Léon Ambard (1876-1962): his priority in using urea as a tool for assessment of kidney function in healthy subjects and in patients undergoing renal surgery


Léon Ambard (1876-1962) was born in Marseille (France). He studied at the Sorbonne in Paris where he received his medical degree in 1905. In the years 1909-1914 he was chief of the laboratory of the Department of Urology at the Necker Hospital. His task was to find a method for assessing renal function with the goals of: 1. prognosticating the effects on the kidneys of surgical operation on the urinary tract and 2. for the early detection of renal impairment. He successfully devised the Urea Secretory Constant which was named after him (Ambard’s Constant). He was able to establish the laws governing urea handling by the kidney in health and disease and attracted to the topic the most innovative physician scientists of those days including Thomas Addis and Donald Van Slyke. His findings ensured his promotion to Professor of Pharmacology at the University of Strasbourg in 1919. In 1930 he was nominated correspondent member of the National Academy of Medicine. In the same year he was promoted to professor of medicine. Ambard is credited with an impressive list of excellent papers and books including Physiologie Normale et Pathologique des Reins which had 3 editions (1914, 1921 and 1930). He retired in 1947 but remained very active till the end of his life (May 19, 1962). His last publication (Ultrafiltration) was written in English with Simone Trautmann (1961).

Keywords: Léon Ambard, Urea Secretory Constant, Urea Clearance, Thomas Addis, Donal D. Van Slyke, laws of renal urea excretion

Ambard’s life

Léon Ambard (Figure 1Table 1), dit Léo Ambard, was born in Marseille in 1876. He studied at La Sorbonne in Paris from which he received his medical degree in 1905. He was assistant to Professor Edward Enriquez (1905-1911) and was called by the French urologist Félix Legueu (1863-1939) to direct the laboratory of the Division of Urology at The Necker Hospital (1911-1914). In those years he made significant contributions to the diagnosis and prognosis of the functional renal impairment that ensues of the kidneys after surgery for urological problems, in the course of which he produced outstanding research on factors governing urea excretion by the kidneys. He wrote an important book on Physiologie Normale et Pathologique des Reins (Figure 2) for which Félix Legueu wrote a preface which also appeared in the subsequent editions of the book (Table 2), published in 1920 and in 1931 (Figure 2). After his return from the 1st World War, to which he participated with honor, in 1919 he moved to Strasbourg as Professor of Pharmacology. On May 20 1930, he was elected National correspondent to the Académie de Médecine (Figure 3). Of 50 members of the Académie 47 voted for him. In the same year he became Professor of Medicine. He died on May 19, 1962 (1-3).


Timeline of building-up a critical mass of data on urea synthesis, metabolism and excretion

It took centuries to build a critical mass of data on urea synthesis, metabolism and excretion (4-6).

Table 3 lists scientists who contributed to that process (7-16).

Nestor Gréhant, an assistant to Claude Bernard (16), was the first to experiment on the ratio of urea concentrations in urine and blood (U/B). In the introduction of his 1904 paper (14) he writes:

“I have started the new investigation in order to allow physiologists and physicians to define exactly kidney failure and to identify when the disease begins its course. At that time it might be possible to reverse the disease and to cure it. I have gained experience with my doctoral thesis entitled Investigations on Urea Excretion by the Kidney (1870) and nurtured it over the years. I use nitric acid”. To this end, red blood cells must be separated. To measure urea, it is necessary to prepare an alcoholic extract. This is necessary since when nitric acid reacts with urea it causes the formation of a gaseous mixture of N, NO2 and H2CO3. The latter is then adsorbed on tablets potassium of carbonate. With this method, Gréhant studied dogs (U/B = 124) and a sample of muscle (psoas) from a patient who died with uremia and who had passed 210 ml of urine the day before dying. The ratio of urea between urine and muscle was 10, a value well below that in dogs.

Ambard had specialized in physiology of the kidney in order to distinguish between the renal excretion of threshold and non-threshold dependent substances. For him non-threshold substances are continually excreted in urine as long as they are present in blood (urea, sulphate).

Threshold substances do not appear in urine below a definite and constant blood level, that is specific for each substance. The best known threshold dependent substance, glucose, was primarily identified by Claude Bernard, who did not mention any threshold and non-threshold substances. This concept was initiated by the German Physiologist and Pharmacologist Rudolph Magnus (1873-1927) years later in his studies on chloride which is another threshold substance, but its threshold is lower than its concentration in blood. Threshold for Ambard was an entity comparable to the height of a dam. It is with his expertise in this concept that he started to experiment on urea.

