Robert Tigerstedt and the Discovery of Renin.

The year 2022 marks the 125th anniversary of the discovery of the first element of the renin-angiotensin-aldosterone system. The importance of this event on the further development of nephrology, cardiology, and endocrinology left us compelled to reminisce about it and its main author, Robert Tigerstedt (1853-1923), who was one of Scandinavia's most famous scientists. He studied medicine at the University of Helsinki, Finland. His doctoral dissertation On the Mechanical Stimulation of the Nervous System and 10 other original publications made him famous among the neurophysiological community. From 1881, he worked in the Physiology Department at Karolinska Institute, Stockholm, where he created a modern laboratory and became a professor at age 33 years. After meeting Carl Ludwig in Leipzig, he became interested in central blood circulation. In 1886, with Per Bergman, he started a series meticulously performed experiments with extracts of the rabbit kidney cortex, which, when injected into other rabbits, increased their blood pressure. The hypothetical responsible substance was called renin. The results were presented at the International Congress of Medicine in Moscow in 1887. Forty years later, Harry Goldblatt confirmed Tigerstedt's theory that "the substance which comes from kidneys increases the blood pressure." After he returned to Finland in 1901, Tigerstedt headed the Physiology Institute in Helsinki. His further activities included scientific work, teaching, and socially oriented issues like healthy nutrition and conditions in prison camps. He was also interested in the history of medicine and was a member of the Nobel Committee. His Textbook of Human Physiology was published in numerous editions in many languages. He also authored the renowned Textbook of Physiological Methodology and Physiology of Circulation. Tigerstedt published over 200 scientific papers and was an honorary doctor at many universities. He was known for his strong personality, critical judgment, idealism, humor, and warm heart.