Showing papers in "British Journal of Pharmacology in 1974"

DEPOLARIZING ACTIONS OF γ-AMINOBUTYRIC ACID AND RELATED COMPOUNDS ON RAT SUPERIOR CERVICAL GANGLIA IN VITRO

Abstract: 1 Potential changes in rat superior cervical ganglia were recorded in vitro with surface electrodes.2 gamma-aminobutyric acid (GABA) produced a transient, low-amplitude ganglion depolarization at rest, and a transient hyperpolarization in ganglia depolarized by carbachol. Depolarization was not prevented by preganglionic denervation. The log dose-response curve for depolarization was sigmoid with a mean ED(50) of 12.5 muM.3 The ganglion was depolarized in similar manner by the following compounds (mean molar potencies relative to GABA (=1) in brackets): 3-aminopropane sulphonic acid (3.4), gamma-amino-beta-hydroxybutyric acid (0.27), beta-guanidino-propionic acid (0.12), guanidinoacetic acid (0.057), delta-aminovaleric acid (0.048), beta-alanine (0.01), 2,4-diaminobutyric acid, gamma-guanidinobutyric acid, taurine and N-methyl-GABA (all <0.01). The following compounds did not depolarize the ganglion at 10 mM concentrations: alpha- and beta-amino-n-butyric acids, alpha-amino-iso-butyric acid, glycine and glutamic acid.4 Depolarization declined in the continued presence of GABA. Ganglia thus ;desensitized' to GABA showed a diminished response to other amino acids but not to carbachol.5 The effect of GABA was not antagonized by hyoscine and hexamethonium in combination, in concentrations sufficient to block responses to carbachol.6 Responses to GABA were blocked more readily than those to carbachol by bicuculline (IC(50), 14 muM) and picrotoxin (IC(50), 37 muM). Strychnine (IC(50), 73 muM) was a relatively weak and less selective GABA-antagonist.7 It is concluded that sympathetic ganglion cells possess receptors for GABA and related amino acids which are (a) different from the acetylcholine receptors and (b) similar to GABA receptors in the central nervous system.

Evidence for involvement of 5-hydroxytryptamine in the actions of amphetamine.

Abstract: 1 Pargyline treatment, 1 h before (+)-amphetamine (1 mg/kg), reduced amphetamine-stimulated motor activity. This inhibition was reversed in animals pretreated with p-chlorophenylalanine (PCPA). 2 Following treatment with PCPA or 5,6-dihydroxytryptamine (5,6-DHT), amphetamine-induced locomotor activity was significantly potentiated. The increased response to amphetamine in PCPA-treated rats was reversed in animals pretreated with 5-hydroxytryptophan. 3 The inhibition of amphetamine-stimulated locomotor activity by treatment with 6-hydroxydopamine was not reversed by PCPA treatment. 4 Stereotypies produced by amphetamine were not found to be altered by depletion of 5-hydroxytryptamine. 5 Induction of adrenal tyrosine hydroxylase activity produced by chronic amphetamine administration was significantly potentiated by PCPA, emphasizing the involvement of a 5-hydroxytryptamine inhibitory system in more than one action of amphetamine.

Gastrin release by bombesin in the dog

Abstract: 1 The intravenous infusion of bombesin produced in intact dogs and, more strikingly in dogs provided with gastric fistulae a sharp increase in plasma levels of immunoreactive gastrin and at the same time a stimulation of gastric acid secretion. Gastrin response was correlated with the dose of bombesin from approximately 0.1 mug kg(-1) h(-1) (threshold) to 1 mug kg(-1) h(-1) (maximum gastrin release).2 Atropine and metiamide reduced or inhibited gastric acid secretion stimulated by bombesin, but did not affect the rise in gastrin levels.3 Acidification of the whole stomach or of a perfused antral pouch caused a reduced or delayed response to bombesin. However, the inhibitory effect of acidification could be surmounted by prolonging the duration of bombesin infusion.4 Antrectomy greatly reduced the rise in gastrin levels and the increase in acid gastric secretion produced by bombesin, but left unaffected the gastric secretagogue effect of pentagastrin.5 It is concluded that bombesin is a potent releaser of gastrin from the antral mucosa.6 The possible influence of the renal effects evoked by bombesin in the dog on the gastrin response to the polypeptide is discussed.

The release of labelled acetylcholine and choline from cerebral cortical slices stimulated electrically.

