Studies of Narcosis
Charles Ernest Overton
Edited by Robert L. Lipnick
United States Environmental Protection Agency, Washington, DC
Title page of Studien uber die Narkose
CHAPMAN AND HALL
London • New York • Tokyo • Melbourne • Madras
WOOD LIBRARY-MUSEUM OF ANESTHESIOLOGY
British Library Cataloguing in Publication Data
Library of Congress Cataloguing-in-Publication Data
Leonard L. Firestone
Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
Robert L. Lipnick
Office of Pesticides and Toxic Substances, United States Environmental Protection Agency, Washington, DC
Keith W. Miller
Department of Anesthesia, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
Peter M. Winter
Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
Keith W. Miller
Peter M. Winter and Leonard L. Firestone
3 Charles Ernest Overton: narcosis studies and a contribution to
Robert L. Lipnick
Studies of Narcosis and a Contribution to General Pharmacology
Part One General Section
1.2 Attempts to distinguish between anaesthetics and narcotics
1.3 Inhalation anaesthetics and other non-specific narcotics
1.4 Non-specific and basic narcotics
1.5 Factors to be considered in developing a theory of narcosis
1.6 Relationship between dose and means of administration
1.7 Calculation of the concentration of a toxicant in the blood plasma
1.8 Conditions affecting blood plasma toxicant concentration
1.9 Bert's method for maintaining a constant concentration of an anaesthetic in the blood
1.10 Bert's experiments with chloroform and ethyl ether
1.11 Concentration of an anaesthetic in the blood plasma
1.12 The intercellular lymph as a pathway between the blood and the tissue cells
1.13 Three groups of compounds differing with respect to their permeability to tissue cells
1.13.1 Compounds unable to penetrate living cells
1.13.2 Compounds that readily penetrate living cells
1.13.3 Compounds that slowly penetrate living cells
1.14 Method of producing known and constant concentrations of non-volatile compounds in the blood: limits of applicability
Critical review of the major hypotheses on the mechanism of narcosis
2.1 Hypotheses based upon the circulation in the brain
2.2 Hypothesis of Claude Bernard
2.3 Hypothesis of Binz
2.4 Hypothesis of Dubois
2.5 Richet's principle
2.6 Hypotheses based upon the chemical composition of the brain
2.6.1 Chemistry of the nervous system
2.6.2 Hypothesis of Bibra and Harless
2.6.3 Contribution of Hermann
2.7 Theory of H. Meyer and the author on narcosis induced by non-specific narcotics
Lipoid theory of narcosis and partition coefficients
3.1 Theory of partition coefficients
3.2 Methods for measuring partition coefficients
3.2.1 Physical methods
3.2.2 Physiological methods
3.3 Measurement of partition coefficients between water and cerebral lipoids
3.4 General foundation of the lipoid theory of narcosis
Part Two Experimental Results4 Narcosis induced by ether and chloroform 4.1 Ether narcosis
Aliphatic non-electrolyte organic compounds and narcosis5.1 Monohydric alcohols
Aromatic compounds6.1 Aromatic hydrocarbons and azobenzene
7 Inorganic anaesthetics7.1 Carbon dioxide
8 Action of basic narcotics and basic compounds8.1 Classification of the basic organic compounds according to their degree of alkalinity
9 Conclusion9.1 Summary of some of the findings
Appendix A Detoxification by means of dialysis
Charles Ernest Overton's 1901 monograph Studien uber die Narkose has become a scientific classic in a number of different fields. This book represents the first English translation, and in fact the first translation into any other language, of the original German work.
In addition to the edited translation, this volume contains introductory chapters by Keith Miller, Peter Winter and Leonard Firestone and myself.
