 Regarding the first area, he worked in London alongside the Australian Una Fielding; together they discovered the vascular link between the hypothalamus and the pituitary gland, publishing their findings on the hypophyseal portal system in medical journals between 1930 and 1935, presenting them before the Royal Medical Society in 1935.Working alongside his Romanian colleague, Eugen Lucinescu, Popa also returned to anatomy with a study on the "mechanostructure" of the pericardium.In 1928, Popa became professor of anatomy at Iași, the city associated with his rivals.