Abstract: 1 In order to establish the origin of the increased efflux of radioactivity caused by electrical stimulation of cerebral cortical slices which had been incubated with [3H]-choline, labelled choline and acetylcholine (ACh) collected by superfusion were separated by gold precipitation. 2 In the presence of physostigmine electrical stimulation (1 Hz, 10 min) increased the release of only [3H]-ACh which was greatly enhanced by the addition of atropine. 3 Continuous stimulation in the presence of physostigmine resulted in an evoked release of [3H]-ACh which declined asymptotically. This evoked release appeared to follow first-order kinetics with a rate constant which remained stable over the course of prolonged stimulation. 4 The rate constant for the evoked release of [3H]-ACh with 1 Hz stimulation was three times greater in the presence of physostigmine and atropine than in the presence of physostigmine alone, while the size of the store from which [3H]-ACh was released was nearly identical under these two conditions. 5 In the absence of physostigmine and atropine, stimulation caused the appearance of only [3H]-choline in the samples. 6 Reduction of [3H]-ACh stores before the application of physostigmine resulted in a reduced evoked release of total radioactivity, both in the absence or presence of physostigmine and atropine, and decreased the evoked release of [3H]-ACh without affecting the release of [3H]-choline. 7 Results suggest that electrical stimulation of cortical slices which had been incubated with [3H]-choline causes the release of only [3H]-ACh, both in the presence or absence of an anticholinesterase. The evoked increase in the efflux of total radioactivity is therefore a good measure of the release of [3H]-ACh.

The modification of lumbar motoneurone excitability by stimulation of a putative 5-hydroxytryptamine pathway.

Abstract: 1 Changes in lumbar motoneurone excitability were monitored by recording spinal reflex activity from the ventral roots of rats anaesthetized with fluothane.2 Electrical stimulation of nucleus raphes medianus increased the amplitude of the monosynaptic reflex via a pathway having a slow conduction velocity. Stimulation elsewhere in the lower brain stem was less effective. This increase in motoneurone excitability was potentiated by the intravenous injection of L-tryptophan and reduced by intravenous injections of lysergic acid diethylamide (LSD), methysergide or Cinanserin.3 Extracellular field potential responses to stimulation of dorsal or ventral roots were recorded with six barrelled microiontophoresis electrodes. Stimulation of nucleus raphes medianus and iontophoretic application of 5-hydroxytryptamine (5-HT) both increased the excitability of lumbar motoneurones as reflected by an increase in field potential amplitude.4 Responses to both stimulation of raphe nuclei and iontophoretic application of 5-HT were reduced by iontophoretic application of Cinanserin and methysergide.5 The similarities of the responses of lumbar motoneurones to applied 5-HT and activity within the raphe-spinal pathway are discussed. It is suggested that activity within the raphe-spinal pathway can increase lumbar motoneurone excitability via the release of 5-HT in the ventral horn of the spinal cord.

Effects on plasma and brain tryptophan in the rat of drugs and hormones that influence the concentration of unesterified fatty acid in the plasma

Abstract: 1 The effects on tryptophan distribution and metabolism of drugs altering plasma unesterified fatty acid (UFA) concentration were investigated in the rat.2 UFA and plasma free (i.e. ultrafilterable) tryptophan altered in the same direction.3 Catecholamines and L-DOPA increased both plasma UFA and free tryptophan. L-DOPA also increased brain tryptophan and 5-hydroxyindoleacetic acid (5-HIAA) but decreased brain 5-hydroxytryptamine (5-HT).4 Aminophylline increased plasma UFA and free tryptophan and also brain tryptophan, 5-HT and 5-HIAA. Food deprivation had qualitatively similar effects.5 Insulin decreased plasma UFA and free tryptophan in both fed and food-deprived rats. However, while in fed rats these changes were associated with small decreases of brain indoles, in food-deprived animals small increases occurred.6 Nicotinic acid had only small effects in fed rats but it opposed both the UFA and indole changes in food-deprived animals. Total plasma tryptophan increased in nicotinic acid treated, food-deprived rats.7 There was a tendency towards inverse relations between changes of plasma free and total tryptophan.8 The results suggest that drugs which influence plasma UFA through actions on cyclic AMP thereby alter the binding of tryptophan to plasma protein and that this leads to altered distribution and metabolism of tryptophan.

Effects of propranolol on gastric secretion in albino rats.

Abstract: 1 Effects of graded doses of propranolol have been studied on gastric secretion and gastric ulcers in pylorus-ligated rats. 2 A dose-dependent action of propranolol was observed; small doses increased total volume, acid output and pepsin secretion along with an increase in the incidence of ulcers but high doses were inhibitory.

Distribution of α- and β-adrenoceptors in human urinary bladder

Abstract: 1 The distribution of α- and β-adrenoceptors in isolated preparations of human bladder neck and detrusor muscle has been studied. 2 Adrenaline caused contraction of the bladder neck which was blocked by phenoxybenzamine but unaltered by propranolol. 3 Isoprenaline caused relaxation of the bladder neck which was blocked by propranolol. High concentrations caused contraction which was enhanced by propranolol but blocked by phenoxybenzamine. 4 Detrusor muscle was relaxed by isoprenaline and this effect was blocked by propranolol. Phenylephrine caused relaxation of detrusor which was unaffected by phenoxybenzamine; in some cases contraction was produced in the presence of propranolol. 5 It is concluded that the bladder neck contains mainly α-receptors and the detrusor mainly β-receptors but both regions posses both types of adrenoceptor.

