Search PubMed⌕ Search

Biomedical subjects

J A Allen

Publications and source records attributed to J A Allen.

At least 55 records · Page 3Linked to original sources
PubMed1983

Changes in heart rate and forearm blood flow following intravenous boluses of isoprenaline in the presence of practolol and propranolol.

1 Increases in heart rate and forearm blood flow following graded intravenous bolus injections of isoprenaline sulphate, were measured in a double-blind randomised study of six subjects who received either placebo, practolol 50 mg, practolol 200 mg, propranolol 10 mg or propranolol 40 mg. 2 Dose related increases in forearm blood flow were produced by the graded boluses of isoprenaline sulphate. 3 Practolol 50 mg attenuated the heart rate response to isoprenaline but did not significantly affect the changes in forearm blood flow. Practolol 200 mg further attenuated the heart rate responses but also decreased the forearm blood flow responses. 4 Propranolol 10 mg and propranolol 40 mg significantly attenuated both the heart rate and forearm blood flow responses. The effect on forearm blood flow tended to be greater than the effect on heart rate. 5 Practolol 200 mg had the same effect on heart rate responses as propranolol 10 mg but a significantly smaller effect on the forearm blood flow responses. 6 The measurement of forearm blood flow following intravenous bolus injections of isoprenaline provides useful information about the beta 2-adrenoceptor antagonism of propranolol and practolol. However, application of the technique may be limited by the magnitude of the heart rate response and by the short-lived nature of the increase in forearm blood flow.

Adult↗
PubMed1980

Covalent binding of polycyclic aromatic compounds to mitochondrial and nuclear DNA.

Since the pioneering work of the Millers it has become clear that most chemical carcinogens require metabolism to reactive electrophiles and then exhibit their carcinogenic potential by reacting chemically with, and modifying, cellular macromolecules. At first modification of proteins was considered most likely to be of importance in carcinogenesis. Later, Brookes and Lawley demonstrated that the extent of binding of several polycyclic hydrocarbons to DNA, but not to RNA or protein isolated from the skin of mice treated topically with these compounds, correlated with their known carcinogenic potency to this tissue. Mammalian cells, particularly mouse embryo cells, treated with chemical carcinogens have often been used, and DNA has been involved almost exclusively from whole cells. However, mitochondria possess unique DNA which accounts for 0.1-1% of the total DNA present in mammalian cells, and three studies have shown that carcinogenic alkylating agents modify the michondrial DNA by a factor about five times greater than the nuclear DNA from the same cells. We demonstrate here that with six polycyclic aromatic compounds, all of which require metabolic activation and bind to DNA to a much smaller extent than direct than direct-acting alkylating agents, the binding to mitochondrial relative to DNA is dramatically increased by a factor of nearly 50 to over 500.

Animals↗
PubMed1980

Effect of increased noise levels by supersonic aircraft on annoyance levels and time estimations.

Several tests designed to assess the effects of increased noise levels created by the Concorde supersonic aircraft were administered to 48 residents living around Dulles International Airport and 31 persons not living near an airport. Results of a pretest questionnaire and lack of significant changes in annoyance levels and time estimations indicate that, while airport-area residents may be more conscious of aircraft noise, changes in the perceived intensities of sounds may not occur.

Adolescent↗
PubMed1978

Effects of experience and short-term practice on drivers' eye movements and errors in simulated dangerous situations.

Two groups of 10 subjects tracked a segment of the Aetna training film, Traffic Strategy, six times by manipulating the controls of the Aetna Drivo-Trainer station. One group was composed of licensed drivers, the other, nonlicensed. No significant differences were found with respect to (1) use of the accelerator, (2) frequency of eye movements, (3) length of eye movements, (4) fixation errors, (5) driving errors, or (6) the relationshiop of control actions to driving errors. Differences were noted with respect to: (1) steering and braking, (2) the effects of practice on control actions and driving errors, and (3) the relationship of amplitude of eye movement to control actions and driving errors. The results are discussed in terms of possible differences in search strategy between experienced and inexperienced drivers.

Adult↗
PubMed1976

Further evidence for apostatic selection by wild passerine birds -9 :1 experiments.

Apostatic selection occurs when predators concentrate disproportionately on the common varieties of non-mimetic polymorphic prey species. This has been tested in 14 experiments by presenting populations of green and brown lard-and-flour "baits" to inexperienced wild passerine birds in their normal surroundings. In seven experiments a 9 green : 1 brown population was presented for a number of days, followed by a 1 green : 9 brown population for a similar period. in the remaining seven experiments the populations were presented in the reverse order. The birds often had strong "natural" colour preferences (for example, blackbirds and songthrushes preferred browns) which were not caused by the relative conspicuousness of the two colours. The data within most of the experiments were very heterogeneous, but in every experiment there was good evidence that the birds tended to concentrate on the common colour. The consistency of the replicated experiements gives strong reason to believe that apostatic selection is a widespread phenomenon among avian predators, and provides an explanation for many of the non-mimetic colour and pattern polymorphisms found among their prey.

Animals↗
PubMed1976

An investigation into the binding of the carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one to DNA in vitro.

After metabolic activation the carcinogen 15,16-dihydro-11-[3H]methylcyclopenta[a]phenanthren-17-one binds to DNA in vitro, and this binding is prevented by 7,8-benzoflavone. Radioactivity cannot be removed from the DNA with organic solvents or by chromatography on Sephadex G-50, even after heat denaturation of the DNA. Enzymatic hydrolysis yields radioactive fractions, which elute from a column of Sephadex LH-20 immediately after the natural nucleosides. At least two species of reactive metabolites are involved in this bending, those with a half-life of a few hr and others with greater stability. After extraction from the aqueous incubation mixture, they could be detected in discrete polar fractions from separations of the complex metabolite mixture by high-pressure liquid chromatography. Their ability to bind to DNA decreased with time at ambient temperature, and they were rapidly deactivated by acid. 7,8-Benzolflavone acted by suppressing the formation of polar metabolites derived from enzymatic oxidation of the aromatic double bonds. The inhibitor had no effect on the enzymes hydroxylating saturated carbon; hence it is unlikely that metabolism of the methyl group is important in conversion of this carcinogen to its proximate form, although the presence of the 11-methyl group is essential for carcinogenic activity in this series.

Animals↗
PubMed1975

Slow growth rate of a deep-sea clam determined by 228Ra chronology.

The age of a deep-sea clam, Tindaria callistiformis, from 3803 m depth has been determined by 228Ra (6.7 year half-life) chronology of separated size fractions of a captured population. A length of 8.4 mm is attained in about 100 years. Shells of this size fraction show about 100 regularly spaced bands, indicating that the growth feature may be an annual one.

Animals↗