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Animals in Medical Progress

THE PRESIDENT, THE EARL OF HALSBURY, in the opening proceedings said:

It is my pleasure this evening to introduce you to my friend and colleague Dr. Burgen, a Fellow of the Royal Society. We sit together on the Medical Research Council and see one another regularly on Council business.

 

Dr. Burgen was educated at the Middlesex Hospital Medical School and he then became a House Physician and Demonstrator and Assist­ant Lecturer there for about three years before he was translated—and this was really a remark­able translation—to be Professor of Physiology at McGill University, Montreal, which chair he held until he became Sheild Professor of Pharmacology at Cambridge in 1962. Subse­quently, and since 1971, he became the Director of the National Institute of Medical Research and Honorary Director of the M.R.C. Molecu­lar Pharmacology Unit. His speciality is indicated by his publications in autonomic and molecular pharmacology, and he is going to talk to us this evening about Animals in Medical Progress.

 

Animals in Medical Progress

By A. S. V. BURGEN. M.D., F.R.C.P.. F.R.S.. Director of the National Institute for

Medical Research

 

THE FOUNDER of these lectures, Stephen Paget, was a distinguished surgeon, but he was also a skilful memorialist and his Life of the Pioneer Brain Surgeon, Victor Horsley (1) pro­vides a good starting point for considering the role that animal experimentation has played in medical progress. Horsley showed himself early to be a man with great curiosity and investigative instincts as well as having an abiding interest in patient care. His early interests were in the pathology of brain injury, and in the nature of consciousness. In pursuit of the latter he had himself anaesthetised over fifty times so that he could observe the order of disappearance and return of sensations—a courageous if foolhardy exercise. Horsley's opportunities for research were greatly expanded when in 1884 (at the age of 27) he was appointed Professor Superinten­dent of the Brown Institution—an organisation founded "for studying and endeavouring to cure maladies, distempers and injuries any quadru­peds or birds useful to man may be found subject to". Its objectives were characteristically Victorian, the seeking of new knowledge with a clear eye on the practical value of this knowledge for both animals and man. It was indeed a remarkable institution that played a noble role in the development of medicine under the direc­tion of a succession of distinguished superinten­dents who included Burdon Sanderson, C. S. Roy, Sherrington, Rose Bradford and Twort.

 

It was at the Brown that Horsley worked on the very serious contemporary problem of rabies and generated the simple and sensible proposals for muzzling dogs which when put into practice eliminated the disease from Britain, but he also developed with Schafer, Beevor, Gotch and others the study of localisation in the brain which had been made possible by the discovery of Fritsch and Hitzig that the cerebral cortex could be excited by electric currents. The result of these studies and those of Ferrier and others led to a rapid transformation of knowledge and of attitudes to brain function.

 

While Horsley's involvement in this advance is unquestioned, it took an entirely new signifi­cance when he was appointed surgeon to the NationalHospital, Queen's Square (then called the NationalHospitalfor the Paralysed and Epileptic) in 1886. He now had the opportunity to put into immediate clinical practice the lessons he was learning from his work on animals. What were these lessons? Quite apart from the diag­nostic value of the localising functions, he had learnt such practical things as to how to turn back scalp flaps and to open the skull adequately, to deal with bleeding from bone edges, meninges and brain and indeed that level of delicacy com­bined with boldness with which the surgeon needs to approach the brain. Two months after his appointment the first opportunity to put his new knowledge to practical use arose in a case of severe post-traumatic epilepsy. Horsley deduced from the clinical findings that there was a scar involving the posterior end of the superior frontal sulcus: this was confirmed at operation, the scar excised, the patient had an uneventful recovery and thereafter was free of fits. A few months later Horsley felt he had enough experi­ence to read a paper on "Brain Surgery" to the Annual Meeting of the BMA in Brighton. His paper in the British Medical Journal the follow­ing year begins:

"In the B.M.J. for October 9th 1886 is pub­lished a paper by myself on what I believed to be the best method of treating the brain surgically, a method which, though contravening many of the accepted cannons of sur­gery at the present time. I had previously derived by experiments on the lower animals not only to be the safest, but also to afford the best results. The further experience gained from operations upon man, as might be expected, has added little to the knowledge gained by experiment".(2)

 

In the following year he performed the first recorded removal of a spinal tumour with com­plete success; once again it followed experience in operations carried out on animals with Beevor. From these beginnings brain surgery developed with great rapidity. This story then illustrates the great importance of animal experiments in enabling new medical procedures to be established and thus contri­buting to the relief of suffering while at the same time advancing our knowledge.

