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Gr.T. Popa in USA ‐ A hypothesis explaining his concept of upward blood flow through the hypothalamo‐pituitary portal system

The Romanian scientist Gr.T. Popa and Unna Fielding described the hypothalamo‐pituitary portal system, by 3D reconstruction of the vessels, in 1930. That started a debate on the direction of blood flow, which he postulated to be upward toward the hypothalamus. Why, then, did Popa propose an ascending direction of blood flow through the portal veins, although he made no dynamic study on microcirculation, but only analysed serial sections of the region? One possible explanation could be that a Rockefeller grant in Chicago, USA (1925‐26) gave him the opportunity to train and act as a demonstrator in embryology in C.R. Moore's lab. There it is quite likely that he would be impressed by the classical embryology concept, stated by Wolff, that any organ ascending or descending during ontogenesis keeps its original neurovascular supply and carries it to its final location. He would also have been aware that Rathke's pouch grows upward to meet the infundibular diverticulum. Therefore, when he came to London in 1930, he doubtless remembered this principle of development, and this led him to presume that blood continues to flow from the superior hypophyseal artery upward, from the pituitary to the hypothalamus, through the portal veins which he discovered.