bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of anion and fluid secretion by apical P2‐purinoceptors in the rat epididymis
Authors: Wong P.Y.D.
Published: July 2012

Exogenous adenosine triphosphate (ATP) stimulated the short circuit current (SCC) in primary monolayer cultures of rat epididymal cells when added to the apical but not to the basolateral side of the monolayers. Half‐maximal stimulation was achieved at 5 × 10−8m ATP.

The increase in SCC induced by ATP was dependent on the presence of extracellular Cl in the bathing solutions.

The effects of other adenosine derivatives, and purine and pyrimidine nucleotides were studied. Their orders of potency in stimulating SCC were: ATP > adenosine diphosphate > adenosine monophosphate, adenosine, and ATP > inosine triphosphate > guanosine triphosphate > cytidine triphosphate. These results indicate that ATP interacts with a P2‐purinoceptor at the apical membrane of the epididymal cells.

The SCC response to ATP was not blocked by 8‐phenyltheophylline, a P1 ‐purinoceptor antagonist or by propranolol. Although pretreatment of the cultures with piroxicam abolished the SCC response to bradykinin, it did not affect the response to ATP. This indicates that the SCC response to ATP was not mediated by an increase in the synthesis of prostaglandins.

Serosal to mucosal Cl flux (Js‐m Cl) and net water flux were measured in the luminally perfused rat epididymis in vivo. ATP (1 μm) added to the luminal perfusion solution caused an increase in Js‐m CI and net water secretion by the epididymal duct.

Since spermatozoa contain a high concentration of ATP, it is proposed that ATP released from spermatozoa may affect anion and fluid secretion by the epididymis. The control of secretion via the apical purinoceptors offers a means by which spermatozoa regulate the fluidity of their own environment.
Sodium‐dependent inhibition by PN200‐110 enantiomers of nicotinic adrenal catecholamine release
Authors: Cárdenas A.M. , Montiel C. , Artalejo A.R. , Sánchez‐García P. , García A.G.
Published: July 2012

Dimethylphenylpiperazinium (DMPP) or high K concentrations evoke catecholamine release from perfused cat adrenal glands; in both cases the secretory response was significantly enhanced in the absence of Na. Tetrodotoxin did not modify the nicotinic secretory response.

The (+)‐ and (−)‐enantiomers of the dihydropyridine Ca channel blocker PN200‐110 show a high degree of stereoselectivity in the inhibition of catecholamine secretion evoked by high K or by DMPP in the presence of Na, the (+)‐enantiomer being 57 and 80 times more potent, respectively, than the (−)‐enantiomer. Both, noradrenaline and adrenaline release were equally depressed by PN200‐110.

The IC50 values for (+)‐ and (−)‐PN200‐110 for blockade of the secretory response induced by K or DMPP in the presence of Na are in the same range. In the absence of Na, (−)‐PN200‐110 did not affect DMPP‐evoked secretion; however, the (+)‐enantiomer partially inhibited it.

The results suggest that the physiological catecholamine release from chromaffin cells is preceded by Na entry through the nicotinic receptor‐associated ionophore; this causes cell depolarization, opening of voltage‐dependent, dihydropyridine‐sensitive Ca channels and Ca entry into the cell. In the absence of Na, additional Ca influx through an alternative pathway (the nicotinic cholinoceptor ionophore?) might also activate secretion.
Antinociception and physical dependence produced by [D‐Arg2] dermorphin tetrapeptide analogues and morphine in rats
Authors: Chaki Kyoji , Kawamura Shunsuke , Kisara Kensuke , Sakurada Shinobu , Sakurada Tsukasa , Sasaki Yusuke , Sato Takumi , Susuki Kenji
Published: July 2012

The antinociceptive effects of [D‐Arg2] dermorphin tetrapeptide analogues, H‐Tyr‐D‐Arg‐Phe‐Gly‐NH2 and H‐Tyr‐D‐Arg‐Phe‐β‐Ala‐OH when administered subcutaneously (s.c.) in rats were measured by the tail‐flick test. In addition, the appearance of typical withdrawal signs upon cessation of administration or on subsequent treatment with naloxone were measured after chronic administration of either peptide or morphine.

The dose of peptides and of morphine in the physical dependence test was determined from the AD50 to inhibit the tail‐flick test in rats. Doses from 4 to 64 times the AD50 doses were employed in the s.c. administration schedules.

The intensity of the antinociception induced by either peptide was greater than that produced by morphine. Moreover, the antinociception induced by the peptides was of much longer duration than that produced by morphine.

Abrupt withdrawal after chronic administration of either peptide produced only slight loss of body weight. In contrast, morphine withdrawal produced sharp loss of body weight.

Naloxone precipitated withdrawal signs after chronic administration of either peptide were less intense than those after chronic morphine.

These results suggest that the antinociception produced by these peptides is more intense and of longer duration than that produced by morphine. It is also interesting to note that the physical dependence produced by these peptides is less marked than that produced by morphine.
Effects of sulphonylureas and diazoxide on insulin secretion and nucleotide‐sensitive channels in an insulin‐secreting cell line
Authors: Sturgess N.C. , Kozlowski R.Z. , Carrington C.A. , Hales C.N. , Ashford M.L.J.
Published: July 2012

The effects of various sulphonylureas and diazoxide on insulin secretion and the activity of various channels have been studied using tissue culture and patch‐clamp methods in an insulinsecreting cell line derived from a rat islet cell tumour.

Tolbutamide, glibenclamide and HB699 increased the rate of insulin release by 2–5 fold. The concentrations of tolbutamide and glibenclamide giving half‐maximum effects on insulin secretion were approximately 40 μM and 0.2 μM, respectively.

