prior treatment of the animals with indomethacin.
GABAergic modulation of a substance P‐mediated reflex of slow time course in the isolated rat spinal cord
Authors: Akagi Hiroyuki , Yanagisawa Mitsuhiko
Published: July 2012

The effects of γ‐aminobutyric acid (GABA) and other drugs which interact with GABA receptors were studied on a reflex of slow time course in the spinal cord preparation isolated from the neonatal rat.

A single shock to a dorsal root (L3‐L5) elicited a stereotyped series of reflexes, consisting of fast and slow components, recorded from the contralateral ventral root of the corresponding segment. The slow component, i.e. the contralateral slow ventral root potential (v.r.p.) had a time‐to‐peak of 2–5 s and lasted 20–30 s.

Bath‐application of GABA (5–20 μm) or muscimol (0.05‐0.5 μm) caused a decrease in the amplitude of the contralateral slow v.r.p. without producing any change in the d.c. potential recorded from the ventral root. The monosynaptic reflex recorded from the ipsilateral ventral root was not changed by the drugs at these concentrations.

Diazepam (0.1−1 μm) potentiated the depolarizing response of the dorsal root to GABA and markedly depressed the contralateral slow v.r.p. Neither the d.c. potential of the ventral root nor the dorsal root was changed by diazepam. The monosynaptic reflex was also unaffected by the drug.

Bicuculline (1 μm) suppressed the GABA‐induced depolarization recorded from the dorsal root whilst it markedly potentiated the contralateral slow v.r.p.

Baclofen at concentrations from 0.01 to 0.1 μm reduced the contralateral slow v.r.p. The inhibitory action of baclofen on the contralateral slow v.r.p. was more marked than on the monosynaptic reflex.

The depolarization of the ventral root induced by a brief application of substance P (SP) was depressed by muscimol, diazepam and baclofen, whereas the depolarization was potentiated by bicuculline.

The present results suggest that an intraspinal GABAergic inhibitory mechanism plays a role in the modulation of certain slow spinal reflexes. They also support the hypothesis that SP released from certain primary afferent fibres is a neurotransmitter involved in the contralateral slow v.r.p.
Identification of 13,14‐dihydro‐15‐oxo‐prostaglandin F2α in the circulation during infusions of bradykinin and prostaglandin E2 in man
Authors: Barrow S.E. , Cockcroft J. , Dollery C.T. , Hickling N.E. , Ritter J.M.
Published: July 2012

Bradykinin, prostaglandin E2 (PGE2), PGD2 and vehicle (saline) were each administered intravenously on separate occasions to 6 healthy men for a period of 60 min.

13,14‐Dihydro‐15‐oxo‐PGF2α was identified in plasma samples obtained during intravenous infusions of bradykinin and PGE2 but not during infusions of PGD2 or saline.

The structure of this metabolite was verified by comparison of three different derivatives with authentic standards, using gas chromatography/electron capture mass spectrometry.

Bradykinin increased plasma concentrations of 13,14‐dihydro‐15‐oxo‐PGF2α from baseline values in the range < 5–10 pg ml−1 to 28–403 pg ml−1. PGE2 increased plasma concentrations of 13,14‐dihydro‐15‐oxo‐PGF2α from baseline values in the range < 5–17 pg ml−1 to 160–603 pg ml−1. Neither PGD2 nor the vehicle affected 13,14‐dihydro‐15‐oxo‐PGF2α concentrations.

We conclude that bradykinin‐stimulated 13,14‐dihydro‐15‐oxo‐PGF2α may be derived from PGE2 or PGF2α. The possibility that these prostaglandins are synthesized by stimulation of microvascular endothelium during bradykinin infusion is discussed.
The effects of intraperitoneal administration of antagonists and development of morphine tolerance on the antinociception induced by stimulating the anterior pretectal nucleus of the rat
Authors: Rees H. , Prado W.A. , Rawlings S. , Roberts M.H.T.
Published: July 2012

The effects of intraperitoneal administration of antagonists to morphine, 5‐hydroxytryptamine (5‐HT), noradrenaline and dopamine have been studied on the antinociceptive effects of electrical stimulation of the anterior pretectal nucleus (APtN) of the rat.

A 15 s period of 35 μA sine wave stimulation of APtN significantly increased the latency of the tail flick reflex to noxious heat for periods up to 1 h.

Naloxone (0.25‐1.0 mg kg−1) attenuated the effects of APtN stimulation in a dose‐dependent manner. In rats made tolerant to morphine by daily administration of morphine, the antinociceptive effects of APtN stimulation were significantly reduced.

The 5‐HT receptor antagonists methysergide (5 mg kg−1) and ketanserin (1 mg kg−1), the dopamine receptor antagonist haloperidol (1 mg kg−1) and the β‐adrenoceptor antagonist propranolol (1 mg kg−1) had little effect on the antinociceptive effects of stimulating the APtN.

α‐Adrenoceptor antagonists caused a dose‐dependent antagonism of the response. The order of potency was; idazoxan > prazosin > phenoxybenzamine, the respective ED50 for each drug being 0.08: 0.45: 1.5 mg kg−1.

