bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro ACTIVITY OF RO363, A β1‐ADRENOCEPTOR SELECTIVE AGONIST
Authors: IAKOVIDIS D. , MALTA E. , McPHERSON G.A. , RAPER C.
Published: July 2012

The β‐adrenoceptor stimulant effects of RO363 and (−)‐isoprenaline have been compared in a variety of isolated tissue preparations.

RO363 is approximately half as potent as (−)‐isoprenaline in tissues where actions are due to β1‐receptor activation (guinea‐pig atrial and ileal preparations and ventricular strips from the rabbit, rat and guinea‐pig).

In uterine and lung strip preparations from the guinea‐pig, where responses are due to β2‐receptor stimulation, RO363 is 100 to 350 times less active than (−)‐isoprenaline and has a low intrinsic activity.

In spontaneously contracted tracheal preparations from the guinea‐pig, RO363 is a full agonist and is approximately half as potent as (−)‐isoprenaline. These effects of RO363 are due to the activation of a population of β1‐receptors in the tissue since RO363 and (−)‐isoprenaline have the same relative potencies in trachea, cardiac and ileal preparations. In addition the KB values for practolol are similar in all these preparations when RO363 is used as the agonist.

The results show that RO363 is a potent and highly selective β1‐receptor agonist.
RELEASE OF OPIOID PEPTIDES IN ANAESTHETIZED CATS?
Authors: DASHWOOD M.R. , FELDBERG W.
Published: July 2012

The effect on arterial blood pressure of intravenous injections of naloxone (200 μg) was examined in cats anaesthetized with chloralose. Usually these injections have no effect on blood pressure unless morphine or opioid peptides have been injected, when they produce a pressor response with tachycardia.

It was found that these injections produced a pressor response with tachycardia after a combination of two or more of the following surgical procedures: (1) tying sinus nerves, (2) removing stellate ganglia, (3) cutting vagi, (4) evisceration.

The pressor responses obtained in these conditions are taken as evidence that such procedures induce the release of endogenous opioid peptides.

The pressor responses to naloxone were greatest when all four surgical procedures had been performed and were then due to adrenaline secretion, evoked centrally by a sympathetic discharge to the adrenals.

If either the stellate ganglia or the viscera were left intact, but the remaining three surgical procedures performed, then the pressor responses to naloxone were due to a sympathetic discharge to adrenals and to blood vessels.

In cats that had received a subcutaneous injection of morphine (2 mg/kg) the adrenals played a minor role in the pressor responses to naloxone, unless the four surgical procedures had been performed. Then the adrenals became entirely responsible for them.

The opioid peptides released after the surgical procedures may be enkephalins or the C‐fragment of lipotropin (β‐endorphin). The stimulus for their release may be interruption of afferent sensory pathways from viscera or the ‘stress’ associated with the surgical procedures.
A STUDY OF SOME PROPRANOLOL ANALOGUES FOR SELECTIVE β‐ADRENOCEPTOR ANTAGONISM USING pA2 VALUES ON ISOLATED TRACHEA AND ATRIA FROM GUINEA‐PIG
Authors: O'DONNELL STELLA R. , WALDUCK KARIN , WANSTALL JANET C.
Published: July 2012

pA2 values for β‐adrenoceptor antagonists were obtained on isolated preparations of guinea‐pig trachea (intrinsic tone) and atria (rate), with isoprenaline, noradrenaline (β1‐selective) and fenoterol (β2‐selective) as agonists. Uptake mechanisms and α‐adrenoceptors were inhibited. The antagonists studied were (±)‐threo‐α‐methylpropranolol, (±)‐1‐(4‐benzimidazoloxy)‐3‐isopropylamino‐2‐propanol (4‐BIP) and (±)‐1‐(5‐benzimidazoloxy)‐3‐isopropylamino‐2‐propanol (5‐BIP).

4‐BIP was a potent β‐adrenoceptor antagonist but it was not selective for trachea (pA2 on trachea 7.88 and on atria 7.73, fenoterol as agonist). 5‐BIP was less than one tenth as active as 4‐BIP and was therefore not studied in detail.

α‐Methylpropranolol was potent and it was also selective for trachea (pA2 on trachea 8.24 and on atria 7.56, fenoterol as agonist). This selectivity was not seen with isoprenaline as agonist. In tracheal preparations contracted by carbachol the slope of the Schild plot for α‐methylpropranolol was less than 1.0 (isoprenaline as agonist).

α‐Methylpropranolol, although not highly selective for β2‐adrenoceptors, is considerably more potent than the alternative β2‐selective antagonists available at present. Therefore, it may be useful in studies designed to classify β‐adrenoceptor subtypes in tissues.
β2‐ADRENOCEPTORS MEDIATE THE STIMULATING EFFECT OF ADRENALINE ON ACTIVE ELECTROGENIC NA‐K‐TRANSPORT IN RAT SOLEUS MUSCLE
Authors: CLAUSEN T. , FLATMAN J.A.
Published: July 2012

The relative role of β1‐ and β2‐adrenoceptors in mediating the stimulating effect of adrenaline on active electrogenic Na‐K‐transport has been assessed in experiments on rat soleus muscles in vitro and in vivo.

In the rat isolated soleus muscle, adrenaline (10−6 m) increases the resting membrane potential (EM) by 5.8 mV and stimulates 22Na‐efflux and ouabain‐suppressible 42K‐uptake by 91 and 94%, respectively.

All of these effects are completely blocked by propranolol (10−5 m), whereas the β1,‐selective adrenoceptor antagonist, metoprolol, was found to be at least 50 times less potent.

The β2‐adrenoceptor agonist, salbutamol, was at least 100 times as potent as H133/22 (a β1‐selective agonist) in stimulating 22Na‐efflux and 42K‐influx.