Diazoxide (0.6‐1.0 mM) per se, had either no effect or produced a small increase in insulin secretion, whereas when secretion was maximally stimulated by the combination of glucose (3 mM) and leucine (20 mM), it produced inhibition. Tolbutamide‐induced release was also inhibited by diazoxide.

Tolbutamide, glibenclamide, HB699 and HB985 reduced the open‐state probability of the ATP‐K+ channel in a dose‐dependent manner. Tolbutamide and glibenclamide were shown to be effective regardless of which side of the membrane they were applied.

In whole cell recording, in which the total ATP‐sensitive K+ conductance of the cell could be measured, dose‐inhibition curves for tolbutamide and glibenclamide were constructed, resulting in Ki values of 17 μM and 27 nM, respectively. The value of Ki for tolbutamide was unchanged when ATP (0.1 mM) was present in the electrode.

Diazoxide (0.6 mM) activated the ATP‐K+ channels only when they had first been inhibited by intracellular ATP (0.1 mM) or bath applied tolbutamide (3–30 μM). The inhibition produced by glibenclamide could not be reversed by diazoxide.

Neither tolbutamide (1.0 mM) nor glibenclamide (10 μM) altered the open‐state probability of the Ca2+‐activated K+ channel or the Ca2+‐activated non‐selective cation channel which are present in this cell line.

It is concluded that the sulphonylureas and related hypoglycaemic drugs and diazoxide regulate insulin secretion by direct effects on the ATP‐K+ channel or a protein closely associated with this channel.
Leucocyte infiltration and cartilage proteoglycan loss in immune arthritis in the rabbit
Authors: Pettipher E.R. , Henderson B. , Moncada S. , Higgs G.A.
Published: July 2012

The relationship between phagocytic leucocyte infiltration and cartilage degradation in immune arthritis has been investigated in groups of normal and neutropenic rabbits.

Injection of antigen into the knee joints of sensitized control animals induced joint swelling, prostaglandin E2 (PGE2) synthesis, leucocyte accumulation and proteoglycan loss from articular cartilage.

Intravenous injection of nitrogen mustard caused a selective depletion of circulating neutrophils and monocytes with little or no effect on platelets or lymphocytes. In neutropenic animals challenged with antigen, there was virtually no joint swelling, PGE2 synthesis or leucocyte infiltration but cartilage proteoglycan loss was unchanged after 1 day and increased by day 4 compared to control animals.

The numbers of circulating leucocytes returned to normal 3–4 days after nitrogen mustard treatment and leucocyte infiltration occurred in antigen‐challenged joints but this was not accompanied by joint swelling. Subsequent intra‐articular injection of PGE2 did, however, cause swelling.

Lysosomal enzyme levels in arthritic joint fluids were measured. The levels of β‐glucuronidase, which is released by activated phagocytes, were decreased in neutropenic animals but the levels of N‐acetyl‐β‐glucosaminidase, which is a marker of tissue damage, were not changed by neutrophil depletion.

Intra‐articular injections of the cytokine interleukin‐1 (IL‐1) induced a pattern of leucocyte infiltration and cartilage proteoglycan loss similar to that seen in immune arthritis. In neutropenic animals, IL‐1 did not cause significant accumulation of leucocytes in the joint but the loss of proteoglycan from cartilage was unimpaired.

These results indicate that both leucocyte infiltration and prostaglandin synthesis are required for joint swelling but that tissue degradation is mediated by resident cells. It is likely that release of IL‐1 by synovial cells stimulates the synthesis and activation of metalloproteinases which initiate the process of tissue degradation.
Estimation of opioid receptor agonist dissociation constants with β‐chlornaltrexamine, an irreversible ligand which also displays agonism
Authors: Leff P. , Dougall I.G.
Published: July 2012

The irreversible opioid receptor antagonist β‐chlornaltrexamine (β‐CNA) has been shown previously to have agonist activity in the guinea‐pig ileum preparation. However, the receptor type or types mediating this effect have not been established.

In this study, the agonism of β‐CNA was investigated by use of the competitive antagonist 16‐methylcyprenorphine (RX8008M). Non‐cumulative concentration‐effect curves for β‐CNA were displaced in a non‐parallel fashion indicating that the agonism was mediated by both μ‐ and κ‐receptors.

In principle, expression of agonism by an irreversible receptor antagonist could compromise its use in estimating agonist dissociation constants (pKAs) due to desensitization operating in addition to receptor inactivation. For κ‐receptors, this possibility was checked by use of ethylketocyclazocine (EKC) to mimic the agonist effects of β‐CNA and test whether subsequent EKC concentration‐effect curves were displaced. For μ‐receptors it was necessary to perform more involved experiments in which [D‐Ala2, MePhe4, Gly‐ol5]enkephalin (DAGOL) was used as a standard agonist and its pKA was estimated under different conditions of β‐CNA incubation.

These analyses indicated that neither the μ‐ nor the κ‐receptor‐mediated agonism of β‐CNA was associated with appreciable receptor desensitization. In turn it was concluded that the usefulness of β‐CNA as a pharmacological tool for the estimation of μ‐ and κ‐opioid receptor agonist dissociation constants is not compromised by the agonist effects that the compound demonstrates at these receptors.
Substance P, neurokinin A and neurokinin B in the ocular response to injury in the rabbit
Authors: Beding‐Barnekow Britt , Brodin Ernst , Håkanson Rolf
Published: July 2012

Substance P (SP) and neurokinin A‐ (NKA)/neurokinin B (NKB)‐like immunoreactivity (LI) were measured by radioimmunoassay in extracts of the rabbit uvea. The iris‐ciliary body complex contained 3–4 times more NKA/NKB‐LI than SP‐LI. Tachykinins are thought to mediate many of the responses to ocular injury in the rabbit. Their possible role in the miosis and breakdown of the blood‐aqueous barrier (BAB) was studied in vitro and in vivo.

