bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypoglycaemic and hypoketonaemic effects of single and repeated oral doses of methyl palmoxirate (methyl 2‐tetradecylglycidate) in streptozotocin/alloxan‐induced diabetic dogs
Authors: Tuman Robert W. , Tutwiler Gene F. , Joseph John M. , Wallace Nathaniel H.
Published: July 2012

The hypoglycaemic and hypoketonaemic effects of orally administered methyl palmoxirate were studied in streptozotocin/alloxan‐induced diabetic dogs.

Single oral 50 mg doses (≅7.5 mg kg−1) of methyl palmoxirate produced statistically significant reductions of plasma glucose (32 ± 6% maximum reduction from baseline) and ketones (74 ± 12% maximum reduction from baseline), with the peak effect on plasma ketones (3.5 h) preceding that for plasma glucose (6.0 h).

Lower doses (0.7‐2.0 mg kg−1 daily) of methyl palmoxirate given repeatedly for seven days produced reductions of blood glucose and ketones equivalent to those produced with the higher single dose. Maximal reductions of plasma ketones were generally observed following the first dose of drug, whereas significant lowering of plasma glucose required several days of continuous dosing.

Repeated daily doses of methyl palmoxirate markedly reduced the overnight fasting ketone levels but not glucose levels of diabetic dogs.

In conclusion, administration of the fatty acid oxidation inhibitor methyl palmoxirate, in the absence of concomitant insulin therapy, was able to lower the plasma glucose and ketone levels of insulin‐deficient streptozotocin/alloxan diabetic dogs. Only the plasma ketones were decreased to normal by this treatment.
An investigation of the pharmacological response to vitamin K1 in the rabbit
Authors: Winn M.J. , Cholerton S. , Park B.K.
Published: July 2012

The relationship between pharmacological response and disposition of a dose of vitamin K1 (10 mg kg−1, i.v.) in normal rabbits and in rabbits treated with the coumarin anticoagulant brodifacoum, has been studied.

High performance liquid chromatography (h.p.l.c.) with electrochemical detection (EC) was used to determine concentrations of vitamin K1 in plasma, whole liver homogenate, and liver microsomes.

After intravenous administration of vitamin plasma concentrations of the vitamin declined in a tri‐exponential fashion. There were no differences between the two groups over the first 24 h of the experiment. However, between 24 h and the end of the study, plasma concentrations of vitamin K1 in the presence of brodifacoum were significantly (P ≤ 0.05) below those of vehicle‐treated rabbits.

Seventy‐two hours after administration of vitamin K1, plasma concentrations of the vitamin were not different from normal.

Three hours after administration of vitamin K1, the concentrations of the vitamin in whole liver were 46.6 ± 4.3 μg g−1 in the presence of brodifacoum, and 32.8 ± 6.4 μg g−1 in the absence of brodifacoum; and were significantly (P ≤ 0.05) greater than normal (127.7 μ 44.3 ng g−1). Likewise, microsomal concentrations of vitamin K1 (4.00 ± 2.38 μg mg−1 protein, and 2.65 ± 1.01 μg mg−1 protein, in the presence and absence of brodifacoum, respectively) were significantly (P ≤ 0.01) greater than normal (16.0 ± 3.5 ng mg−1 protein).

In conclusion, there appears to be no direct effect of coumarins on clearance of vitamin K1 from either plasma or liver; the need for large doses of vitamin K1 during coumarin poisoning is due to a greatly increased requirement for the vitamin.
The failure of endothelin to displace bound, radioactively‐labelled, calcium antagonists (PN 200/110, D888 and diltiazem)
Authors: Gu X.H. , Liu J.J. , Dillon J.S. , Nayler Winifred G.
Published: July 2012

The effect of endothelin, a potent vasoconstrictor polypeptide, on three types of calcium antagonist binding sites was examined, in rat cardiac membrane fragments. Endothelin 10 nM affected neither the affinity nor density of dihydropyridine binding sites. At concentrations of 10−12‐10−7m, endothelin failed to displace bound (+)−[3H]‐PN 200/110, (−)−[3H]‐D888 and (+)−cis‐[3H]‐diltiazem. These results suggest that the calcium antagonist binding sites associated with L‐type calcium channels are not the primary site of action of endothelin.
Pharmacological modulation of Paf‐induced rat pleurisy and its role in inflammation by zymosan
Authors: Martins Marco A. , e Silva Patricia M.R. , Neto Hugo C. Castro Faria , Bozza Patricia T. , Dias Paulo M.F.L. , Lima Marcia C.R. , Cordeiro Renato S.B. , Vargaftig B. Boris
Published: July 2012

The intrapleural injection of Paf‐acether into rats caused, at 30 min, a marked exudation accompanied by a reduction in the pleural leucocyte count. At 6 h, the exudate volume had decreased and a significant increase in the total leucocyte count, particularly eosinophils was noted.

Two Paf‐acether antagonists, WEB 2086 and 48740 RP abrogated the pleural leucopenia observed 30 min after Paf‐acether administration, whereas the exudation was inhibited only by the former. Pleurisy was also reduced by about 60% with dexamethasone, by about 45% with BW 755C or LY 171883, a mixed cyclo‐oxygenase/lipoxygenase inhibitor and a peptido‐leukotriene antagonist respectively, and by about 30% with indomethacin, flurbiprofen or piroxicam.

Repeated daily intrapleural injections of Paf‐acether led to a state of progressive desensitization to Paf‐acether itself, whereas responsiveness to 5‐hydroxytryptamine was maintained. In addition, the Paf‐induced auto‐desensitization was largely inhibited by WEB 2086.

Pleurisy induced by zymosan, but not by carrageenin, was significantly reduced in Paf‐acether‐desensitized animals. These results were consistent with those obtained with WEB 2086 which supressed zymosan‐induced but not carrageenin‐induced pleurisy.

