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Sheffield BioScience Programs

The Langendorff Heart A computer simulation of the effects of drugs on the isolated perfused mammalian heart preparation

By: David Dewhurst & Malachy Doherty

____________________________________________________________________

Introduction

The isolated perfused heart is a useful preparation both for teaching and research. The method, first

described by Langendorff in 1895 and subsequently modified by many other workers is the most

widely used and allows a number of cardiovascular parameters to be monitored simultaneously:

• Coronary blood flow

  • Cardiac force

  • Heart rate

  • Electrocardiogram

The principle is to rapidly remove the heart and perfuse the coronary vessels by forcing, in a

retrograde direction, an appropriate oxygenated fluid through a cannula inserted into the ascending

aorta. After passing through the coronary circulation the perfusate drains away and may be collected.

The chambers of the heart are essentially empty throughout the experiment, the heart muscle does

very little work and there is no real cardiac output

As a teaching preparation in pharmacology and physiology it may be used to investigate the actions

of drugs or ions on the heart and can also be used to demonstrate the effects of pre-load (Starling's

Law of the Heart).

Menu Options

INTRODUCTION: a brief textual introduction to the aims of the program.

METHOD: a brief textual description of the preparation and experimental setup used.

EXPERIMENTS: allows you to investigate the effects of a range of drugs or ions on the heart The

effects of changing pre-load (Starling's Law) may also be demonstrated. The three sub-sections

DRUGS; IONS and STARLING’S LAW will be discussed more fully in a moment.

EXPERIMENTS

Selecting EXPERIMENTS leads to a sub-menu with three further options. Move the highlight using

the up and down arrow keys to the option you wish to select and press <Enter> to confirm your

choice.

DRUGS

Selecting this menu option leads to a further sub-menu offering a choice of different types of drugs.

Selecting one of these leads to a second sub-menu giving a choice of drugs of that type and selecting

one of these allows you to investigate the effects of:

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• the drug alone (Drug Only)

• the drug in the presence of another drug which may antagonise its action (Antagonist)

• the drug in the presence of another drug which may enhance its action (Potentiator)

If you select Antagonist or Potentiator you will be given a further choice of either possible

antagonists or possible potentiators.

On confirming your choice of "experiment" the program will present simulated responses, in high-

resolution graphics, appropriate to your choice of drugs. The screen display mimics a chart recorder

display and shows contractile force, heart rate and coronary blood flow. A horizontal time scale and

appropriate calibrated vertical scales are provided if you wish to quantify drug effects, though for the

most part qualitative effects are sufficient for teaching purposes. The point of administration of the

drug is indicated by a vertical dotted line and the name of the drug or drugs is confirmed in a text

window at the bottom of the screen.

 Drug Doses and Administration

In this program all drugs are administered by bolus injection into a cannula inserted into the

ascending aorta and are thus rapidly distributed throughout the coronary vessels. The drug doses are

those which will produce the primary pharmacological effects of the drug. The responses shown are,

for the most part, derived from real data obtained from a variety of sources (see bibliography).

 Drug + Antagonist or Drug + Potentiator 

The program also allows you to choose to investigate the action of a drug in the presence of either a

potential antagonist or potentiator. The screen display is as for the drug alone except that the point of

administration of each drug is separately indicated by a vertical dotted line. The antagonist or

potentiator is always given immediately before the agonist.

It is useful, when investigating the action of a potential antagonist or potentiator, to be able to

compare the results with those of the drug alone. If you were doing this experiment for real you

would probably have a trace of the drug alone to directly compare. In this program this facility is also

available by pressing the COMPARE button which will display the trace for the agonist (drug only).

Pressing COMPARE again returns you to the original trace i.e. drug + antagonist or drug +

potentiator. By moving from trace to trace it is much easier to assess the effects of antagonists or

potentiators.

 IONS 

The effects of a number of ions on the preparation may be investigated in much the same way as the

drugs. Where the effects of a high concentration of an ion (higher than the normal perfusion fluid)

are to be investigated, the ion is administered as a bolus injection in the same way as the drugs.

Where the effects of a low concentration of the ion are to be investigated (lower than the normal

perfusion fluid concentration) a sub stance is injected which will lower the concentration of the ion

e.g. EGTA is given to lower calcium ion concentration.

STARLING'S LAW 

Selecting this menu option leads to a sub-menu with two options: Introduction and Experiment.

 Introduction: presents brief textual information as background to the experiment.

 Experiment: presents data to illustrate the effects of increasing pre-load on the contractile force. The

upper trace shows left ventricular pressure and the lower trace indicates the end diastolic pressure.