A non‐adrenergic inhibitory nervous pathway in guinea‐pig trachea

Abstract: 1 Electrical stimulation of the guinea-pig isolated tracheal tube causes a biphasic response, initially excitatory and then inhibitory. The excitatory response was abolished by atropine leaving the inhibitory response unaffected. 2 The inhibitory response was greatly reduced but not abolished by propranolol or guanethidine. A residual inhibitory response was still present in tracheas in which sympathetic nerve function had been abolished by pretreatment with syrosingopine or 6-hydroxydopamine. These results show that the inhibitory response is predominantly adrenergic but that a small non-adrenergic component is also present. 3 The non-adrenergic inhibitory response was abolished by lignocaine and tetrodotoxin suggesting that it is nervous in origin. 4 Optimal stimulation parameters for the predominantly adrenergic inhibitory response were a pulse width of 0.7-2 ms, a stimulation period of 7 s and a frequency of 20 Hz. For the non-adrenergic inhibitory response, optimal stimulation parameters were a pulse width of 2 ms, a stimulation period of 12 s and a frequency of 20 Hz. 5 Evidence obtained with pharmacological antagonists, enzyme inhibitors and activators suggested that the transmitter mediating the non-adrenergic inhibitory nervous response is unlikely to be: acetylcholine, histamine, 5-hydroxytryptamine, cyclic 3′,5′-adenosine monophosphate or a prostaglandin. 6 The adenosine uptake blocking drugs dipyridamole, hexobendine and Dilazep potentiated the non-adrenergic inhibitory nervous response and unmasked inhibitory responses to adenosine and adenosine 5′-triphosphate. 7 It is concluded that electrical stimulation of the guinea-pig trachea, in addition to activating cholinergic and adrenergic nervous pathways, may activate a separate and distinct inhibitory nervous pathway. This pathway has some features in common with the non-adrenergic non-cholinergic inhibitory pathways in gastro-intestinal muscle.

The binding of [3h]-propylbenzilylcholine mustard by longitudinal muscle strips from guinea-pig small intestine

Abstract: 1 The synthesis of tritium labelled propylbenzilylcholine mustard ([(3)H]-PrBCM; N-2'-chloroethyl-N-[2'', 3''-(3)H(2)] propyl-2-aminoethyl benzilate) is described.2 The uptake by muscle strips was measured and shown to be considerably increased by previous immersion of the muscle in distilled water.3 A considerable part of the uptake is inhibited selectively by atropine, but not by nicotinic antagonists. A number of muscarinic agonists also inhibit uptake and their apparent affinity constants have been determined.4 The uptake by atropine-sensitive sites is temperature-insensitive, whereas the other sites are temperature-sensitive. Recovery is highly temperature-sensitive and there is good agreement between recovery of sensitivity to agonists and loss of radioactivity from the muscle.

Evidence of cholecystokinin release by bombesin in the dog

Abstract: 1 The intravenous infusion of bombesin elicited in the dog a contraction of the gall bladder with decreased opening pressure of the choledocho-duodenal junction and stimulation of pancreatic secretion. 2 The pancreatic juice produced under the influence of bombesin was poor in bicarbonate and rich in protein. Threshold doses of the peptide were of the order of 0.25 μg kg-1 h-1 and maximum protein output was obtained with 1 μg kg-1 h-1. The pancreatic protein response to bombesin was very similar, in its onset and duration, to that elicited by intraduodenal infusion of L-tryptophan. Infusions of bombesin repeated at short intervals produced tachyphylaxis. 3 Antrectomy did not affect the stimulant action of bombesin on the pancreas. Atropine however, reduced the pancreatic protein response to bombesin. 4 It is suggested that bombesin acts on the gall bladder and the exocrine pancreas through release of cholecystokinin from the duodenal mucosa. No release of secretion could be demonstrated. It is likely that the releasing activity of bombesin is limited, in the field of gastrointestinal peptides, to those belonging to the gastrin-cholecystokinin family.

Calcium dependence of the inhibitory effect of angiotensin on renin secretion in the isolated perfused kidney of the rat

Abstract: 1 The effect of calcium on the inhibition of renin secretion by biologically active angiotensin was investigated in the isolated rat kidney perfused with Krebs-Ringer saline. 2 In the presence of calcium (3.7 mM), asp(NH2)′-angiotensin II suppressed both basal and isoprenaline-stimulated renin secretion. Renal perfusion pressure, which was increased by the infusion of angiotensin, returned to control levels when isoprenaline was added. 3 When the calcium concentration was reduced to 0.32 mM, the vasoconstriction produced by angiotensin was abolished although the inhibitory effect on renin secretion was still evident. 4 In the absence of calcium, angiotensin no longer suppressed basal renin secretion and a prompt increase in renin secretion occurred when isoprenaline was added. 5 The higher basal renin levels which were observed in calcium-free perfusions, suggest the existence of an intrarenal calcium-dependent mechanism that regulates basal renin secretion. 6 These observations indicate that the inhibitory effect of biologically active angiotensin, on basal and isoprenaline-stimulated renin secretion, is functionally related to the contractor response by its dependence on calcium. The recognition that the renin-producing cells are modified smooth muscle cells supports this association

Inhibition of the prostaglandin synthetase systems in ocular tissues by indomethacin.