This study suggests that Paf‐acether‐induced pleurisy in the rat may be mediated by lipoxygenase arachidonic acid metabolites and that pleurisy induced by zymosan, but not by carrageenin, is largely dependent upon Paf‐acether.
Effects of the bradykinin antagonist B4310 on smooth muscles and blood pressure in the rat, and its enzymatic degradation
Authors: Griesbacher Thomas , Lembeck Fred , Saria Alois
Published: July 2012

Six competitive bradykinin (Bk) antagonists were tested for their agonistic properties on the rat uterus. Five of these peptides showed agonistic effects only at concentrations at least two orders of magnitude higher than those of bradykinin.

The antagonistic potency of Lys‐Lys‐3‐Hyp‐5,8‐Thi‐7‐DPhe‐Bk (B4310) in the rat uterus (pA2 = 7.24) and in the rat duodenum (pA2 = 7.31) was very similar to that determined in an earlier study for the antagonism of the bradykinin‐induced stimulation of the trigeminal nerve in the rabbit iris sphincter muscle preparation (pA2 = 7.59).

The fall in mean arterial blood pressure induced by i.a. injections of bradykinin was greatly reduced during an i.a. infusion of B4310, but not 10 min thereafter, which indicates a rapid inactivation of B4310 in vivo. Bacitracin possibly interferes with the enzymatic cleavage of B4310 but seems to have no effect on the degradation of bradykinin.

An i.a. infusion of captopril greatly enhanced the potency of bradykinin in inducing a fall in arterial blood pressure, confirming the important role of angiotensin converting enzyme in the cleavage of bradykinin. However, the design of this experiment did not allow conclusions about the effect of captopril on the degradation of B4310.

B4310 incubated with rat lung tissue disappeared from the incubation medium within a few minutes, i.e. as fast as bradykinin, which explains its short duration of action in vivo. Captopril partially inhibited the cleavage of both bradykinin and B4310.

The present results show that the bradykinin antagonists available at present are useful tools for the investigation of the biological role of bradykinin. However, the susceptibility to enzymatic degradation may limit their usefulness in animal experiments or in clinical studies.
N‐methylhydroxylamine inhibits and M&B 22948 potentiates relaxations of the mouse anococcygeus to non‐adrenergic, non‐cholinergic field stimulation and to nitrovasodilator drugs
Authors: Gibson A. , Mirzazadeh S.
Published: July 2012

The effects of N‐methylhydroxylamine (NMH) and of M&B 22948 on relaxations of the mouse anococcygeus to non‐adrenergic, non‐cholinergic (NANC) field stimulation and to a number of smooth muscle relaxant drugs were investigated.

Relaxations to NANC field stimulation (10 Hz; 60s train) were reversibly blocked by NMH (1–5 mm), which also caused weak, transient reductions of carbachol (50 μm)‐induced tone. N,N‐dimethylhydroxylamine (2 mm) and hydroxylamine (5 μm) reduced tone to the same extent as NMH, but neither produced any inhibition of NANC relaxations.

M&B 22948 10 μm, which by itself reduced tone by 12%, potentiated submaximal but not maximal relaxations to NANC field stimulation; overall the log frequency‐response curve was displaced to the left by a factor of 2.

Sodium nitroprusside (0.01–1 μm), hydroxylamine (0.5–100 μm), and nitric oxide (2–200 μm) all relaxed carbachol‐induced tone; relaxations to submaximal concentrations of these nitro‐vasodilators were reduced in the presence of 2 mm NMH, and potentiated in the presence of 10 μm M&B 22948.

Neither NMH (2 mm) nor M&B 22948 (10 μm) affected relaxations induced by submaximal concentrations of vasoactive intestinal peptide (VIP; 1 μm), papaverine (10 μm), 3‐isobutyl‐1‐methylxanthine (10 μm), or 8‐bromo‐cyclic guanosine monophosphate (100 μm); relaxations to adenosine 5′‐triphosphate (ATP, 2 mm) were unaffected by M&B 22948, but were potentiated by NMH.

The selective inhibition by NMH, and potentiation by M&B 22948, of NANC and nitrovasodilator‐induced relaxations of the mouse anococcygeus suggests that the NANC transmitter is neither VIP nor ATP, but resembles the nitrovasodilator drugs in its mode of action. The NANC transmission system is therefore similar to that recently described in the bovine retractor penis.
Factors inducing endothelium‐dependent relaxation in the guinea‐pig basilar artery as estimated from the actions of haemoglobin
Authors: Nishiye E. , Nakao K. , Itoh T. , Kuriyama H.
Published: July 2012

Factors inducing dilatation of guinea‐pig basilar artery were investigated in intact and endothelium‐denuded tissues by measurement of isometric tension and by electrophysiological methods.

The amplitudes of contractions induced by 9,11,epithio‐11,12‐methanothromboxane A2 (STA2) and by high K+ were enhanced by haemoglobin (oxyhaemoglobin, Hb) in a concentration‐dependent fashion (above 1 μm). For the high K+‐induced contraction, the initial tonic component was enhanced to a greater extent than the secondary phasic component. Mechanical responses evoked by STA2 and by high K+ were greater in endothelium‐denuded tissues, but Hb (below 10 μm) had no effect on them.

Hb (10 μm) had no effect on the contractile proteins as estimated from the actions of Hb on Ca2+‐induced contractions in skinned muscle tissues. Further, Hb had no effect on the release of Ca2+ from intracellular stores but it accelerated the Ca2+ accumulation into the sarcoplasmic reticulum as judged from the caffeine‐ or STA2‐induced contraction generated in intact tissues.

Acetylcholine (ACh) relaxed tissues that were precontracted by STA2 but Hb prevented this relaxation, in a concentration‐dependent fashion. The ACh‐induced relaxation was sustained for over 10 min in the absence of Hb, but following application of Hb, ACh caused only a transient relaxation.

STA2 (up to 100 nm) did not modify the resting membrane potential of smooth muscle cells of the basilar artery. ACh (10 μm) caused transient hyperpolarization which was only slightly inhibited by Hb (10 μm) whether or not STA2 was present. The hyperpolarization induced by ACh required the presence of endothelial cells.

A23187 (0.01–1 μm) relaxed tissues which were precontracted by STA2, in a concentration‐dependent fashion but had no effect on the membrane potential.