As editor, I have attempted above all else to ensure that the translation faithfully represents Overton's ideas and data, while making the material readily understandable to the modern scientific reader. This has frequently required that extremely long sentences, common in turn-of-the-century German but considered cumbersome today, be simplified into two or even three sentences. In addition, I have paid particular attention to the correct translation of scientific terms, and I accept complete responsibility for any inaccuracies in this area. Overton's original contents list included headings and subheadings, but only a fraction of these appear in the original text. For the sake of clarity they have all been included in the body of the translated work. Also included is an index containing all chemicals mentioned in the book, along with their Chemical Abstracts System Registry Numbers for unambiguous identification, a complete list of Overton's publications (Appendix B), and a list of all biographical articles about Overton and articles dealing specifically with analyses of his data (Appendix C). Although the original book contains no figures, four have been added here. They were either cited in the book by Overton, who referred the reader to the original source for the figures, or obtained from Overton's 1895 publication, and were included for the sake of clarity.
I first became aware of Studien uber die Narkose in the early 1980s when I saw it cited numerous times in both the recent and older literature.
At the time I was beginning work on the use of quantitative structure-activity relationships (QSAR) in the correlation of toxicity with chemical structure. QSAR is used by the US Environmental Protection Agency's Office of Toxic Substances to estimate the potential hazard posed by the release of industrial organic chemicals into the environment. Since such assessments tend to focus on potential release into rivers and other aquatic systems, Overton's use of aquatic organisms is directly pertinent to this mission. With the support of Dr James H. Gilford, Chief (now retired) of the Office of Toxic Substances' Environmental Effects Branch, I was able to arrange for the English translation of this book through a government contract with SCITRAN Inc., Santa Barbara, California. By the summer of 1985 I had in hand a complete translation of the book, and it was immediately clear to me that it would be of great importance to make an edited version of this translation available to the scientific community since many of Overton's ideas and observations were continually being rediscovered. In September 1985 I was invited as the result of a recommendation by Professor Roelef Rekker in the Department of Pharmacochemistry at Vrije Universiteit, Amsterdam (now retired) to prepare a leader article for publication in Trends in Pharmacological Sciences (TiPS) to better inform the scientific community of the importance of this seminal book. This article was published in April 1986, and is reproduced in full in Chapter 3 with the kind permission of the publisher, Elsevier. Several months after the publication of this article, I was contacted by Dr Leonard Firestone, then with the Department of Anesthesia, Massachusetts General Hospital. Dr Firestone indicated that he had read the TiPS article and suggested that the Wood Library Museum (WLM) of Anesthesiology might be interested in supporting the publication of the Overton book translation. He contacted Dr Elliott Miller, also with the Department of Anesthesia, Massachusetts General Hospital, who was then Chairman of the Publication Committee of the WLM; he supported this idea, as did Dr Nicholas Greene, Department of Anesthesiology, Yale University School of Medicine, who is currently Chairman of the WLM Publication Committee, and is the one who eventually brought this book before the WLM Board to request sponsorship and financial support. Dr Greene worked persistently to obtain funds for this project and met on several occasions in London with officials from Chapman and Hall. During this time I performed the first QSAR study of all of the test data on tadpoles that Overton provided in this book. The analysis clearly demonstrates that although Overton did not have the benefit of modern statistical methods, his reported toxicity values are as reliable as any aquatic toxicity data in the modern literature. This reflects the fact that Overton was a very careful observer and also that he took great pains to choose highly reproducible end effects. During the summer of 19891 was extremely fortunate to receive a grant from the Swedish Crafoord Foundation to spend five weeks working with Overton's unpublished data at the University of Lund, where Overton served as the first Professor of Pharmacology from 1907 until his retirement in 1930. Stephen Thesleff, who is the second person after Overton to hold the Chair of the Pharmacological Institute, alerted me to the existence of Overton's unpublished papers, obtained grant funds, made all the necessary arrangements for me to live and work in Lund, and served as my sponsor for this trip.