 

Scientific enlightenment comes about when men become dissatisfied with dogmatic state­ments and instead regard such statements merely as working hypotheses subject to experimental evaluation. A landmark of this transformation of attitude in medicine was William Harvey's study of the circulation of the blood. In the Introduction to his book(3),Harvey surveys the theories then current and then goes on to ask a series of very pointed questions. Why are the structures of the ventricles so nearly the same if they serve entirely different functions? In particular why should the valves not perform the same function on both sides of the heart in ensuring the unidirectional motion of the blood? Why should the pulmonary vessels have the private function of nourishing the lungs, when the aorta and venae cavae have a more general function? How is it possible that the lungs can need so much blood for their nutrition? The answer to these questions was sought not by recourse to authority but by the devising of experiments whose scope go far beyond these initiating questions, experiments that discrimi­nated between systole and diastole, established that the auricles contracted before the ventricles, that isolated arteries did not pulse, but that the pulse was due to blood ejected from the left ventricle, and most importantly the direction of blood flow—this all in a variety of animals. He then recounts his elegant and devastatingly simple experiments on the motion of blood in the superficial veins of the forearm. All is synthesised into a grand concept, a confluence of human and animal anatomy with an entirely original physiology which convinces by its logic and selfconsistency. In the development of his train of argument, the role of animal experiments is quite indispensible. This is a very clear example of that scientific principle that while the observation of spontaneous occurrences. Nature's experiments, is valuable, the creation of opportunities by the devising and execution of experiments leads to a more rapid and pene­trating analysis of the problem under study.

 

To take a quite different example, much the most successful application of scientific method to the conquest of disease was the recognition of infective organisms as causal agents. Before the time of Pasteur and Koch there had been some persuasive examples of transfer of infection but it was with these two men that a real causal logic was developed, in particular Koch insisted that for causality to be proved it was necessary to isolate the organism in pure culture and then to show that inoculation of this organism into an animal could reproduce the pathological effects seen in the original host. These requirements Koch himself was to attain brilliantly first with anthrax and later with tuberculosis. These examples were to initiate a change in thought that has had incalculable effects in medicine. Firstly, it established that disease could come from an exogenous cause and this was of in­estimable value, because if a cause could be identified, could it not be dealt with? Indeed the results of specific immunotherapy and chemo­therapy have more than fulfilled their promise and as a result these infective diseases have become those which medicine has been most successful in dealing with. Compare the more mediocre results that have been obtained where no causal sequence has been established and no prime step identified, such as in the continued search for causes of cancer. In those few cases where the cause has been firmly established as in bladder cancer due to naphthalene derivatives, or the nasopharyngeal cancer of wood workers, the appropriate public health measures have not been hard to find. What a contrast there is in the cases of cancer of the breast or of the stomach where no cause has been identified. Let me emphasise again that the causality established by Koch involved reproduction of disease in animals, that is the establishment of an animal model of disease. But this was in itself a revolu­tionary idea, produce the disease in animals and you can study the evolution of the disease and the various factors influencing the course of the disease including immunology and chemo­therapy. What an invaluable concept this has turned out to be; how useful it has been to com­pare an animal model such as adjuvant arthritis, or immune-complex nephritis or dietary vascular lipoidosis with human disease. When no animal model is available how handicapped we find ourselves in elucidating the characteristics of that disease, as may be the case of psychiatric disorders or osteoarthritis, or drug induced skin lesions.

 

The third important strand of the work of Pasteur and Koch was the cultivation of causa­tive organisms in artificial media. This led almost immediately to the testing of antibac­terial substances on cultures. Lister, in his search for wound healing by first intention, realised that chemical sterilisation might have promise and after first trying zinc chloride and sodium bisulphite, on cultures of organisms hit upon carbolic. The results were revolutionary for the development of surgery.

 

Before long systematic studies were in pro­gress testing the wide range of organic and inorganic compounds available at the time. There was no difficulty in finding antibacterial substances, they were indeed abundant, but when applied to wounds they were toxic and delayed healing and were far too toxic for systemic administration. It was against this background that Paul Ehrlich enunciated the concept of the therapeutic index, i.e. for a chemo-therapeutic substance to be effective it must be toxic to the invader without being toxic to the host. The application of this principle to chemo-therapeutic substances for bacterial diseases was so discouraging that the search was abandoned— but great advances were made in chemotherapy of parasitic diseases, arsphenamine for syphilis, and arsenophenylglycine for trypanosomiasis, and later synthetic antimalarials—but these were based on animal models since it was not possible to make use of in vitro systems.