In vitro, NKA had a more short‐lasting contractile effect on the sphincter pupillae muscle than either SP or NKB, but SP was more potent than the other two. The tachykinin antagonist, spantide, dose‐dependently suppressed the response to electrical stimulation (by 90% at 10−4 M) and to the three tachykinins. An antiserum against SP (no cross‐reaction with NKA or NKB) greatly suppressed the response to SP (by 90%) as well as to electrical field stimulation (by 40%). The responses to NKA and NKB were unaffected.

In vivo studies revealed that SP was more potent than NKA and NKB as a miotic. SP evoked a moderate breakdown of the BAB at high doses while NKA and NKB were virtually inactive.

We conclude that besides SP other tachykinins might play a role in the mediation of miosis in the rabbit eye but, of the three peptides investigated, only SP can be of importance for the break‐down of the BAB.
Properties of intracellular calcium stores in pregnant rat myometrium
Authors: Kanmura Y. , Missiaen L. , Casteels R.
Published: July 2012

The properties of the Ca2+ stores in myometrium of 21‐day pregnant rats were studied by recording the contractile responses of saponin‐treated skinned muscles.

After accumulation of Ca2+ into the stores in the presence of 5mM NaN3, inositol 1,4,5‐trisphosphate (InsP3) at concentrations exceeding 3 μM produced a contraction. The amplitude of this contraction was maximal at about 20 μM. A second application of 20 μM InsP3 produced a smaller contraction than the first one. However after reloading the stores with Ca2+, 20 μM InsP3 produced a contraction of the same amplitude as the initial one.

After application of 20 μM InsP3, 1 μM A23187 still evoked a large contraction. If A23187 was applied first, the subsequent application of InsP3 or A23187 no longer induced a contraction, even after Ca2+ loading.

Guanosine triphosphate (GTP) or arachidonic acid, both 100 μM neither evoked a contraction nor enhanced the subsequent contraction elicited by 20 μM InsP3.

Caffeine 25 mM did not induce a contraction nor did it affect the contraction elicited by 20 μM InsP3.

The results indicate that in pregnant rat myometrium InsP3 releases Ca2+ from intracellular stores as has been proposed in vascular smooth muscles.
Na+‐K + pump activity in rat peritoneal mast cells: inhibition by extracellular calcium
Authors: Knudsen Torben , Johansen Torben
Published: July 2012

Pure populations of rat peritoneal mast cells were used to study cellular potassium uptake. The radioactive potassium analogue, 86rubidium, was used as a tracer for potassium for measurements of the activity of the cellular potassium uptake process.

The ouabain‐sensitive and the ouabain‐resistant potassium (86rubidium) uptake of mast cells incubated in the presence of calcium, 1 mmol l−1, were very low, 52 and 147 pmol per 106 cells min−1.

Calcium‐deprivation of the cells uncovered a large capacity ouabain‐sensitive potassium (86rubidium) uptake mechanism. The activity of the uptake mechanism was decreased by reintroduction of calcium into the cell suspension, and it was dependent on cellular energy metabolism, temperature and pH.

The potassium (86rubidium) uptake of mast cells incubated in a calcium‐free medium occurs through an active and ouabain‐sensitive mechanism that has the nature of an enzyme, and it is mediated by the Na+‐K+ pump located in the plasma membrane. It is demonstrated that the activity of the Na+‐K+ pump mechanism is inhibited by low concentrations of extracellular calcium (0.1–1.2 mmoll−1). The possibility is discussed that calcium‐deprivation may increase the pump activity by increasing the permeability of the plasma membrane for Na+.
Potentiation of atrial natriuretic peptide‐stimulated cyclic guanosine monophosphate formation by glucocorticoids in cultured rat renal cells
Authors: Kanda K. , Ogawa K. , Miyamoto N. , Hatano T. , Seo H. , Matsui N.
Published: July 2012

The effect of steroid hormones on atrial natriuretic peptide (ANP)‐stimulated cyclic guanosine monophosphate (cyclic GMP) formation was studied in cultured rat renal cells.

ANP increased cyclic GMP formation in a dose‐dependent manner, while cyclic AMP was not changed by ANP.

Steroid hormones did not affect basal cyclic GMP levels in cultured rat renal cells.

Dexamethasone at 10−8m increased ANP (human and rat ANP)‐stimulated cyclic GMP dose‐dependently in cultured rat renal cells. Cortisol, corticosterone and aldosterone at a concentration of 10−7m also potentiated ANP‐stimulated cyclic GMP formation, although triiodothyronine, oestradiol and testosterone were ineffective. Potentiation of ANP action by these steroids seems to parallel glucocorticoid activity.

Dexamethasone did not affect cyclic GMP formation stimulated by sodium nitroprusside which stimulates soluble guanylate cyclase in the cytosol. Therefore, the potentiating action of dexamethasone may be mediated through the action on particulate guanylate cyclase at the plasma membrane.

It is suggested that the diuretic action of glucocorticoids may, at least in part, be mediated through the potentiating effect of glucocorticoids on cyclic GMP response to ANP.
Castor oil increases intestinal formation of platelet‐activating factor and acid phosphatase release in the rat
Authors: Pinto A. , Calignano A. , Mascolo N. , Autore G. , Capasso F.
Published: July 2012

When castor oil was administered by gavage to rats, the duodenum and jejunum but not ileum and colon produced large amounts (5–6 fold greater than control) of platelet activating factor (Paf).

Intraluminal release of acid phosphatase (AP) was also markedly increased (5–6 fold greater than control) in the duodenum and jejunum of castor oil‐treated rats and there was a correlation between the elevated release of AP and intestinal hyperaemia.