Since I have lived with Overton's work for several years now, it was especially meaningful during this time in Lund to have the opportunity to meet with his daughters, Harriet Overton and Margaret Overton-Haikola, who graciously shared their father's papers, books, and family photographs, as well as anecdotes about him. Professor Thesleff and the Overton family were all extremely hospitable and made Charles Ernest Overton come alive as a person as well as a scientist to me. Overton indicated in his 1899 publication that he attempted to obtain samples of and test every chemical that was commercially available at that time, and the data published in this book represent only a portion of his studies. Plans are now being formulated for organizing these unpublished Overton data in Lund and making them available to the scientific community. Overton's Studien uber die Narkose is viewed by scientists in many different fields as the turning point in understanding the relationship between chemical structure and cell permeability, and between chemical structure and the potency of chemicals acting by an anaesthetic mechanism. (Hans Horst Meyer, working at the University of Marburg, independently and at the same time as Overton, also concluded that anaesthetic potency correlates with partition coefficient, and for this reason, this theory is commonly referred to as the Overton-Meyer or Meyer-Overton lipoid theory. (Lipnick, R.L. (1989) Hans Horst Meyer and the lipoid theory of narcosis. Trends Pharmacol. Sci., 10, 265-9.) I am grateful to the Wood Library-Museum of Anesthesiology for supporting the publication of this book, to Keith Miller, Peter Winter, and Leonard Firestone for contributing to this work, and to Drs Greene and Miller, and especially to my wife Anne R. Lipnick for proofreading the entire manuscript and for suggesting helpful changes.Robert L. Lipnick Alexandria, Virginia
|Fig. 1.1 Overton's Rule illustrated here by plotting on a double logarithmic scale data for the permeability of human red cells to ten non-electrolytes against their oil-water partition coefficients, K oil/water -The linear regression through the data was fitted with a slope of 1.0, as required by Overton's Rule. From left to right the non-electrolytes are: erythritol, glycerol, urea, ethanediol, thiourea, water, methanol, ethanol, n-propanol, n-hexanol. (After Jain, M. (1988) Introduction to Biological Membranes, Wiley, New York, p. 121).|
...available until well into the twentieth century, and, in the meantime, biologists, armed with the light microscope and various dyes, came to consider the cell as a mass of protoplasm containing a nucleus. By the last decade of the nineteenth century, Verworn could state that the concept of a cell membrane had disappeared. Against this tide, it was the osmotic properties of cells that brought the concept of the plasma membrane back into biology, and, of course, it was the plant physiologists and botanists who were most concerned with osmosis. It had been known since the middle of the century that cells of all origins shrunk when surrounded by solutions that were more concentrated than those in the interior of the cell (a process then referred to as plasmolysis). This suggested that the cell surface possessed a differential permeability to solvent and solute; the cell's solvent alone passing through the membrane to equalize the concentration on either side. The analogy with the semipermeable membrane of osmosis was clear and it was Pfeffer, who, considering the properties of plant cells in his classic book on osmotic pressure, first coined the term plasma membrane to describe a barrier he inferred to exist, even though he could not demonstrate it morphologically - a serious failing in the eyes of experimental biologists. In any event, the ideas of a cell membrane with holes of sufficient size to allow the passage of water could be said to exist well before Overton's time. Another conceptually important piece of work preceding Overton's contribution was that of the German physicist, Georg Quincke. He studied oil droplets interacting with water and the myelin figures formed by lipids in water. Considering plasmolysis, he suggested in 1888 that the protoplasm boundary consisted of an enveloping fluid membrane too thin to be perceived by the light microscope (less than 100nm). Since fatty oils or liquid fats were the only substances he knew to possess the property of forming such films, he concluded they must be the constituents of the plasma surface. Such physical studies drew attacks from biologists, and, although Quincke defended himself stoutly against the 'descriptive' sciences, his ideas were apparently given little weight. Nonetheless, by 1897 Pfeffer seems to have taken in Quincke's point on thickness, going so far as to speculate about a single or double molecular layer, whilst firmly rejecting any idea of a film of oil. The stage was set for Overton. Further plasmolysis studies had demonstrated that the concept that the plasma membrane (as we would now call it) behaved as a semipermeable membrane was incomplete. Thus, with certain solutes the shrunken cells gradually regained their original volume, suggesting that the plasma membrane was slowly permeable to such solutes. Overton  studied the rate of reversal of plasmolysis induced by hundreds of such solutes in plant cells, coming to the conclusion that /... the peculiar osmotic properties of living protoplasts are dependent on the phenomenon of "selective solubility" ...'. Moreover, he concluded that, 'the general osmotic properties of the cell are due to an impregnation of the boundary layers of the protoplast by a substance whose solvent properties for various compounds, correspond overall to those of a fatty oil.' Since the lipid impregnated the 'boundary layers', the concept of a semipermeable membrane was retained while the lipid soluble solutes were able to diffuse through the non-porous lipid. Although Overton went on to speculate that it might be cholesterol and lecithin that impregnated the...