These results suggest that in guinea‐pig basilar artery, ACh induces relaxation of tissues that were precontracted by STA2 by causing release of both endothelium‐derived relaxing (EDRF) and endothelial dependent hyperpolarizing factor (EDHF) (sustained and initial transient relaxation, respectively), but via different mechanisms. Hb inhibits the former and to a lesser extent, the latter. Since A23187 produced relaxation of pre‐contracted tissue but caused no detectable change in the membrane potential, this agent may release EDRF but not EDHF.
Prostanoid‐induced contraction of human bronchial smooth muscle is mediated by TP‐receptors
Authors: Coleman R.A. , Sheldrick R.L.G.
Published: July 2012

A range of naturally‐occurring prostaglandins sulprostone, 16,16‐dimethyl prostaglandin E2 (DME2) and the thromboxane A2 (TXA2)‐mimetic, 11α,9α‐epoxymethano prostaglandin H2 (U‐46619) have been tested for contractile agonist activity on human isolated bronchial smooth muscle.

Prostaglandin D2 (PGD2), PGF2α, 9α,11β‐PGF2 (11β‐PGF2) and U‐46619 all caused concentration‐related contractions. U46619 was at least 300 fold more potent than the other prostanoids with a mean EC50 of 12 nm. Sulprostone caused contraction only at the highest concentration tested (30 μm). PGE2 and PGI2 caused relaxations at low concentrations, and only caused contractile responses at high concentrations (≥ 10 μm). In contrast, DME2 caused small contractions at low concentrations but relaxation at the highest concentration tested (30 μm).

The rank order of contractile agonist potency was: U‐46619 > 11β‐PGF2 > PGF2α > PGD2 > PGE2 > PGI2 > sulprostone > DME2.

The TP‐receptor blocking drug, AH23848 (1 μm) antagonized the contractile effects of U‐46619, PGD2, PGF2α and 11β‐PGF2, but had no effect against contractions to carbachol. In a single experiment, a pA2 of 8.3 (slope = 1.2) was obtained for AH23848 against U‐46619.

In most preparations, administration of AH23848 (1 μm) to human bronchus resulted in small, transient contractile responses.

The results obtained with both the agonists and the antagonist, AH23848 are therefore consistent with prostanoid‐induced contractions of human bronchial smooth muscle being mediated by TP‐receptors.
Augmentation and subsequent attenuation of Ca2+ current due to lipid peroxidation of the membrane caused by t‐butyl hydroperoxide in the rabbit sinoatrial node
Authors: Sato Nobuyuki , Nishimura Masao , Tanaka Hideo , Homma Nobuo , Watanabe Yoshio
Published: July 2012

Cellular electrophysiological effects of membrane lipid peroxidation by t‐butyl hydroperoxide (TBH) were studied in the rabbit sinoatrial (SA) node. Superfusion for 1–5 min with 300 μm TBH caused an initial increase and subsequent decrease in the spontaneous firing frequency of the SA node. Voltage clamp experiments revealed that TBH initially enhanced but later blocked the Ca2+ current. Thus, membrane lipid peroxidation appears to accelerate and then suppress physiological automaticity by causing biphasic changes in the Ca2+ current.
S‐nitrosothiols as vasodilators: implications regarding tolerance to nitric oxide‐containing vasodilators
Authors: Henry Peter J. , Drummer Olaf H. , Horowitz John D.
Published: July 2012

The formation of an S‐nitrosothiol compound, S‐nitroso‐N‐acetylcysteine (SNAC) has recently been proposed to mediate the augmentation of the anti‐aggregatory and haemodynamic effects of glyceryl trinitrate observed in the presence of N‐acetylcysteine. This study investigated the effects on an isolated coronary artery preparation of acute and prolonged exposure to S‐nitrosothiol compounds and nitric oxide (NO).

Single doses of NO and of the S‐nitrosothiol compounds, SNAC and S‐nitroso‐N‐acetylpenicillamine (SNAP), induced rapid, but transient, relaxations in U46619‐contracted bovine isolated coronary artery rings. Peak relaxation responses to SNAP and NO were attenuated in the presence of N‐acetylcysteine, cysteine, ascorbic acid and methylene blue. The duration of the relaxation responses to SNAC was two to three times longer than those to SNAP and NO. In the presence of N‐acetylcysteine (but not cysteine, ascorbic acid or methylene blue) the duration of the relaxation responses to SNAP and NO (but not to SNAC) was markedly increased. H.p.l.c. assay confirmed that, in the presence of N‐acetylcysteine, SNAP and, to a lesser degree, NO were converted to the relatively more stable and longer acting vasodilator, SNAC.

When compared to control rings, coronary artery rings superfused with glyceryl trinitrate were subsequently markedly less responsive to the vasodilator actions of glyceryl trinitrate, whereas responsiveness to SNAC or NO was only marginally reduced. On the other hand, coronary artery rings superfused with SNAC or NO were subsequently less responsive to glyceryl trinitrate, SNAC and NO. Thus prolonged vascular exposure to SNAC or NO induced a form of tolerance different from that induced with glyceryl trinitrate and which is possibly associated with impaired guanylate cyclase activity.

Coronary artery rings superfused with NO were markedly less responsive to glyceryl trinitrate and NO, whereas responses to the endothelium‐dependent vasodilator A23187 and to theophylline were not significantly attenuated.

It is concluded that formation of the more stable vasodilator SNAC occurs on incubation of N‐acetylcysteine with SNAP or NO. While coronary artery responsiveness to SNAC and NO is virtually unchanged in the presence of glyceryl trinitrate‐induced tolerance, after prolonged exposure to SNAC or NO tolerance may develop to these vasodilators with cross‐tolerance to glyceryl trinitrate but not A23187. Thus, formation or therapeutic utilization of SNAC may acutely circumvent the problem of glyceryl trinitrate‐induced tolerance but, during prolonged vascular exposure to SNAC, attenuation of vascular responsiveness may occur to a wide range of vasodilators.
Endothelium‐dependent relaxation and hyperpolarization of canine coronary artery smooth muscles in relation to the electrogenic Na‐K pump
Authors: Chen Guifa , Hashitani Hikaru , Suzuki Hikaru
Published: July 2012

In the smooth muscle cells of canine coronary artery, acetylcholine (ACh) produced a transient, endothelium‐dependent hyperpolarization of the membrane. A similar hyperpolarization was also elicited by exposure to Krebs solution after incubation of the artery in K‐free solution for 30 min.