Abstract: 1 We have compared the sensitivity of the prostaglandin synthetase systems derived from microsomal fractions of rabbit ocular tissues (anterior uvea, conjunctiva and retina) with other rabbit tissues such as the kidney medulla and spleen, to inhibition by indomethacin.2 Generation of prostaglandin-like activity by the microsomal fractions from added arachidonic acid varied with the tissue used. Highest activity was found in the kidney medulla, then in descending order, the conjunctiva, anterior uvea, spleen, retina and cornea.3 Indomethacin was most potent in the spleen (ID(50) 0.045 mug/ml) then in decreasing order in the kidney medulla, conjunctiva, anterior uvea and weakest in the retina, where the ID(50) for indomethacin was 50 mug/ml.4 The differential sensitivity to inhibition of the prostaglandin synthetase systems from different tissues is an important consideration in the development of new ocular anti-inflammatory agents.

The role of brain 5-hydroxytryptamine in the hyperactivity produced in rats by lithium and monoamine oxidase inhibition

Abstract: 1 Administration to rats of LiCl (3 mEq/kg) subcutaneously twice daily for 3 days followed by monoamine oxidase inhibition with either tranylcypromine (TCP; 20 mg/kg) or pargyline (75 mg/kg) on the fourth day produces a syndrome of hyperactivity indistinguishable from that produced by monoamine oxidase inhibition and L-tryptophan administration.2 At least 3 injections of LiCl (3 mEq/kg) are necessary before hyperactivity is seen but one dose of LiCl (10 mEq/kg) 5 h before TCP also caused hyperactivity. The hyperactivity is blocked by prior administration of p-chlorophenylalanine, a tryptophan hydroxylase inhibitor.3 LiCl pretreatment does not alter the concentration of L-tryptophan in the brain. However after monoamine oxidase inhibition the 5-hydroxytryptamine (5-HT) accumulation was significantly greater in animals given lithium indicating an increase in 5-HT synthesis of 70%. This was confirmed by measuring 5-hydroxyindoleacetic acid accumulation after probenecid (200 mg/kg).4 The hyperactivity produced by the 5-HT analogue, 5-methoxy N,N-dimethyltryptamine was not potentiaed by lithium pretreatment but one injection of LiCl (3 mEq/kg) which did not alter the rate of 5-HT synthesis, did potentiate the hyperactivity following TCP (20 mg/kg) and L-tryptophan (50 mg/kg).5 These results suggest that lithium administration may cause an initial alteration of the 5-HT available for release at the nerve ending, which is followed after subsequent treatment by an increase in the rate of 5-HT synthesis. The possible clinical significance of these findings is discussed.

CENTRAL α‐ AND β‐ADRENOCEPTORS MODIFYING ARTERIAL BLOOD PRESSURE AND HEART RATE IN CONSCIOUS CATS

Abstract: 1 In conscious unrestrained cats noradrenaline, alpha-methylnoradrenaline and clonidine, infused into the lateral cerebral ventricles (i.c.v.) caused dose-related falls in blood pressure and heart rate; both effects were abolished after i.c.v. phentolamine.2 In 12 out of 20 cats, i.c.v. isoprenaline and salbutamol when given caused dose-related pressor responses and tachycardias. These effects were abolished after i.c.v. beta-adrenoceptor blocking drugs but were unaffected by alpha-adrenoceptor blocking agents.3 In 5 out of 20 cats, i.c.v. isoprenaline regularly produced dose-related falls in blood pressure with associated tachycardias; both effects were abolished after i.c.v. beta-adrenoceptor blocking agents.4 Intracerebroventricular dopamine produced cardiovascular responses which were qualitatively similar to those produced by i.c.v. isoprenaline.5 Intracerebroventricular adrenaline produced complex responses in untreated animals but typical alpha-effects were obtained after prior i.c.v. treatment with a beta-adrenoceptor blocking agent and typical beta-effects after i.c.v. pretreatment with an alpha-adrenoceptor blocking agent.6 The cardiovascular changes produced by i.c.v. beta-adrenoceptor agonists were abolished after systemic administration of hexamethonium or bethanidine.7 The results are discussed in the light of the mode of action of beta-adrenoceptor stimulants and beta-adrenoceptor blocking agents in the treatment of hypertension.