In experiments performed under pentobarbitone anaesthesia, the intravenous injection of adrenaline (5 μg) or salbutamol (0.5 to 50 μg) led to a rapid and marked increase in the EM of the exposed soleus muscle. This hyperpolarizing effect could not be accounted for by the concomitant, relatively modest change in extracellular K.
THE ACTION OF SODIUM CROMOGLYCATE ON ‘C’ FIBRE ENDINGS IN THE DOG LUNG
Authors: DIXON M. , JACKSON D.M. , RICHARDS I.M.
Published: July 2012

The effect has been studied of sodium cromoglycate (SCG) on the activity of ‘C’ fibre sensory nerve endings in the canine lung. Pretreatment with SCG (100 μg/kg i.v.) reduced the excitation of these endings by capsaicin (10 μg/kg i.v.) for approximately 45 min. This property of SCG may explain its ability to suppress certain types of bronchoconstrictor responses in man.
CORRELATION BETWEEN CATECHOLAMINE SECRETION FROM BOVINE ISOLATED CHROMAFFIN CELLS AND [3H]‐OUABAIN BINDING TO PLASMA MEMBRANES
Authors: AUNIS DOMINIQUE , GARCÍA ANTONIO G.
Published: July 2012

Secretion of catecholamines (CA) evoked by ouabain, chlormadinone acetate (CMA), phenoxybenzamine (Pbz) and vanadate, four agents known to inhibit Na+, K+‐dependent Mg2+‐activated adenosine triphosphatase (ATPase) activity has been studied in suspensions of bovine isolated adrenal medullary cells.

Acetylcholine (ACh) evoked a 5 fold increase of the basal CA secretion from isolated cells suspended in oxygenated Krebs‐bicarbonate solution kept at 27°C. Secretion was antagonized by Ca2+‐deprivation or hexamethonium, indicating good functional viability of the cells.

Ouabain (10−7to 10−4m) evoked a progressive, dose‐dependent release of CA from cell suspensions. Study of the time course of the secretory response for 2h allowed the separation of two components in the secretory response at all doses studied: a slow initial component (0.011 pg/min CA) and a second faster component (0.032 pg/min CA).

CMA evoked a clear‐cut CA secretory response. The ED50for CMA was 10−4m, as compared to 3 × 10−6m for ouabain. Pbz and vanadate did not induce CA release.

[3H]‐ouabain was taken up and bound to intact isolated cells by a non‐saturable binding process. However, in semi‐purified plasma membranes from bovine adrenal medulla a saturable specific [3H]‐ouabain binding process was observed with a KD of 8.1 nm. Binding to the membranes was ATP‐dependent and antagonized by K+.

[3H]‐ouabain specific binding to membranes was antagonized by ouabain and CMA, but not by Pbz or vanadate; the ID50 for ouabain and CMA were 10−6and 10−5m respectively.

Ouabain partially inhibited, in a dose‐dependent manner, Na+, K+‐Mg2+ATPase activity of the semi‐purified plasma membranes.

The results demonstrate a good correlation between the ability of different drugs, known to inhibit ATPase activity, to displace [3H]‐ouabain binding to adreno—medullary plasma membranes and their capacity to evoke a CA secretory response from isolated chromaffin cells. The data also suggest that the CA secretory effects of ouabain may not be due simply to inhibition of the Na+pump and the subsequent ionic redistribution across the plasma membrane; a second mechanism may also be involved.
THE ANTICOAGULANT ACTIVITY OF DERMATAN SULPHATES: EVIDENCE AGAINST THE INVOLVEMENT OF ANTITHROMBIN III
Authors: KINDNESS G. , LONG W.F. , WILLIAMSON F.B.
Published: July 2012

Anticoagulant activity of dermatan sulphates is unaffected by antiserum specific for antithrombin III (AT III) unless the glycosaminoglycan preparation contains demonstrable heparin.

Only dermatan sulphate preparations of considerable heparin content potentiate AT III inhibition of thrombin, factor Xa and plasmin.

These data suggest that dermatan sulphates exert anticoagulant activity which, unlike that of heparin, is largely or totally independent of AT III.
EFFECTS OF INFLAMMATORY AGENTS ON ENDOTHELIAL LYSOSOMAL FRAGILITY AND THEIR INHIBITION BY ANTIINFLAMMATORY DRUGS
Authors: YOFFE JOAN R.
Published: July 2012

Endothelial cells from human unbilical veins were maintained in tissue culture. The fragility of lysosomal membranes were studied by microdensitometry.

Histamine (50 μm to 10 mm), 4‐methylhistamine (100 nm to 10 mm) and dimaprit (100 nm to 10 mm) increased lysosomal fragility. 2‐Thiazolyethylamine and 2‐pyridylethylamine (100 nm to 10 mm) had no effect.

Prostaglandins E1 and E2 (3 nm to 30 μm) and prostaglandin F2α (2 nm to 20 μm) had no direct effect. Low concentrations of prostaglandins E1 and E2 inhibited the fragility induced by histamine 100 μm.

Bradykinin (100 nm to 100 μm) decreased fragility.

The increase in fragility induced by histamine 100 μm or dimaprit 100 μm was inhibited by cimetidine (100 μm and 1 mm) but not by mepyramine (1 μm to 1 mm).

Pretreatment with indomethacin, hydrocortisone, ibuprofen and sodium salicylate caused a dose‐dependent inhibition of histamine‐induced fragility. Threshold concentrations were 1 pm, 100 pm, 10 nm and 10 μm, respectively.

Lignocaine (1 μm to 1 mm) had no direct effect and did not decrease histamine‐induced fragility.
CAPTOPRIL AND THE MAINTENANCE OF BLOOD PRESSURE AFTER SINOAORTIC DENERVATION IN THE RABBIT
Authors: PETTY MARGARET A. , REID J.L.
Published: July 2012

At a dose of 1 mg/kg intravenously, captopril lowered blood pressure in conscious rabbits, that had undergone denervation of sinoaortic baroreceptors, but had no effect on heart rate. In sham‐operated controls, this dose caused only an increase in heart rate.

In the same experiments, captopril caused a substantial inhibition of plasma angiotensin converting enzyme (CE) activity of rapid onset and gradual decline over 2 to 3 h. The time course of recovery of blood pressure and plasma CE activity were similar.

Saralasin, by intravenous infusion, lowered blood pressure in sinoaortic rabbits but to a smaller extent than captopril.

The fall in blood pressure observed after captopril is not dependent on the integrity of baroreceptor afferents.
THE ACTION OF DANTROLENE SODIUM ON RAT FAST AND SLOW MUSCLE in vivo
Authors: LESLIE G.C. , PART N.J.
Published: July 2012

Rats, anaesthetized with urethane, were injected intravenously with dantrolene sodium in a carrier solution of 5% mannitol taken to pH 10 with NaOH. This carrier solution itself was without effect on extrafusal muscle contraction.