It is concluded that antagonism at opioid receptors and α‐adrenoceptors but not β‐adrenoceptors, dopamine or 5‐HT receptors reduces the antinociceptive effects of APtN stimulation. This differs from the reported effects of these antagonists on the antinociception caused by stimulating other sites in the brain.
Calcitonin gene‐related peptide (CGRP) is a potent non‐endothelium‐dependent inhibitor of coronary vasomotor tone
Authors: Greenberg Barry , Rhoden Kerry , Barnes Peter
Published: July 2012

Ring segments of bovine left circumflex coronary artery were pre‐contracted with 5‐hydroxytryptamine or phenylephrine and then exposed to increasing concentrations of calcitonin gene‐related peptide (CGRP) and other drugs.

CGRP administration resulted in dose‐dependent inhibition of induced tone. Maximal relaxation to CGRP was 89 ± 5% and the concentration required to achieve 50% maximal relaxation (EC50) was 2.11 ± 1.35 × 10−9 m.

CGRP‐induced relaxation was not affected by removal of endothelial cells nor was it significantly altered by incubation of coronary vessels with atropine, propranolol, phentolamine (all 10−6 m) or indomethacin (10−5 m).

From these data we conclude that CGRP is a potent inhibitor of coronary artery vasomotor tone which appears to act directly on vascular smooth muscle rather than through the release of a secondary mediator. These data support the possibility that CGRP may play a role in non‐adrenergic, non‐cholinergic regulation of coronary artery tone.
Inhibition of adrenomedullary catecholamine release by propranolol isomers and clonidine involving mechanisms unrelated to adrenoceptors
Authors: Orts Alfredo , Orellana Carmen , Cantó Tomás , Ceña Valentín , González‐García Carmen , García Antonio G.
Published: July 2012

Transmural electrical stimulation (10 Hz, 40 V, 1 ms for 60 s) increased total catecholamine secretion from perfused cat adrenal glands; this respnse was enhanced by neostigmine and inhibited by mecamylamine, suggesting that release of acetylcholine from splanchnic nerve terminals was stimulating nicotinic receptors and enhancing catecholamine secretion.

Isoprenaline, (‐)‐propranolol and (+)‐propranolol (10−7‐10−5 m) inhibited the electrically‐evoked secretory response by 40–70%; similar reductions were obtained with clonidine and yohimbine. Neither, (+)‐propranolol nor (‐)‐propranolol inhibited K‐evoked secretion from cat adrenals; in contrast, nimodipine potently inhibited it (IC50 = 24 nm).

Either, racemic propranolol or the (+)‐ or (‐)‐isomers (1–10 μm) equally inhibited [3H]‐noradrenaline release evoked by nicotine or acetylcholine from cultured bovine adrenal chromaffin cells; clonidine (10 μm) inhibited secretion by 50% and yohimbine or isoprenaline did not affect it.

The results indicate that adrenomedullary catecholamine release evoked by splanchnic nerve stimulation is not modulated by α‐or β‐adrenoceptors and suggest that propranolol may inhibit secretion by blocking ion fluxes through the acetylcholine receptor ionophore. Clonidine may inhibit secretion by this same mechanism, and/or by interfering with some intracellular event in the secretory mechanism.
New synthetic antagonists of bradykinin
Authors: Schachter M. , Uchida Y. , Longridge D.J. , Labedz T. , Whalley E.T. , Vavrek R.J. , Stewart J.M.
Published: July 2012

A new synthetic bradykinin analogue was found to be an antagonist of bradykinin‐induced vascular permeability in rabbit skin. It was effective in equimolar concentrations.

These analogues also antagonized the action of bradykinin in contracting the guinea‐pig isolated ileum. The mean pA2 values of five different antagonists ranged from 5.3–6.4 respectively, on this preparation.

Our observations, together with those of others suggest that these antagonists act on the same receptor types, viz., B2, in rabbit blood vessels and in smooth muscle of guinea‐pig ileum.

Our results support the view that the way is now promising for the synthesis of potent specific antagonists of bradykinin for experimental and therapeutic use.
[3H]‐verapamil binding to rat cardiac sarcolemmal membrane fragments; an effect of ischaemia
Authors: Dillon J. S. , Nayler W.G.
Published: July 2012

The [3H]‐verapamil binding activity of rat cardiac sarcolemmal fragments was studied, using membranes harvested from non‐perfused, aerobically‐perfused and ischaemic hearts.

Glass‐fibre filters were found to contain specific, high affinity ‐(KD 38 ± 3.1 nm) [3H]‐verapamil binding sites‐making them unsuitable for use in [3H]‐verapamil binding studies.

Incubation of membranes from non‐perfused hearts in a medium containing 150 mm NaCl, 1 mm CaCl2 and 50 mm Tris revealed two populations of [3H]‐verapamil binding sites. When centrifugation instead of filtration was used to separate bound and free [3H]‐verapamil, high affinity sites with a KD of 0.57 ± 0.19 μm and a Bmax of 38 ± 5.2 pmol mg−1 protein, and low affinity sites with a KD of 78 ± 27.5 μm and a Bmax of 2.9 ± 1.3 nmol mg−1 protein were detected. However, only low affinity binding sites could be detected in membranes which had been incubated in a cation‐free medium containing 50 mm Tris.

[3H]‐verapamil binding to the low and high affinity sites was saturable, reversible, stereospecific and displaceable by D600>diltiazem>Ca2+ but not by nifedipine, nitrendipine, nisoldipine or prazosin.