The properties of muscarinic receptors in mammalian cerebral cortex

Abstract: 1 The reaction of tritiated propylbenzilylcholine mustard ([3H]-PrBCM; N-2′-chloroethyl-N-[2″,3″-3H2] -propyl-2-aminoethylbenzilate) with homogenates of mammalian brain has been studied. 2 The uptake can be divided into an atropine-sensitive component of fixed capacity (380 pmol/g protein in the rat) and an atropine-insensitive part. 3 The atropine-sensitive portion is identified as muscarinic receptor by its insensitivity to nicotinic antagonists and anticholinesterases and its sensitivity to a range of muscarinic antagonists. 4 The uptake of [3H]-PrBCM is also inhibited by muscarinic agonists and there is reasonable quantitative agreement between the affinities of agonists estimated in this way and in intact tissues by physiological responses. 5 The fraction of [3H]-PrBCM uptake inhibited by muscarinic antagonists and agonists is the same. 6 The amount of receptor found in six mammalian species was inversely related to the size of the brain, but the rates of alkylation and the sensitivity to atropine were not dissimilar.

Changes in monoamine concentrations in mouse brain associated with ethanol dependence and withdrawal.

Abstract: 1 Chronic administration of ethanol to mice by inhalation induced tolerance to ethanol and produced an increase in the concentration of brain monoamines. 2 Withdrawal of ethanol from dependent mice caused behavioural changes associated with a further transient rise in brain monoamine concentrations which then declined to control levels. 3 Inhibition of the withdrawal syndrome by the administration of ethanol postponed the changes in monoamines associated with withdrawal. 4 Administration of inhibitors of catecholamine synthesis before withdrawal of ethanol modified the withdrawal syndrome.

Indoleamine antagonists: relative potencies as inhibitors of tryptamine- and 5-hydroxytryptophan-evoked responses.

Abstract: Four indoleamine antagonists were evaluated for relative potencies as inhibitors of tryptamine-induced forepaw clonus and 5-hydroxytryptophan-evoked head twitches. Methergoline was approximately three times more potent against the forepaw clonus than the head twitch response, whereas methysergide exhibited nearly equal activity in both tests. Cyproheptadine and cinanserin showed a profile opposite to methergoline and a greater degree of selectivity, being 25 to 40 times more potent as inhibitors of the 5-hydroxytryptophan- than of the tryptamine-induced response. These findings clearly demonstrate that the rank order of potency of indoleamine antagonists varies greatly depending upon the test procedure employed.

The output per stimulus of acetylcholine from cerebral cortical slices in the presence or absence of cholinesterase inhibition.

Abstract: 1 The release of endogenous acetylcholine (ACh) from cerebral cortical slices stimulated at 0.25, 1, 4, 16 and 64 Hz was measured in the presence either of physostigmine or of physostigmine and atropine. 2 Atropine potentiated the evoked release of endogenous ACh especially at low frequencies resulting in an output per stimulus which sharply declined with increasing frequency of stimulation, while in the absence of atropine the output of ACh per stimulus was low and fairly constant. 3 The evoked release of [3H]-ACh per stimulus following the incubation of the slices with [3H]-choline, as estimated by means of rate constants of the evoked release of total radioactivity, showed a frequency dependence similar to endogenous ACh when the two were tested under identical conditions. 4 In the absence of an anticholinesterase the evoked release of [3H]-ACh per stimulus was dependent on frequency of stimulation in a similar way to that in the presence of physostigmine and atropine. 5 Results suggest that under physiological conditions, i.e. in the absence of an anti-cholinesterase, the release of ACh per stimulus decreases with increasing frequency of stimulation and that this decrease is due to a lag in the mobilization of stored ACh rather than in the synthesis of new ACh.

Effects of marihuana in laboratory animals and in man

Abstract: 1 The pharmacological potencies of the resins from three different samples of Brazilian marihuana (A, B and C) were determined through corneal areflexia in rabbits, decrease of spontaneous motor activity and induction of catatonia in mice, and decrease of rope climbing performance of rats.2 The Delta(9)-tetrahydrocannabinol (Delta(9) THC) content of the marihuanas, measured by gas chromatography, was 0.82, 2.02 and 0.52%, respectively, for samples A, B and C. Approximately 2% cannabinol was present in samples A and B whereas the content of cannabidiol was approximately 0.1%.3 The petroleum ether extraction of the samples A, B and C yielded, respectively, 12.06, 14.56 and 4.26% of resin.4 In all animal tests resin B was nearly twice as active as resin A, whereas C was the weakest.5 The smoke of the marihuana samples was inhaled by 33 human subjects, under a double-blind standardized procedure. Pulse rate, a time production task and an evaluation of psychological effects were recorded.6 The smoke of 250 mg of sample B provoked disruption of the time production task, increased pulse rate, and induced strong psychological reactions in four of the six subjects who received it. Similar effects, although slightly smaller, were obtained with 500 mg of sample A. On the other hand, 500 mg of sample C did not differ from placebo.7 It is suggested that it is possible by means of animal tests to predict the potency of a marihuana sample in man.8 In parallel experiments, Delta(9)-THC was administered to other human subjects and to laboratory animals in a manner similar to that in which the marihuana samples were administered.9 Comparison of the results between the marihuanas and Delta(9)-THC showed that in man and in the laboratory animals marihuanas A and B induced effects two to four times greater than expected from their Delta(9)-THC content.10 It is suggested that there may be potentiation of the effects of Delta(9)-THC by other substances present in these marihuana samples.

