Nicolai Kravkov’s pancreotoxine

Professor Nikolai Pavlovich Kravkov (1865–1924), Full Member of the Imperial Military Medical Academy (1914) and Corresponding Member of the Russian Academy of Sciences (1920), is considered in Russia to be the founder of the national school of pharmacologists. In 2015, Professor Kravkov’s Sesquicentennial was widely celebrated by the scientific community of Ryazan, his native city, and Saint Petersburg, where he lived and worked for the most part of his life. The prominent pharmacologist is remembered as an audacious experimentalist, splendid lecturer, and excellent teacher, one of the first laureates of the Lenin Prize (1926, posthumously), the most prestigious award in the USSR for scientific achievements (Figure 1). OPEN IN VIEWER

After Professor Kravkov’s demise, his life and work were analyzed in a number of publications in Russia, ¹ but the scientist’s name is still scarcely known abroad. The first significant attempt to draw attention of the Western public to Professor Kravkov’s figure was a brief article by one of his disciples, the Soviet academician Vasily V. Zakusov, ² published in the International Journal of Neuropharmacology on the occasion of the scientist’s Centennial. ³ The present occasion of Professor Kravkov’s Sesquicentennial gives a good opportunity to remember some of his research works, not devoid of interest for the history of science.

Nikolai Kravkov’s name is associated with the development and introduction into the clinical practice of noninhalation intravenous anesthesia. In the beginning of the 20th century, surgeons used chloroform as inhalation anesthesia, which often had negative effects on heart, as well causing or aggravating excitement stage. Professor Kravkov decided to solve this problem. Having conducted long and thorough experimental studies of various hypnotic drugs, the scientist suggested intravenous administration of gedonal, prior to which he had confirmed nontoxicity of the drug in animal studies. On 7 December 1909, intravenous gedonal anesthesia was used for the first time in the Clinic of Surgery of the Military Medical Academy by Professor Fedorov ⁴ during successful leg amputation surgery. ⁵ This type of anesthesia was called la narcose russe abroad. Later Professor Kravkov suggested the surgeons to combine intravenous gedonal administration as basic anesthesia with chloroform inhalation (inhalation anesthesia), so that a combination of these two substances would allow reduced doses of the drugs to be used and, thus, lower their side effects.

Professor Kravkov has world priority in application of the method of isolated organs fed on the Ringer–Locke’s solution. ⁶ In order to study the influence of pharmacological substances on peripheral blood vessels, he developed the method of perfusion of vessels of the isolated rabbit ear, which was later applied in laboratories worldwide. His student Sergey A. Pisemsky took part in such experiments. This method has gone down in history as the Kravkov–Pisemsky method. ⁷

Using the method of isolated organs, Professor Kravkov made a number of discoveries in physiology, pathology, and pharmacology. Prior to Kravkov’s works, vessels were believed to contract rhythmically together with heart contractions and vascular muscular activity was absolutely denied. Experiments carried out by Professor Kravkov and his disciples proved that blood vessels periodically, not rhythmically contracted and dilated as a result of changes in the arterial tonus. The blood vessels do not contract at the same time with the cardiac muscle contraction. ⁸

Kravkov’s doctrine of phases of action of pharmacological substances was a significant contribution to pharmacology. Experiments on isolated vessels of various organs carried out at his laboratory showed that drugs’ action was wave like and included three phases: entering the organ, saturation, and leaving the organ. Blood vessels were most affected during “entering” and “saturation” phases, with possible side effects observed in the phase of “leaving.” For example, alcohol in the “entering” and “saturation” phases suppressed cardiac activity, but in “leaving” phase excited it. Professor Kravkov believed that before prescribing a drug to a patient, an experimental study of its phase action should be carried out. ⁹

Nikolai Kravkov introduced many new and bright ideas in the study of action of pharmacological substances under pathological conditions. From this cycle of works, studies on identification of changes in blood vessel reactivity in isolated organs (heart, kidneys, spleen) of people, suffering from camp and recurrent fever, atherosclerosis, spontaneous gangrene, are of the greatest interest. Such studies are very valuable both for theory and practice, as were those carried out using natural objects, not artificial models. ¹⁰

Professor Kravkov also made a significant discovery using the developed isolated pancreas method and studying pharmacological properties of its hormone. According to the scientist’s widow Xenia Kravkova, by the beginning of 1924, her husband revealed his plan to summarize in one volume the results of his experimental works in endocrinology of the postrevolutionary years. ¹¹ Unfortunately, Professor Kravkov’s premature death did not allow this plan to come true. One of the few sources of information on his works in that field was a paper by the scientist’s disciple Anatoly I. Kuznetsov, presented 1 April 1924 at the ordinary session of the Therapeutic Society in Leningrad and later published as an article in an important medical journal of that period Vrachebnoye Delo ¹² (Figure 2). OPEN IN VIEWER