A hyperpolarization of reproducible amplitude was generated when ACh was applied at intervals greater than 30 min. Repetitive application of ACh at 15 min intervals caused a successive reduction in the amplitude of hyperpolarization.

The reduction in the amplitude of relaxation during five successive applications of ACh at 15 min intervals was less than 10% of the first relaxation.

The ACh‐induced hyperpolarization was blocked by atropine but not by ouabain, whereas the K‐free induced hyperpolarization was blocked by ouabain. In low Na (Li‐substituted) solution, ACh still induced a hyperpolarization but the K‐free induced hyperpolarization was absent.

In coronary artery precontracted by high‐K solution, ACh produced an endothelium‐dependent relaxation, without membrane hyperpolarization. The associated relaxation was resistant to ouabain but sensitive to atropine.

It is concluded that in the canine coronary artery, the electrogenic Na‐K pump does not contribute to the endothelium‐dependent hyperpolarization or relaxation. The results are consistent with the release of two different inhibitory factors from the vascular endothelium.
Difference in the potentiating effect of adenosine triphosphate and α,β‐methylene ATP on the biphasic insulin response to glucose
Authors: Bertrand G. , Gross R. , Chapal J. , Loubatières‐Mariani M.M.
Published: July 2012

The effects of exogenous adenine nucleotides and structural analogues on the biphasic insulin response to an increase of glucose concentration in the physiological range (from 4.2 to 8.3 mm) were studied in the isolated perfused rat pancreas. Purinoceptor agonists were added either simultaneously or 15 min before increasing glucose.

ATP and ADP at 16.5 μm were ineffective per se in the presence of the non stimulatory glucose concentration (4.2 mm) but markedly potentiated the biphasic insulin response to glucose rise in both experimental protocols.

Two more stable analogues of ATP and ADP (adenylylimidodiphosphate and α,β‐methylene ADP (α,β‐MeADP)) at 16.5 μm behaved like the natural compounds: they were ineffective at a glucose concentration of 4.2 mm and potentiated both phases of insulin response to glucose rise.

α,β‐MeATP added simultaneously with the high glucose concentration, markedly potentiated the first phase of insulin response to glucose rise but did not potentiate the second one. When α,β‐MeATP infusion began 15 min before glucose rise, the biphasic response to glucose was not potentiated, in contrast to what occurred with ATP.

In the presence of α,β‐MeATP, the ATP potentiating effect was unaffected.

It is concluded that ATP and ADP, via activation of β cell P2y purinoceptors, potentiates the biphasic insulin response to an increase of glucose concentration. On the other hand, α,β‐MeATP did not behave like natural and other structural analogues of ATP and ADP: this difference appears not to be the consequence of desensitization of β cell P2y purinoceptors by α,β‐MeATP.
Mechanisms of long‐lasting effects of benidipine on Ca current in guinea‐pig ventricular cells
Authors: Yamamoto M. , Gotoh Y. , Imaizumi Y. , Watanabe M.
Published: July 2012

Benidipine (KW‐3049), a new derivative of 1,4‐dihydropyridine (DHP), showed dose‐dependent inhibition of Ca current (ICa) which was elicited by depolarization from −40 mV to +10 mV at 0.2 Hz in single cardiac cells isolated from guinea‐pig ventricle under whole cell voltage clamp. Half inhibition doses (IC50) of benidipine and nifedipine for the peak ICa at +10 mV were 2.7 nm and 63.1 nm, respectively.

A change in holding potential from −40 to −75 mV partially removed the block induced by both 10 nm benidipine and 100 nm nifedipine. The block of ICa by benidipine strongly depended upon holding potentials as did that induced by nifedipine.

The effect of 100 nm nifedipine was mostly removed when the cells were kept quiescent at holding potentials negative to −75 mV for 5 min after withdrawal of nifedipine. In contrast, hyperpolarization for several minutes did not significantly accelerate the removal of benidipine‐induced block after withdrawal of the drug. Effects of 10 nm benidipine could not be washed out for up to 30 min regardless of the holding potentials.

It is suggested that the dissociation of benidipine from the DHP binding site, like that of nifedipine, is greatly accelerated by hyperpolarization. Benidipine but not nifedipine may have an additional interaction with the channel or lipid membrane and cannot be washed away even after the dissociation. Alternatively, the dissociation of benidipine from the DHP binding site may be too slow to occur substantially during the limited period of hyperpolarization in the present study (<30 min). In that case, however, the Ca channel bound by benidipine must become unblocked and available to be opened during the hyperpolarization.
Mechanisms for cardiac depression induced by phorbol myristate acetate in working rat hearts
Authors: Karmazyn Morris , Watson Joanne E. , Moffat Margaret P.
Published: July 2012

The effects of the phorbol ester, phorbol myristate acetate (PMA) were examined on function and energy metabolism in the isolated working heart of the rat.

At a concentration of 10−9 m. PMA produced a rapid loss in cardiac function in terms of aortic flow rate (AFR) and coronary flow rates (CFR) whereas a similar concentration of 4α‐phorbol 12,13‐didecanoate was ineffective. At a concentration of 10−10 m., the PMA‐induced depression was more gradual but nevertheless very pronounced with an almost total loss in AFR after 30 min perfusion. The reduction in CFR was more moderate than that observed with respect to AFR.

The protein kinase C (PKC) inhibitor (±)‐l‐O‐hexadecyl‐2‐O‐acylglycerol significantly attenuated the loss in AFR and CFR following addition of PMA.

Two inhibitors of Na+/H+ exchange, amiloride and quinacrine, totally prevented the reduction in AFR. Although the PMA‐induced depression in CFR was also attenuated by both amiloride and quinacrine, these effects were not significant, probably reflecting the less pronounced effect of PMA on this parameter.

