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Biomedical subjects

J R Fozard

Publications and source records attributed to J R Fozard.

At least 109 records · Page 6Linked to original sources
PubMed1978

Dual mechanism of the stimulant action of N,N-dimethyl-5-hydroxy-tryptamine (bufotenine) on cardiac sympathetic nerves.

The indirect sympathomimetic effects of N,N-dimethyl-5-hydroxytryptamine (bufotenine) have been analysed on the rabbit heart perfused in vitro by the Langendorff technique. Comparisons have been made with the effects of 5-hydroxytryptamine (5-HT), which activates tryptamine receptors, and dimethylphenylpiperazinium (DMPP), which stimulates nicotine receptors. Bufotenine, 5-HT and DMPP stimulated the rate and force of cardiac contraction but whereas all were powerful stimulants of cardiac rate, bufotenine and DMPP were much stronger stimulants of atrial and particularly ventricular tension than 5-HT. Responses to 5-HT were markedly reduced by perfusion of hearts with an excess of 5-HT, and those to DMPP, during perfusion with hexamethonium. A combination of 5-HT with hexamethonium was necessary to abolish the effects of bufotenine. The data suggest a dual mechanism of stimulant action of bufotenine on the cardiac sympathetic nerves of the rabbit heart involving activation of receptors sensitive to 5-HT and nicotine receptors.

Animals↗
PubMed1978

Blockade of neuronal tryptamine receptors by metoclopramide.

Metoclopramide (0.13, 0.51, 2.0 and 8.1 X 10(-6) M) caused parallel, rightward, shifts in the dose response curves to 5-HT on the isolated rabbit heart. A significant straight line relationship was found between log (5-HT dr--1) and log [metoclopramide] (molar) with a slope of 1.08 +/- 0.13 and giving a pA2 value of 7.20. Metoclopramide did not significantly alter responses to noradrenaline and was 575 times less effective as an inhibitor of DMPP than of 5-HT. The results indicate that metoclopramide is a potent, surmountable and selective antagonist of tryptamine receptors on rabbit cardiac sympathetic nerves.

Animals↗
PubMed1978

Spasmogen release from an extracranial vascular bed evoked by neurohumoral stimuli and periods of vascular stasis.

The hypothesis that pro-inflammatory spasmogens may be generated locally in the vessels of the head by neurohumoral stimuli has been tested using an isolated extracranial vascular bed from the rabbit. No spasmogen release was detected after adenosine triphosphate, histamine, acetylcholine or noradrenaline and was seen rarely after tyramine and 5-hydroxytryptamine. Both sympathetic nerve stimulation and periods of vascular stasis released spasmogen, probably an E-type prostaglandin. The local generation of pro-inflammatory substances by excess sympathetic stimulation and/or vascular stasis might contribute to the development and maintenance of the acute migraine attack.

Acetylcholine↗
PubMed1977

Suxamethonium pains and electromyograph recordings in children.

Surface electromyography was used to investigate muscle activity in children following the administration of suxamethonium. The duration, amplitude and frequency of muscle action potentials recorded in children were similar to those in adults. Twenty-three children had muscle action potential frequencies in excess of 50 Hz, but only two suffered pain after operation. The relationship between high frequency discharge rates of motor units noted in adults in earlier studies does not apply to children.

Action Potentials↗
PubMed1977

A controlled clinical trial of oral droperidol and droperidol plus diazepam for premedication in children.

In 87 children aged 2-9 yr, oral droperidol and oral droperidol plus diazepam were compared as premedicants in a controlled double-blind clinical trial. Atropine was given orally to all the patients. Droperidol was well absorbed and produced good sedation, associated with a low incidence of vomiting after operation. Droperidol plus diazepam did not appear to offer any advantage over droperidol alone. Anxiety and extrapyramidal effects were not observed and may have been obviated by the addition of atropine. Droperidol syrup was noted to be more palatable than other oral premedicants in use.

Administration, Oral↗
PubMed1976

Comparative effects of four migraine prophylactic drugs on an isolated extracranial artery.