Dantrolene sodium (5 mg/kg) had a greater depressant action on the twitch contraction of the fast extensor digitorum longus (EDL) muscle than on the slow soleus (SOL) muscle. The EDL twitch was depressed to 25.9% ± 1.2% (mean + s.e. mean, n = 7) of control whereas the SOL twitch was depressed to 31.3% ± 0.4% (n = 9). These values are significantly different at the P<0.001 level.

The twitch contraction time to peak was reduced by approximately 35% in both EDL and SOL by dantrolene sodium. However, the drug reduced the half relaxation time of SOL by approximately 30% but that of EDL was hardly affected.

The effect of dantrolene sodium on contractions elicited by repetitive stimulation was dependent upon the stimulation frequency. For the SOL muscle the greatest depression was produced at a stimulation frequency of 25 Hz and for EDL at 75 Hz. The minimum of depression was produced for a full fused tetanus for both muscles.

The significance of these findings is discussed in terms of the action of dantrolene sodium on motor control in the intact animal.
ARACHIDONIC ACID METABOLISM AND MODULATION OF in vitro ANAPHYLAXIS BY 5,8,11,14‐EICOSATETRAYNOIC ACID AND 9a,12a‐OCTADECADIYNOIC ACID
Authors: HITCHCOCK MARGARET , KOKOLIS NICHOLAS A.
Published: July 2012

5,8,11,14‐Eicosatetraynoic acid (ETYA) inhibited the antigen‐induced contractions of tracheal spirals obtained from actively sensitized guinea‐pigs. Consistent data were obtained only when the spirals were treated with indomethacin.

ETYA did not affect histamine‐induced contractions of indomethacin‐treated tracheal spirals.

9a, 12a‐Octadecadiynoic acid (Ro‐3–1314) a potential inhibitor of linoleic acid metabolism, stimulated the antigen‐induced contraction of guinea‐pig tracheal spirals and the immunological release of slow reacting substance of anaphylaxis (SRS‐A) from actively sensitized guinea‐pig lung fragments.

Both ETYA and Ro‐3–1314 inhibited the immunological release of malondialdehyde from guinea‐pig lung fragments.

The data indicate that the effects of ETYA were due to inhibition of lipoxygenase and the effects of Ro‐3–1314 were due to inhibition of cyclo‐oxygenase.

The results suggest that products of lipoxygenase contribute to the antigen‐induced contraction of guinea‐pig lung, particularly when cyclo‐oxygenase is inhibited. Under these conditions there may be redirection of the metabolism of arachidonic acid to favour production of constrictor products of lipoxygenase such as SRS‐A.
SUPPRESSION BY ORALLY‐ADMINISTERED NIFEDIPINE, NISOLDIPINE AND NILUDIPINE OF EARLY, LIFE‐THREATENING VENTRICULAR ARRHYTHMIAS RESULTING FROM ACUTE MYOCARDIAL ISCHAEMIA
Authors: FAGBEMI O. , PARRATT J.R.
Published: July 2012

The oral administration to rats of the calcium antagonists nifedipine, nisoldipine and niludipine (3 mg/kg, 1 —1.25 h before acute coronary ligation) greatly reduced the duration of ventricular tachycardia and fibrillation (VF) occurring in the first 30min post‐ligation period. The duration of VF was especially reduced (by 74–92%). None of the animals so treated died compared with a 40% mortality in the controls.
POTENTIATION BY NALOXONE OF PRESSOR REFLEXES
Authors: MONTASTRUC JEAN‐LOUIS , MONTASTRUC PAUL , MORALESOLIVAS FRANCISCO
Published: July 2012

The effect of intravenous naloxone, an opiate antagonist, was studied on the pressor responses elicited by stimulation of afferent nerves (vagus and laryngeal superior nerves) in anaesthetized dogs

Although naloxone (0.1 mg/kgi.v.) alone failed to modify basic blood pressure, the pressor responses induced by stimulation of either the vagus or laryngeal nerve were potentiated by naloxone

Morphine (0.2mg/kgi.v.) suppressed these two cardiovascular responses. These depressor effects of morphine were reversed by subsequent injection of naloxone (0.1 mg/kg i.v.)

The results suggest the involvement of endogenous opiate peptides in pressor reflexes elicited by stimulation of the afferent nerves.
THE EFFECTS OF PROSTAGLANDINS E2, F2α, PROSTACYCLIN, FLURBIPROFEN AND ASPIRIN ON ARRHYTHMIAS RESULTING FROM CORONARY ARTERY LIGATION IN ANAESTHETIZED RATS
Authors: COKER SUSAN J. , PARRATT J.R.
Published: July 2012

Various prostaglandins and inhibitors of prostaglandin synthesis were administered prior to acute coronary artery ligation in anaesthetized rats and their effects were assessed on the number and severity of the resulting early arrhythmias (ventricular ectopic activity; incidence and duration of ventricular tachycardia and of ventricular fibrillation)

Prostaglandin E2 (PGE2), PGF2α and prostacyclin all showed antiarrhythmic activity; in contrast flurbiprofen increased the incidence of ventricular fibrillation and mortality

Both the number of ventricular ectopic beats and the incidence of ventricular fibrillation were reduced by aspirin

The results suggest that the release of endogenous PGE2, PGF2α and prostacyclin could reduce early post‐infarction ventricular arrhythmias whilst the protective effect of aspirin in this model adds further support for the hypothesis that thromboxane release is involved in the genesis of these arrhythmias.
TIME COURSE OF OUABAIN UPTAKE IN ISOLATED MYOCARDIAL CELLS: DEPENDENCE ON EXTRACELLULAR POTASSIUM AND CALCIUM CONCENTRATION
Authors: MELDGAARD L. , STEINESS E. , WALDORFF S.
Published: July 2012

Spontaneously beating myocardial cells isolated from newborn rats have been used to evaluate the time course of cellular ouabain uptake.

The rate of cellular uptake and the amount of ouabain bound at equilibrium were computed by fitting the experimental data to the conventional exponential equation for receptor binding of drugs.

At normal extracellular potassium and calcium concentrations a biexponential equation was the best fit to the experimental data, indicating two receptor sites of ouabain with different rates of uptake.