Charles Ernest Overton: narcosis studies and a contribution to general pharmacology Robert L. Lipnick
The year 1986 marked the 85th anniversary of the publication of Charles Ernest Overton's classic monograph Studien uber die Narkose ('Studies of Narcosis') . This book has been cited widely by scientists studying the correlation of biological activity with partition coefficients and the mechanism of anaesthesia. It is of enormous value to modern toxicologists, particularly those involved in the development of quantitative structure-toxicity relationships, and the predictive limitations of such models. Overton reported a wealth of precise physiological and histological observations on the response of a variety of plant and animal species to a large number of organic compounds. His remarkable deductions continue to serve as an inspiration for new scientific research and discovery.
Overton was born in England in 1865 and moved to Switzerland in 1882, where he received a PhD in botany at the University of Zurich in 1889. In 1907, he accepted the Chair of Pharmacology at the University of Lund in Sweden, where he remained until his death in 1933 [2, 3]. Overton was a brilliant and versatile researcher whose work in narcosis and other areas presaged important discoveries in many areas of modern pharmacology. Most of his publications are in German and, despite the fact that only a few excerpts of the narcosis book have, until now, been available in English translation , it has been cited frequently over the years and up to the present by numerous authors in a variety of fields including quantitative structure-activity relationships, pharmacology, anaesthesiology, medicine, toxicology and biophysics. Working alone, Overton performed most of the experiments reported in his book between 1890 and 1898; they evolved from systematic studies published in 1895 and 1896 of the permeability of living plant and animal cells to a large number of organic compounds [5, 6]. He first presented his theory of narcosis in a lecture to the Society for Natural History Research in Zurich on October 31, 1898, and published this work in 1899 , the same year that Hans Horst Meyer  and his collaborator Fritz Baum  independently set forth what was essentially the same hypothesis.
3.1 NARCOSIS THEORY
Overton asserted that a viable theory of narcosis must account for the complete and rapid reversibility of narcosis following removal of a narcotic or anaesthetic agent. As the starting point for his new theory, he chose the solubility of narcotics in cholesterol, lecithin and other lipoid substances contained in cells. Since the narcotics produce no observable chemical change upon these fatty substances, he attributed narcosis solely to physical changes induced from solution of the narcotic in these lipoid constituents. Although this explanation would predict that the intensity of effect is related primarily to the quantity of narcotic absorbed,Overton did not rule out the possibility that the qualitative nature of the compound itself could play some role. He postulated that the intensity could be proportional to either the number of narcotic molecules absorbed or the volume which they occupy at the site of action. The latter hypothesis may have served as the inspiration to Mullins in investigating the thermodynamic consequences of a volume fraction theory of narcosis . Over toil also suggested that water molecules may be displaced from the lipoid phase following absorption, in a fashion not explained simply by solution theory. The deathrate theory of narcosis proposed independently by Pauling  and Miller  can be viewed as an expansion of Overton's early speculation.
3.2 ANAESTHETICS AND NARCOTICS
Overton considered the frequent distinction made by his contemporaries between anaesthetics and narcotics to be both artificial and inconsistent. Anaesthetics were considered to affect all types of plant and animal cells in a reversible fashion, while narcotics were believed to act only upon animal ganglia cells, and not necessarily in a reversible fashion. Overton found that the concentration required to suppress activity, that is, produce narcosis in plant cells, was generally six to ten times greater than that required to anaesthetize brain cells in higher animals. Therefore, those substances producing narcosis in animals at almost saturated solution are limited by their water solubility with respect to their ability to narcotize plant cells. He observed that substances of such limited solubility may or may not produce narcosis in cold blooded animals depending upon the temperature at which the experiment is conducted. Furthermore, substances of low solubility, producing no narcotic effect on either plant or animal cells at saturation, were found to reduce the concentration required of a second narcotic through their additive contribution.