The two populations of binding sites survived aerobic perfusion and 60 min ischaemia at 37°C. Ischaemia reduced the Bmax and KD but selectivity was maintained.
Differential effect of temperature on histamine‐ and carbachol‐stimulated inositol phospholipid breakdown in slices of guinea‐pig cerebral cortex
Authors: Carswell Heather , Galione A.G. , Young J.M.
Published: July 2012

Slices of guinea‐pig cerebral cortex were incubated with [3H]‐inositol at 37°C before exposure to histamine or carbachol at 37°C or 25°C. Histamine‐stimulated accumulation of [3H]‐inositol 1‐phosphate ([3H]‐IP1) at 25°C was only 5–7% of that at 37°C, whereas for carbachol the response at 25°C was 45–49% of that at 37°C.

The affinity of benzilylcholine, obtained from inhibition of carbachol‐induced accumulation of [3H]‐IP1 was similar at 25°C and 37°C, but the EC50 for carbachol was lower at 25°C (20 ± 2 μm) than at 37°C(42 ± 2 μm).

The IC50 for histamine inhibition of [3H]‐mepyramine binding to homogenates of guinea‐pig cerebral cortex did not differ significantly at 25°C and 37°C.

Histamine‐induced accumulations of [3H]‐IP2 and [3H]‐IP3 at 25°C, expressed as a percentage of the accumulation at 37°C, were also much less than the corresponding value for carbachol.

These observations imply that the locus or pathway(s) of agonist‐induced formation of([3H]‐IP1) are not the same for histamine and carbachol.
Effects of tachykinins on inositol phospholipid hydrolysis in slices of hamster urinary bladder
Authors: Bristow D.R. , Curtis N.R. , Suman‐Chauhan N. , Watling K.J. , Williams B.J.
Published: July 2012

Tachykinin‐stimulated inositol phospholipid hydrolysis was examined in slices of hamster urinary bladder.

In the presence of lithium, to inhibit inositol monophosphatase activity, substance P, eledoisin and related tachykinins induced large, dose‐dependent increases in [3H]‐inositol monophosphate accumulation.

The responses to substance P and eledoisin were not antagonized by the cholinoceptor antagonist, atropine.

The rank order of potency for various tachykinins was kassinin ≫ neurokinin A ≫ neurokinin B ≫ eledoisin ≫ physaelamin ≫ substance P ≫ substance P methyl ester.

The synthetic analogue [p‐Glu6, D‐Pro9] SP (6–11) was considerably more potent than its L‐prolyl stereoisomer at stimulating inositol phospholipid hydrolysis.

These results suggest that in the hamster urinary bladder, tachykinin‐induced inositol phospholipid breakdown is mediated via tachykinin receptors of the SP‐E type, as opposed to the SP‐P type.
Celiprolol: a positive inotropic β‐adrenoceptor blocking agent in conscious dogs
Authors: Nganele David M. , DeLeonardis V. Maria , Hintze Thomas H.
Published: July 2012

β‐Adrenoceptor blocking agents are used to manage various cardiovascular disorders. A limiting factor in their use is the suppression of the cardiac contractile state. In our study, we examined the cardiac effects of celiprolol, a new β‐adrenoceptor blocking agent with reported positive inotropic effects.

Dogs were instrumented by use of sterile surgical techniques for the study of myocardial inotropic state, heart rate and internal left ventricular dimensions. Following complete recovery from surgery, experiments were conducted in the conscious state.

Intravenous injection of celiprolol (3 mg kg−1) in nine dogs, increased LV dP/dt by 13 ± 2.6%, velocity of shortening (LV dD/dt) by 9.2 ± 3.4%, and heart rate by 19 ± 4.6% and decreased LV end‐diastolic diameter by 1.8 ± 0.8%, all significantly (P < 0.05). Celiprolol blocked the inotropic actions of isoprenaline (0.5 μg kg−1) but only partially reduced its hypotensive effects. Propranolol, in contrast, reduced LV dP/dt by 17 ± 3.3% and heart rate by 8.1 ± 2.7% (P < 0.05) while totally abolishing the hypotension, tachycardia and increase in LV dP/dt caused by isoprenaline. Following β‐adrenoceptor blockade with propranolol and with heart rate held constant by electrical pacing, celiprolol increased LV dP/dt by 16 ± 4.0%, LV dD/dt by 12 ± 3.0% and reduced LV end‐diastolic diameter by 3.5 ± 0.5% (P < 0.05).

Thus, in conscious dogs, celiprolol increases inotropic state and reduces preload independently of β‐adrenoceptor mechanisms and the Bowditch phenomenon, while effectively blocking β‐receptors in the heart. These properties would make celiprolol useful in patients where a conventional β‐adrenoceptor blocking agent might lead to pump failure.
Secretion, pain and sneezing induced by the application of capsaicin to the nasal mucosa in man
Authors: Geppetti Pierangelo , Fusco Bruno M. , Marabini Simone , Maggi Carlo Alberto , Fanciullacci Marcello , Sicuteri Federigo
Published: July 2012

Topical application of capsaicin to the human nasal mucosa induced a burning sensation and sneezing. A dose‐dependent seromucous nasal secretion was also observed. Capsaicin (75 μg) was more potent than methacholine (50 mg) in producing nasal secretion, while topical histamine (200 μg), substance P (135 μg) and calcitonin gene‐related peptide (36 μg) did not induce rhinorrhea.

Pretreatment with either topical ipratropium bromide, systemic dexchlorpheniramine or indomethacin did not influence the effects induced by capsaicin. Topical pretreatment with lidocaine inhibited the painful sensation but failed to block the rhinorrhea. Desensitization to the effects of capsaicin occurred following 4–5 subsequent applications, and full recovery was observed within 30–40 days.