These findings support a role for Paf as a mediator of intestinal damage induced by castor oil.
EP 171: a high affinity thromboxane A2‐mimetic, the actions of which are slowly reversed by receptor blockade
Authors: Jones R.L. , Wilson N.H. , Lawrence Ruth A.
Published: July 2012

Replacement of the four‐carbon ω‐terminus in 9,11‐endoxy‐10a‐homo prostaglandin H2 with a p‐fluorophenoxy group produces a compound (EP 171) with very high agonist potency at TP‐receptors.

On six isolated smooth muscle preparations EP 171 was 33–167 times more potent as a TP‐receptor agonist than U‐46619 (11,9‐epoxymethano PGH2); EC50 values ranged from 45 to 138 pm. The actions of EP 171 were difficult to study because of their slow onset and offset. For example, on the guinea‐pig trachea the time required for 50% reversal of EP 171‐induced contractions during washout was about 3 h.

On the pig pulmonary artery, a more rapidly responding preparation, it was possible to show that the TP‐receptor antagonist EP 092 blocked the contractile actions of EP 171 and U‐46619 to similar extents: pA2 = 8.09 and 8.15 respectively.

EP 171 was also a very potent activator of human blood platelets, being about 90 times more potent than U‐46619. Both shape change (0.1 nm) and aggregation (1 nm) were slow in onset, a profile not previously observed for a thromboxane A2‐mimetic.

When potencies at TP‐, EP1‐(guinea‐pig fundus) and FP‐(dog iris sphincter) receptors were compared, EP 171 showed a higher specificity as a TP‐receptor agonist than either STA2 or U‐46619. These studies also showed that contrary to earlier reports, the guinea‐pig fundus does contain TP‐receptors mediating muscle contraction. However, the maximal response due to activation of TP‐receptors was only about 35% of the PGE2 maximum.

Established responses to EP 171 were slowly reversed following addition of a high concentration of a TP‐receptor antagonist (EP 092, GR 32191 or BM 13177). Faster reversals of three less potent 16‐p‐halophenoxy prostanoids and U‐46619 were obtained. Half‐times for offset (and onset) of agonist action appeared to correlate with potency rather than with lipophilicity.

Competition between the agonists and a radio iodinated PTA2 derivative ([125I]‐PTA‐OH) for binding to TP‐receptors on intact human platelets was studied. IC50 values correlated well with aggregating potency, EP 171 having the lowest IC50 of 2.9 nm. The true Ki for EP 171 may be about 1 nm if both its racemic nature and reduction of initial free ligand concentration due to TP‐receptor binding are taken into account.

It is concluded from a comparison of agonist potency rankings that subclassification of the TP‐receptor is not warranted at this time. The factors that may be responsible for the slow kinetics of EP 171 action are discussed.
Arterial catecholamine levels in morphine‐treated rats subjected to sympathetic nerve stimulation
Authors: Leung Christopher M.K. , Dai Soter , Ogle Clive W.
Published: July 2012

The effect of acute or chronic morphine treatment on the changes in arterial noradrenaline and adrenaline levels in response to sympathetic nerve stimulation was studied in rats.

Rats which had been chronically treated with morphine in their drinking fluid for 21 days were shown to be morphine‐tolerant, as revealed by the tail‐immersion test for analgesia.

It was found that animals given either acute or chronic morphine treatment had similar basal concentrations of arterial catecholamines to their controls.

Sympathetic nerve stimulation produced significant increases in arterial noradrenaline and adrenaline levels in both the control and morphine‐treated animals. However, the degree of arterial noradrenaline elevation was significantly less in morphine‐tolerant animals.

This phenomenon was not observed in acutely morphine‐treated rats or at 2 weeks following opiate withdrawal in animals which had been treated previously with morphine for 3 weeks.

The findings suggest that chronic morphine treatment in rats not only leads to opiate tolerance but also reduces catecholamine release in response to sympathetic nerve stimulation.
Agonist‐induced glycogenolysis in rabbit retinal slices and cultures
Authors: Ghazi Hani , Osborne Neville N.
Published: July 2012

The effects of different putative retinal transmitters and/or modulators on glycogenolysis in rabbit retinal slices and in retinal Müller cell cultures were examined.

Incubation of rabbit retinal slices or primary retinal cultures (either 3–5 day‐old or 25–30 day‐old) in a buffer solution containing [3H]‐glucose resulted in the accumulation of newly synthesized [3H]‐glycogen.

Noradrenaline (NA), isoprenaline, vasoactive intestinal peptide (VIP), 5‐hydroxytryptamine (5‐HT) and 8‐hydroxy‐dipropylaminetetralin (8‐OH‐DPAT) stimulated the hydrolysis of this newly formed 3H‐polymer. The potency order of maximal stimulations was: VIP > NA > isoprenaline > 5‐HT > 8‐OH‐DPAT.

The putative retinal transmitters, dopamine, γ‐aminobutyric acid (GABA), glycine and taurine and the muscarinic agonist carbachol (CCh) had no effect on [3H]‐glycogen content.

The glycogenolytic effects of NA/isoprenaline and 5‐HT/8‐OH‐DPAT appear to be mediated by β‐adrenoceptors and 5‐HT1 receptors (possibly 5‐HT1A), respectively while the VIP‐induced response involved another receptor subtype.

Agonists which mediated [3H]‐glycogen hydrolysis also stimulated an increase in adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) formation. Both responses are blocked to a similar extent by the same antagonists and so are probably mediated via the same receptor subtypes. Moreover, dibutyryl cyclic AMP (db cyclic AMP) promoted tritiated glycogen breakdown in the three retinal preparations.