3.3 BASIC ORGANIC COMPOUNDS
Overton found that in contrast to the non-electrolyte narcotics, basic organic compounds including certain alkaloids produce strikingly different effects which vary greatly both qualitatively and quantitatively depending upon the test organism. He attributed such variations to each compound's ability to form salt-like complexes with proteins. He considered differences in toxicity between such basic compounds to reflect variations in the solubility properties of their corresponding protein complexes, which may be similar for two alkaloids of different chemical constitution. He accounted for variations in organism sensitivity by the small differences in the chemical structure of proteins that correspond histologically and physiologically to one another. Thus, while a 1:2000 saturated aqueous solution of morphine produces almost no effect upon tadpoles, the maximum tolerated dose in humans of 0.1 gram would correspond to about 1:400 000, if distributed throughout the body.
3.4 ROUTE OF ADMINISTRATION
Overton made no distinction between anaesthesia produced via inhalation and narcosis produced by other routes of administration, since he thought that in each case, a chemical acts by a common mechanism and reaches the same site of action, i.e. the brain cells, from the blood in the same fashion. He considered the pathways by which narcosis-inducing substances, i.e. narcotics, enter the bloodstream to be unimportant so long as they achieve the required concentration in the blood. Overton interpreted the variation in toxic response observed with administration via the stomach, rectum, skin or peritoneum to be a manifestation of different rates of absorption. To calculate an approximate concentration in the bloodstream, Overton concluded that knowledge would be required of the ability of a substance to penetrate various tissue cells, the approximate fat content of the animal, partition coefficients between water and the fats in question, metabolism, excretion and volatilization via the lung.
3.5 EXPERIMENTS AT KNOWN AND CONSTANT BLOOD PLASMA CONCENTRATION
Overton found that he could study toxicity at a known blood plasma concentration if compounds were administered via the lungs at a constant and known partial pressure and temperature. Similarly, the blood plasma or cellular fluid concentration could be defined in corresponding controlled experiments conducted on aquatic plants and animals submerged in a solution of known and fixed concentration and temperature, and of sufficient volume to ensure that the concentration would not change appreciably as a result of uptake during the experiment. In general, he found that the time required to produce an effect was similar for both gaseous and aquatic routes of administration. Overton determined that an ether concentration of 20ghl~1 in air was just sufficient to maintain complete narcosis in dogs, which have a body temperature of approximately 38°C. Based upon the Henry-Dalton Law, he calculated that at equilibrium this vapour concentration would produce a 0.25% concentration of ether in the blood plasma, the same concentration he found sufficient to produce narcosis in tadpoles.
3.6 TEST ORGANISMS AND CHEMICALS
Overton reported test results for over 130 compounds in this book. However, this represents only a portion of the data from which his conclusions are drawn for he had attempted to obtain samples of and test every organic compound that was commercially available at the time. Overton employed algae and a wide variety of aquatic animals including tadpoles, daphnia, fish, crustaceans, bryozoa, and annelids to study toxicity at a constant blood plasma concentration. Most of the experiments which he reported in detail were conducted using tadpoles of the species Rana temporaria. The compounds tested included monohydric, dihydric, and polyhydric alcohols, aliphatic and aromatic hydrocarbons, nitriles, nitroparaffins, aldehydes, ketones, sulfones, esters of organic and mineral acids, various aromatic compounds, amines and alkaloids.