It is proposed that the effects of capsaicin in human nasal mucosa are due to excitation of primary afferent neurones that (a) convey burning and painful sensation, (b) evoke a sneezing reflex and (c) induce nasal secretion by releasing transmitter(s) from their peripheral terminals.
Evidence that inhibitory factor extracted from bovine retractor penis is nitrite, whose acid‐activated derivative is stabilized nitric oxide
Authors: Martin William , Smith Jerry A. , Lewis Malcolm J. , Henderson Andrew H.
Published: July 2012

Unactivated extracts of bovine retractor penis (BRP) contain 3–7 μm nitrite. Acid‐activation of these extracts at pH 2 for 10 min followed by neutralization generates the active form of inhibitory factor (IF; assayed by its vasodilator action on rabbit aorta), and is associated with partial loss of nitrite.

Increasing the time of acid‐activation at pH 2 from 10 to 60 min with intermittent vortex mixing generates greater vasodilator activity and increases nitrite loss.

When acid‐activated and neutralized extracts are incubated at 37°C or 30 min or boiled for 5 min, vasodilator activity is lost and nitrite content increased. Reactivation of these samples at pH 2 for 10 min followed by neutralization leads to partial recoveries of vasodilator activity with loss in nitrite content.

Addition of sodium nitrite to BRP extracts increases acid‐activatable vasodilator activity pro rata.

Acid‐activation of aqueous sodium nitrite solutions results in less loss of nitrite and generation of less vasodilator activity than BRP extracts. Vasodilatation is only transient and is rapidly abolished on neutralization, whereas responses to acid‐activated BRP extracts are more prolonged and activity is stable on ice.

Bovine aortic endothelial cells yield vasodilator activity that is indistinguishable from that isolated from BRP. It is activated by acid, stable on ice, abolished by boiling or by haemoglobin, and appears to be due to the generation of nitric oxide (NO) from nitrite.

The data provide confirmatory evidence that nitrite in BRP extracts is IF, that acid‐activation of BRP extracts yields NO which is responsible for its vasodilator action, and that inactivation occurs by decay of NO to nitrite and nitrate. They further suggest that BRP extracts contain a NO‐stabilizing agent which favours conversion of nitrite to NO.

The finding that bovine aortic endothelial cells yield an agent indistinguishable from IF suggests that nitrite in endothelial cells may likewise be the precursor of endothelium‐derived relaxing factor (EDRF), itself identified as NO.
Endothelium‐derived relaxing factor (EDRF) and resistance vessels in an intact vascular bed: a microangiographic study of the rabbit isolated ear
Authors: Griffith T.M , Edwards D.H. , Davies R. Ll , Harrison T.J. , Evans K.T.
Published: July 2012

Microradiographic techniques have been used to show that endothelium‐derived relaxing factor (EDRF), which is believed to be nitric oxide, influences vasomotor responses in small arteries and arterioles down to 25 μm in diameter in an isolated, intact, buffer‐perfused ear preparation of the rabbit. Arteries down to 75 μm in diameter, i.e. the central ear artery (G0) and its first three generations of branch vessels (G1, G2 and G3) were studied quantitatively.

Relative constrictor responses to 1 μm 5‐hydroxytryptamine (5‐HT) and the combination of 1 μm 5‐HT and 1 μm histamine diminished progressively from G0 to G3. Constrictor responses to 5‐HT were doubled in all generations by 1 μm haemoglobin which abolishes EDRF activity.

Relative dilator responses to acetylcholine or to substance P in preconstricted arteries were, in contrast, equal in the different generations. Mean —log (IC50) values calculated from diameter measurements were 7.63 ± 0.10 m and 9.80 ± 0.11 m, respectively. These dilator responses were abolished by 1 μm haemoglobin, implying that they were EDRF‐mediated. Spatial homogeneity of relative dilator responses was found also with glyceryl trinitrate (10 or 50 μm) whose activity is thought to depend on biotransformation to nitric oxide, in both the presence and the absence of haemoglobin.

This finding of spatial homogeneity of the diameter response to changes in EDRF activity (or to glyceryl trinitrate) implies that EDRF influences hydrodynamic resistance more in vessels where constrictor tone is high.
Suramin: a reversible P2‐purinoceptor antagonist in the mouse vas deferens
Authors: Dunn P.M. , Blakeley A.G.H.
Published: July 2012

The trypanocide Suramin was tested as a possible antagonist at the P2‐purinoceptor of the mouse vas deferens. At a concentration of 100 μm, Suramin antagonized the response to α,β‐methylene ATP, while responses to carbachol and noradrenaline were unaffected. These results suggest that Suramin may provide a starting point for the development of specific antagonists for P2‐purinoceptors.
Benoxaprofen activates membrane‐associated oxidative metabolism in human polymorphonuclear leucocytes by apparent modulation of protein kinase C
Authors: Lukey Pauline T. , Anderson Ronald , Dippenaar Ursula H.
Published: July 2012

The non‐steroidal anti‐inflammatory drug (NSAID) benoxaprofen at concentrations of 15, 30 and 60 μg ml−1 caused a dose‐related activation of superoxide generation by human polymorphonuclear leucocytes (PMNL) in vitro.

The protein kinase C (PKC) inhibitor H‐7 prevented benoxaprofen‐mediated activation of superoxide generation by PMNL.

Benoxaprofen, by apparent substitution for phosphatidylserine, caused a dose‐related activation of purified PKC from rat brain and in cytosolic extracts from human platelets.