Increasing extracellular potassium or calcium concentrations decreased the amounts of ouabain bound at equilibrium. 5 High and low extracellular concentrations of potassium or calcium decreased the rate of ouabain uptake. 6 It is well known that ouabain changes ionic fluxes. Changes in the extracellular potassium and calcium concentrations also influence the amount of ouabain taken up by myocardial cells, as demonstrated in the present study.
PARALLEL MATURATION OF THE PANCREATIC SECRETORY RESPONSE TO CHOLINERGIC STIMULATION AND THE MUSCARINIC RECEPTOR POPULATION
Authors: DUMONT Y. , LAROSE L. , MORISSET J. , POIRIER G.G.
Published: July 2012

The appearance of pancreatic muscarinic receptors during development has been measured by use of the specific ligand [3H]‐quinuclidinyl benzilate ([3H]‐QNB).

QNB binding sites are present in foetal pancreas; their maximal concentration is attained at the age of 30 days and a significant decrease is observed in one year old animals.

Affinity of [3H]‐QNB for the muscarinic receptor does not change with age.

An evaluation of the pancreatic secretory response to a cholinoceptor agonist as a function of age indicates that the development of this response parallels that of the receptor population.

It is suggested that, at all ages from 3 days after birth onwards, the maximal secretory response of the exocrine pancreas to a cholinoceptor agonist mobilizes the same proportion of the total population of QNB binding sites.
EFFECTS OF RP AND SP DIASTEREOISOMERS OF ADENOSINE 5′‐O‐(1‐THIODIPHOSPHATE) ON HUMAN PLATELETS
Authors: CUSACK N.J. , HOURANI S.M.O.
Published: July 2012

RP and SP diastereoisomers of adenosine 5′‐O‐(1‐thiodiphosphate) ((R)‐ADP‐β‐S and (S)‐ADP‐β‐S), an adenosine 5′‐diphosphate (ADP) analogue, were tested on intact human platelets.

Each diastereoisomer induced aggregation, (S)‐ADP‐α‐S being 5 times more potent than (R)‐ADP‐α‐S but they achieved only 75% of the maximal effect of ADP.

Aggregation induced by each diastereoisomer was competitively inhibited by ATP (50 μm)

Simultaneous addition of each diastereoisomer inhibited aggregation induced by ADP but not by 11α, 9α‐epoxymethano prostaglandin H2, a stable endoperoxide analogue. Both diastereoisomers are therefore partial agonists at the ADP receptor mediating aggregation.

Unlike ADP, neither diastereoisomer inhibited prostaglandin E1 (PGE 1‐stimulated adenylate cyclase, but each competitively inhibited the effect of ADP, with (S)‐ADP‐α‐S again being 5 times more potent than (R)‐ADP‐α‐S.

These are the first reported examples of ADP analogues to induce platelet aggregation without inhibiting PGE 1‐stimulated adenylate cyclase.
SPONTANEOUS ACTIVITY IN THE TRACHEA OF DOGS TREATED WITH INDOMETHACIN: AN EXPERIMENTAL MODEL FOR ASPIRIN‐RELATED ASTHMA
Authors: ITO YUSHI , TAJIMA KIKUO
Published: July 2012

Electrical and mechanical properties of smooth muscle cells or of neuro‐effector transmission in the smooth muscle layer of the dog trachea, were studied after treatment with indomethacin, by means of the double sucrose gap, microelectrode or tension recording methods.

After several subcutaneous injections of indomethacin (1.0 mg/kg daily), 6 out of 12 dogs were coughing and wheezing.

Smooth muscle tissues dissected from the trachea of the coughing dog showed spontaneous electrical and mechanical activities at the frequency of 8–15 per min. These spontaneous electrical and mechanical activities were completely suppressed by treatment with atropine (106 m), isoprenaline (5 × 10−7m) or prostaglandin E2 (10−9m) but not by tetrodotoxin (1.5 × 10−6m).

Direct muscle stimulation induced oscillatory potential changes followed by tension development in the trachea of the indomethacin‐treated dog.

In the indomethacin‐treated dog, mean membrane potential of the tracheal smooth muscle cells was −52.4 mV, and in the control trachea, the potential was −59.0 mV.

In the trachea from control dogs, the amplitude of test e.j.ps after conditioning e.j.ps was always smaller than the conditioning e. j.p., at any time interval between the two stimuli. In the trachea from indomethacin‐treated dogs, facilitation phenomena were observed.

In the trachea from the indomethacin‐treated dog, prostaglandin E1 (PGE1 or PGE 2 (10−10—10−9 m) markedly suppressed the amplitude of the e.j.p. but did not affect the facilitation phenomenon.

These results indicate that endogenous prostaglandins play important physiological roles in the feed‐back inhibitory mechanisms for acetylcholine release from the nerve terminals during the resting and active states.

The results are also discussed in relation to the genesis of aspirin‐induced asthma in man.
EFFECTS OF HALOTHANE ON THE INCORPORATION OF [14C]‐SERINE INTO PHOSPHOLIPID IN THE GUINEA‐PIG ILEUM
Authors: PATON W.D.M. , WING D.R.
Published: July 2012

The effects of halothane on the incorporation of l‐[3‐14C]‐serine into phospholipid were studied in the resting, innervated longitudinal muscle preparation of the guinea‐pig ileum.

The anaesthetic, at clinical concentrations, caused a dose‐dependent, partial inhibition of incorporation. The effect was rapid and reversible, and did not show characteristics of competitive inhibition.

The incorporation was reduced by a decrease in the Ca2+ concentration of the Krebs incubation buffer. Part of the activity persisted in the absence of added Ca2+ and this was most susceptible to inhibition by halothane. Sensitivity to external Ca2+ was not influenced at the halothane concentrations studied.

Evidence in support of the 14C‐incorporation being due to l‐[3‐14C]‐serine‐phospholipid base‐exchange activity included: (a) the rapid appearance of radioactivity in phosphatidylserine; (b) the kinetics of this incorporation in relation to that in phosphatidylethanolamine; (c) its dependence on Ca2+, and (d) its insensitivity to 2,4‐dinitrophenol and its sensitivity to temperature.