The effect of indomethacin on the release of prostaglandin E2 and acetylcholine from guinea-pig isolated ileum at rest and during field stimulation.

Abstract: 1 Guinea-pig ileum suspended in Krebs solution showed a continuous increase of tone which was lost by changing the bath fluid. Prostaglandin E2 was released from the ileum during incubation, and its concentration in the bath fluid appeared to correlate with the increase in tone. 2 Supramaximal field stimulation (10 Hz) resulted in increased release of prostaglandin E2 from the ileum. At lower rates of stimulation, the increase in the release of E2 compared with the resting output was not significant. 3 Indomethacin (1 and 10 μg/ml) produced a significant, dose-related reduction of the amount of prostaglandin E2 measured in the bath fluid at rest and with field stimulation. Indomethacin inhibited the contraction of the ileum during incubation in Krebs solution. 4 Indomethacin (10 and 20 μg/ml) had no significant effect on the release of acetylcholine during field stimulation, but reduced the resting output of acetylcholine from guinea-pig ileum in some experiments. 5 The results are discussed in the context of the role ascribed to prostaglandins as physiological modulators in transmitter release. No evidence for a prostaglandin-mediated negative feedback mechanism on acetylcholine release was obtained.

A modulating role of prostaglandins in contractions of the guinea-pig ileum.

Abstract: 1 The role of prostaglandins in contractions of the guinea-pig ileum evoked either directly by acetylcholine or indirectly by angiotensin and by coaxial stimulation has been investigated2 Prostaglandin E(2) in low concentration (6 nM) slightly augmented both types of contraction Indomethacin, an inhibitor of prostaglandin synthesis, markedly reduced the indirectly evoked contractions but did not affect contractions in response to acetylcholine The addition of prostaglandin E(2) to the preparation treated previously with indomethacin restored the effect of indirect stimulation3 The pretreatment of the preparation with guanethidine or alpha-methyl-p-tyrosine prevented the inhibitory effect of indomethacin on indirectly evoked contractions Prostaglandin E(2) addition to such preparations considerably augmented both types of contraction4 The stimulation of non-cholinergic, non-adrenergic inhibitory nerves in the taenia coli and ileum preparations evoked hyperpolarization and relaxation of the preparations followed by action potentials and contraction These responses were not changed by indomethacin pretreatment and prostaglandin E(2), but rebound contraction was sometimes augmented by the prostaglandin5 Two mechanisms for the effects of prostaglandin E(2) are suggested: a direct effect on smooth muscle, and an indirect action through the sympathetic nerves which by release of noradrenaline affect the acetylcholine release from parasympathetic nerve endings

Morphine and neurotransmitter substances: microiontophoretic study in the rat brain stem

Abstract: 1 The effects of microiontophoretically applied morphine and its interactions with the effects of microiontophoretic applications of either acetylcholine, (-)-noradrenaline or 5-hydroxytryptamine have been studied on single neurones in the brain stem of rats anaesthetized with urethane. 2 Morphine excited or inhibited most neurones tested and the effects, especially excitation, were often extremely powerful. However, the time course of the excitatory and inhibitory effects were somewhat different. 3 Desensitization to the excitation produced by morphine was seen after repeated or prolonged applications and it is suggested that this phenomenon may be related to the tolerance which develops after chronic administration of morphine. No desensitization was observed to inhibition of neuronal activity by morphine. 4 Morphine usually reduced the excitation of neurones by acetylcholine, noradrenaline or 5-hydroxytryptamine but sometimes potentiated the effect, although not always on the same neurones. Inhibition of neuronal activity by these compounds was never modified by morphine and neither were the effects of glutamate or D,L-homocysteic acid when used as control agonists. 5 The in vitro release of morphine from six micropipettes was determined and the transport number was calculated to be 0.051 (s.d. 0.021). 6 The implications of these observations in explaining the pharmacological actions of morphine are discussed.

Antagonism of tone and prostaglandin-mediated responses in a tracheal preparation by indomethacin and SC-19220.