Benoxaprofen‐mediated stimulation of PMNL membrane‐associated oxidative metabolism is due to apparent activation of PKC by this NSAID. These findings establish the molecular basis of the pro‐oxidative properties of benoxaprofen.
Zn2+ stimulates spontaneous transmitter release at mouse neuromuscular junctions
Authors: Nishimura Masakazu
Published: July 2012

Experiments were carried out to examine the effect of Zn2+ on the rate of spontaneous release of transmitter at the neuromuscular junction of the mouse diaphragm muscle, in the presence and absence of external Ca2+. Miniature endplate potentials (m.e.p.ps) were measured in vitro.

Zn2+ markedly elevated the frequency of m.e.p.ps without affecting the resting membrane potential of muscle fibres. This effect was time‐ and concentration‐dependent but was independent of the presence of external Ca2+. In a Ca2+‐free bathing solution, Zn2+ frequently produced twitching in several fibres. The twitching dislodged the microelectrode. Replacement of the 10 mm NaCl in the Ca2+‐free solution with equimolar KCl overcame this difficulty. The experiments summarized below were done in the Ca2+‐free bathing solution which contained 10 mm KCl instead of 10 mm NaCl.

The effect of Zn2+ was transient and required a latent period of many minutes. Low temperature (24°C) increased the length of this latent period and reduced the maximum effect of Zn2+.

Zn2+ increased the frequency of m.e.p.ps in K+‐free (replaced with NaCl) solution. The effect appeared with shorter latency in this solution compared to the standard Krebs‐Ringer solution.

The effect of Zn2+ was partially antagonized by dantrolene sodium or by neomycin. Both agents also reduced the effect of external Ca2+ on m.e.p.ps in depolarizing solution.

Cd2+ and 2,3‐bisphosphoglycerate also elevated the frequency of m.e.p.ps in a manner independent of external Ca2+, but the latter compound was much less potent than Cd2+.

These experiments provide evidence for a role of intracellularly stored Ca2+ in the release of transmitter at the motor nerve terminal. The release of Ca2+ from the storage site may be coupled with the metabolism of phosphatidylinositol.
14β‐Hydroxyprogesterone binds to the digitalis receptor, inhibits the sodium pump and enhances cardiac contractility
Authors: Bose D. , Elliott D. , Kobayashi T. , Templeton J.F. , Kumar V.P.S. , LaBella F.S.
Published: July 2012

Certain derivatives of progesterone are potent inhibitors of high affinity, specific binding of 3H‐cardiac glycosides. The steroids interact at the cardiac glycoside site on Na,K‐ATPase and inhibit the enzyme (the sodium pump) in cardiac and other tissues. However, the active congeners identified previously have been, unlike the cardiac glycosides, predominantly cardiodepressant.

Because a 14β‐hydroxy substituent is an important determinant of activity of the cardiotonic cardiac glycosides, we synthesized 14β‐hydroxyprogesterone. This derivative has about one‐tenth the potency of the aglycone, ouabagenin, in a [3H]‐ouabain binding assay.

Like ouabagenin, but in contrast to the cardiodepressant congeners of progesterone, 14β‐hydroxyprogesterone consistently elicited positive inotropy in isolated cardiac muscle and enhanced both the magnitude and frequency of fluctuations in scattered light (an index of oscillatory intracellular release of calcium).

Thus, at least one hydroxylated derivative (and putative endogenous metabolite) of progesterone, mimics the cardiac effects of cardiac glycosides including enhanced contractility.
The inhibitory effect of somatostatin peptides on the rat anococcygeus muscle in vitro
Authors: Priestley T. , Woodruff G.N.
Published: July 2012

Electrically evoked contractions of the rat anococcygeus muscle were inhibited in a concentration‐dependent manner by somatostatin‐14 (SS14), −28 (SS28) and two synthetic hexapeptide analogues: L‐363,301 and L‐363,586 , with pIC50 values of 7.41, 7.38, 7.07 and 8.34, respectively.

The inhibitory effects of SS14 were dependent on stimulation frequency and external calcium ion concentration. Calcium behaved as a non‐competitive antagonist of SS14, it reduced the maximal inhibitory effect of the peptide and at a concentration of 5.08 mm it significantly affected the pIC50 value.

SS14 (3 times 10−7 m) did not affect the tonic actions of bath‐applied noradrenaline in the absence of field stimulation.

The effects of SS14 persisted in naloxone (10−5 m) and were, therefore, not due to an action at opiate receptors. Furthermore, experiments involving the lyophilisation of bath contents, showed no evidence to support an indirect mechanism involving the release of an endogenous inhibitory substance.

High concentrations (10−5 m) of SS14 or L‐363,301 inhibited the relaxation response evoked by electrical stimulation of guanethidine (3 times 10−4 m)‐treated preparations.

These results are consistent with similar actions of SS14 on other smooth muscle preparations and are presumed to reflect a presynaptic inhibition of transmitter release by a direct action on somatostatin receptors. The antagonistic effect of calcium on this response is discussed with reference to a possible role in receptor desensitization.
Blockade of vasopressor and vas deferens responses by α, β‐methylene ATP in the pithed rat
Authors: Bulloch J.M. , McGrath J.C.
Published: July 2012

The pressor responses produced by the intravenous administration of α,β‐methylene ATP were tachyphylactic.

α,β‐Methylene ATP can attenuate pressor responses to sympathetic nerve stimulation both in the presence and in the absence of α‐adrenoceptor blocking agents.