 

This unfortunate experience with in vitro test­ing led to a very negative attitude towards bacterial chemotherapy. The first break to impasse came with Domagk's paper on Prontosil in 1935(4) and it is worth quoting from this paper;

"Until now it has been generally thought only protozoal infections would respond to chemotherapeutic agents a systematic search for chemical agents which produce a therapeutic effect can only be undertaken if a suitable model is available. With streptotocci it was possible to produce in mice infection which consistently caused death… we found a number of azo and acridine compounds that were relative effective against streptococci in vitro... this antibacterial action could never reproduced in vivo. At a later stage in investigations we came across some compounds which have a very low toxicity and hardly any antibacterial activity against streptococci in vitro but produced a definite therapeutic action in experiments in mice. Amongst these substances was Prontosil…”

 

It was later in the same year that the Trefoui Nitti and Bovet(5) showed that Prontosil its was not antibacterial but was metabolised in I body to the active compound sulphanilamide. This story is very instructive—here in a highly developed form is the in vitro test that we often urged to develop by opponents of animal experimentation, holding up progress by misdirecting efforts. The lesson had been well learned when Chain and Florey and the colleagues renewed their search for antibacterial substances concentrating on bacterial and mould products. They used a combination of in vitro, and in vivo testing. When penicillin was available in large enough quantity its effectiveness was; evaluated on infections in mice with streptococci, staphylococci, and Clostridia before the whole laboratory supply was put into that famousOxford policeman!

 

A major use of animals at the present time in the testing of toxicity of new drugs. There little question that this is a necessary operation because there are not going to be frequent repetitions of the good fortune of Withering in introducing a drug, digitalis, that has essential no toxic effects other than those due to over-dosage. Nor will it ever again be acceptable use new drugs in man after only very perfunctory examination in animals. A favourite example of this comes from the brilliant work of Fischer and Mering(6) that was the basis of most of the hypnotics and anti-epileptics in use today. The most promising of these compounds appears to be barbitone, indeed when 1 g was administered orally to a dog, it fell into sound sleep for a few hours and then woke up and was lively. On a second occasion this experience was repeated. On the basis of these observations the authors came to the conclusion that barbitone was suitable for use in man! So it was, but how lucky they were.

 

We now expect any potential new drug to go through a most extensive battery of toxicity test­ing in animals. This battery has grown in the wake of the tragedy of thalidomide until the diffi­culties placed in the way of bringing new agents into use have been so great, that in some areas, such as drugs for rarer ailments, and for some tropical diseases, the commercial return has become so problematical as to stifle research. There are manifest anomalies in this position some of which were neatly illustrated by Jukes(7) in an article about marmalade, a food he regarded as thoroughly virtuous. He pointed out that it was very unlikely that orange oil would pass all the safety tests for new food additives, especially since one of the constituents of the oil. tangeretin caused foetal deaths when injected into pregnant rats in quite moderate doses. As he points out, there is no logic in one law for natural products and another for synthetics. When the expansion of animal testing was first introduced, its difficulties soon became apparent, in many ways there was no good yardstick for using animal toxicity as a predictor for human toxicity. There was often great disparity between tests on different animals and no way of knowing which should be taken notice of. There were also human toxic effects previously observed for which no animal models were known. However, the definition of these problems has led to their progressive resolution, for instance, many of the differences in animal toxicity are attributable to qualitative or quanti­tative differences in the metabolism of the compound and a comparison with the metabol­ism in man has led to a great refinement of the predictive capabilities of the animal test. Search for new animal models has also been successful. Two areas remain in a state of flux and are relevant to this talk. Tests of carcino­genicity in animals have been a difficult problem. They are by their nature very prolonged and costly and of doubtful predictive value. For instance what are we to do when a valuable drug produces an obscure tumour in only one strain of mice and no other species examined? The manufacturer had no alternative but to withdraw the drug. Because of the clumsiness of conven­tional testing of this sort and the sheer impracti­cability of greatly extending its scope, much effort is going into finding in vitro tests based on the equation mutagenic = carcinogenic. These tests rely on testing in bacterial and other culture systems in which quantitative methods for numeration and analysis of mutational events are far advanced. Since some drugs would only be expected to become mutagens after metabolic activation, a suitable mammalian metabolic system can be added. The results of such in vitro systems have shown so far a very encouraging predictive capacity and at least in the first place offer a readily applicable method for screening environmental chemicals. Whether they will become acceptable as a definitive method that can replace testing in animals remains to be seen. Similar problems relate to evaluating the poten­tial of chemicals to induce hypersensitivity reactions.

 

The examples I have drawn on are naturally very few out of a multitude available that show how inextricably the use of animal experimenta­tion has been bound up in the extraordinary improvement of medical knowledge and the power of the doctor to understand disease and treat his sick fellow men. I would emphasise the need to think about understanding and applica­tion together, they do not always proceed hand in hand, sometimes an empirical observation is the basis of an advance that is consolidated by development of a deeper understanding, some­times the fundamentals lead straight to the applied, as for instance happened with X-irradiation, but rapid advance nearly always needs both in harness. This brings us straight up against a contemporary question that one hears again and again. Do we already know so much that there is no need for more fundamental knowledge and all that is needed is application? The answer to this in terms of medicine must be an emphatic no. Can anyone seriously suggest that the most obvious unsolved problems of practical medicine in cancer, vascular disease, arthritis, multiple sclerosis, or mental disease are due to a failure of application? This clearly is not the case—our primary failure is one of under­standing the nature of the disease, let alone its cause. To find the road to understanding we will need to use all the means that we have available from clinical observation at one end (remember Hench's clue to the action of adrenocortical steroids from the remission of arthritis in jaundice and pregnancy) to the powerful new ways of thinking about gene action given to us by molecular biology. At each of these hier­archies of approach, a variety of technologies will be needed amongst which animal experi­ments will often remain an integral part.