Abstract: 1 The effects of the prostaglandin synthetase inhibitor, indomethacin and the prostaglandin antagonist SC-19220 (1-acetyl-2-[8-chloro-10,11-dihydrodibenz (b,f) (1,4)oxazepine-10-carbonyl] hydrazine), were examined on the tone of the guinea-pig isolated tracheal preparation and on the responses of the preparation to prostaglandin F2α, arachidonic acid and methacholine. 2 Indomethacin (0.05-1.6 μg/ml) produced a long-lasting inhibition of the intrinsic tone of the tracheal preparation and of the contractile responses to arachidonic acid. Much higher concentrations of indomethacin also reduced the responses of the preparation to methacholine. This effect was readily reversible and appeared to be unrelated to the action on tone. 3 The contractile responses of the preparation to prostaglandin F2α were enhanced by low concentrations of indomethacin (1-5 μg/ml) and inhibited by higher concentrations (2.5-80 μg/ml). 4 SC-19220 was shown to inhibit responses of the preparation to prostaglandin F2α in concentrations (0.1-1 μg/ml) which had no effect on responses to methacholine. Similar concentrations also inhibited the intrinsic tone of the preparation and the responses to arachidonic acid. 5 The evidence suggests that prostaglandins may be involved in the maintenance of tone of the guinea-pig isolated tracheal preparation.

The role of prostaglandins in rabbit monoarticular arthritis.

Abstract: 1 Old English (OE) rabbits produced more severe monoarticular arthritis (MAA) after sensitization and intra-articular challenge with ovalbumin than did either New Zealand White (NZW) or Dutch rabbits. NZW rabbits were better responders than Dutch rabbits. 2 The swelling of the joint in all three strains of rabbits was triphasic. There was an initial acute swelling which appeared to peak at 2–4 days after challenge. This was followed by a decrease in joint size, and then a secondary increase in size beginning 1–2 weeks after challenge. 3 An investigation of MAA in OE rabbits showed that there was an increase in E-type prostaglandins, total leucocyte counts and free acid phosphatase activity in the synovial fluid of the challenged joints at 6 h, 19 h, 47 h, 7 days and 46 days following challenge. There were also histopathological changes at these times. In addition, there was an increase in the surface temperature of both the challenged and non-challenged knees, and a rise in the body temperature. 4 Prostaglandin levels peaked at 19 h and were equivalent to 19 ng E2 per joint. In a separate experiment, the prostaglandin present at 18 h was shown to be mainly E1. Maximum levels of prostaglandin appeared to coincide with maximum joint temperature, but preceded maximum joint swelling and a significant rise in both the number of inflammatory cells and the free acid phosphatase activity in the synovial fluid, all of which occurred at 47 hours. 5 Indomethacin, 7.5 mg/kg orally twice daily, almost completely inhibited the increase in prostaglandin levels in the challenged joints and produced a moderate reduction in joint swelling. It also reduced the increased surface temperature of both knee joints and the raised body temperature. However, indomethacin had no effect on the number of leucocytes present, the free acid phosphatase levels, or the histopathological changes in the joint. 6 The mean plasma level of indomethacin ranged from 0.5 to 3 μg/ml at the time when the animals were killed. 7 Lysosomal enzymes may be more important than prostaglandins in rabbit MAA, and the lack of effect of indomethacin on joint histopathology may be due to its inability to prevent the release of these enzymes.

Morphine analgesia and the bulbospinal noradrenergic system: increase in the concentration of normetanephrine in the spinal cord of the rat caused by analgesics.

Abstract: 1 Administration of an analgesic dose (10 mg/kg, s.c.) of morphine increased the concentration of a noradrenaline metabolite, normetanephrine (NM) in the spinal cord of normal rats. The time course of the change in the NM concentration corresponded approximately to that of the morphine analgesia. The concentration of noradrenaline was not affected.2 A similar effect on the NM concentration was also observed after the administration of pentazocine (30 mg/kg, s.c.) and nalorphine (20 mg/kg, s.c.).3 The NM increasing effect of morphine, pentazocine and nalorphine was found in the dorsal half of the spinal cord but not in the ventral half.4 The increase in the concentration of NM induced by morphine, pentazocine or nalorphine was completely suppressed by naloxone (1 mg/kg, s.c.) given 5 min before the administration of these drugs.5 When the spinal cord was transected at C1, the NM increasing effect of morphine disappeared, yet when the brain stem was transected at the inter-collicular level, the effect remained.6 In morphine-tolerant rats, the concentration of NM in the spinal cord was almost the same as that observed in normal rats, but the increase in the concentration of NM in the spinal cord after the acute administration of morphine did not take place.7 The NM concentration in the spinal cord of normal rats was not modified by aminopyrine (75 mg/kg, s.c.), chlorpromazine (10 mg/kg, s.c.), mephenesin (100 mg/kg, i.p.) or naloxone (25 mg/kg, s.c.).8 The possible relation between morphine analgesia and the descending noradrenergic neurones in the spinal cord of rats is discussed.