α,β‐Methylene ATP has no effect on the pressor responses produced by bolus injections of noradrenaline.

In the presence of α‐adrenoceptor blocking agents, α,β‐methylene ATP further attenuates contractions of the vas deferens produced by nerve stimulation.

The results, together with previous data, suggest that the vasopressor response to stimulation of the sympathetic outflow in the rat is partly purinergic and partly α‐adrenergic and that this occurs as co‐transmission. The same applies to rat vas deferens, confirming in vitro data. The pithed rabbit had an α‐blocker‐resistant vasopressor nerve‐mediated response but this was resistant to α,β‐methylene ATP.
Effects of atropine and tetrodotoxin on neurotensin‐induced ileal sodium transport in the dog
Authors: Mailman David
Published: July 2012

Neurotensin was infused intravenously, in the presence or absence of intravenous atropine or intraarterial tetrodotoxin, into dogs anaesthetized with sodium pentobarbitone. Net and unidirectional fluxes of sodium and blood flows in the ileum were measured. Arterial and mesenteric venous blood pressures, haematocrits and plasma total solids were also determined.

Neurotensin caused a transient increase in net sodium absorption which was not associated with significant changes in unidirectional fluxes. This was followed by prolonged net secretion which was associated with an increase in unidirectional sodium secretion and a smaller decrease in sodium absorption. Potassium secretion was also increased when net sodium secretion increased.

Neurotensin increased haematocrit and total solids and decreased arterial pressure at the same time that secretion occurred.

Atropine blocked all the cardiovascular effects of neurotensin and reduced its early effects on both absorption and secretion but not the later effects on secretion. Tetrodotoxin only blocked the increase in absorption but not the secretion or the cardiovascular effects.

It was concluded that there is a cholinergic step in the cardiovascular effects of neurotensin and that the early effects of neurotensin on secretion are due to active secretion supported by fluid leakage from the plasma. The later effects of neurotensin on secretion do not have a cholinergic step and are due primarily to an active secretion. The increased absorption is mediated partly through intrinsic nerves of the gut.
Neurokinin3‐receptors are linked to inositol phospholipid hydrolysis in the guinea‐pig ileum longitudinal muscle‐myenteric plexus preparation
Authors: Guard S. , Watling K.J. , Watson S.P.
Published: July 2012

Tachykinin‐stimulated inositol phospholipid hydrolysis was examined in slices of longitudinal muscle from guinea‐pig ileum.

Substance P, neurokinin A and neurokinin B induced a concentration‐dependent accumulation of total [3H]‐inositol phosphates in the presence of 12 mm lithium with similar maximal responses and EC50 values.

The selective NK1‐receptor agonist, substance P methyl ester, and the selective NK3‐receptor agonist succ‐[Asp6, MePhe8]‐SP(6–11) (senktide) also stimulated [3H]‐inositol phosphate formation with maximum responses of 50.69 ± 0.96 and 45.64 ± 1.17% relative to 10 μm substance P, respectively. Substance P methyl ester was approximately equipotent with substance P, whereas senktide was approximately 100 times more potent.

When added together, maximally effective concentrations of substance P methyl ester and senktide gave responses that were fully additive. In contrast, responses to substance P and neurokinin B were not additive.

The stimulation of [3H]‐inositol phosphate formation by substance P, neurokinin B and senktide was not affected by atropine (2 μm) or tetrodotoxin (TTX, 0.3 μm).

The contractile effect of senktide was inhibited completely by TTX and partially blocked by atropine. Contractions induced by substance P methyl ester were not changed in the presence of TTX or atropine.

[d‐Pro4, d‐Trp7,9,10]‐SP(4–11) competitively antagonized the action of substance P methyl ester on inositol phospholipid hydrolysis and contraction, but had no significant effect on senktide‐induced inositol phospholipid breakdown or contraction.

These results suggest that NK3‐receptors in the guinea‐pig ileum are coupled to inositol phospholipid hydrolysis.
Correlation between log POCT/H2O and pKB estimates for a series of muscarinic and histamine H2‐receptor antagonists
Authors: Shankley N.P. , Black J.W. , Ganellin C.R. , Mitchell R.C.
Published: July 2012

With histamine used as agonist, pKB values were estimated for seventeen histamine H2‐receptor antagonists on assays involving acid secretion by the mouse isolated stomach and contraction frequency of the guinea‐pig right atrium.

With the exception of oxmetidine, SK&F 94,826 and SK&F 94,206 on the right atrium assay, the compounds behaved as simple competitive antagonists on both assays. Although the former three compounds produced concentration‐dependent, parallel, displacement of the histamine concentration‐effect curves, subsequent analysis indicated Schild plot slope parameters significantly less than unity. However, the application of a combined dose‐ratio analysis indicated that their antagonistic behaviour did not differ from expectations for simple competition at dose‐ratios of approximately 20, and pKB values were estimated on this basis.

In accordance with previously reported data, pKB values were found to be consistently lower on the stomach than atrial assays. The pKB value for tiotidine was underestimated to the same extent on the stomach assay when impromidine was used as agonist.

The removal of the serosal muscle from the mouse stomach, achieved by using an isolated, perfused, mucosal sheet preparation, did not significantly affect the underestimation of the pKB value for metiamide.