It is concluded that this preparation makes it possible for a membrane‐bound lipid‐dependent activity (l‐serine‐phospholipid base‐exchange) to be studied in conditions of cellular integrity under which the normal functional effects of lipophilic drugs can be simultaneously tested.

A rapid gas‐chromatographic assay for halothane from an aqueous medium is also described.
ANOMALOUS COMPARTMENTATION OF 5‐HYDROXYTRYPTAMINE IN INTACT HUMAN PLATELETS
Authors: COSTA J.L. , KIRK K.L. , MURPHY D.L. , STARK H.
Published: July 2012

The movement of radiolabelled 5‐hydroxytryptamine (5‐HT) between the extracellular medium, the thrombin‐releasable (vesicular) compartment, and a non‐thrombin‐releasable compartment has been investigated in washed human platelets.

Appreciable amounts of extracellular 5‐HT can accumulate in a non‐releasable compartment. Depending on the incubation conditions and the amount of 5‐HT already present inside the cell, non‐releasable 5‐HT can either remain non‐releasable or rapidly migrate into the vesicular compartment.

Measurable amounts of vesicular 5‐HT can also enter a non‐releasable compartment. However, vesicular 5‐HT which becomes non‐releasable does not appear to mix with 5‐HT becoming non‐releasable following uptake from the extracellular medium.

Extracellular 5‐HT can be added to vesicles and to the non‐releasable compartment in the presence of appreciable quantities of 5‐HT already in one or both compartments.

The vesicular and non‐releasable compartments appear to accumulate 5‐HT independently of one another. Furthermore, most vesicular accumulation of 5‐HT occurs from the extracellular medium, rather than by translocation of non‐releasable 5‐HT into the vesicular compartment.
HYPOTENSIVE AND SEDATIVE EFFECTS OF α‐ADRENOCEPTOR AGONISTS: RELATIONSHIP TO α1‐AND α2‐ADRENOCEPTOR POTENCY
Authors: CLOUGH D.P. , HATTON R.
Published: July 2012

The purpose of this study was to investigate whether the separation between the hypotensive and sedative effects of a new series of centrally acting antihypertensive drugs was due to differences between the relative pre‐junctional (α2) and post‐junctional (α1) adrenoceptor agonist properties of the compounds.

In anaesthetized rats the intravenous doses of clonidine, ICI 101187, ICI 106270, ICI 109683 and ICI 110802 required to lower blood pressure (BP) by 20 mmHg were 1.2, 5.1, 5.5, 3.3 and 5.4 μg/kg respectively.

In a test for sedation, ICI 101187 had at least 10 times less sedative effect than clonidine, ICI 106270 and ICI 109683 had at least 30 times less sedative effect than clonidine while ICI 110802 was not active. In a locomotor activity test the intravenous dose of clonidine required to reduce activity by 50% was 15.3 μg/kg, for ICI 101187 it was 194, for ICI 106270 it was 238 and for 110802 it was 313 μg/kg.

In the pithed rat the ED50s of clonidine, ICI 101187, ICI 106270, ICI 109683 and ICI 110802 as α2‐agonists were 19.4, 9.3, 63.2, 43.0 and 78.5 μg/kg respectively. The α1‐adrenoceptor potencies were quite similar for the five drugs and varied between 3.2 μg/kg for ICI 110802 and 8.7 μ/kg for ICI 106720. Potency as α2‐adrenoceptor agonists was also assessed in the mouse vas deferens. Clonidine and ICI 101187 were similar in potency with IC50Ss of 9.3times 10−9M and 8.9 × l0−9M respectively. ICI 106270 and ICI 110802 were much weaker with IC50Ss of 4.9 × 10−8M and over 5.7 × 10_8M respectively.

Since all the compounds had similar potencies as α1‐agonists, this could not explain their different sedative effects. The weakest compounds as sedatives were also weakest as α2‐agonists, although ICI 101187 which was as potent as clonidine as an α2‐agonist was still 10 times weaker as a sedative.

Hypotensive activity appears to be more closely related to α1‐ than to α2‐potency.

Clonidine was more potent as both a sedative and a hypotensive agent than would be predicted from its activity at either the α1‐ or the α2‐adrenoceptor.
ACTIVATION OF PREJUNCTIONAL β‐ADRENOCEPTORS IN RAT ATRIA BY ADRENALINE APPLIED EXOGENOUSLY OR RELEASED AS A CO‐TRANSMITTER
Authors: MAJEWSKI H. , RAND M.J. , TUNG L.‐H.
Published: July 2012

Adrenaline (10 nM) significantly enhanced the stimulation‐induced efflux of radioactivity from rat atria previously incubated with [3H]‐noradrenaline ([3H]‐NA). This effect was abolished by metoprolol (0.1 μm).

Adrenaline in a higher concentration (1μm) and NA (1μm) significantly reduced the stimulation‐induced efflux of radioactivity. However, in the presence of phenoxybenzamine (10μm), adrenaline (1μm) enhanced the efflux, whereas NA (1μm) had no effect.

In rat isolated atria pre‐incubated with adrenaline and then incubated with NA, both catecholamines were taken up and were released by field stimulation. When pre‐incubation was with adrenaline and incubation was with [3H]‐NA, metoprolol decreased the stimulation‐induced efflux of radioactivity. This effect did not occur if the atria were pre‐incubated with NA instead of adrenaline, suggesting that neuronally released adrenaline activates prejunctional β‐adrenoceptors.

In conscious rats, intravenously administered adrenaline (6.0 and 0.6 nmol/kg) was taken up and retained in the atria and could be released by field stimulation. The release was calcium‐dependent from these rats up to 24 h after administration.
A BEHAVIOURAL AND BIOCHEMICAL STUDY IN RATS OF 5‐HYDROXYTRYPTAMINE RECEPTOR AGONISTS AND ANTAGONISTS, WITH OBSERVATIONS ON STRUCTURE‐ACTIVITY REQUIREMENTS FOR THE AGONISTS
Authors: GREEN A.R. , HALL J.E. , REES A.R.
Published: July 2012

The effect of the putative 5‐hydroxytryptamine (5‐HT) receptor antagonists, methysergide, methergoline, mianserin, cyproheptadine, cinanserin (all at 10 mg/kg), methiothepin (5 mg/kg) and (−)‐propranolol (20 mg/kg) on the behavioural responses to tranylcypromine (10 mg/kg) followed 30 min later by L‐tryptophan (100 mg/kg) was examined.