Anti-inflammatory property of 401 (MCD-peptide), a peptide from the venom of the bee Apis mellifera (L.)

Abstract: 1 Peptide 401, a potent mast cell degranulating factor from bee venom, substantially inhibited the oedema provoked by subplantar injection of carrageenin or intra-articular injection of turpentine in the rat. The ED50 of 401 was c. 0.1 mg/kg. The anti-inflammatory effect was assessed by measurement of the increased 125I-albumin content of an injected site in comparison with an uninjected contralateral site. 2 Peptide 401 also suppressed the increased vascular permeability due to intradermal injection of various smooth muscle spasmogens (histamine, bradykinin, 5-hydroxytryptamine (5-HT), and prostaglandins). 3 Other comparable mast cell degranulating agents (48/80 and melittin) showed little evidence of anti-inflammatory activity when tested at comparable dosage on turpentine arthritis and carrageenin oedema. 4 The anti-inflammatory effects were not abolished by pretreatment with mepyramine and methysergide, which abolished the increased vascular permeability produced by local injection of 401. 5 The anti-inflammatory action of 401 was not affected by regional denervation or pretreatment with phenoxybenzamine, and was reduced but not abolished by adrenalectomy. 6 Measurement of skin temperature, fractional extraction of 86Rb and blood flow in perfused mesentery gave no evidence that the anti-inflammatory action of 401 was due to reduced tissue perfusion. 7 It is concluded that 401 may exert its anti-inflammatory action directly by making the vascular endothelium anergic to phlogistic stimuli.

Muscarinic excitation: a microelectrophoretic study on cultured smooth muscle cells

Abstract: 1 Acetylcholine was applied iontophoretically to smooth muscle cells cultured from taeniae coli of new-born guinea-pigs. Responses were recorded with intracellular microelectrodes. 2 Acetylcholine induced depolarization, spike generation and contraction. Large conductance increases could be measured during the action of acetylcholine. 3 Injection of depolarizing currents through the recording electrode reversed the sign of potential responses. The reversal potential was -5 to -25 mV. 4 Minimum latencies of responses to acetylcholine were 120-500 ms. These values were not attributable to diffusion time. 5 Attention is drawn to the long latencies of a variety of muscarinic responses, and the suggestion made that muscarinic mechanisms as a class may be characterized by a long activation time.

The effects of acutely administered analgesics on the turnover of noradrenaline and dopamine in various regions of the rat brain

Abstract: 1 Noradrenaline and dopamine turnover rates were determined following blockade of synthesis by α-methyl-p-tyrosine. Morphine, pentazocine and methadone had no effect on steady state levels or on turnover of noradrenaline in whole brain and in the hypothalamus. Although morphine was without action on medulla-pons noradrenaline steady state levels, a drug-induced increase in turnover rate was observed which was antagonized by pretreatment with naloxone (5 mg/kg). Pentazocine and methadone failed to alter either the steady state level of noradrenaline in the medulla-pons or its turnover rate. 2 Morphine accelerated the decline in striatal α-methyl-m-tyramine levels following subcutaneous injection of α-methyl-m-tyrosine 18 h previously. 3 All three drugs increased the turnover of dopamine in whole brain and corpus striatum although the striatal effect was prevented by naloxone pretreatment. The minimum doses of morphine, pentazocine and methadone required to elicit a significant effect on striatal dopamine turnover were 10 mg/kg, 30 mg/kg and 10 mg/kg respectively. 4 The possibility of a dopaminergic involvement in the antinociceptive effect of analgesics is discussed.

The effect of indomethacin on the cardiovascular and metabolic responses to E. coli endotoxin in the cat

Abstract: 1 The response of pentobarbitone-anaesthetized cats to the intravenous administration of E. coli endotoxin (2 mg/kg) consisted of acute pulmonary vasoconstriction (3-5 min after the injection) and a secondary shock phase characterized by delayed systemic hypotension, decreased central venous pressure and cardiac output, and metabolic acidosis with arterial lactate levels three to four times normal. Only one of 25 animals survived 6 hours. 2 Indomethacin (10 mg/kg), administered intravenously 30 min before the endotoxin, reduced both systemic arterial pressure and myocardial blood flow. It abolished the pulmonary vasoconstriction induced by endotoxin. 3 Indomethacin modified some of the characteristic features of the delayed, endotoxin shock phase. Systemic hypotension was not observed and the blood pressure in the indomethacintreated cats 1, 2 and 4 h after endotoxin was 30 mmHg higher than in those cats administered endotoxin alone. The decrease in arterial pH was also significantly delayed. Six out of 15 animals survived 6 hours. 4 It is suggested that indomethacin may abolish the initial pulmonary hypertension and oedema by antagonizing the release, or vasoconstrictor effect, of histamine and that part of its action during the shock phase is due to inhibition of prostaglandin release.