Linear regressional analysis indicated a significant, positive, correlation between lipophilicity (log POCT/H2O) of the antagonists and the degree of antagonist pKB value underestimation on the gastric secretion assay.
The actions of neuropeptide Y and peptide YY on the hepatic arterial and portal vascular beds of the anaesthetized dog
Authors: Corder R. , Withrington P.G.
Published: July 2012

The vascular actions of the two peptides, neuropeptide Y (NPY) and peptide YY (PYY) were compared with the transmitter noradrenaline (NA) on the arterial and portal vascular beds of the in situ liver of the anaesthetized dog.

The sole vascular response of the hepatic arterial vasculature to intra‐arterial administration of either NPY or PYY was vasoconstriction; the duration of these responses was longer than that to NA.

The maximum hepatic arterial vasoconstrictor responses to PYY and to NPY were significantly different and they were both significantly less than the maximum to NA (P > 0.001).

In contrast to its activity on the splenic arterial vasculature PYY was not more potent, on a molar basis, than NPY as an hepatic arterial vasoconstrictor agent. However, both peptides were significantly more potent than NA (P > 0.005).

Neither peptide, when injected intraportally, caused any change in intrahepatic portal inflow resistance.

Both peptides when administered intraportally in doses which were free of systemic effects caused hepatic arterial vasoconstriction.
Altered function of pulmonary endothelium following monocrotaline‐induced lung vascular injury in rats
Authors: Ito Katsuaki , Nakashima Teruyuki , Murakami Kazuyasu , Murakami Takayuki
Published: July 2012

Based on the findings in the preceding paper we investigated the ability of pulmonary endothelial cells to metabolize prostaglandin F2α (PGF2α) and angiotensin I (AI), and to produce endothelium‐derived relaxing factor (EDRF) following lung vascular injury induced by monocrotaline in rats. The isometric tension of pulmonary artery rings isolated from rats 3–5 weeks after an injection of monocrotaline or saline was measured. For comparison the responses to drugs of the artery denuded of endothelium by rubbing were tested.

Acetylcholine‐induced relaxation of the rings precontracted by noradrenaline was diminished in the artery from moncrotaline‐treated rats, depending on the duration after treatment. The diminution was comparable to that in the control artery denuded of endothelium.

The contractile response to PGF2α was significantly augmented in the artery injured by monocrotaline. The similar augmentation was observed after the mechanical removal of endothelium in the control artery. Decrease of EDRF was not involved in the enhancement of contractile response to PGF2α in the monocrotaline‐injured artery.

AI caused a contraction, which was sensitive to captopril, in control rings, and also in moncrotaline‐injured rings to a similar degree. Removal of endothelium from the control artery did not modify the response to AI or to AII.

These results suggest that the monocrotaline treatment of rats suppresses the ability of pulmonary endothelium to produce EDRF and to degrade prostaglandins. The relative resistance of the AI response to endothelial injury suggests that the existence of converting enzyme is not restricted to the endothelium.
Pharmacological analysis of the effects of Bay K 8644 and organic calcium antagonists on the mouse isolated distal colon
Authors: Fontaine Jeanine , Lebrun Philippe
Published: July 2012

Bay K 8644 (10−8 to 10−6 m) induced concentration‐related contractions of the longitudinal muscle of the mouse distal colon. The maximal responses were enhanced and the EC50 was lowered in the presence of tetrodotoxin (TTX; 1.5 × 10−7 m). The responses were not affected by atropine (10−7 m), mepyramine (2.5 × 10−7 m), methysergide (5 × 10−7 m), propranolol (10−6 m), phentolamine (10−6 m) or naloxone (4 × 10−7 m). By contrast, the contractile responses were inhibited by Ca2+ entry blockers (verapamil, nifedipine) and abolished in Ca2+‐free EGTA solution. These observations indicate that the contractile effects of Bay K 8644 are dependent on its ability to promote Ca2+ influx.

At 10−4 m, Bay K 8644 provoked a slow relaxation of the preparation. Moreover, from 10−5 m, Bay K 8644 markedly reduced the contractile responses to ACh and K+ depolarization. These inhibitory effects were comparable with those produced by nifedipine. Such data suggest that, at high concentrations, Bay K 8644 could act in part as a dihydropyridine Ca2+ channel antagonist.

Bay K 8644 (10−9 m) preferentially enhanced, while nifedipine (10−10 to 10−8 m) as well as verapamil (3 × 10−9 to 10−6 m) preferentially inhibited, the tonic component of the contractile response evoked by K+ depolarizing solution. This may indicate that different populations of voltage‐sensitive Ca2+ channels are involved in the biphasic response to K+ depolarization.

The biphasic contractile activity induced by ACh was barely enhanced by Bay K 8644 (10−9 m) and was less sensitive to Ca2+ entry blockers than the responses to KCl. These findings are discussed in terms of receptor‐operated channels and mobilization of bound calcium.
Inhibitory actions of amoxapine, a tricyclic antidepressant agent, on electrophysiological properties of mammalian isolated cardiac preparations
Authors: Kinugawa Toru , Kotake Hiroshi , Mashiba Hiroto
Published: July 2012

The electrophysiological effects of amoxapine were examined in guinea‐pig isolated papillary muscles and rabbit sinoatrial nodes using a conventional microelectrode technique.

In papillary muscles, amoxapine above 10 μm caused a dose‐dependent decrease in the maximum upstroke velocity () of the action potential and in the action potential amplitude (APA), whereas the action potential duration at 90% repolarization (APD90) was significantly prolonged. For a decrease in , amoxapine produced a negative shift of the curve relating to the resting potential (Em) along the voltage axis to more negative membrane potentials.

Amoxapine also decreased and the overshoot potential of K+‐depolarized slow action potentials of papillary muscle preparations.