Ambard, alone as well as in association with other scientists (17-45), studied dogs and young men capable to empty their bladder easily in order to evaluate the ratio between urea concentration in urine and blood. Both were measured in g/100 ml. In preliminary studies on the time course of changes of urea in blood and urine, they noticed that blood urea was at its nadir early in the morning after a night of sleep and peaked after lunch. Urinary urea excretion varied between 0.42 g/hour between 9:00 A.M. and 10:00 A.M. and 2.40 g/hour 4 hours after lunch.

Then they decided to perform experiments collecting urine for periods lasting 36 min (36 min represents 1/40 of the total number of minutes of a day) and by obtaining blood by venipuncture at an intermediate time. They studied a substance without threshold (urea) and a substance with threshold (NaCl). In dogs, urine collections were obtained through catheters and lasted 1 hour while blood was obtained after the end of urine collection. Forty ml of blood or urine were needed to measure urea by the sodium hypobromite method.


Laws regulating urea excretion by the kidneys

Analysis of generated data allowed the formulation of 3 laws governing urea and sodium chloride excretion and established the Coefficient of Urea Excretion corrected for body weight and for maximal urea excretion of 25 g/ day. For sodium chloride –having a threshold- it was possible to calculate the augmentation limit of the threshold.

The constant (K) for urea was in the range 0.06-0.081 in man and 0.03-0.034 in dogs. It was concluded that to calculate the coefficient of secretion for urea, one had to measure urea in blood and urine and have knowledge of the urine flow rate as well as that of urea concentration. The series of outstanding publications (17-44) that followed established the laws governing urea excretion by the kidney (Figure 4).


The destiny of the Ambard coefficient

Donald Van Slyke (1873-1971), who ultimately  who ultimately established the clearance concept as we know it now (46), emphasized that his studies devised to assessing the functional capacity of the kidney was based on urea excretion rate that had introduced as criterion by Ambard.

“Ambard and his collaborators (Ambard 1910, 1920), Ambard and Papin (1909), Ambard and Weill (1912), whose work has inspired many investigations including our own”.

Van Slyke et al. (46) proposed and identified 2 factors that determine urea excretion. One is represented by urea concentration in plasma, the other was identified in the urea concentration in urine. Ambard held that the excretion rate of urea increases as the square root of the blood urea concentration, i.e. doubling the blood urea quadruples its excretion rate. In the work of Van Slyke et al. (46) the first law of Ambard was confirmed. In addition, they developed a new formula which resembled that of Ambard but they claimed “far greater accuracy than that originally conceived by Ambard” […] “If this belief is confirmed, the present work is to be regarded not as a disproof of Ambard’s, but rather as an accurate advance which has proceeded along the path opened by his researches, and which has resulted in a somewhat closer approximation to his ideal of accurate functional measurement” (46).

Marshall and Davis (47) in 1914 found that when plenty of water was given the rate of urea excretion in a normal animal was directly proportional to the concentration of urea in the blood. Working on animals and using a method described by Marshall, they showed the rate of urea excretion in normal animals was directly proportional to urea concentration in the blood, and disclosed a reduced urea excretion following dehydration (47). An approximate proportionality between blood urea concentration and rate of urea excretion was published by Pepper and Austin (48) in 1915, by Addis, Barnett and Shevky (49) in 1916 and by Addis Barnet and Shevsky (48) in 1918.

Addis and Watanabe demonstrated that the first law was perfect, but there was a problem with the second law showing variations of 10% (50). They wrote:

“The approximate constancy of the combined formula which after all is roughly approximate, is due in part to the tendency for increased urea concentration in the blood to be accompanied by increased rate of urea excretion. But in large part is to be ascribed to its mathematical construction, to more variable factors―the concentration in the urine, the volume of urine and the amount of urea in the urine occur as the square or the fourth roots of their values. Their disturbing effect on the constancy of the resultant of the formula is thus greatly reduced, while the only factor used without such modifications―the concentration in the blood―is itself the most constant quantity used”.
McLean and Selling (51) measured urea and non-protein nitrogen in urine and blood of healthy volunteer persons aged 20 to 40 years by collecting urine for 60 minutes periods. They used the Davis’ method. They found that urea excretion in normal subjects and also in nephritics was governed by the two laws of Ambard relating output to blood and urine concentration respectively. Finally they expressed great interest in the future of creatinine assessment.