Nifedipine, a dihydropyridine calcium channel blocker reduced PMA toxicity to a similar degree as Na+/H+ exchange inhibition whereas the calcium channel agonist Bay K 8644 was without effect.

Tissue content of energy metabolites including high energy phosphates, total adenine nucleotides or lactate were not significantly affected by PMA perfusion.

We conclude that PKC activation is necessary for phorbol ester‐induced cardiac dysfunction. The consequence of PKC stimulation includes (1) Na+/H+ exchange activation and a subsequent elevation in intracellular calcium [Ca2+]i via Na+/Ca2+ exchange and (2) PKC‐dependent phosphorylation of the calcium channel, both of which would produce toxicity by elevation of [Ca2+]i. Pharmacological manipulation of any of these steps prevents PMA toxicity by virtue of a reduction in the accumulation of [Ca2+]i. PMA effects or their prevention are unrelated to any changes in energy metabolism.
Pharmacological modulation of the contractile response to toluene diisocyanate in the rat isolated urinary bladder
Authors: Mapp Cristina E. , Chitano Pasquale , Fabbri Leonardo M. , Patacchini Riccardo , Maggi Carlo A.
Published: July 2012

Toluene diisocyanate produced concentration‐dependent contractions of the rat isolated urinary bladder.

The contractions were tetrodotoxin‐resistant and were abolished by previous exposure of the strips to capsaicin.

Indomethacin (5 μm) and ruthenium red (30 μm) inhibited toluene diisocyanate‐induced contractions. Responses expressed as a percentage of the response obtained with substance P, 30 nm, were respectively 141.6 ± 24.8% and 20.1 ± 5.1% in control and indomethacin‐treated strips (P < 0.005); 123.0 ± 30.2% and 14.0 ± 6.5% in control and ruthenium red‐treated strips (0.01 < P < 0.05).

These results suggest that toluene diisocyanate‐induced contractions of the rat isolated bladder are the result of the release of cyclo‐oxygenase products which may act by activating the capsaicin receptor.
Prevention by the NMDA receptor antagonist, MK801 of neuronal loss produced by tetanus toxin in the rat hippocampus
Authors: Bagetta G. , Nisticò G. , Bowery N.G.
Published: July 2012

The behavioural and neuropathological effects of tetanus toxin, microinjected directly into the hippocampus, were studied in rats.

A single dose (1000 minimum lethal doses, MLDs) of tetanus toxin, injected unilaterally into the hippocampus produced a time‐dependent neuronal loss in the CA1 pyramidal cell layer. In comparison with the contralateral, untreated side these effects became statistically significant (P > 0.05) 7 days (22.0 ± 1.1% reduction) and 10 days (29.2 ± 1.7% reduction) after the injection. No significant changes were observed 7 days after treatment with 500 MLDs whereas a reduction of 37.5 ± 3.1% in the CA1 area cell number was produced 4 days after the injection of 2000 MLDs.

Behavioural stimulatory effects were also induced by tetanus toxin (1000 MLDs) within 48 h of the injection and these culminated in generalized convulsions 5–7 days later. Convulsions were observed after a shorter period of latency in rats receiving 2000 MLDs tetanus toxin whereas 500 MLDs were ineffective.

No behavioural and neuropathological effects were observed in rats treated with neutralized tetanus toxin (1000 MLDs), bovine serum albumin or phosphate buffer.

Pretreatment with MK801 (0.3 mg kg−1, i.p., given 1 h before and after the injection with tetanus toxin and then once daily for 4 or 7 days) prevented the behavioural and neuropathological effects induced by tetanus toxin (1000–2000 MLDs). In addition, such treatment fully protected the animals from the lethal effects induced by 1000 MLDs tetanus toxin. By contrast, pretreatment with diazepam (3.0 mg kg−1, i.p.) using the same schedule as for MK801 did not antagonize the effects of tetanus toxin (1000–2000 MLDs).

In conclusion, the present experiments have demonstrated that the intrahippocampal injection of tetanus toxin produces in rats a dose‐ and time‐dependent behavioural stimulation and neuronal loss in the CA1 pyramidal cell layer which can be prevented by the non‐competitive NMDA antagonist, MK801.
Effects of the cyclo‐oxygenase inhibitor, fenbufen, on clenbuterol‐induced hypertrophy of cardiac and skeletal muscle of rats
Authors: Palmer R.M. , Delday M.I. , McMillan D.N. , Noble B.S. , Bain P. , Maltin C.A.
Published: July 2012

When rats were fed with clenbuterol for 7 days skeletal muscle mass increased by 21% in the tonic soleus and phasic plantaris muscles and a 16% hypertrophy of the heart was also induced. Fenbufen, fed to rats for the same period, blocked the hypertrophy of the heart but not that of the skeletal muscles.

When feeding of fenbufen commenced 3 days before the administration of clenbuterol, plasma prostaglandin F2α (PGF2α) was reduced by 79%; there was again no effect of fenbufen on clenbuterol‐induced increases in the RNA or protein content of plantaris, nor in the increased area of fast or slow twitch fibres in the soleus. In the heart the clenbuterol‐induced increases in the RNA (+ 21%) and protein content (+ 20%) were totally inhibited.

The effects of clenbuterol on heart muscle appear to be mediated by a cyclo‐oxygenase metabolite of arachidonic acid whilst the effects on skeletal muscle are not.
Functional characterization of neuronal pre and postsynaptic α2‐adrenoceptor subtypes in guinea‐pig submucosal plexus
Authors: Shen K.‐Z. , Barajas‐Lopez C. , Surprenant A.
Published: July 2012

The α2‐adrenoceptors on cell bodies of submucosal neurones, on presynaptic cholinergic nerve terminals innervating submucosal neurones, and on presynaptic sympathetic fibres innervating submucosal arterioles were characterized in functional studies by use of subtype selective ligands.

Both membrane hyperpolarization and presynaptic inhibition of nicotinic excitatory synaptic potentials (e.p.s.ps) produced by UK 14304 were similarly antagonized by idazoxan, yohimbine, SKF 104078, WB 4101 and ARC‐239. Antagonism was competitive and dissociation equilibrium constants were the same for both effects.