Not all receptors linked to cyclic AMP production however promote glycogenolysis. Dopamine and apomorphine stimulated cyclic AMP formation via D1‐receptors without influencing glycogenolysis. These receptors are exclusively associated with neurones.
Kinins act on B1 or B2 receptors to release conjointly endothelium‐derived relaxing factor and prostacyclin from bovine aortic endothelial cells
Authors: D'Orléans‐Juste Pedro , de Nucci Gilberto , Vane John R.
Published: July 2012

Bradykinin (Bk) induced the coupled release of endothelium‐derived relaxing factor (EDRF) and prostacyclin (PGI2) from bovine aortic endothelial cells grown in culture. The B2 kinin receptor antagonist, [d‐ArgO,Hyp3,Thi5,8,d‐Phe7]‐Bk, abolished this release by Bk.

Des‐Arg9‐Bk, a B1 kinin receptor agonist, also induced the release of EDRF and PGI2, but much higher concentrations were required to obtain a similar release to that induced by Bk.

[Leu8],des‐Arg9‐Bk, a B1 receptor antagonist, significantly reduced the response to des‐Arg9‐Bk without affecting the release induced by Bk.

The release of EDRF and PGI2 induced by arachidonic acid or ADP was not significantly affected by the B2 or the B1 antagonist.

We conclude, therefore, that Bk and des‐Arg9‐Bk were acting respectively on B2 and B1 bradykinin receptors.

The possible role of kinin receptors in the release of EDRF and PGI2 from endothelial cells is discussed.
The effects of calcium antagonists on calcium overload contractures in embryonic chick myocytes induced by ouabain and veratrine
Authors: Patmore Leslie , Duncan Greig P. , Spedding Michael
Published: July 2012

The protective effects of some calcium antagonists against different forms of calcium overload contracture were investigated in embryonic chick cardiac myocytes.

Tetrodotoxin‐sensitive sodium currents were recorded from the myocytes by the whole‐cell voltage‐clamp technique. Although the peak current was attenuated by veratrine, the inactivation process was markedly inhibited, resulting in a large increase in the total inward current. Action potentials were prolonged by veratrine, automaticity was inhibited and the membrane potential depolarized from −79 to around −45 mV.

Measurements of contraction were made from aggregates of myocytes using a video edge detection technique which quantified edge movement. Veratrine caused an initial positive inotropism then inhibited automaticity of aggregates with subsequent development of a tonic contracture to around 300% of the twitch contraction.

Veratrine‐induced contractures were not significantly affected by 10 μm diltiazem or verapamil. Nifedipine (5 μm), nimodipine (5 μm) and ryanodine (5 μm) also had little effect whilst nicardipine and flunarizine caused a concentration‐dependent inhibition of veratrine‐induced contractures with IC50 s of 3 μm and 2 μm respectively.

Veratrine‐induced contractures were found to be very sensitive to extracellular calcium concentration with an EC50 of 32 μm. Edge movement associated with beating of the myocytes was much less sensitive to calcium (EC50 = 1 mm). Submaximal veratrine contractures in 20–50 μm extracellular calcium were not potentiated by 1 μm Bay K 8644.

Tetrodotoxin also inhibited veratrine‐induced contractures but did not affect contractions induced by ouabain in the presence of 10 μm diltiazem.

Ouabain‐induced contractures were also inhibited by nicardipine and flunarizine indicating that these drugs can protect against calcium overload in embryonic chick heart by a mechanism independent of the normal form of voltage‐sensitive sodium or calcium channels.
GABAA receptor‐mediated positive inotropism in guinea‐pig isolated left atria: evidence for the involvement of capsaicin‐sensitive nerves
Authors: Maggi Carlo Alberto , Giuliani Sandro , Manzini Stefano , Meli Alberto
Published: July 2012

Isolated left atria from reserpine‐pretreated guinea‐pigs, electrically driven (3 Hz) in the presence of atropine (1 μm), phentolamine (0.3 μm) and propranolol (1 μm), responded to a train of stimuli (10 Hz for 2.5 s) with a delayed neurogenic positive inotropic response which was insensitive to hexamethonium (10 μm) but abolished by either tetrodotoxin (1 μm), ω‐conotoxin (0.1 μm), in vitro capsaicin desensitization or desensitization to calcitonin gene‐related peptide (CGRP).

In these experimental conditions, γ‐aminobutyric acid (GABA) produced a concentration‐related (10 μm‐1 mm) positive inotropic response similar to that produced by electrical field stimulation. The effect of GABA was competitively antagonized by bicuculline methiodide (10 μm), a GABAA receptor antagonist.

The selective GABAA receptor agonists, muscimol and homotaurine mimicked the positive inotropic effect of GABA while baclofen, the selective GABAB receptor agonist, did not.

The action of GABA (1 mm) was abolished by either tetrodotoxin (1 μm), ω‐conotoxin (0.1 μm), in vitro capsaicin desensitization or desensitization to CGRP, while it was unaffected by hexamethonium. In contrast, the inotropic response to CGRP was unaffected by tetrodotoxin, ω‐conotoxin, bicuculline methiodide, hexamethonium or in vitro capsaicin desensitization, but was abolished by CGRP desensitization.

In the spontaneously beating guinea‐pig right atrium, GABA (1 μm) produced a small and transient positive chronotropic effect that was no longer observed after in vitro desensitization with capsaicin (1 μm).

In the guinea‐pig isolated perfused heart from reserpine‐pretreated animals (with atropine, phentolamine and propranolol in the perfusion medium), GABA (1 μm) produced a transient tachycardia and a small increase in coronary flow. Both capsaicin (1 μm) and CGRP (1 μm) produced marked tachycardias and increases in coronary flow. After exposure to capsaicin (1 μm), no effect of GABA could be detected.