“Van Hoogenhuyze, Verploegh (1905) and Shaffer (1908-1909) then have showed that the hourly elimination of creatinine throughout the day in a given individual is approximately constant. By calculating the creatinine ratio stimulating results are obtained which indicate that creatinine may be used in those who can’t empty the bladder”.

Möller E, McIntosh JF and Van Slyke DD (52) studied urea excretion in normal adults and analyzed its relationship with urine volume. They came to the following conclusions:

“Ambard and Weill were the first to include both urea output and urine volume in attempting to quantitatively to relate urea excretion to blood content”. However the square of V is valid only for volume <2 ml, at higher volume flow rates Ambard’s formula becomes more inaccurate”.

From the historical point of view is the study of D.S. Lewis (53). That paper asked to focus attention on the paper of Lamy and Meyer (54) published in 1905. In fact Lamy and Meyer endeavored to compare the concentration of urea in the blood with the rate of excretion in urine but failed to determine the importance of the rate of blood flow and consequently did not disclose any relation between the two values. That link (53) was detected five years later by Ambard and Moreno with their laws of renal function which “under routine conditions are remarkably accurate. They are correct in principle. They allow the follow-up of renal function and the rate of progress of the disease and prognosis. Any coefficient below 0.6 or above 0.9 should be regarded as abnormal. It is depressed in mixedema, fever, hyperthyroidism, in myocardial insufficiency, raised in myxedema”.


Ambard a scientist with broad interests

Léo Ambard was a great investigator who every day did experiments, saw patients and wrote reports (55-60). Reference no. 56 refers to the last book co-authored by Ambard and Trautmann (Figure 5) indicating that he continued to work till the end of his life. One can say that the data and the work done before getting the chair in Strasbourg, may be considered a paradigm. He used his knowledge on threshold and non-threshold substances in order to develop a tool capable of allowing the renal prognosis of patients undergoing surgery for urological problems. His findings were highly original and opened a new field of study. He was able to stimulate scientists from all over the world verify his findings. His experiments were repeated, discussed and of course acquired a new light. When he felt really mishandled by American Scientists, he let Donald Van Slyke know about his feelings and made it clear that all new things had a foothold in his Coefficient of Urea secretion, the “Constante” he had invented. Van Slyke, a great scientist magnanimously appreciated Ambard’s sadness and wrote him a letter on December 7, 1926 where he pointed out that Ambard deserved all the credit for the discovery of urea excretion (Figure 6). The letter appeared in La Presse Médicale.

In the obituary read before the Académie Nationale de Médecine on April 23 1963, Alexandre Marcel Monnier― member of the Academy, a famous French physiologist at La Sorbonne― reported on Ambard’s sadness for the unjust attempt to delete his name from the history of clearances (3). He says that after the 1st World War, English became the language of science. So French authors were read rarely and with difficulty.

However we disagree with this sadness, for two reasons. The first is represented by the Letter of van Slyke. Not a personal letter but a letter to a very important French scientific journal. The second reason is to be found in page 94 and 95 of the 1930 Edition of Physiologie Normale et Pathologique des Reins. Therein we read “all French authors have given their support to the Coefficient for Urea Secretion, thus I will not cite them”. The statement is followed by a list of 18 papers from abroad which have given credit to Ambard for the discovery and are introduced by country―USA, Uruguay, Belgium, Austria, Germany, Norway, Czechoslovakia, Romania.



Thanks are due to Professor Raymond Ardaillou, Académie Nationale de Médecine, Paris, for many helpful suggestions. We thank Bernadette Molitor, a traditional supporter of our investigations on French speaking scientists during the last 20 years. Mrs Dr. Pinto, Biblioteca Nazionale di Napoli, helped in locating specific documents in Italy.

Natale G. De Santo is thankful to Professor Garabed Eknoyan for an intonso copy of the 1930 edition of Physiologie Normale et Pathologique des Reins. The final thanks are due to Mrs. Filomena Tucciarone, Southington, CT, USA, who has improved this manuscript, and to the reviewers of the abstracts submitted to the 11th IAHN Congress for ranking this abstract number one.



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  39. Ambard L, Boyer G and Schmid F. Effets de l’insuline sur certaines affections vasculaires. Bull et Mém Soc Méd des Hôpitaux de Paris, 1926; pp. 144-148.
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