 

The President thanked Dr. Burgen for his interesting and informative lecture and called upon Miss Olga Uvarov. Vice-President of the Royal College of Veterinary Surgeons and a member of the Council of the Research Defence Society to propose the official Vote of Thanks to Dr. Burgen.

"President, Dr. Burgen. Ladies and Gentle­men", Miss Uvarov said: "may I say that all of us look forward to this particular annual event with the greatest appreciation. I am sure I speak for everyone when I say that Dr. Burgen has ful­filled his task in every single way by giving us this splendid lecture which is obviously going to stimulate a great deal of discussion. I was under the impression, Mr. President, that you got up to announce a difference of procedure and we could in fact start a discussion now. However, knowing how you chair these meetings, I know that you would wish me to be brief. It is obvious that this lecture when published will be of great interest to R.D.S. members. It is most appro­priate that it should take place here at the Royal Society of Medicine where there are a number of sections, including the section of Comparative Medicine, embracing many disciplines, and so the lecture which we have had today is as fitting to all the sections of the Society as it is to the Research Defence Society. The President has already indicated to the audience the distin­guished work of our speaker in the field of Pharmacology, Physiology, molecular pharma­cology, and not only in this country but in many other countries. I was fascinated by the diseases which Dr. Burgen enumerated at the beginning of his lecture since these fall into the category of zoonoses. The first disease mentioned was rabies. This terrible scourge which is not very far from these shores was the subject of a meeting held recently by the Section of Comparative Medicine to discuss the present controls and up to date research work on this particular disease. It was very interesting to have a reminder from our Lecturer of the early work on rabies and the need for experimental work. How irresponsible it would be if we stopped scientific investiga­tions, including the testing of vaccines against rabies, so exposing many more patients, two legged and four legged to this particular disease. Dr. Burgen mentioned other diseases such as tuberculosis, now very much reduced in man and animals, but other pathogens are now emerging. The importance of animal models in elucidating characteristics of diseases is also of great interest to this audience. The lecture was a reminder of many scientific achievements and recognition of current requirements in research.

 

Society as a whole is demanding more and more safety, the public wants re-assurance that all it uses is safe so we have much more legisla­tion, perhaps one of the most important being the Medicines Act 1968. I could only disagree with the Speaker on one point. I don’t think that we should be too ready to say that we are doing too much testing because of that Act or asking for a great deal of information on medi­cinal products. The various disciplines that are required for the future of this legislation are having to work very hard—all this is merely the beginning and already we are learning a great deal from it'. It is obvious that the Speaker has great experience in the use of laboratory animals and in assessing medical progress. At times one hears strident voices of emotional people who endeavour to stifle scientific research with insufficient understanding of what is involved. Surely scientists may have a choice in the way they carry out their research work—which in the main is done with judgment and compassion— and this too was illustrated in tonight's lecture. We can now look forward to its publication and a wider distribution in the Paget memorial lectures.

Dr. Burgen, on behalf of the Research Defence Society, may I thank you most sincerely for your address, not only on behalf of the Society, but also of all those present here and those who are going to read your lecture. Ladies and Gentlemen, may I ask you to be generous in your appreciation of this lecture and show this in the
usual way."


References

  1. Paget, S.   Sir Victor Horsley.   Constable, 1919.
  2. Horsley V. Remarks on ten consecutive cases of oper­ation upon the brain and cranial cavity to illustrate the details and safety of the method employed. Brit. Med. J. 1887, 1373 (April 23).
  3. Harvey, W. An anatomical disquisition on the motion of the heart and blood in animals. Sydenham Society edition 1847.
  4. Domagk, G. Ein Beitrag zur Chemotherapie der bakteriellen Infektionen. Dtsch. Med. Wschr., 1935, 61, 250.
  5. Trefougl, J., Trefouel, J., Nitti, F. and Bovet, D. Acti­vity du p-aminophenylsulfamide sur les infections streptococciques de la souris et du lapin. C. R. Soc. Biol. Paris, 1935, 120, 756.
  6. Fischer, E. and von Mering, J. Ueber eine neue Classe von Schlafmitteln.   Ther. d. Gegenw., 1903, 44. 97.
  7. Jukes, T.   Peel meal.   Nature 1975, 256, 454.

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