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Starling's Law (Heterometric autoregulation) is best demonstrated by plotting contractile force

(systolic pressure - diastolic pressure) against diastolic pressure. The graph of the experimental

results may also be displayed.

TUTORS' NOTES

The Preparation

Langendorff preparations using the heart of rat, guinea pig, rabbit and cat have been describedfrequently though the rabbit or guinea pig preparations seem to be the most widely used in teaching.

The animal is pretreated with the anticoagulant heparin, anaesthetised, and a tracheal cannula

inserted for ventilation. The thorax is opened, the pericardium removed and the ascending aorta freed

from surrounding connective tissue. A cannula is inserted into the aorta and coronary perfusion

initiated. The inferior vena cava is clamped and the pulmonary artery incised. Retrograde perfusion

closes the aortic valve and the perfusate passes into the coronary vessels and out via the coronary

sinus and inferior vena cava.

Finally the heart, which is now attached to the cannula, is removed from the animal and transferred

to the constant pressure perfusion apparatus. It should then be left for 15-30 minutes to adjust to the

in vitro conditions. Several perfusion fluids have been used e.g. Krebs-Henseleit, Tyrode and Locke

saline solutions, and

McEwens Ringer solution. The fluids are oxygenated, filtered, equilibrated to pH 7.4 and maintained

at 37 ˚C. This method greatly reduces the possibility of myocardial damage due to ischaemia and is

preferable to removal of the heart from a freshly killed animal.

The following cardiovascular parameters are measured:

Contractile ForceEither: insert a small hook or attach a spring-loaded clip to the ventricle and connect to a balanced

isotonic lever (tension transducer).

or: insert a small (latex) balloon, fixed to a catheter tip and filled with water, into the left ventricle

via one of the pulmonary veins, the left atrium and mitral valve. Attach the end of the catheter to a

pressure transducer. Optimise ventricular preload by expanding the balloon.

 Heart Rate

Instantaneous heart rate is measured using a ratemeter or tachograph triggered from the tension

transducer.

Coronary Blood Flow (CBF)

If the heart is perfused at constant pressure (normally 50-60 mm Hg in guinea pig) the mean volume

of perfusion fluid draining from the heart is a measure of the coronary blood flow. This may be

collected per unit time, or the number of drops of perfusate falling off the heart may be counted using

an electrical drop counter. In guinea pigs the normal coronary blood flow is approximately l0

ml/min; in rabbits approximately 20 ml/min. If a vasoconstrictor drug is added then coronary vessels

will constrict and blood flow will be reduced; likewise a coronary vasodilator will increase CBF.

It should be remembered that blood flow through coronary vessels is normally phasic being highest

during diastole and much reduced during systole. Drugs which affect the force of contraction and/orthe heart rate will thus also affect CBF even though they may have no direct effect on coronary

vessels. In addition myogenic autoregulation of the coronary vascular system will occur in response

to either an increase or a decrease in CBF.

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Bibliography

Doring, HJ. & Dehnert, H. (1988) The isolated perfused heart. in Methods in Experimental

Physiology and Pharmacology, Biological Measurement Techniques V. Biomesstechnik-Verlagmarch GmbH, D-7806 march, West Germany.

Bowman, W.C. & Rand, M.J. (1980) Textbook of Pharmacology (2nd edition) Blackwell Scientific

Publications.

Burn, J.H. & Walker, J.M. (1954) Anticholinesterases in the heart lung preparation. J. Physiol.

124,489-501.

Burn, J.H., Gunning, AJ. & Walker, J.M. (1957) Effects of noradrenaline and adrenaline on the atrial

rhythm in the heart lung preparation. J. Physiol. 137, 141-153.

Flack, M. & Hill, L. (1919) A textbook of physiology. Arnold

Harper, B. & Hughes, I.E. (1977) A comparison in rabbit isolated hearts of the dysrrhythmogenic

potential of amitriptyline, maprotiline and mianserin in relation to their ability to block noradrenaline

uptake. Br. J. Pharmac. 59, 651-660.

Katz, LN., et al (1938) Effects of various drugs on the coronary circulation of the denervated isolated

heart of the dog and cat. Pharmacol. Rev. 399-415.

Kitchen, I. (1984) textbook of in vitro practical pharmacology. Blackwell Scientific Press.

McDowall, R.J.S. (1946) The stimulating action of acetylcholine on the heart. J. Physiol. 104, 392-

403.

Acknowledgements

We would like to acknowledge the financial support of The Lord Dowding Fund and the advice and

contributions made by Dr G.G.S. Collins and Dr I.E. Hughes towards the successful completion ofthis package.

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