Vasoconstriction of submucosal arterioles in response to stimulation of the sympathetic nerves (20 Hz for 2 s) was inhibited by UK 14304 and clonidine; concentrations producing half‐maximum responses were 6 nm and 10 nm respectively. Idazoxan, yohimbine, WB 4101 and SKF 104078 antagonized this action, with dissociation constants similar to those for antagonism of the postsynaptic membrane hyperpolarization and presynaptic inhibition of nicotinic e.p.s.ps.

Oxymetazoline was a partial agonist when membrane hyperpolarization or presynaptic inhibition of nicotinic e.p.s.ps were measured but a full agonist when presynaptic inhibition of sympathetically‐mediated arteriolar vasoconstriction was measured. As an agonist, oxymetazoline produced half maximum responses at 80–120 nm; the dissociation constant for oxymetazoline as an antagonist was 130 nm.

Neither prazosin nor chlorpromazine (up to 30 μm) altered any of the three responses to α2‐adrenoceptor agonists.

It is concluded that α2‐adrenoceptors present on submucosal neuronal cell bodies, on presynaptic cholinergic nerve terminals and on presynaptic sympathetic nerve terminals are the α2A subtype. However, functional characterization of this subtype differs from that provided by ligand binding studies.
Renal selective N‐acetyl‐γ‐glutamyl prodrugs: a study on the mechanism of activation of the renal vasodilator prodrug CGP 22979
Authors: Drieman J.C. , Thijssen H.H.W. , Zeegers H.H.M. , Smits J.F.M. , Boudier H.A.J. Struyker
Published: July 2012

In this study the processes underlying the renal selectivity of the vasodilator prodrug CGP 22979 (N‐acetyl‐l‐glutamic acid‐N‐[N2‐(5‐n‐butyl‐2‐pyridyl) hydrazide]) were studied in rats.

The active drug CGP 18137 (2‐hydrazino‐5‐n‐butyl pyridine) selectively accumulated in the renal tissue following administration of the prodrug.

The kidney concentrations of active drug following prodrug administration were significantly lower than control values when either buthionine sulphoximine, glutathione or probenecid was coadministered (29 ± 11; 33 ± 14 and 61 ± 20% of control values, respectively). Inhibition of γ‐glutamyl transpeptidase by AT‐125 did not cause a significant decrease of renal CGP 18137 levels.

In order to correlate tissue drug concentrations with pharmacological effect, the renal haemodynamic responses to CGP 22979 were measured and the effect of buthionine sulphoximine, glutathione and AT‐125 on these responses evaluated. All three of the compounds attenuated the renal response to the prodrug: an approximately 50% lesser decrease in renal resistance was found. The compounds had no effect on the haemodynamic actions of CGP 18137 itself.

In vitro, it was found that kidney cytosol was able to convert the prodrug, whereas microsomes were not, unless acylase was added.

The results indicate that, upon prodrug administration, γ‐glutamyl transpeptidase is not involved in the renal accumulation of CGP 18137 but is partly responsible for the renal haemodynamic responses to CGP 22979. Active transport of the prodrug into the tubular cells appears to be the major reason for the renal selectivity. A model is proposed for the renal action of CGP 22979, in which the important parts are the uptake of the prodrug via a transport system followed by an intracellular conversion to the active drug.
Comparison of the effects of xamoterol and isoprenaline on rat cardiac β‐adrenoceptors: studies of function and regulation
Authors: Kowalski M.T. , Haworth D. , Lu X. , Thomson D.S. , Barnett D.B.
Published: July 2012

The effects of the β1‐selective partial agonist xamoterol and the full agonist isoprenaline on rat cardiac β‐adrenoceptors were compared in functional studies of heart rate response in vivo and in vitro. In addition, the ability of both agents to cause receptor down‐regulation in the rat heart following chronic (6 days) subcutaneous infusions was assessed by radioligand binding with [125I]‐pindolol.

In the functional studies, xamoterol produced a maximal effect equivalent to approximately 65% of that of isoprenaline and was overall less potent than the full agonist.

Compared to saline control, the density of β‐adrenoceptors was reduced approximately 39% in ventricular membranes prepared from animals after 6 days of isoprenaline infusion but was unaffected by xamoterol. The relative proportions of the β‐adrenoceptor subtypes were unchanged by either active treatment.

Plasma xamoterol level at the end of the infusion period was equivalent to that associated with maximum tachycardia in vivo and to the concentration producing maximal stimulation of the rat isolated atrium in vitro. Thus suggesting 100% β‐adrenoceptor occupancy during the period of xamoterol infusion.

These results indicate that in this animal model xamoterol does not induce cardiac β‐adrenoceptor down‐regulation during chronic treatment, with doses that produce a maximal functional response both in vitro and in vivo.
Effects of selective phosphodiesterase inhibition on cyclic AMP hydrolysis in rat cerebral cortical slices
Authors: Challiss R.A. John , Nicholson C. David
Published: July 2012

The effects of selective inhibition of phosphodiesterase activities on the concentration and rate of hydrolysis of adenosine 3′: 5′ cyclic‐monophosphate (cyclic AMP) in rat cerebral cortical slices has been studied.

Isoprenaline caused a rapid, concentration‐dependent increase in cyclic AMP concentration to new steady‐state levels (basal: 7.1 ± 0.7; 10 μm isoprenaline: 14.3 ± 1.4 pmol mg−1 protein). Addition of a β‐adrenoceptor antagonist to isoprenaline‐stimulated cerebral cortical slices caused a rapid decrease in cyclic AMP concentration to basal levels (t1/2: 58 ± 18 s).

Preincubation of slices for 30 min with the phosphodiesterase inhibitors 1‐methyl‐3‐isobutylxanthine, denbufylline, rolipram or Ro20 1724 caused concentration‐dependent increases in basal and isoprenaline‐stimulated cyclic AMP concentrations and decreased the rate of cyclic AMP hydrolysis measured after addition of a β‐adrenoceptor antagonist. However, SKF 94120 and zaprinast had none of these effects.

