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Biomedical subjects

A M Barrett

Publications and source records attributed to A M Barrett.

At least 19 recordsLinked to original sources
PubMed1990

Age differences in imagery abilities.

Age differences were examined in 4 aspects of visual mental imagery, namely, image generation, maintenance, scanning, and rotation. The results suggested that one or more distinct processes are used to carry out each aspect of imagery, and that this is true for 5-year-olds, 8-year-olds, 14-year-olds, and adults. There was no evidence that younger children have fewer processing components, which become differentiated into more specialized subsystems over age. In addition, the results suggested that younger children are relatively poor at scanning, rotating, and generating objects in images, but are relatively good at maintaining images.

Adolescent↗
PubMed1985

Cardiac beta-adrenoceptor blockade: the quest for selectivity.

In the search for improved drugs much attention has been focussed on the need for greater selectivity of action. Knowing that all drugs are poisons, the pharmacologist must attempt to define the required effect more narrowly but remain aware of potential unwanted effects. These may come as a result of the primary pharmacological effect or be due to other properties of the drug molecule manifesting themselves in clinical use. This paper illustrates the process of drug discovery and development with special reference to beta-adrenoceptor antagonists. Starting from the role of noradrenaline in sympathetic transmission, many compounds have been synthesized with therapeutic aims in mind. From a series of bronchodilators, dichloro-isoprenaline emerged which unexpectedly blocked stimulation of beta-receptors. This compound proved unsatisfactory leading to the introduction of the first clinically successful beta-blocker, pronethalol. Concern about potential carcinogenic effects led to its being replaced by propanolol. Failure to recognise the full range of clinical contra-indications resulted in propranolol causing severe cardio-vascular and bronchial adverse reactions. Soon it was recognized that propranolol was a powerful local anaesthetic potentially acting as a myocardial depressant. More serious was the recognition that in certain circumstances high levels of sympathetic tone were an adaptive response to pathophysiological change and that interruption by beta-blockade was inevitably serious for the patient. Attempts to identify the properties responsible for unwanted effects directed attention to comparison with non-local anaesthetic water soluble compounds still retaining beta-blocking activity. One such compound, practolol, also proved to exhibit a higher affinity for beta-receptors in the heart than elsewhere leading to the concept of cardioselective beta-blockade. The pharmacology of this agent is reviewed but it proved to have unacceptable side effects in clinical use. The importance of practolol was to demonstrate that anginal relief was due to beta-blockade and not local anaesthetic activity. It also showed that cardiovascular adverse reactions and bronchospasm were significantly less common than with propranolol. However, in addition to being cardioselective, practolol also showed intrinsic sympathomimetic activity. This resulted in a smaller bradycardia at rest. Contrary to predictions this property did not prevent practolol becoming well accepted by both doctors and patients as an effective anti-anginal drug. It was the unrelated skin, eye and mucous membrane reactions which led to the compound being withdrawn.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic beta-Antagonists↗
PubMed1978

Accuracy of an automated blood-gas analyser operated by untrained staff.

Performance of the IL 613 automatic blood-gas analyser has been assessed using a group of 100 "analysts" with no previous training or experience in the use of the instrument. Test material consisted of blood equilibrated to a known PO2 and PCO2 in a tonometer: pH estimations were carried out on thawed aliquots of a large batch of frozen serum which were then equilibrated to a known PCO2. Eighty-six per cent of analyses were within acceptable limits of error. The largest proportion of errors was in the measurement of pH. Satisfactory results were obtained in 98% of the analyses of PO2 and PCO2. Eighty-eight per cent of operators were able to use the analyser after instruction lasting less than 1 min. These results were significantly better than those obtained in a regional survey of 16 blood-gas laboratories, staffed by trained technicians.

Autoanalysis↗
PubMed1975

Inhibition of drug-induced anorexia in rats by methysergide.

Iproniazid was found to reduce food consumption in fasting rats. Combined treatment of iproniazid with tryptophan resulted in a significantly greater anorexic action whilst tryptophan alone had no effect on food consumption. Iproniazid treatment was associated with a significant increase in brain 5-hydroxytryptamine (5-HT) concentration but in association with tryptophan higher brain 5-HT concentrations were recorded. The anorexic action of the iproniazid-tryptophan combination was antagonized in a dose-dependent fashion by methysergide. Equivalent levels of anorexia induced by fenfluramine and mazindol were similarly antagonized by methysergide in a dose-related manner. The results suggest a common role of 5-HT in the inhibition of eating behaviour in fasting rats when anorexia is induced by iproniazid, fenfluramine or mazindol, sensitive to a specific 5-HT antagonist.

Animals↗
PubMed1970

Comparative chronotropic activity of beta-adrenoceptive antagonists.

1. Chronotropic dose-response curves (non-cumulative) for beta-adrenoceptive antagonists were constructed from results in rats anaesthetized with pentobarbitone and depleted of catecholamines by pre-treatment with syrosingopine.2. Depletion of catecholamines lowered resting heart rate and reduced the threshold to the chronotropic action of isoprenaline by about 50%. Eight beta-adrenoceptive antagonists produced a dose-dependent chronotropic response but the maximum response was in all cases smaller than that obtained with isoprenaline. The order of activity was dichloroisoprenaline>LB 46>practolol>INPEA>oxprenolol>pronethalol>alprenolol>I.C.I. 45,763 (Kö 592). Propranolol and sotalol were without significant activity. The duration of the chronotropic response to the antagonists was more prolonged than that to isoprenaline. Propranolol caused a parallel shift to the right of the dose-response curves for the agonist effects of the antagonists.3. Estimation of beta-adrenoceptor blocking activity in anaesthetized cats gave an order of activity dissimilar to that found for maximum agonist responses: LB 46 > oxprenolol > alprenolol > propranolol > I.C.I. 45,763 > practolol > dichloroisoprenaline > sotalol > INPEA > pronethalol.4. Consideration of chemical structure and physico-chemical properties did not explain the differences between the agonist activities of the adrenoceptive antagonists.

Acetanilides↗