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Biomedical subjects

B J Williams

Publications and source records attributed to B J Williams.

At least 127 records · Page 7Linked to original sources
PubMed1975

Effect of acetylcholine on changes in contractility, heart rate and phosphorylase activity produced by isoprenaline, salbutamol and amino-phylline in the perfused guinea-pig heart.

1. Isolated perfused hearts of guinea-pigs were given graded doses of isoprenaline, salbutamol and aminophylline, both before and during acetylcholine infusion. 2. The three agonists produced increases in contractile force, heart rate and ventricular glycogen phosphorylase activity. 3. Acetylcholine, in the concentration used, had no effect on any of the measured variables but did antagonize the effects of the three agonists on contractility and phosphorylase activity. The positive chronotropic responses were unaltered by acetylcholine infusion. 4. The ratio of the dose required for a standard heart rate response to the dose producing a standard contractile force response was different for each agonist. 5. The selective antagonism of the contractile response to isoprenaline, salbutamol and aminophylline suggest that different mechanisms are involved in the initiation of positive inotropic and chronotropic responses.

Acetylcholine↗
PubMed1972

Phytochrome control of growth cessation and initiation of cold acclimation in selected woody plants.

Short day enhancement of cold acclimation in twigs of Cornus (red-osier dogwood), Weigela, and Pyracantha (firethorn) was studied using dark interruptions with red or with red-far red radiation. Hardiness was estimated by freezing stem tissues to preselected temperatures and evaluating injury electrolytically. Dark-period interruptions with red radiation suppressed cold acclimation in Cornus and Weigela. When red light was followed by far red light, suppression was relieved. No radiation control of acclimation was found with Pyracantha. The short day enhancement of cold acclimation in Cornus and Weigela appears to be phytochrome-mediated.

Journal Article↗
PubMed1971

Factors which influence synergism by neomycin and oxytetracycline.

Six strains of enteropathogenic gram-negative bacteria were tested for susceptibility to neomycin or oxytetracycline alone and combined in fixed ratios. The minimal inhibitory concentration for the combination was less than one-half of that expected if the antibiotic activities were simply additive. Neomycin alone was more effective against bacteria multiplying in the presence of abundant oxygen, whereas oxytetracycline alone was more effective against bacteria multiplying in relatively anaerobic environments; when combined, the antibiotics complemented each other by their opposing optima for activity. Oxygen concentration, pH, and neomycin activity are related, and the depression of acid production by oxytetracycline is believed to be partially responsible for the synergistic activity of this pair of antibiotics.

Agar↗