3.7 NARCOTICS AND ORGANIC BASES
Overton found that most of the organic non-electrolytes that he tested produced narcosis. By contrast, organic bases such as alkaloids generally did not produce narcotic effects. He observed no sharp delineation, but rather a continuum of effects between the neutral and basic classes of organic compounds. For example, ethyl alcohol exhibited almost purely narcotic effects. Tadpoles could be kept in a 1% solution of ethyl alcohol for days without showing any narcosis or ill effect. However, in a 1.5% solution, they became narcotized in 2-3 minutes and could be maintained in this state for 20 hours; the narcosis faded once they were returned to pure water.
3.8 ESTER HYDROLYSIS
Overton found that esters of monovalent aliphatic acids behaved in an interesting fashion with respect to the length of time a tadpole could be maintained in a narcotic state without dying. For example, he reported that the length of undisturbed narcosis for amyl acetate was 2.5-3 hours, but for ethyl valerate, which has the same chain length, it was 15 hours. Within each homologous series of esters (e.g. acetates), he found this duration to be a reflection of the rate of metabolic ester cleavage within the tadpole. Overton confirmed and expanded these findings for a more diverse group of esters in a later study .
3.9 PROGRESSIVE TOXICITY
Overton observed that some compounds such as hydrocyanic acid and the lower molecular weight monovalent aldehydes produced an initial rapid response resembling narcosis, but required a much longer period of time to produce their maximum effect. He ascribed the second response to a slow progressive chemical reaction with one or more cellular constituents.
3.10 CHEMICAL STRUCTURE AND NARCOTIC POTENCY
Overton discovered that substances having little or no solubility in a mixture of cholesterol and lecithin, such as alcohols containing four or more hydroxyl groups, produced no narcotic response in tadpoles at any concentration. He concluded that no equalization of the concentration in the blood and the external aqueous phase could be achieved for such substances as long as the animal was alive. He discovered a systematic increase in narcotic potency with increasing chain length among groups of related compounds. Beyond a certain chain length, however, he noted that narcotic properties could no longer be detected. Within a series of isomers, he observed that the isomer with the least branching or which was furthest removed from a spherical shape had the strongest activity. In addition, replacement of a hydrogen or halide by hydroxyl reduced activity. Similarly, he noted that in general, activity increased in the order iodide > bromide > chloride.
3.11 PARTITION COEFFICIENT AND NARCOTIC POTENCY
From these experiments, Overton concluded that only one physical property, the lipoid-water partition coefficient, changed in a way that reflected the regularities he observed between chemical structure and narcosis action. Linear correlations between n-octanol-water partition coefficient and molar toxicity on a log log scale subsequently derived for a variety of organisms have confirmed Overton's findings . A study using Overton's original data provided a high correlation (r2 = 0.913) in this type of analysis, but a much poorer correlation with other parameters (polarizability, molar attraction, parachor and molecular weight) .
3.12 CHEMICAL STRUCTURE AND PARTITION COEFFICIENT
Overton's early observations regarding a systematic trend in the contribution of structure fragments to partition coefficient have now been confirmed and amplified as the fragment constant methodology [16, 17]. The recent computerization of this fragment constant methodology  has given a strong impetus to the advancement of predictive toxicology and pharmacology [19, 20].
3.13 LIMITING SOLUBILITY
Overton found that within a homologous series, although the partition coefficient continues to increase with chain length, the absolute solubility in oil or a mixture of cholesterol and lecithin at room or blood temperatures decreases rapidly beyond a certain point in the series. For example, phenanthrene, which is readily soluble in olive oil and related substances at room temperature, is a narcotic, but anthracene, an isomer, is not soluble and does not show narcotic effects. Overton concluded that low water solubility alone will not limit narcotic toxicity, as in the case of phenanthrene which dissolves in about 300000-400000 parts of water, but produces narcosis at one part in 1 500 000. For experiments conducted at this very low concentration, 36 hours were required for complete narcosis to take place, which Overton accounted for based upon the slow rate of transport and accumulation of phenanthrene into the ganglia cells. Overton concluded from his physiological experiments, and a large number of measurements of partition coefficient and solubilities in water and oil phases, that the narcotic strength depends primarily upon its partition coefficient between water and the lipoid substances in cells. Overton's ingenious experiments and remarkable deductions have provided a stepping stone for work by investigators in many disciplines, and are expected to continue serving as an inspiration for new scientific research and discovery. His book is of enormous value to modern toxicologists, particularly those involved in the development of quantitative structure-toxicity relationships and the limitations of such models.Acknowledgement: The author is grateful to Dr James H. Gilford, Chief, Environmental Effects Branch, and Dr Irwin Baumel, Director, Health and Environmental Review Division, EPA; and to Professor Roelof R. Rekker, Department of Pharmaco-chemistry, Vrije Universiteit, Amsterdam, for their encouragement in the preparation of this article.