In spontaneously beating sinoatrial node preparations, amoxapine above 3 μm reduced the heart rate, , APA and the slope of phase 4 depolarization in a dose‐dependent manner.

It was concluded that amoxapine exerts inhibitory actions on fast‐ and slow‐ response fibres of the heart and these actions can be mainly explained by inhibition of both fast Na+ and slow Ca2+ channels.
Paradoxical reversion of the inhibitory effects of dihydropyridine enantiomers on the calcium current in frog heart by CGP 28861
Authors: Filippov Alexander , Kobrinsky Evgeny , Porotikov Vladimir , Saxon Maya
Published: July 2012

A dihydropyridine CGP 28861 (5 × 10−6m) did not change slow inward Ca current as measured by the double sucrose gap method in frog atrial fibres but decreased the agonist effects of Bay K 8644, CGP 28392, (+m)−(S)−202–791 and the antagonist effects of nifedipine and (+m)−(PN)−200–110. Paradoxically, the weak antagonists (−)−(R)−202–791, (−)−(PN)−200–110 and (+)‐Bay K 8644 increased Ca‐current after washout of CGP 28861. These data suggest that CGP 28861 can convert the dihydropyridine Ca‐channel receptor from an antagonistic site into an agonistic one.
Tricyclic antidepressants block N‐methyl‐d‐aspartic acid‐induced lethality in mice
Authors: Leander J. David
Published: July 2012

It has been suggested on the basis of in vitro studies that tricyclic antidepressants interact with the N‐methyl‐d‐aspartic acid (NMDA)‐receptor complex to block the action of NMDA. The present study showed that tricyclic antidepressants prevented lethality produced by a large dose of NMDA. The potency of the drugs in preventing NMDA‐induced lethality correlated with the inhibition of [3H]‐MK‐801 binding at the NMDA receptor complex, and not with effects on amine uptake. These in vivo data support the in vitro data of Reynolds & Miller (1988a, b).
Interactions of calcium antagonists and the calcium channel agonist Bay K 8644 on neurotransmission of the mouse isolated vas deferens
Authors: Rae Giles A. , Calixto João B.
Published: July 2012

The present study compares the effects of verapamil and Bay K 8644 on twitches of the mouse vas deferens induced by field stimulation at 0.1 Hz. The influence of interactions between these drugs and nifedipine on neurotransmission was also investigated.

Bay K 8644 (0.1 nm‐3 μm) and verapamil (1–100 μm) potentiated twitches maximally by about 1000% (EC50 17.3 nm) and 300% (EC50 17.5 μm), respectively. Nifedipine (0.1 nM‐1μm) only reduced twitch magnitude (IC50 7.7 nm). All effects were reversed following washout.

Yohimbine (1–100 μm) reversed twitch potentiation caused by verapamil but not by Bay K 8644. Prazosin (1 μm) did not reduce basal twitch tension nor antagonize twitch potentiation by verapamil.

Twitch inhibition by nifedipine was unaltered by previous incubation with verapamil (30 μm), but Bay K 8644 (1 μm) shifted the curve to nifedipine 120 fold to the right. Previous incubation with nifedipine (1 μm) blocked potentiation induced by verapamil but did not modify responsiveness to Bay K 8644.

Previous addition of verapamil (30 μm) markedly enhanced twitch potentiation caused by Bay K 8644 in a supra‐additive fashion. In experiments conducted in the reversed condition, Bay K 8644 (1 nM but not 10 nm) potentiated the effect of verapamil in a similar manner but to a lesser extent.

It is concluded that verapamil, in contrast to nifedipine, markedly enhances neurally‐evoked twitches of the mouse vas deferens. Bay K 8644 produces essentially the same effect as verapamil, but its potency is 1000 fold and its maximal effect about 3 fold greater than that observed for verapamil. It is suggested that the mechanism of twitch potentiation by verapamil is different from that of Bay K 8644 and may involve an increased release of non‐adrenergic co‐transmitter(s).
Cardiovascular interactions between vasopressin, angiotensin and noradrenaline in the Brattleboro rat
Authors: Laycock J.F. , Lightman S.L.
Published: July 2012

The cardiovascular effects of bolus intravenous injections of vasopressin, angiotensin II and noradrenaline were studied in 6‐hydroxydopamine pretreated, anaesthetized Brattleboro rats with hereditary diabetes insipidus and normal rats of the parent Long Evans strain.

Pretreatment with 6‐hydroxydopamine did not significantly affect control values for mean arterial blood pressure, cardiac output or total peripheral resistance in either Brattleboro or Long Evans rats but the pressor response to haemorrhage was reduced in both strains compared to the control animals.

The pressor responses of the untreated Brattleboro rats to 250 mu kg−1 vasopressin were significantly greater and more prolonged than in control rats of the Long Evans strain.

Pretreatment with 6‐hydroxydopamine significantly enhanced the peak pressor response to vasopressin, but not to angiotensin II (1 μg kg−1), in Brattleboro and Long Evans rats.

Pretreatment with 6‐hydroxydopamine resulted in an enhanced pressor response to 1 μg kg−1 noradrenaline in both Brattleboro and Long Evans rats, but the effect was significantly greater in the vasopressin‐deficient animals.

These results indicate differences in the pressor responsiveness of Brattleboro rats to vasopressin and noradrenaline, but not to angiotensin II, compared with control Long Evans rats and provide evidence for important interactions between the sympathetic nervous system and these pressor hormones.