Clonidine and methysergide constrict the rabbit auricular artery by activating smooth muscle alpha-adrenoceptors. Clonidine inhibits and methysergide enhances responses to stimulation of the sympathetic nerves. Both drugs sensitise the artery to a variety of vasoconstrictor stimuli, although not to potassium chloride. This weak generalised sensitisation may depend on clonidine and methysergide themselves being vasoconstrictor since sensitisation after clonidine did not occur when vasoconstriction was abolished with phentolamine. The marked potentiation of 5-HT and tryptamine observed during clonidine perfusion may reflect a property of the tryptamines since it was observed during perfusion with histamine but not when histamine vasoconstriction was abolished with mepyramine. Cyproheptadine and pizotifen neither constrict the artery nor sensitise it to vasoconstrictor agents. They inhibit responses to nerve stimulation, alpha-adrenoceptor agonists, potassium chloride and particularly histamine. Sensitisation of blood vessels reinforced by direct vasoconstriction may contribute to the mechanism of action of clonidine and methysergide in migraine. Conversely, alterations in vascular function may be less important to the antimigraine actions of either cyproheptadine or pizotifen.

Animals↗
PubMed1976

Mechanism of the indirect sympathomimetic effect of 5-hydroxytrypt-amine on the isolated heart of the rabbit.

1 Rabbit isolated hearts, perfused by the Langendorff technique, were used to investigate the indirect sympathomimetic effects of 5-hydroxytryptamine (5-HT). Comparisons were made with noradrenaline and with two indirectly acting sympathomimetic agents with entirely different mechanisms of action, tyramine and dimethylphenylpiperazinium (DMPP). 2 The cardiac stimulant effects of 5-HT, tyramine and DMPP were inhibited by propranolol and practolol and the pA2 values obtained were similar to those obtained with noradrenaline as the agonist. 3 Responses to 5-HT, tyramine and DMPP were greatly reduced on hearts from rabbits pretreated with 6-hydroxydopamine. Such hearts had less than 7% of their normal catecholamine concentration and no fluorescence characteristic of noradrenaline in the cardiac sympathetic nerves could be demonstrated. 4 Rapid, reversible and selective tachyphylaxis to 5-HT was demonstrated during perfusion with 5-HT. In hearts desensitized to DMPP by perfusion with DMPP, responses to 5-HT were also reduced. 5 Perfusion of hearts with colchicine inhibited stimulant responses to 5-HT and DMPP but had little effect on responses to noradrenaline or tyramine. 6 Desmethylimipramine enhanced cardiac stimulant responses to noradrenaline and to a lesser extent, those to 5-HT and DMPP. Responses to tyramine were consistently inhibited by desmethylimipramine. 7 Tetrodotoxin abolished responses of the heart to electrical nerve stimulation but left responses to noradrenaline, 5-HT and DMPP unaffected. 8 5-HT, tyramine and DMPP evoked 3H-release from hearts whose neuronal noradrenaline stores had been labelled by perfusion with [3H]-(-)-noradrenaline. The pattern of release evoked by 5-HT was similar to that of DMPP but differed from that of tyramine. 9 Reducing the calcium concentration in the Tyrode solution from 3.6 to 0.2 mEq/1 did not affect 3H-overflow after tyramine but greatly inhibited that evoked by 5-HT and DMPP. 10 The results confirm that the stimulatn effects of 5-HT on the rabbit isolated heart are the result of noradrenaline release. They further suggest that the site of the release is the terminal sympathetic nerve network. The mechanism of release shows more similarities to that of DMPP (calcium-dependent depolarization and exocytosis) than to that of tyramine (neuronal uptake and stoichiometric displacement).

Animals↗
PubMed1976

Interactions between antimigraine drugs and a high affinity uptake and storage mechanism for 5-hydroxytryptamine.

Rabbit hearts removed 3H-5-hydroxytryptamine (3H-5-HT) from a perfusion concentration of 2.6 X 10(-9) g/ml. 15.8% of the extractable cardiac total radioactivity consisted of metabolites, mainly 5-hydroxyindoleacetic acid, and metabolism appeared in the perfusion fluid during the course of the perfusion. Ergotamine tartrate (1.0 X 10(-6) g/ml) caused a small increase in 3H-5-HT uptake by the heart. Methysergide bimaleate (1.0 X 10(-6) g/ml) slowed the appearance of metabolites in the perfusion fluid. Because of the high concentrations required, neither observation seems likely to be of clinical significance to migraine. The results do, however, suggest that the frequently observed sensitisation of tissues to 5-HT by ergotamine and methysergide is not the result of inhibition of its tissue uptake.

Animals↗