The results are discussed with respect to previous studies of phosphodiesterase isozymic activities isolated from cerebrum and it is suggested that the Ca2+/calmodulin‐independent, low Km cyclic AMP phosphodiesterase isozyme, which is selectively inhibited by denbufylline, rolipram and Ro20 1724, and is present in cerebrum is of critical importance to the regulation of cyclic AMP concentration in this tissue.
Evidence against an involvement of the haloperidol‐sensitive σ recognition site in the discriminative stimulus properties of (+)‐N‐allylnormetazocine ((+)‐SKF 10,047)
Authors: Singh L. , Wong E.H.F. , Kesingland A.C. , Tricklebank M.D.
Published: July 2012

The involvement of the haloperidol‐sensitive, σ recognition site and the N‐methyl‐d‐aspartic acid (NMDA) receptor in the mediation of the discriminative stimulus properties of (+)‐N‐allylnormetazocine ((+)‐NANM, (+)‐SKF 10,047), has been investigated in the rat by use of a two‐lever, operant drug discrimination paradigm.

Six compounds with nanamolar affinity for the σ recognition site ((±)‐pentazocine, (+)‐3‐(hydroxyphenyl)‐N‐propylpiperidine ((+)‐3‐PPP), ditolylguanidine (DTG), haloperidol, (−)‐butaclamol and BMY 14802) were investigated for their ability to generalise or antagonise the (+)‐NANM discriminative stimulus. Each drug was tested at doses found in an ex vivo radioligand binding assay to displace [3H]‐DTG from the central σ recognition site by more than 40%.

While (±)‐pentazocine (in the presence of naloxone) generalised and (+)‐3‐PPP partially antagonised the (+)‐NANM cue, the other putative σ ligands were ineffective either as agonists or antagonists at doses clearly occupying the σ site in vivo.

Dose‐dependent generalisation to the (+)‐NANM cue was seen with the selective non‐competitive NMDA receptor antagonist, MK‐801, a compound devoid of significant affinity for the σ recognition site.

(±)‐Pentazocine was found to antagonise seizures induced in the mouse by NMDLA, a model reflecting antagonism of central NMDA receptors, and a strong correlation was found between the rank order of potency of compounds to generalise to the (+)‐NANM discriminative stimulus and their potencies as anticonvulsants.

In conclusion, no evidence was found to substantiate the contention that the discriminative stimulus properties of (+)‐NANM are mediated by the haloperidol‐sensitive σ recognition site. On the other hand, the results are consistent with the interoceptive stimulus being mechanistically based in the NMDA receptor complex.
Agmatine acts as an antagonist of neuronal nicotinic receptors
Authors: Loring Ralph H.
Published: July 2012

Tritiated agmatine has been used by others in ion flux methods to measure nicotinic receptor function in neurones. However, as shown here, agmatine blocks nicotinic receptor function in both the chick retina and the rat superior cervical ganglion at high concentrations.

In intact chick retina, agmatine 1 mm decreases dimethylphenylpiperazinium (DMPP)‐induced depolarizations measured in the optic nerve by approximately 70%, while having little effect on responses induced by glutamate analogues. DMPP dose‐response curves are reduced in a manner consistent with a non‐competitive effect of agmatine, and agmatine at 1 mm does not prevent binding of 125I‐labelled neuronal bungarotoxin, a snake venom neurotoxin that competitively binds and blocks functional nicotinic receptors in chick retinal homogenates.

Agmatine (10 μm) substantially blocks both DMPP‐induced depolarizations of rat superior cervical ganglion and synaptic transmission through the ganglion. Others have established that [3H]‐agmatine will pass through nicotinic receptor channels in the rat ganglion. These data suggest that agmatine acts both as a cation and as a weak channel blocker at neuronal nicotinic receptors.
Sumatriptan (GR43175) inhibits cyclic‐AMP accumulation in dog isolated saphenous vein
Authors: Sumner M.J. , Humphrey P.P.A.
Published: July 2012

Sumatriptan (GR43175) contracts rings of dog isolated saphenous vein by an action at 5‐HT1‐like receptors. We have now examined the effects of sumatriptan on prostaglandin E2 (PGE2)‐stimulated adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) accumulation in this tissue. Sumatriptan and 5‐hydroxytryptamine (5‐HT) produced a concentration‐dependent inhibition of PGE2‐stimulated cyclic AMP accumulation (EC50 values of 250 nm and 80 nm respectively), responses that were mimicked by 5‐carboxamidotryptamine but not by U‐46619 or methoxamine. The response to sumatriptan (1 μm) was antagonised by methiothepin (1 μm), but not by metergoline (0.1 μm), spiperone (1 μm) or ondansetron (GR38032, 1 μm). These results suggest that 5‐HT1‐like receptors which mediate contraction of the dog isolated saphenous vein are negatively coupled to adenylate cyclase in this preparation.
Characterization of presynaptic vascular muscarinic receptors inhibiting endogenous noradrenaline overflow in the portal vein of the freely moving rat
Authors: Remie R. , Coppes R. P. , Meurs H. , Roffel A.F. , Zaagsma J.
Published: July 2012

In the portal vein of permanently cannulated, freely moving, unanaesthetized rats, methacholine (MCh) is able to inhibit the electrically‐evoked endogenous noradrenaline (NA) overflow. This inhibition is mediated by presynaptic inhibitory muscarinic heteroreceptors.

By use of pirenzepine, 4‐diphenylacetoxy‐N‐methylpiperidine methobromide (4‐DAMP) and AF‐DX 116 as M1‐, M3‐, and M2‐selective antagonists respectively, the MCh (0.1 μm)‐induced inhibition of the electrically‐evoked NA overflow could be reversed to the control stimulation value dose‐dependently.

The potency order of the antagonists was: 4‐DAMP > AF‐DX 116 > pirenzepine, pIC50 values being 8.50, 7.96 and 7.01, respectively.