We conclude that, in the guinea‐pig heart, GABAA receptors, presumably located on the preterminal region of capsaicin‐sensitive sensory nerves, initiate a conducted impulse (since it is tetrodotoxin‐sensitive) which leads to transmitter release (endogenous CGRP‐like material) by activation of ω‐conotoxin‐sensitive, voltage‐sensitive calcium channels and a functional response.
Contraction of the rat isolated aorta caused by Clostridium perfringens alpha toxin (phospholipase C): evidence for the involvement of arachidonic acid metabolism
Authors: Fujii Yoshio , Sakurai Jun
Published: July 2012

Alpha toxin produced by Clostridium perfringens contracted the rat isolated aorta and stimulated release of arachidonic acid in the tissue.

Quinacrine did not inhibit contraction caused by the toxin.

Indomethacin blocked contraction caused by the toxin in a dose‐dependent manner and markedly increased levels of arachidonic acid released by the toxin.

The toxin‐induced contraction was blocked by the thromboxane synthetase inhibitor OKY‐046 and the thromboxane A2 (TXA2) antagonist ONO‐3708.

The toxin stimulated production of TXB2 and this was blocked by pretreatment with either indomethacin or OKY‐046.

Toxin‐induced contraction was diminished by pretreating aorta with collagenase or by rubbing the intimal surface to remove the endothelium.

These data suggest that the contractile response to the toxin is associated with stimulation of TXA2 production from arachidonic acid released by the toxin in the endothelial cells of the aorta.
Regional haemodynamic effects of vasopressin infusion in conscious, unrestrained, Brattleboro rats
Authors: Gardiner S.M. , Compton A.M. , Bennett T.
Published: July 2012

Incremental rates of infusion (0.027–4.0 pmol min−1) of exogenous vasopressin were given for 10 min periods to conscious, Brattleboro (i.e. vasopressin‐deficient) rats, which had been chronically instrumented with pulsed Doppler probes and intravascular catheters (to permit assessment of regional haemodynamic changes).

There were no significant effects of the two lowest rates of infusion (0.027 and 0.105 pmol min−1) but, after 10 min of vasopressin infusion at 0.313 pmol min−1, superior mesenteric vasoconstriction had occurred unaccompanied by any other changes. Infusion of vasopressin at 0.687 pmol min−1 produced increases in blood pressure and in both mesenteric and hindquarters vascular resistance, but no change in renal vascular resistance or heart rate. These results do not indicate specific interactions between exogenous vasopressin and baroreflex mechanisms to offset the pressor effect of the neuropeptide.

The marked bradycardia, hypertension and renal, mesenteric and hindquarters vasoconstriction seen after 10 min infusion of vasopressin at 4.0 pmol min−1 were all abolished 10 min after administration of an antagonist of V1‐receptors ((+)−(CH2)5Tyr(Et)DAVP); additional antagonism of V2‐receptors (with the non‐selective antagonist (+)−(CH2)5Tyr(Et)VAVP) had no effects on any measured variable. Hence, the present experiments provide no evidence for important vasodilator effects of vasopressin in conscious, Brattleboro rats.
An in vivo dialysis and behavioural study of the release of 5‐HT by p‐chloroamphetamine in reserpine‐treated rats
Authors: Adell A. , Sarna G.S. , Hutson P.H. , Curzon G.
Published: July 2012

Reserpine (2.5 mg kg−1 i.p.) decreased rat brain 5‐hydroxytryptamine (5‐HT) by 86% 24 h later but most components of the 5‐HT‐dependent behavioural syndrome induced by p‐chloroamphetamine (PCA, 5 mg kg−1 i.p.) or 5‐methoxy‐N,N‐dimethyltryptamine (5‐MeODMT, 5 mg kg−1 i.p.) over 1 h after administration were unaffected. However, Straub tail was increased after giving PCA or 5‐MeODMT and head weaving was decreased after giving 5‐MeODMT.

Frontal cortex extracellular 5‐HT concentrations of vehicle pretreated rats before injection of PCA, as calculated from dialysate 5‐HT concentrations, were about 1/1000th of corresponding brain values. Extracellular 5‐hydroxyindoleacetic acid (5‐HIAA) and brain values were comparable with each other. Dialysate 5‐HT increased after PCA with peak values at 20–40 min.

Reserpine pretreatment reduced dialysate 5‐HT concentration before PCA was given but the net increase (AUC) over the 1 h after PCA did not differ significantly from that seen in animals pretreated with vehicle. Dialysate 5‐HIAA values slowly decreased after PCA injection in both reserpine and vehicle pretreated groups.

The results suggest that PCA causes the 5‐HT syndrome by releasing 5‐HT from the neuronal cytoplasm but that physiological release of 5‐HT occurs from vesicular stores.
5‐HT3 receptor antagonists injected into the area postrema inhibit cisplatin‐induced emesis in the ferret
Authors: Higgins G.A. , Kilpatrick G.J. , Bunce K.T. , Jones B.J. , Tyers M.B.
Published: July 2012

The purpose of the present study was to identify and investigate the role of 5‐hydroxytryptamine3 (5‐HT3) receptors in the area postrema in the control of cisplatin‐induced emesis in the ferret.

Homogenate binding and autoradiography experiments using the high affinity 5‐HT3 receptor ligand, [3H]‐GR65630, identified the presence of a high concentration of 5‐HT3 receptors in the area postrema of the ferret.

Intraperitoneal injection of the 5‐HT3 receptor antagonists, GR38032F, GR65630A and MDL72222, at doses of 1, 0.1 and 1 mg kg−1 respectively, inhibited emesis induced by cisplatin, 9 mg kg−1 i.p.

Discrete injection of low doses of the 5‐HT3 receptor antagonists directly into the area postrema region also inhibited cisplatin‐induced (9 mg kg−1 i.p.) emesis. The dose ranges used were: GR38032F, 0.01–1 μg; GR65630A, 0.001–0.1 μg; MDL72222, 0.1–10 μg.

Cisplatin‐induced emesis was not inhibited by discrete injection of ketanserin (30 μg) or methiothepin (30 μg) into the area postrema. Injection of the 5‐HT3 receptor agonist, 2‐methyl‐5‐HT, directly into the area postrema produced an incomplete emetic response.