Methysergide, methergoline, methiothepin and (−)‐propranolol inhibited head weaving, forepaw treading and hind‐limb abduction. Methysergide and methergoline increased reactivity. In contrast, cypropheptadine, cinanserin and mianserin had no effects on the behaviour.

Similar findings were obtained when the behaviours were elicited by administration of tranylcypromine (10 mg/kg) followed by the putative 5‐HT receptor agonist, 5‐methoxy‐N, N‐dimethyltryptamine (5‐MeODMT) (2 mg/kg).

When the behaviours were elicited by the putative 5‐HT receptor agonist, quipazine (50 mg/kg), all the drugs effectively inhibited head weaving and forepaw treading.

When the dose of cypropheptadine was doubled to 20 mg/kg an inhibition of the tranylcypromine/L‐tryptophan induced behaviours was seen.

Methiothepin produced a marked inhibition of apomorphine‐induced locomotor activity whilst all the others enhanced this response, suggesting that only methiothepin inhibits the 5‐HT behaviours by dopamine antagonism and that the increased reactivity seen following tranylcypromine/L‐tryptophan after pretreatment with methysergide or methergoline might be due to enhanced dopamine function.

Pretreatment with p‐chlorophenylalanine resulted in enhanced behavioural responses to both 5‐MeODMT and quipazine.

Both methergoline and methiothepin decreased the rate of 5 ‐HT synthesis in whole brain but not spinal cord and methergoline decreased spinal cord 5‐HIAA concentration. None of the other drugs had any significant effects on the concentration of 5‐HT, 5‐HIAA or 5‐HT synthesis rate in brain or spinal cord.

Experiments with compounds structurally related to quipazine and with molecular models suggested that quipazine produces behavioural changes probably by stimulating the 5‐HT receptor in a similar way to 5‐HT but that it would bind weakly, in agreement with ligand‐receptor binding studies.

It is suggested, therefore, that cyproheptadine, cinanserin and mianserin fail to inhibit 5‐HT and 5‐MeODMT‐induced behaviours because they are weak antagonists whilst they are able to inhibit the same behaviours induced by quipazine because it is a weak agonist.

These data indicate that extreme care should be taken in accepting or rejecting 5‐HT as a mediator of behaviours or of other responses unless several antagonists or agonists have been examined.
THEOPHYLLINE DOES NOT AFFECT MORPHINE INHIBITION OF THE ISOLATED VAS DEFERENS
Authors: STONE T.W.
Published: July 2012

Adenosine and morphine both produced an inhibition of the electrically‐evoked twitch of the isolated superfused vas deferens of the mouse.

Theophylline, 10 or 100 μm, reduced the inhibitory action of adenosine but did not change inhibition by morphine.

It is suggested that adenosine release is not a necessary prerequisite for morphine inhibition of transmitter release. It is also suggested that the involvement of adenosine may follow activation only of opiate μ‐receptors.
THE ROLE OF PRESYNAPTIC α‐ADRENOCEPTORS IN THE REGULATION OF BLOOD PRESSURE IN THE CONSCIOUS RABBIT
Authors: HAMILTON C.A. , REID J.L. , ZAMBOULIS C.
Published: July 2012

Changes in mean arterial pressure, heart rate and plasma noradrenaline after α‐adrenoceptor blockade with several α‐adrenoceptor antagonists have been studied in the conscious rabbit in order to investigate the possible role of presynaptic α‐adrenoceptors in cardiovascular regulation.

Prazosin (0.05–2 mg/kg) and phentolamine (0.5–20 mg/kg) produced dose‐dependent falls in mean arterial pressure and rises in plasma noradrenaline. These changes were related to the degree of postsynaptic α‐adrenoceptor blockade determined by the pressor response to intravenous phenylephrine.

Similar changes in mean arterial pressure and plasma noradrenaline were observed after administration of the direct vasodilators hydralazine (1–10 mg/kg) and nitroprusside (2.5–55 μg kg−1 min−1).

After baroreceptor deafferentation by sinoaortic denervation the falls in mean arterial pressure were much greater and the rise in plasma noradrenaline was markedly attenuated.

Yohimbine (1 mg/kg) increased mean arterial pressure and plasma noradrenaline but it was not possible to exclude the possibility that central nervous effects of yohimbine underlay the increased sympathetic activity.

The magnitude of the baroreflex response to changes in pressure make it unlikely that the functional significance of the presynaptic α‐adrenoceptor can be readily determined by measurement of plasma noradrenaline in intact animals.
THE EFFECT OF γ‐HYDROXYBUTYRATE ON MOUSE STRIATAL TYRAMINE, DOPAMINE AND HOMOVANILLIC ACID
Authors: JUORIO A.V.
Published: July 2012

The concentrations of p‐ and m‐tyramine, dopamine and homovanillic acid were measured in the mouse striatum following the subcutaneous injection of γ‐hydroxybutyrate; their control levels were 19.8, 6.3, 9600 and 1130 ng/g respectively.

The administration of 500–1000 mg/kg of γ‐hydroxybutyrate produced a reduction in p‐tyramine that lasted at least 8 h. m‐Tyramine and dopamine were significantly increased for at least 4 h. The levels of homovanillic acid were increased at 1 and 2 h after drug administration.

These experiments strongly suggest that the increases in dopamine turnover produced by γ‐hydroxybutyrate caused reciprocal changes in striatal tyramine that are similar to those produced by drugs or treatment that increase dopamine turnover and tyrosine hydroxylase activity.
DILTIAZEM‐INDUCED VASODILATATION OF SMOOTH MUSCLE CELLS OF THE CANINE BASILAR ARTERY
Authors: FUJIWARA SHIGERU , ITO YUSHI , ITOH TAKEO , KURIYAMA HIROSI , SUZUKI HIKARU
Published: July 2012

The effects of diltiazem on smooth muscle cells of the canine basilar artery were investigated by means of microelectrode, double sucrose gap and isometric tension recording methods.

The mean membrane potential of the smooth muscle cells was −49.8 mV and they were electrically quiescent. Diltiazem (over 10−5 m) depolarized the membrane. After pretreatment with 5 and 10 mm tetraethylammonium (TEA), an outward current pulse (1 and 2 s in duration) produced a spike and this spike was abolished by application of 10−5 m diltiazem.