1. Overton, E. (1901) Studien uber die Narkose, zugleich ein Beitrag zur allgemeiner Pharmakologie, Gustav Fischer, Jena.
Until very recently, the statement has appeared in the literature that no actual non-specific narcotic is known among the aromatic compounds. In fact, as long ago as 1848, no less a person than Simpson found that benzene itself is a narcotic, although it proved to be unsuitable for medical use. More recently, Meyer has studied the narcotic effect of the amides of the various aromatic acids. We will see in the following that among the aromatic compounds can be found some of the most interesting nonspecific narcotics, and that it is within this group that the relationships among the non-specific narcotics, antipyretics, and antiseptics on the one hand, and between non-specific and basic narcotics on the other, can be most clearly seen. Without further introduction, I will proceed to a discussion of the specific groups.
6.1 AROMATIC HYDROCARBONS AND AZOBENZENE (Table 6.1)
|compound||parts by weight of water per one part by weight of narcotic||mol/l||solubility|
|Benzene||6000||0.0021||Soluble in about 1000 parts of water; miscible with oil|
|Xylene||25000||0.00038||Soluble in about 8000 parts of water; miscible with oil|
|Naphthalene||100,000 - 150,000||0.000052 - 0.000078||Soluble in about 20 000- 30 000 parts of water; readily soluble in ether and oil|
All of these compounds penetrate the blood and tissues very readily. In solutions of 1 : 4000 benzene, for example, 16-17 mm long tadpoles become fully narcotized within 2V-i minutes. In contrast, at 1 : 8000, complete narcosis does not take place even within 24 hours. Narcosis induced by benzene is fatal within a few hours. Strong agitation occurs before the onset of narcosis and this can produce spasms. In solutions of naphthalene, of 1 : 50 000, complete narcosis occurs in tadpoles 11-12 mm long after 10 minutes. After 6 minutes, it is not quite complete. In 1 : 200 000 solutions of naphthalene, complete narcosis does not occur even after several days. In 1:50 000 azobenzene, (C6H5)2N2 12 mm long tadpoles still moved somewhat after 8 minutes, but became completely unresponsive after 14 minutes, although the circulation was still good after 22 minutes. In 1:200 000 azobenzene, 12 mm long tadpoles still moved around fairly vigorously after 1 hour and 30 minutes. After 2 hours 45 minutes, they did not move around, but responded readily to stimuli. When stimulated, they even moved for about 3 seconds. Narcosis was complete after 50 hours and the tadpoles did not respond to even the strongest stimuli, although circulation was still excellent. When the concentration was then decreased to 1:400 000, narcosis was maintained for about 16 hours while the tadpoles became somewhat responsive to stimuli, but remained immobile. The circulation was good. When placed directly in a solution of 1:400 000 azobenzene, tadpoles become almost completely immobile after a few hours, but remain responsive to stimuli for days.
In more dilute solutions, for example 1 : 40 000 or 1 : 20 000, of normal (Japan) camphor, which is an alicyclic ketone, tadpoles display a considerable degree of agitation. This agitated state persists for a very long period of time without the tadpoles exhibiting any further signs of abnormality. They can survive for days in solutions of 1:12 000, without their movements being noticeably affected. In solutions of 1:5000 (1.3 x 10-3 mol/l), all spontaneous movements cease after about 15 minutes, although the tadpoles continue to respond to stimuli for about 1 hour. After complete narcosis has occurred, the tadpoles survive , for about 6 hours, but their circulation becomes very slow. The tadpoles do not usually recover after being maintained in the solution for 8-10 hours.