According to Kuznetsov, at the beginning of the 1920s, Professor Kravkov in his laboratory in Petrograd performed experiments on dogs using a method of isolating the pancreas and extracting its perfusate, based on passing Ringer–Locke’s solution through the vessels of the isolated gland. Blood was accurately washed out of the organ, then it was put in the thermostat (at 38℃). The Ringer–Locke’s solution prior saturated with oxygen and heated to 37–38℃ passed via a glass cannula inserted in arteria coeliaca through the gland. By this method, a hormone produced by the pancreas did not enter the general circulatory system, but the Ringer–Locke’s solution which was going through the vessels of the isolated pancreas; this way the pancreas conserved its functions for a rather long time after being isolated from the organism. ¹³ It is important to note that the perfusate which contained the hormone did not mix with the pancreatic juice, excreted by the pancreas in the gastrointestinal tract.

The scientist discovered that the perfusate contained a substance that reduced the level of glucose in the blood of healthy animals and, in a large dose, caused hypoglycemic coma. ¹⁴ Professor Kravkov named this substance pancreotoxine. ¹⁵

Nikolai Kravkov and his disciples undertook extensive research on the biologic and pharmacologic properties of pancreotoxine in experiments on dogs, rabbits, and frogs. In experiments on the isolated hearts of animals they showed that, for a heart in the normal condition, pancreotoxine decelerated the heart beat and reduced the amplitude of contractions whilst for the heart tired above a certain threshold, the effect was the opposite. ¹⁶

The study of the blood vessels in isolated ears of rabbits and eyes of frogs showed antagonism between pancreotoxine and adrenaline: pancreotoxine weakened the vasoconstrictive effect of adrenaline and reduced its influence on the size of the pupil. It was shown that passing the perfusate containing pancreotoxine through the adrenal gland increased the secretion of adrenaline. ¹⁷

After successful experiments studying the hypoglycemic action of pancreotoxine, contained in the Ringer–Locke’s solution which went through the pancreas, pancreotoxine was obtained in dry form in Professor Kravkov’s laboratory ¹⁸ and was used to prepare a drug prescribed in Petrograd hospitals to patients suffering from diabetes. ¹⁹ On their labels it was possible to read: “Obtained according to Professor Kravkov’s method.”

When the news of the researches of the Canadians Frederick Banting and Charles Best reached Russia, it became clear that their insulin and Nikolai Kravkov’s pancreotoxine were identical in their properties. It is important to mention that the methods of extraction of the hormone applied by the discoverers of insulin and by Kravkov were quite different. The method of pancreotoxine extraction is described above. The method of insulin production suggested by Banting and Best was as follows. The pancreas performs a double function: excretes a digestive enzyme going through the duct to the gastrointestinal tract, and a sugar-reducing hormone, produced by beta-cells of gland islets, which flows into blood. In a living organism, such substances do not mix. During extraction of the pancreas in animals, the pancreatic enzyme is mixed with the hormone, which is a protein, and the hormone is destroyed. Initially, Banting and Best bound the pancreatic ducts and allowed the gland to atrophy over a few weeks, then ground the gland, added normal saline, filtered the extract, and administrated it to a dog with experimental diabetes, with resultant reduction in the dog’s blood glucose. However, this method seemed too wasteful. Then Banting and Best developed the method of hormone extraction from newborn calves, as they have well-formed istets of beta cells while the tissue producing digestive enzymes is relatively undeveloped. This extract was introduced to the dog with experimental diabetes model. The hormone obtained by scientists reduced sugar level in animals’ blood. Later this hormone called insulin was used in patients suffering from diabetes. ²⁰ It is interesting to note that the method of preparation of pancreine, another insulin analog, reported in 1921 by the Rumanian researcher Nicolae Paulescu, was similar to insulin extraction by Banting and Best in dogs. ²¹

This fact and the successful experience of clinical use of pancreotoxine obtained using Kravkov’s method in Petrograd hospitals in the early 1920s give reason to affirm that Professor Kravkov and the Canadian researchers discovered insulin almost simultaneously and independently. It is important to mention that, unlike pancreine discovered by Paulescu, Nikolai Kravkov’s pancreotoxine had clinical use.

It seems that only the scarcity of scientific contacts between Soviet Russia, which was recovering after a devastating Civil War, and the rest of the world prevented Nikolai Kravkov from giving proper publicity to his discovery. Or perhaps, like many Russian scientists of his generation, he paid no attention to the question of scientific priority, being satisfied with practical benefit that his discovery gave to society.

The prominent Russian physiologist and Nobel laureate Ivan Pavlov highly appreciated Kravkov’s works in endocrinology. He said that “Kravkov was the first to offer a very fruitful idea—to extract hormones directly from that liquid that went through the vessels of an isolated gland, and that is one of the most reasonable ways to “catch” hormones that have such a colossal influence on a living organism.” ²²