The spike could also be generated by the excitatory junction potential (e.j.p.) evoked by perivascular nerve stimulation (0.05 ms in pulse duration) in the presence of 5 mm TEA. Diltiazem (> 10−6 m) suppressed both the spike and the e.j.ps, the suppression being more apparent for spike generation. The amplitude of the e.j.ps was reduced by diltiazem in concentrations greater than 10−6m. The effects were dose‐dependent: when the amplitude of e.j.ps was reduced by application of diltiazem, the resulting mechanical response was also proportionally smaller.

The contractions evoked by 128 mm [K]o, 10−3m adenosine 5′‐triphosphate (ATP) or, NaCl‐free solution were abolished in Ca‐free solutions containing 2 mm EGTA, but the amplitude of caffeine‐induced contraction (10 mm) was only slightly reduced. Diltiazem, in concentrations above 3 × 10−7m suppressed the contraction evoked by excess [K]o, ATP or caffeine, but the inhibitory action of diltiazem on the K‐induced contraction was greatest.

Following pretreatment with 2.5 mm [Ca]o, a contraction was evoked by caffeine in Ca‐free solution. The amplitude of the caffeine‐induced contraction was increased by simultaneous application of 2.5 mm [Ca]o with 128 mm [K]o and to a lesser extent by simultaneous application of 2.5 mm [Ca]o with 5.9 mm [K]o. The amplitude of the caffeine‐induced contraction generated in the presence of 5.9 mm or 128 mm [K]o was suppressed to the same extent by application of diltiazem [10−5m) during preincubation in [Ca]o. This result suggests that the Ca stored in the cell is replenished by Ca‐influx from [Ca]o during the resting and active states of the membrane, and that diltiazem has no effect on the mobilization of Ca stored in the cell.

Thus, diltiazem acts on the canine basilar artery suppressing the Ca‐influx during the active condition as a Ca‐spike suppressor and the voltage‐dependent Ca‐influx induced by excess [K]o or by chemical depolarization. Diltiazem has no effect on the Ca mobilization from the store site. This agent also suppresses the amplitude of e.j.ps due to inhibition of the release of chemical transmitter from nerve terminals following the suppression of the Ca‐influx. Diltiazem appears to act as a vasodilator on the canine basilar artery.
β2‐ADRENOCEPTORS REGULATE INDUCTION OF MYOCARDIAL ORNITHINE DECARBOXYLASE IN MICE in vivo
Authors: COPELAND JACK G. , LARSON DOUGLAS F. , ROESKE WILLIAM R. , RUSSELL DIANE H. , WOMBLE J.R.
Published: July 2012

The pharmacological characteristics of the myocardial adrenoceptor of the mouse have been examined during embryogenesis by measuring ornithine decarboxylase (ODC, EC 4.1.1.17) induction.

A four fold elevation of ODC activity was observed after isoprenaline (10 mg/kg, s.c), and enzyme activity was increased two to three fold following adrenaline (1 mg/kg, s.c.) or terbutaline given by direct injection to the foetus (10 μg/500 mg).

Pretreatment with the β‐adrenoceptor antagonist, propranolol (10 mg/kg), totally blocked the increase in ODC activity.

Elevation of myocardial ODC activity was not inhibited by metoprolol, a relatively specific β1‐adrenoceptor antagonist, at a dose of 10 mg/kg.

Since the increase in ODC activity was blocked by a β‐adrenoceptor antagonist (propranolol) and enzyme activity was stimulated by terbutaline, a β2‐agonist, we conclude that β2‐adrenoceptors are selectively coupled to the regulation of murine cardiac ODC activity following catecholamine stimulation.
THE IONIZATION OF MORPHINE, HYDROXY AMPHETAMINE AND (+)‐TUBOCURARINE CHLORIDE AND A NEW METHOD FOR CALCULATING ZWITTERION CONSTANTS
Authors: BARLOW R.B.
Published: July 2012

An improved method for estimating the zwitterion constants of phenolic amines is described which involves the exploratory least‐squares fit of absorbance (at a suitable wavelength) to pH, starting with estimates of pK1 and pK2 obtained electrometrically.

With the method it is possible to see that hydroxyamphetamine (α‐methyltyramine) has a higher zwitterion constant than tyramine and the zwitterion constants of both compounds are lower at 37°C than at 25°C.

The zwitterion constant of morphine is not reduced by raising the temperature from 25° to 37°C and the effect of temperature is much greater in compounds with a primary or secondary amino group than with those containing a tertiary amino group. Some zwitterions may be stabilized by hydration and their formation will be reduced by a rise in temperature which will break up water structure.

From electrometric titrations with (+)‐tubocurarine chloride in 0.1 m NaCl estimates of pK1, pK2 and pK3 were 7.6, 8.65 and 9.65 at 25°C and 7.4, 8.6 and 9.7 at 37°C, compared with 7.8, 8.85 and 9.75 given by Perrin (1980). However, the effects of pH on absorbance show that the phenolic groups lose a proton before the ammonium group so there is extensive zwitterion formation which is probably greater at 25° than at 37°C. The p‐phenolic group (position 13) probably ionizes first with the phenate form stabilized by hydration involving water molecules and the protonated form of the (1‐) ammonium group.
THE EXISTENCE OF A NEW SUBTYPE OF α‐ADRENOCEPTOR ON THE RAT ANOCOCCYGEUS IS REVEALED BY SGD 101/75 AND PHENOXYBENZAMINE
Authors: COATES JILL , JAHN U. , WEETMAN D.F.
Published: July 2012

Noradrenaline and Sgd 101/75 (4(2‐imidazoline‐amino)‐2‐methylindazol‐chlorhydrate) acted as full agonists in contracting the rat anococcygeus.

Very low concentrations of phenoxybenzamine (0.3 nm for 2–30 min) reduced preferentially the effects of Sgd 101/75. Preparations made insensitive to Sgd 101/75 by phenoxybenzamine still contracted to noradrenaline, this contraction occurring in the presence of high concentrations (400 μm) of Sgd 101/75.

