Biomedical subjects
J L BROADBENT
Publications and source records attributed to J L BROADBENT.
EFFECT OF SUPERFUSED OUABAIN ON THE CONTRACTILITY OF THE HEART OF THE FROG.
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ANTHELMINTIC CONSTITUENTS OF FERNS.
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THE INTERACTION OF SOME STIMULANT AND DEPRESSANT DRUGS ON THE FROG HEART.
THE ACTIVITY OF FROG ISOLATED HEARTS WAS DEPRESSED BY ALTERING THE PERFUSING RINGER SOLUTION IN FIVE DIFFERENT WAYS: by reducing the calcium content, by increasing the potassium content, and by adding ether, thiopentone or acetylcholine. Depressed hearts were perfused with Ringer solution containing the following stimulant drugs: paullinia tannin, tannic acid, hydrogen peroxide, sodium oleate, sodium caprylate and ouabain. All these stimulant drugs had similar actions on hearts depressed by calcium lack, ether and thiopentone; hearts depressed by acetylcholine were, however, only weakly stimulated. Hearts depressed by potassium were readily stimulated by oleate, caprylate and paullinia tannin; ouabain and hydrogen peroxide had weak stimulant actions on hearts depressed by potassium, and tannic acid had a negative inotropic action. The differing actions on hearts depressed by potassium are probably related to differences in the degrees of fixation of the stimulant drugs. The mode of action of ouabain and the functional lesion in hearts depressed by narcotics are discussed.
Cardiotonic action of two tannins.
A tannin isolated from Paullinia pinnata Linn., and tannic acid, have cardiotonic actions on the isolated perfused frog heart. Paullinia tannin is more firmly "fixed" than tannic acid. Tannin solutions contain peroxide, but the cardiotonic action is not dependent on this, since drugs believed to prevent peroxide formation, and sodium pyruvate which destroys peroxides, do not prevent the cardiotonic action. Maximal stimulation by tannin greatly reduces subsequent stimulation by ouabain. If calcium is omitted from the Ringer solution tannins cannot stimulate the heart. In this respect they differ from ouabain. However, the ouabain stimulation can be prevented by prior perfusion with tannin. It is suggested that the antagonism between tannin and ouabain is due to the former preventing ouabain from reaching its receptor sites, and that tannin stimulation is dependent on the formation of a calcium-tannin complex at the heart surface. In the isolated perfused mammalian heart preparation tannins increase diastolic tonus and coronary flow.
Importance of calcium in the actions of some drugs that stimulate the isolated hypodynamic frog heart.
Eight drugs that stimulate the isolated hypodynamic frog heart have been tested for their ability to stimulate hearts freshly perfused in calcium-free Ringer solution. Ouabain and digitoxigenin regularly caused stimulation, veratridine did so occasionally. Hydrogen peroxide, tannic acid, paullinia tannin (from Paullinia pinnata, Linn.), sodium oleate and sodium caprylate did not stimulate. The stimulant action of ouabain could be prevented or greatly reduced by prior perfusion with either of the two tannins or with hydrogen peroxide. Hearts perfused for 3 to 4 hr with calcium-free Ringer solution, or hearts perfused for shorter periods of time with calcium-free Ringer solution containing the disodium salt of ethylenediaminetetra-acetic acid, behave unusually in that when perfusion with low-calcium Ringer solution is resumed twitch tension does not return for periods ranging from 10 to 90 min. Ouabain is unable to stimulate these "calcium-depleted" hearts. It is suggested that hydrogen peroxide, the two tannins, oleate and caprylate stimulate by causing the heart to increase the uptake of calcium from the perfusion fluid to a superficial site where calcium is necessary for the propagation of excitation from the cell membrane inwards. A special feature of the action of cardiac glycosides may be their ability to enable the heart to utilize in a similar way the intracellular stores of calcium.
A comparison of some pharmacological properties of dioscorine and dioscine.
The alkaloids, dioscorine and dioscine, both obtained from yams, have been compared in respect of their convulsant activity, toxicity, analeptic action, local anaesthetic activity, adrenaline potentiating action, antidiuretic effect, and anti-acetylcholine activity. The alkaloids have similar properties, but in most respects dioscorine was the more potent. Aqueous solutions of dioscine are unstable.
A convulsant alkaloid of Dioscorea dumetorum.
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Laboratory studies on the detection and treatment of yam poisoning (Dioscorea dumetorum).
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Observations on histamine-induced pruritus and pain.
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Observations on itching produced by cowhage, and on the part played by histamine as a mediator of the itch sensation.
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