From these results it was concluded that the inhibitory presynaptic heteroreceptors in the portal vein of concious unrestrained rats are of the cardiac M2‐subtype.
Eosinophil accumulation in pulmonary airways of guinea‐pigs induced by exposure to an aerosol of platelet‐activating factor: effect of anti‐asthma drugs
Authors: Sanjar S. , Aoki S. , Boubekeur K. , Chapman I.D. , Smith D. , Kings M.A. , Morley J.
Published: July 2012

Exposure of guinea‐pigs to aerosols of platelet activating factor (PAF) (0.01 to 100 μg ml−1) induced a dose‐dependent increased incidence of eosinophils in bronchoalveolar lavage fluid (BAL) at 48 h. Total leucocyte numbers and the percentages of lymphocytes and neutrophils were unchanged in BAL fluid.

Increased numbers of eosinophils were detected in BAL 1 h after exposure to PAF but eosinophilia was not maximal until 48 h. One week after exposure to PAF, the percentage of eosinophils in BAL was within the normal range.

Depletion of circulating platelets or neutrophils by intravenous injection of specific antisera did not modify accumulation of eosinophils in the airway lumen following inhalation of PAF (10 μg ml−1).

PAF‐induced pulmonary airway eosinophil accumulation was inhibited by treatment with SDZ 64–412, a selective PAF‐antagonist, whether the compound was administered before, or 30 min after, inhalation of PAF.

Pulmonary airway eosinophil accumulation due to inhaled PAF (10 μg ml−1) was inhibited by prior treatment with aminophylline, cromoglycate, ketotifen, dexamethasone and AH 21–132.

Pulmonary airway eosinophil accumulation due to inhaled PAF (10 μg ml−1) was not inhibited by prior treatment with indomethacin, salbutamol or mepyramine.
Effect of ethanol on eicosanoid synthesis by human gastric and colonic mucosal pieces
Authors: Goel R.K. , Tavares I.A. , Bennett A.
Published: July 2012

Human gastric and colonic mucosa obtained at operation was cut into small pieces and incubated with different concentrations of ethanol.

Ethanol (5–40%) caused a concentration‐dependent increase in the amounts of prostaglandin E (PGE), thromboxane B2 (TXB2), 6‐keto‐prostaglandin F1α (6‐keto‐PGF1α) and (up to 20% ethanol) leukotriene C4/D4 (LTC4/D4) in incubates of mucosal pieces from either region.

Higher concentrations of ethanol usually caused small increases or reductions of eicosanoid levels; gastric mucosal PGE and 6‐keto‐PGF1α were still increased by 100% ethanol, whereas TXB2 was unaltered, and LTC4/D4 was reduced. With the colonic mucosa, 100% ethanol increased PGE but reduced the other eicosanoids.

Gastric mucosal pieces incubated in water or phosphate buffer yielded generally similar amounts of eicosanoids. However, colonic mucosa yielded more when incubated in water, possibly indicating a greater sensitivity to osmotic damage. This difference between the two regions is consistent with the ability of the gastric mucosa to resist damage by water on its epithelial surface.
Segregation of discrete Gsα‐mediated responses that accompany homologous or heterologous desensitization in two related somatic hybrids
Authors: Kelly Eamonn , Keen Mary , Nobbs Peter , MacDermot John
Published: July 2012

Prostacyclin and adenosine A2 receptors activate adenylate cyclase in the neuroblastoma hybrid cell lines NG108–15 and NCB‐20. Prolonged exposure of NG108–15 cells to iloprost (a stable analogue of prostacyclin) results in a subsequent reduction in the capacity for adenylate cyclase activation by iloprost, the adenosine analogue 5′‐(N‐ethyl)‐carboxamidoadenosine (NECA) or NaF. In contrast prolonged exposure of NCB‐20 cells to iloprost results only in the loss of iloprost responsiveness.

Iloprost pretreatment of NG108–15 cells also magnified the morphine‐dependent inhibition of iloprost‐stimulated adenylate cyclase activity from 36 to 48%. This change was not due to lower iloprost stimulation following desensitization, since the % inhibition of adenylate cyclase activity by morphine in control cells was constant irrespective of enzyme activity.

These heterologous effects observed in NG108–15 cells following iloprost pretreatment may involve changes in the Gsα protein, since there was a reduction of about 30% in the cholera toxin‐induced [32P]‐ADP‐ribosylation of a 45 kDa protein from cell membranes (corresponding to the extent of loss of NECA or NaF responsiveness). A similar reduction was not observed in NCB‐20 cells.

These results indicate that iloprost pretreatment induces different forms of desensitization in NG108–15 and NCB‐20 cell lines. The heterologous desensitization in the former may, like the human platelet, involve a functional loss of Gsα from the cell membrane. Changes in the activity of Gsα may also account for the heterologous effects on receptors that mediate inhibition of adenylate cyclase.
Anti‐inflammatory activity of bee venom peptide 401 (mast cell degranulating peptide) and compound 48/80 results from mast cell degranulation in vivo
Authors: Banks Barbara E.C. , Dempsey Christopher E. , Vernon Charles A. , Warner Jane A. , Yamey Jill
Published: July 2012

The relationship between the anti‐inflammatory activity of the bee venom peptide 401 in the carrageenin‐induced oedema of the rat hind paw and its mast cell degranulating activity has been reinvestigated.

Mast cell degranulation caused by compound 48/80 (10 mg kg−1) or by allergen challenge in rats sensitized to Nippostrongylus brasiliensis also suppressed rat hind paw oedema in the same test.

The anti‐inflammatory activities of peptide 401 and compound 48/80 were partially suppressed by pretreatment of rats with mepyramine and methysergide, at doses (2.5 mg kg−1) that completely suppressed skin reactions to these mast cell‐derived amines. Pretreatment of rats with compound 48/80 also suppressed the apparent anti‐inflammatory actions of peptide 401 and of compound 48/80.

Injection of peptide 401 together with carrageenin increased the inflammatory response in the rat hind paw.

The anti‐inflammatory activity of peptide 401 and of compound 48/80 in the carrageenin‐induced swelling of the rat hind paw arises from mast cell degranulation in vivo.