It is concluded therefore that the α1‐adrenoceptor in this preparation is not a homogeneous entity and must be subdivided into at least two subtypes.
EFFECT OF CONVERTING ENZYME INHIBITION ON THE RENAL HAEMODYNAMIC RESPONSES TO NORADRENALINE INFUSION IN THE RAT
Authors: ARUNDELL LEWIS A. , JOHNS EDWARD J.
Published: July 2012

The renal haemodynamic responses to a close arterial infusion of noradrenaline (29.7–177.9 nmol kg−1h−1) were measured in rats anaesthetized with pentobarbitone. Systemic blood pressure was unaffected by noradrenaline infusion at this dose level. Renal blood flow was significantly reduced by 16% while glomerular filtration rate remained unchanged. These responses resulted in a rise in filtration fraction of some 10%.

In a separate group of animals, noradrenaline infusion in this manner and at a similar dose rate increased plasma renin activity approximately 3 fold.

Continuous infusion of the angiotensin converting enzyme inhibitor, teprotide (3.36 μmol kg−1h−1), had no measurable effect on systemic blood pressure, renal blood flow, glomerular filtration rate or filtration fraction.

Infusion of noradrenaline into these animals receiving teprotide caused a significant fall in renal blood flow of 16%. There was a fall in glomerular filtration rate of some 17% which was significantly different from the response observed in the animals not receiving teprotide. There was a consequent small but insignificant fall in filtration fraction.

These data show that the regulation of glomerular filtration rate in response to the vasoconstrictor drug, noradrenaline, is partly mediated via the renin‐angiotensin system. They provide evidence for a role of intrarenal angiotensin II in regulating glomerular filtration by causing efferent arteriolar vasoconstriction.
KININS STIMULATE NET CHLORIDE SECRETION BY THE RAT COLON
Authors: CUTHBERT ALAN W. , MARGOLIUS HARRY S.
Published: July 2012

Short circuit current (SCC), transepithelial conductance and ion fluxes were measured across the isolated descending colon of the rat in response to bradykinin or kallidin.

Kinins added to the serosal bath caused immediate increases in SCC but were ineffective when added to the mucosal bath. Increases in SCC were accompanied by significant increases in transepithelial conductance. Threshold kinin concentration was 0.5 nm and maximal increases were seen at 50–100 nm.

A rat glandular kallikrein (7 nm) or mellitin (2 μm) also increased SCC if added to the serosal bath.

Responses to kinins were unaffected by mucosal amiloride (100 μm) but attenuated or blocked by serosal frusemide (100 μm), indomethacin (1 μm) or mepacrine (50 μm).

Replacement of chloride ion in the serosal bath by gluconate and sulphate ions abolished responses to kinins which reappeared after chloride re‐addition.

Measurement of 36Cl, 22Na and 86Rb fluxes across the tissue showed that the kinin‐induced increase in SCC resulted principally from increased net chloride secretion. Effects upon 22Na or 86Rb flux were minimal and made no contribution to the current responses observed in this tissue.

The results prove that kinins stimulate net chloride secretion in the rat colon, most probably via a prostaglandin‐dependent pathway.
LIDOFLAZINE IN THE EARLY STAGES OF ACUTE MYOCARDIAL ISCHAEMIA
Authors: COKER SUSAN J. , FAGBEMI O. , PARRATT J.R.
Published: July 2012

Pretreatment of anaesthetized rats with intravenously administered lidoflazine (an antianginal agent) reduced the incidence and severity of ventricular arrhythmias which resulted from acute coronary artery ligation. Ventricular fibrillation was completely prevented by doses of 50 μg/kg and 2 mg/kg and no animal so treated died (contrast 50% incidence of fibrillation in the controls and 30% mortality).

In anaesthetized greyhound dogs, lidoflazine (2 mg/kg) administration resulted in transient reductions in systemic arterial pressure, LV dP/dt max and cardiac output. Coronary sinus PO2 was markedly increased, indicating pronounced coronary vasodilatation.

Lidoflazine pretreatment inhibited the increase in epicardial ST‐segment elevation which resulted, in dogs, from short (3 min) occlusions of the left anterior descending coronary artery. This effect was especially marked at sites where, in control occlusions, ST‐segment elevation was most pronounced.

Lidoflazine greatly reduced the number of ventricular ectopic beats which usually resulted from more prolonged (30 min) periods of acute coronary artery occlusion. There was no ventricular fibrillation in these dogs (contrast 25% incidence in the controls).

Lidoflazine did not modify the ventricular fibrillation which results from reperfusion of a previously ischaemic area of the left ventricular wall.
EVIDENCE FOR AN A2/Ra ADENOSINE RECEPTOR IN THE GUINEA‐PIG TRACHEA
Authors: BROWN C.M. , COLLIS M.G.
Published: July 2012

An attempt was made to determine whether the extracellular adenosine receptor that mediates relaxation in the guinea‐pig trachea is of the A1/Ri or A2/Ra subtype.

Dose‐response curves to adenosine and a number of 5′‐ and N6‐substituted analogues were constructed for the isolated guinea‐pig trachea, contracted with carbachol.

The 5′‐substituted analogues of adenosine were the most potent compounds tested, the order of potency being 5′‐N‐cyclopropylcarboxamide adenosine (NCPCA) > 5′‐N‐ethylcarboxamide adenosine (NECA) > 2‐chloroadenosine > l‐N6‐phenylisopropyladenosine (l‐PIA) > adenosine > d‐N6‐phenylisopropyladenosine (d‐PIA).

The difference in potency between the stereoisomers d‐ and l‐PIA on the isolated trachea was at the most five fold.

Responses to low doses of adenosine and its analogues were attenuated after treatment with either theophylline or 8‐phenyltheophylline. The responses to 2‐chloroadenosine were affected to a lesser extent than were those to the other purines.

Adenosine transport inhibitors, dipyridamole and dilazep, potentiated responses to adenosine, did not affect those to NCPCA, NECA, l‐PIA and d‐PIA but significantly reduced the responses to high doses of 2‐chloroadenosine.

Relaxations evoked by 9‐β‐d‐xylofuranosyladenosine which can activate intracellular but not extracellular adenosine receptors, were attenuated by dipyridamole but unaffected by 8‐phenyltheophylline.

The results support the existence of an extracellular A2/Ra subtype of adenosine receptor and an intracellular purine‐sensitive site, both of which mediate relaxation.