Aqueous solutions of all essential oils have a rather marked narcotic effect, but many also have additional effects at the same time, e.g. paralysis of the heart. In very dilute solutions, they also frequently show a camphor-like agitating effect. These solutions also often affect the epithelia, which in many cases probably reflects the level of peroxide present. Although I have performed numerous experiments on the narcotic effects of these oils, mainly in the interest of certain problems in plant physiology, it seems unnecessary to explore these in further detail. It will suffice to say that narcosis usually occurs in solutions between 1:10 000 and 1:100 000 and that they are fatal within a few minutes to several hours, depending upon the essential oil used.
The experimental results with this compound are so instructive that I will reproduce a rather complete account of one experiment.
Experiment At 9.45 am on May 4, 1895, three tadpoles of Rana temporaria were placed in 1:5000 (1.23x lO-3mol/l) of nicotine. At 9.56am, two tadpoles no longer responded to stimulus; the third barely responded and reacted with only a faint jerk. One minute later, all three were completely unresponsive. At 10.17am there was still no noticeable caustic effect from the solution. At 10.21 am, the circulation was still excellent. At 11.07am, corresponding to 1 hour and 13 minutes from the start of the experiment, the circulation was still good, and the epithelia were not affected. At 11.08am, two of the tadpoles were transferred to fresh water. At 11.15 am, they still did not move or respond to stimulus, nor at 11.35am. At 12.05pm, they still did not respond but the circulation was still very good. At 12.18pm, one of the tadpoles became faintly responsive, and soon after this made spontaneous swinging movements with its tail. At 2.25pm this tadpole had almost completely recovered. The remaining one was easy to stimulate, but did not move much. The tadpole left in the nicotine solution was now dead, but the body epithelia were not affected. At 4.00pm, one of the tadpoles transferred to fresh water was entirely vigorous and healthy, and subsequently behaved quite normally as well. The remaining tadpole which had been transferred to fresh water worsened after 2.25pm in that it could move less and its circulation became weaker; it finally died after a while. In solutions of 1:20 000 (3.1 x l0-4mol/l) of nicotine, all spontaneous movements ceased after 5-10 minutes, with responsiveness disappearing in 15-20 minutes. The solution was fatal within less than 8 hours. In a 1:50 000 solution, tadpoles moved spontaneously for more than an hour, although their movements were of very short duration and the tadpoles appeared to tire very quickly. In one experiment, a tadpole maintained its responsiveness for more than 4 hours, and when transferred to fresh water after 10 hours, recovered completely in 24 hours, even though it was unresponsive within the first few hours. Two other tadpoles in the same experiment lost their responsiveness within 3 hours and did not recover. In solutions of 1:80 000 nicotine, tadpoles behaved almost normally for days, although their movements seemed to drag somewhat. In 1:100000 (6.2 x 10-5 mol/1) tadpoles can survive for 10 days or longer without showing any noticeable signs of disturbance. In the case of both nicotine and coniine, their effects vary somewhat depending upon the type of amphibia and their age, i.e. the concentrations required to produce certain effects are not always identical for different species and different ages of tadpoles. In the case of some other alkaloids, there are yet much greater differences in this respect.
Nicotine is miscible in all proportions with water and is soluble in about 4 parts of oil, with the partition coefficient favouring water. The possibility of a mechanism of action like that of the non-specific narcotics is therefore entirely excluded in the case of nicotine. According to the known experiments performed with adult frogs, nicotine appears to act on the motor nerve endings, directly on the muscle fibres, and on the central nervous system.
Publications about Overton and analyses of his data
Collander, R. (1959) in Plant Physiology: A Treatise, (ed. F.C. Steward) Vol. 1, Academic Press, New York, pp. 7-9.
Collander, P.P. (1962-3) Ernest Overton (1865-1933): a Pioneer to Remember. Leopoldina, 8-9, 242-54.
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