These results confirm a role of 5‐HT, and in particular 5‐HT3 receptors, in the control of cisplatin‐induced emesis, and show that at least one functional site for these receptors in modulating the emetic response is the area postrema, the locus of the chemoreceptor trigger zone.
(+)−[3H]‐PN 200–110 binding to cell membranes and intact strips of portal vein smooth muscle: characterization and modulation by membrane potential and divalent cations
Authors: Dacquet C. , Loirand G. , Rakotoarisoa L. , Mironneau C. , Mironneau J.
Published: July 2012

Specific binding of the calcium‐antagonist dihydropyridine derivative, (+)−[3H]‐PN 200–110 (isradipine), to cell membranes of equine portal vein smooth muscle was compared with binding to intact strips isolated from rat portal veins.

Specific binding to vascular smooth muscle membranes was of high affinity, saturable and reversible. The dissociation constant obtained from association and dissociation kinetics of (+)−[3H]‐PN 200–110 was similar to that obtained from equilibrium binding and competition experiments.

Specific binding of (+)−[3H]‐PN 200–110 was completely displaced by unlabelled dihydropyridines. Among other calcium antagonists, D888 and (+)−cis‐diltiazem partially inhibited the binding at 25°C. At 37°C, only (+)−cis‐diltiazem stimulated the binding. LaCl3, CdCl2, NiCl2, CoCl2 had inhibitory effects, whereas KCl and NaCl had no effect.

When intact strips of portal vein were incubated in high external potassium concentrations for 30 min, the Kd was lowered to 0.04 ± 0.01 nm from the control value of 0.14 + 0.02 nm (n = 5), thereby indicating that (+)−[3H]‐PN 200–110 bound to voltage‐dependent calcium channels, with a higher affinity, in the depolarized state.

When external Ca2+ was removed or substituted with Ba2+ or Sr2+, Kd values increased suggesting that the dihydropyridine binding to intact strips was modulated by binding of Ca2+ ions to voltage‐dependent calcium channels.
An investigation into the mechanisms of inhibition of calcium channel currents in cultured sensory neurones of the rat by guanine nucleotide analogues and (−)− baclofen
Authors: Dolphin A.C. , McGuirk S.M. , Scott R.H.
Published: July 2012

The mechanism of inhibition of calcium channel currents by the guanine nucleotide analogue guanosine 5′‐O‐3 thiotriphosphate (GTP‐γ‐S) and by the GABAB agonist (−)‐baclofen has been studied in cultured dorsal root ganglion neurones of the rat. The inhibition by GTP‐γ‐S is particularly characterized by an abolition of the transient component of calcium channel currents carried either by Ba2+ (IBa) or by Ca2+ (ICa).

The effect of agents increasing intracellular cyclic AMP levels has been examined. Neither internal cyclic AMP nor forskolin prevented the inhibition of IBa by baclofen. Neither forskolin nor pretreatment of cells with cholera toxin prevented the inhibition of the transient component of IBa by GTP‐γ‐S. However, both these treatments increased the amplitude of the sustained IBa in the presence of GTP‐γ‐S. The ATP analogue adenosine imido‐diphosphate which inhibits many ATP requiring enzymes did not prevent the effect of GTP‐γ‐S although it reduced the amplitude of IBa.

Baclofen (100 μm) produced a 22 ± 2% increase in inositol phosphate production in 30 s, whereas the increase produced by bradykinin (1 μm) was 70 + 14%. However, unlike baclofen, bradykinin did not inhibit IBa or ICa in these cells.

The effect of protein kinase C inhibitors was examined. Polymixin B (20 μm in patch pipette) had no effect on the inhibition of IBa by baclofen or GTP‐γ‐S. A higher concentration (100 μm) alone inhibited IBa and no further inhibition by baclofen was observed. Neither H7 (50 μm) nor staurosporine (100 nm), applied extracellularly, prevented the response to GTP‐γ‐S.

The protein kinase C activator di‐octanoyl glycerol (20 μm) did not inhibit IBa. Arachidonic acid (100 μm) also produced no inhibition of IBa.

In conclusion we have obtained no evidence that a second messenger system mediates the inhibition of calcium channel currents by GTP‐γ‐S or baclofen in dorsal root ganglion neurones. These results support the hypothesis that GABAB receptors are directly coupled to calcium channels by G proteins.
Facilitation by tachykinins of neurotransmission in guinea‐pig pulmonary parasympathetic nerves
Authors: Hall Anthony K. , Barnes Peter J. , Meldrum Lorna A. , Maclagan Jennifer
Published: July 2012

The effect of tachykinins on cholinergic neurotransmission was studied in an innervated tracheal tube preparation isolated from guinea‐pigs anaeshetized with urethane. The tracheal tube was bathed in Krebs‐Henseleit solution containing 5 μm indomethacin.

Neurokinin A (NKA), eledoisin (El) and substance P (SP) caused concentration‐dependent increases in intraluminal pressure (ILP), with an order of potency NKA > El >> SP.

Low concentrations of tachykinins, that had little effect on ILP, caused an increase in the contractions elicited by stimulation of the preganglionic vagal nerve fibres and by postganglionic (transmural) stimulation. The order of potency was NKA ≤ El > SP. Contractions induced by exogenous acetylcholine (ACh) were not increased by the tachykinins.

The magnitude of the tachykinin‐induced augmentation of responses to nerve stimulation was inversely related to stimulation voltage and frequency.

These results suggest that tachykinins act on NK2 receptors, both on the trachealis muscle and on postganglionic pulmonary parasympathetic nerve terminals. Activation of the neuronal receptors may increase the probability of transmitter release from the nerve terminals.
Effect of aminophylline on cisplatin nephrotoxicity in the rat
Authors: Heidemann H.Th. , Müller St. , Mertins L. , Stepan G. , Hoffmann K. , Ohnhaus E.E.
Published: July 2012

The effect of the methylxanthine aminophylline on cisplatin (5 mg kg−1 i.v.)‐induced acute renal failure was investigated in the rat. Renal function was measured 5 days after cisplatin administration.

Cisplatin caused a polyuric acute renal failure. The creatinine clearance was significantly reduced.

Aminophylline (24 mg kg−1 12 h−1) ameliorated the cisplatin nephrotoxicity when administered during the maintenance phase of acute tubular necrosis. However, it had no effect when only administered prophylactically before the cisplatin application.

Enprofylline (20 mg kg−1 4 h−1 with dose adjustment), a methylxanthine lacking adenosine receptor antagonism in comparison to aminophylline, had no protective effect on cisplatin nephrotoxicity.

Adenosine is a renal vasoconstrictor and decreases glomerular filtration rate. Endogenous adenosine in the kidney is formed by degradation of ATP and is thought to be involved in various forms of acute renal failure. The results suggest that adenosine may be involved in the haemodynamic changes in the kidney induced by cisplatin.
Vasoactive actions of local anaesthetics on human isolated umbilical veins and arteries
Authors: Monuszko Eileen , Halevy Simon , Freese Kenneth , Liu‐Barnett Maida , Altura Burton
Published: July 2012

An in vitro study, using helical preparations of human umbilical arteries and veins obtained from healthy women at term pregnancy, was designed to determine: (a) whether three local anaesthetics commonly utilized in obstetric anaesthesia (bupivacaine, 2‐chloroprocaine, and lignocaine) can induce contraction or relaxation of resting umbilical vessels; (b) whether these agents can induce contraction or relaxation of umbilical vessels which have been previously induced to contract by a known activator, potassium chloride (KCl); and (c) the relative potency of these agents as compared to KCl.

The results indicate that: (a) these local anaesthetics are vasoactive on human umbilical vascular smooth muscle; (b) bupivacaine induces contraction in over 90% of the resting vessels examined, while 2‐chloroprocaine consistently causes relaxation and lignocaine causes a small degree of contraction in 40% of vessels examined; (c) bupivacaine causes further contraction (or potentiation) of KCl‐contracted muscle in 50% of the vessels studied, while 2‐chloroprocaine and lignocaine both induce relaxation of these contracted vessels.
Tissue noradrenaline and the polyol pathway in experimentally diabetic rats
Authors: Lucas P.D. , Qirbi A.
Published: July 2012

The effects of a six week period of streptozotocin‐induced diabetes on tissue catecholamines and on in vivo noradrenaline turnover were assessed in rats.

Noradrenaline concentrations measured in heart ventricle, terminal ileum, vas deferens, spleen and adrenal tissue from the diabetic rats were all found to be elevated compared to those found in control rat tissues. The adrenaline contents of the adrenal glands were also raised in these animals.

Noradrenaline turnover in heart ventricle, terminal ileum and vas deferens was estimated from the decline in tissue content of the amine following inhibition of its synthesis with α‐methyl‐p‐tyrosine. Turnover was found to be increased in all three tissues.

The involvement of the polyol pathway in the above changes was investigated by examining the effects of continuous treatment with an aldose reductase inhibitor, Statil (ICI 128436) or dietary myo‐inositol supplementation. Either treatment was found to prevent or reduce the increases in tissue noradrenaline and in its turnover. Myo‐inositol treatment also partially prevented the rise in adrenal adrenaline.

It is concluded that the elevation of tissue catecholamines and of noradrenaline turnover by diabetes was related to myo‐inositol depletion secondary to excessive sorbitol synthesis. Possible mechanisms for the observed increase in noradrenaline turnover could involve Na+, K+‐ATPase depression.
Limited interference of specific Paf antagonists with hyper‐responsiveness to Paf itself of lungs from actively sensitized guinea‐pigs
Authors: Pretolani Marina , Lefort Jean , Vargaftig B. Boris
Published: July 2012

The interference of various platelet‐activating factor (Paf) antagonists with Paf‐ and antigen‐induced effects in isolated lungs from actively sensitized guinea‐pigs was investigated.

WEB 2086 and BN 52021, two antagonists structurally unrelated to Paf, at concentrations 10–100 fold above those exerting a potent and selective inhibition of the effects of Paf in lungs from non‐immunized guinea‐pigs, failed to inhibit bronchoconstriction and mediator release evoked by the phospholipid when administered into lungs from actively sensitized animals.

In contrast to WEB 2086 and BN 52021, antagonists such as Ro 19–3704 and Ro 19–1400, structurally related to the Paf molecule, at concentrations which abrogate the effects of Paf in lungs from non‐immunized guinea‐pigs, inhibited bronchoconstriction and release of histamine and leukotriene‐like material evoked by the intra‐arterial administration of Paf into lungs from actively sensitized animals.

Ro 19–3704 and Ro 19–1400 also inhibited markedly the release of leukotriene C4 (LTC4)‐like material and, to a smaller extent, the histamine secretion induced by 10 μg arachidonic acid.

CV 6209, another Paf antagonist structurally related to the phospholipid, failed to antagonize its bronchopulmonary and secretory effects in sensitized lungs.

All the antagonists used, irrespective of their ability to interfere or not with bronchoconstriction and mediator release triggered by Paf, suppressed oedema formation as measured by the increase in lung wet weight induced by either Paf or ovalbumin.

Our results indicate that: (i) the increase in vascular permeability and the subsequent oedema formation on one hand and the bronchopulmonary effects of Paf on the other hand are mediated by different mechanisms; and (ii) active sensitization provokes a marked modification of the lung reactivity to Paf.